Abstract
Background
Procedure volumes are associated with outcomes for many cardiovascular procedures, leading to guidelines on minimum volume thresholds for certain procedures; however, the volume outcome relationship with left atrial appendage occlusion (LAAO) is poorly understood. As such, we sought to determine the relationship between hospital and physician volume and Watchman LAAO procedural success overall and with the new generation Watchman FLX device.
Methods
We performed an analysis of Watchman procedures (1/2019–10/2021) from the National Cardiovascular Data Registry LAAO Registry. Three-level hierarchical generalized linear models were used to assess the adjusted relationship between procedure volume and procedural success (device released with peri-device leak <5mm, no in-hospital major adverse events).
Results
Among 87,480 patients (76.2±8.0 years, 58.8% men, mean CHA2DS2-VASc 4.8±1.5) from 693 hospitals, the procedural success rate was 94.2%. With hospital volume Q4 (greatest volume) as the reference, the likelihood of procedural success was significantly less among Q1 (OR 0.66, CI 0.57–0.77) and Q2 (OR 0.78, CI 0.69–0.90), but not Q3 (OR 0.95, CI 0.84–1.07). With physician volume Q4 (greatest volume) as the reference, the likelihood of procedural success was significantly less among Q1 (OR 0.72, CI 0.63–0.82), Q2 (OR 0.79, CI 0.71–0.89), and Q3 (OR 0.88, CI 0.79–0.97). Among Watchman FLX procedures, there was attenuation of the volume-outcome relationships, with statistically significant but modest absolute differences of only approximately 1% across volume quartiles.
Conclusions
In this contemporary national analysis, greater hospital and physician Watchman volumes were associated with increased procedure success. The Watchman FLX transition was associated with increased procedural success and less heterogeneity in outcomes across volume quartiles. These findings indicate the importance of understanding the volume-outcome relationship for individual LAAO devices.
Keywords: left atrial appendage closure, volume, hospital, physicians
Graphical Abstract
INTRODUCTION
Procedure volumes are associated with outcomes for many surgical and percutaneous procedures, including percutaneous coronary intervention (PCI),1,2 coronary artery bypass grafting (CABG),3 implantable cardioverter defibrillator implantation,4,5 and transcatheter aortic valve replacement.6 A volume-outcomes relationship has additionally been identified among non-cardiovascular procedures including breast cancer surgery, bariatric surgery, and colorectal cancer surgery.7 However, there are limited8 data on the relationship between hospital and physician volume and outcomes for percutaneous left atrial appendage occlusion (LAAO), which has experienced rapid growth in utilization by physicians and hospitals.9 Data on the relationship between procedure volume and outcomes may inform procedure dissemination, procedural training, and the establishment of volume requirements for maintenance of procedural competency. To address this key knowledge gap, we performed a retrospective analysis of contemporary Watchman LAAO procedures reported to the National Cardiovascular Data Registry (NCDR) LAAO Registry, to assess the relationship between annual physician and hospital procedure volumes and in-hospital outcomes. Prespecified analyses were performed to determine if the transition to the newer-generation Watchman FLX device modified the volume-outcome relationship.
METHODS
The Yale University Human Investigation Committee approved analysis of data from the LAAO Registry with a waiver of informed consent. Data from the LAAO Registry is owned by the NCDR and the authors cannot grant data access; any requests should be made directly to the NCDR.
NCDR LAAO Registry
The NCDR LAAO Registry has been previously described.9 The LAAO registry is a US registry of LAAO procedures that functions as the FDA mandated post-market surveillance strategy for the Watchman device (Boston Scientific, Natick, MA). Further, to qualify for Medicare reimbursement, US hospitals are required to submit data from all Watchman procedures to the registry as part of a CMS coverage with evidence development decision. Importantly, the contractual agreement between participating hospitals and the NCDR requires submission of data for all patients that are “eligible for inclusion” in the LAAO Registry. Thus, the NCDR LAAO Registry reflects a comprehensive registry of Watchman LAAO procedures across US hospitals that provide LAAO care for Medicare beneficiaries beginning in 2016. The LAAO Registry collects approximately 220 data elements from the implant hospitalization, and as with all NCDR Registries, there is an established data quality reporting processes employed to ensure submissions are complete, valid, and accurate; annually, ~5% of sites are randomly selected for audits.10,11 Adjudication of adverse events is performed by a computer-based automated adjudication algorithm using discrete combinations of registry data elements and standard definitions for the following endpoints: ischemic stroke, hemorrhagic stroke, undetermined stroke, transient ischemic attack, intracranial hemorrhage, systemic arterial embolism (other than stroke), major bleeding, and major vascular complication.12 When data elements are incomplete or conflicting, manual adjudication is performed by the Yale Cardiovascular Research Group.12
Inclusion and Exclusion Criteria
All patients who underwent attempted LAAO between January 2019 and October 2021 were considered. We excluded patients who were implanted with a non-Watchman device, had no reported device type, had a prior left atrial appendage intervention, or had a cancelled procedure (defined as a procedure terminated prior to vascular access).
Study Endpoints
The study endpoint was in-hospital procedural success, defined as a procedure in which a first-generation Watchman 2.5 or second-generation Watchman FLX device was deployed and released with peri-device leak of <5mm and no in-hospital majored adverse event (MAE). MAE was defined as a composite of death, cardiac arrest, ischemic stroke, hemorrhagic stroke, undetermined stroke, transient ischemic attack, intracranial hemorrhage, systemic arterial embolism, major bleeding, major vascular complication, myocardial infarction, pericardial effusion requiring intervention (percutaneous or surgical), and device embolization.
Statistical Analysis
Annual hospital procedure volume was calculated by tabulating the number of procedures per calendar month for each hospital during the study period and multiplying that number by 12. The monthly procedure volume calculation began during the first month during which a LAAO procedure was performed at the hospital. In order to ensure contemporary estimates, annual procedure volume calculations were performed using months from January 2019 through October 2021. The transition from the first to second generation Watchman device began August 2020.Physician procedure volume was calculated by tabulating the number of procedures per calendar month for each physician during the study period and multiplying that number by 12. Physicians were only given credit for the procedure if they were the primary operator reported to the LAAO Registry. The monthly procedure volume was only calculated for months including and subsequent to the first reported Watchman procedure for a physician or hospital. As with hospital volume calculations, annual physician volumes reflect procedures from January 2019 through October 2021. Quartiles were defined on the hospital or physician level, so there is an equal number of hospitals or physicians in each quartile, depending on the model.
Each procedure was categorized by the primary physician implanter (by national provider identification) and the procedure number for that specific physician (regardless of hospital location); physician procedure number accounted for all procedures performed since LAAO Registry reporting began in 2016. This variable was used to account for overall physician experience and a potential learning curve for newer implanters. Similarly, cumulative hospital volume accounted for the all procedures performed at each hospital since reporting began in 2016. Data on physician specialty was obtained from the American Medical Association Masterfile Physician Professional Data file. Physician specialties were categorized as cardiac electrophysiology, interventional cardiology, both, or neither.
Characteristics of the hospitals, patients, and procedures overall and by quartile of hospital or physician volume were compared (separately) using the Kruskal-Wallis test for continuous variables and the χ2 test for categorical variables. The relationship between procedure and outcomes was assessed with volume considered (separately) as a continuous and categorical variable (using quartiles). Logistic regression was used to compare the relationship between volume quartile and likelihood of procedural success compared to the highest volume quartile (quartile 4). Three level (patient, hospital, physician) hierarchical generalized linear models were used to assess the adjusted relationship between procedure volume and likelihood of procedural success. To facilitate model convergence, the patient level was summarized to a logit score derived from patient characteristics associated with likelihood of procedural success and clinical relevance. Adjustment variables for generation of the logit score to account for the patient level included: hemoglobin, age, sex, body mass index, glomerular filtration rate, heart failure, left ventricular systolic dysfunction, hypertension, diabetes, prior stroke, prior transient ischemic attack, prior thromboembolic event, vascular disease, previous attempts at termination of atrial fibrillation, increased fall risk, and a history of a clinically relevant bleeding event.
The continuous relationship between hospital volume and outcomes was assessed using generalized linear mixed models and marginal estimates were reported. Adjusted and unadjusted models were created. Restricted cubic splines were created to assess for a non-linear relationship between annualized procedure volume and outcomes with procedure volume on the x-axis and procedural success on the y-axis. Splines were additionally created for physician volume.
Pre-specified sensitivity analyses were performed to assess if introduction of the newer-generation Watchman FLX device has changed any observed relationship between volume and outcomes. In this series of analyses, we repeated all volume outcome analyses using only the subset of procedures during which a Watchman FLX implant was attempted.
A p-value of <0.05 was considered statistically significant. Analyses were performed using SAS (version 9.4, SAS institute, Cary, North Carolina). Drs. Friedman and Freeman, Ms. Zimmerman and Mr. Tan, had full access to all data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
RESULTS
Between January 2019 and October 2021, a total of 87,480 patients from 693 hospitals underwent attempted Watchman LAAO implant and met study criteria, of which 38,610 (44.1%) were Watchman FLX procedures. The mean patient age was 76.2 years (standard deviation [SD] 8.0), 58.8% of patients were men, the mean CHA2DS2-VASc score was 4.8 (SD 1.5), and the mean HAS-BLED score was 2.9 (SD 2.2). The overall rate of procedural success was 94.2%.
Annual Hospital Volume and Outcomes
The median annual hospital procedure volume was 71 (interquartile range [IQR] 69.1) and the distribution of annual hospital volumes is depicted in Figure S1A. The median number of annual procedures across hospital volume quartiles (with interquartile range) was: Q1, 18 (8.4); Q2, 32.7 (8); Q3, 49.9 (12); and Q4, 107.3 (58.3). Table 1 summarizes patient and hospital characteristics stratified by hospital volume quartiles. Higher volume hospitals tended to more frequently implant Watchman in patients with prior ischemic stroke and/or increased thromboembolic risk as the indication for occlusion but were less likely to implant devices for a history of major bleeding and in Black, Asian, and Hispanic patients.
Table 1.
Patient and hospital characteristics stratified by hospital volume quartiles.
| Characteristic | Hospital Volume Q1 | Hospital Volume Q2 | Hospital Volume Q3 | Hospital Volume Q4 | p-value |
|---|---|---|---|---|---|
| Hospital Annual Volume | 18(8.37) | 32.73(8.00) | 49.88(12.00) | 107.27 (58.30) | <.0001 |
| Age, years | 75.9(8.1) | 76.0(7.8) | 76.2(8.0) | 76.4(8.0) | <.0001 |
| Male sex | 3141(59.7%) | 7140(58.0%) | 12889 (59.2%) | 28231(58.7%) | 0.0929 |
| Race | |||||
| White | 4713(89.4%) | 11360(92.3%) | 20336 (93.4%) | 45025(93.6%) | <.0001 |
| Black | 292(5.5%) | 613(5.0%) | 846(3.9%) | 2150(4.5%) | <.0001 |
| Asian | 133(2.5%) | 171(1.4%) | 269(1.2%) | 483(1.0%) | <.0001 |
| Other | 58(1.1%) | 68(0.6%) | 78(0.4%) | 167(0.3%) | <.0001 |
| Hispanic | 324(6.2%) | 541(4.4%) | 804(3.7%) | 1101(2.3%) | <.0001 |
| Insurance payer | |||||
| Private | 2848(54.0%) | 6379(51.8%) | 11357(52.2%) | 28680(59.6%) | <.0001 |
| Medicare | 4022(76.3%) | 9565(77.7%) | 16848(77.4%) | 37697(78.3%) | 0.0008 |
| Medicaid | 315(6.0%) | 676(5.5%) | 1049(4.8%) | 2300(4.8%) | <.0001 |
| State-Specific plan | 60(1.1%) | 79(0.6%) | 207(1.0%) | 336(0.7%) | <.0001 |
| Other | 229(4.3%) | 655(5.3%) | 995(4.6%) | 2601(5.4%) | <.0001 |
| Admitted for LAAO procedure | 5071(97.0%) | 11941(97.3%) | 21065(97.0%) | 46761(97.4%) | 0.008 |
| Patient History and Risk Factors | |||||
| CHA2DS2-VASc Score | 4.9(1.5) | 4.8(1.5) | 4.9(1.5) | 4.8(1.5) | 0.0039 |
| Congestive heart failure | |||||
| NYHA Class I | 587(11.1%) | 1515(12.3%) | 2360(10.8%) | 5464(11.4%) | 0.0006 |
| NYHA Class II | 833(15.8%) | 1969(16.0%) | 3749(17.2%) | 8527(17.7%) | <.0001 |
| NYHA Class III | 410(7.8%) | 886(7.2%) | 1714(7.9%) | 3546(7.4%) | 0.0521 |
| NYHA Class IV | 38(0.7%) | 69(0.6%) | 122(0.6%) | 184(0.4%) | 0.0001 |
| Hypertension | 4880(92.7%) | 11299(91.9%) | 20058(92.1%) | 44148(91.7%) | 0.0532 |
| Diabetes | 2054(39.0%) | 4602(37.4%) | 8141(37.4%) | 17224(35.8%) | <.0001 |
| Stroke | 1350(25.6%) | 2834(23.1%) | 5095(23.4%) | 10526(21.9%) | <.0001 |
| TIA | 681(12.9%) | 1480(12.0%) | 2836(13.0%) | 5807(12.1%) | 0.0015 |
| Prior thromboembolism | 885(16.8%) | 1726(14.1%) | 3246(14.9%) | 7711(16.0%) | <.0001 |
| Vascular disease | 2787(52.9%) | 6566(53.4%) | 11831(54.3%) | 26224(54.5%) | 0.0409 |
| Prior MI | 810(15.4%) | 1911(15.5%) | 3277(15.0%) | 7920(16.5%) | <.0001 |
| PAD | 577(10.9%) | 1366(11.1%) | 2310(10.6%) | 5420(11.3%) | 0.0851 |
| Known aortic plaque | 134(2.5%) | 335(2.7%) | 548(2.5%) | 1149(2.4%) | 0.18 |
| HAS-BLED Score | 3.0(1.2) | 2.9(1.2) | 2.9(1.1) | 2.9(1.1) | <.0001 |
| Ischemic stroke | 819(58.8%) | 1718(58.6%) | 3231(61.2%) | 7020(63.8%) | <.0001 |
| Hemorrhagic stroke | 360(25.8%) | 781(26.6%) | 1152(21.8%) | 2232(20.3%) | <.0001 |
| Undetermined stroke | 276(19.8%) | 601(20.5%) | 1109(21.0%) | 2237(20.3%) | 0.6752 |
| Labile INR | 438(8.3%) | 959(7.8%) | 1594(7.3%) | 2859(5.9%) | <.0001 |
| Alcohol use | 316(6.0%) | 686(5.6%) | 1167(5.4%) | 2313(4.8%) | <.0001 |
| Antiplatelet medication use | 1653(31.4%) | 3735 (30.4%) | 7077(32.5%) | 15401(32.0%) | 0.0005 |
| NSAID | 853(16.2%) | 2061(16.8%) | 3969(18.2%) | 10294(21.4%) | <.0001 |
| Other History and Risk Factors | |||||
| Clinically relevant prior bleeding | 3790(72.0%) | 8567(69.7%) | 14449(66.5%) | 28380(59.0%) | <.0001 |
| Intracranial | 615(11.7% ) | 1386(11.3%) | 2280(10.5%) | 4416(9.2%) | <.0001 |
| Epistaxis | 322(6.1%) | 785(6.4%) | 1365(6.3%) | 2788(5.8%) | 0.0221 |
| Gastrointestinal | 2332(44.3%) | 5126(41.7%) | 8620(39.6%) | 16716(34.7%) | <.0001 |
| Other | 819(15.5%) | 1988(16.2%) | 3400(15.6%) | 6763(14.1%) | <.0001 |
| Indication for occlusion | |||||
| Increased thromboembolic risk | 3031(57.5%) | 7419(60.3%) | 12664(58.2%) | 31268(65.0%) | <.0001 |
| History of major bleeding | 3503(66.5%) | 7977(64.8%) | 13646(62.7%) | 26632(55.3%) | <.0001 |
| High fall risk | 1948(37.0%) | 4331(35.2%) | 8142(37.4%) | 18147(37.7%) | <.0001 |
| Labile INR | 305(5.8%) | 778(6.3%) | 1242(5.7%) | 2254(4.7%) | <.0001 |
| Patient preference | 1799(34.1%) | 4443(36.1%) | 8683(39.9%) | 19106(39.7%) | <.0001 |
| Non-compliance with anticoagulation therapy | 199(3.8%) | 467(3.8%) | 879(4.0%) | 1298(2.7%) | <.0001 |
| Fall risk | 2266(43.1%) | 4876(39.7%) | 9221(42.5%) | 19689(41.0%) | <.0001 |
| Genetic coagulopathy | 38(0.7%) | 97(0.8%) | 160(0.7%) | 314(0.7%) | 0.3404 |
| LVEF | 54.5(9.8) | 54.4(10.1) | 54.3(9.9) | 53.6(10.0) | <.0001 |
| Chronic Lung Disease | 1101(20.9%) | 2607(21.2%) | 4828(22.2%) | 9814(20.4%) | <.0001 |
| CAD | 2428(46.1%) | 5705(46.4%) | 10137(46.6%) | 22284(46.3%) | 0.9016 |
| OSA | 1394(26.5%) | 3463(28.2%) | 6335(29.1%) | 14040(29.2%) | 0.0002 |
| Atrial fibrillation calssification | |||||
| Paroxysmal | 2964(56.2%) | 7115(57.8%) | 13332(61.2%) | 28872(60.0%) | <.0001 |
| Persistent | 1059(20.1%) | 2497(20.3%) | 4026(18.5%) | 10260(21.3%) | <.0001 |
| Long standing persistent | 489(9.3%) | 813(6.6%) | 1412(6.5%) | 2634(5.5%) | <.0001 |
| Permanent | 710(13.5%) | 1754(14.3%) | 2814(12.9%) | 6074(12.6%) | <.0001 |
| Physical Exam and Laboratory Results | |||||
| Body Mass Index | 30.3(10.4) | 30.3(9.0) | 30.1(10.5) | 29.9(9.1) | <.0001 |
| Hemoglobin | 12.6(2.1) | 12.6(2.1) | 12.6(2.1) | 12.7(2.0) | <.0001 |
| Creatinine | 1.3(1.1) | 1.3(1.1) | 1.3(1.0) | 1.3(1.0) | 0.0233 |
| Albumin | 3.8(0.5) | 3.9(0.5) | 3.8(0.5) | 3.9(0.5) | <.0001 |
| Platelet count <50,000 | 193(3.7%) | 441(3.6%) | 548(2.5%) | 1293(2.7%) | <.0001 |
| Hospital Characteristics | |||||
| Rural | 559(10.6%) | 1462(11.9%) | 2719(12.5%) | 3499(7.3%) | <.0001 |
| Suburban | 1420(26.9%) | 3783(30.7%) | 7564(34.7%) | 12478(25.9%) | <.0001 |
| Urban | 3291(62.4%) | 7062(57.4%) | 11494(52.8%) | 32149(66.8%) | <.0001 |
| U.S. Region | |||||
| Northeast | 1036(19.7%) | 1808(14.7%) | 4288(19.7%) | 6922(14.4%) | <.0001 |
| West | 1303(24.7%) | 2161(17.6%) | 3999(18.4%) | 9798(20.4%) | <.0001 |
| Midwest | 1116(21.2%) | 3681(29.9%) | 5622(25.8%) | 10533(21.9%) | <.0001 |
| South | 1792(34.0%) | 4585(37.3%) | 7868(36.1%) | 20873(43.4%) | <.0001 |
| Type of facility | |||||
| Government | 163(3.1%) | 207(1.7%) | 265(1.2%) | 895(1.9%) | <.0001 |
| Private | 3869(73.4%) | 10553(85.7%) | 17790(81.7%) | 39345(81.8%) | <.0001 |
| University | 1238(23.5%) | 1547(12.6%) | 3722(17.1%) | 7886(16.4%) | <.0001 |
| Teaching hospital | 3285(62.3%) | 7686(62.5%) | 12346(56.7%) | 28852(60.0%) | <.0001 |
| Hospital number of certified beds | 446.1(226.0) | 424.4(181.1) | 474.5(243.4) | 554.8(295.5) | <.0001 |
CAD = coronary artery disease, INR = international normalized ratio, LAAO = left atrial appendage occlusion, LVEF = left ventricular ejection fraction, MI = myocardial infarction, NSAIDS = nonsteroidal anti-inflammatory drugs, NYHA = New York Heart Association, OSA = obstructive sleep apnea, PAD = peripheral arterial disease, TIA = transient ischemic attack
Continuous variables are displayed as median and interquartile ranges
The unadjusted procedural success rate increased across hospital volume quartiles: Q1 92.0%, Q2 93.2%, Q3 94.3%, Q4 94.6%. With Q4 as the reference, the adjusted likelihood of procedural success was significantly less among Q1 (0.74, CI 0.59–0.92) but not Q2 (0.86, CI 0.71–1.04) or Q3 (1.01, CI 0.86–1.19)(Figure 1 & Table 2). In a sensitivity analysis of 38,610 Watchman FLX procedures, the unadjusted procedural success rate increased across hospital volume quartiles: Q1 94.2%, Q2 94.9%, Q3 95.9%, Q4 95.2%. The likelihood of procedural success among FLX procedures, with Q4 as the reference, was significantly less among Q1 (0.56, CI 0.41–0.76), but not Q2 (0.80, CI 0.62–1.04), or Q3 (0.86, CI 0.69–1.07) (Figure 1 & Table 2). Figure 2 depicts the unadjusted and adjusted linear relationship between hospital volume and procedural success among all procedures (A) and FLX procedures (B). While an adjusted 95% procedural success rate (depicted by the dotted orange line) is achieved with an average hospital volume of ~75 or more annual cases in the overall cohort, 95% success rate was achieved, on average, at an annual volume of 30–40 procedures with the FLX device. However, the variability in outcomes was greater among lower volume hospitals.
Figure 1.
The adjusted relationship between annual physician or hospital volume and acute procedure success in the overall cohort (Watchman 2.5 or Watchman FLX device) and in a cohort restricted to FLX implants.
Pane A depicts the relationship for annual physician volume in the overall cohort. Pane B depicts the relationship for the annual hospital overall volume for the overall cohort. Pane C depicts the relationship for annual physician volume in the FLX cohort. Pane D depicts the relationship for annual hospital volume in the FLX cohort. Use of the Watchman FLX device attenuates both the hospital and physician volume outcome relationships.
Table 2.
Adjusted relationship between annual hospital volume quartile and procedural success
| Overall Cohort | FLX Procedures | |||||||
|---|---|---|---|---|---|---|---|---|
| Volume Quartile | Odds Ratio | Lower 95% confidence bound | Upper 95% confidence bound | p-value | Odds Ratio | Lower 95% confidence bound | Upper 95% confidence bound | p-value |
| I vs. IV | 0.739 | 0.592 | 0.921 | 0.0072 | 0.560 | 0.413 | 0.761 | 0.0002 |
| II vs. IV | 0.859 | 0.712 | 1.038 | 0.1153 | 0.799 | 0.616 | 1.038 | 0.0928 |
| III vs. IV | 1.014 | 0.865 | 1.190 | 0.8615 | 0.862 | 0.691 | 1.074 | 0.1855 |
Figure 2.
The unadjusted and adjusted linear relationships between annual procedure volume (hospital or physician) and procedural success (overall and among Watchman FLX procedures).
The unadjusted (red) and adjusted (blue) linear relationships between hospital volume and procedural success overall and among Watchman FLX procedures are described in Pane A & B, respectively. The unadjusted (red) and adjusted (blue) linear relationships between physician volume and procedural success overall and among Watchman FLX procedures are described in Pane C & D, respectively. The shaded regions represent the 95% confidence interval and the orange dashed line denotes a 95% rate of procedural success.
Additional analyses demonstrated increased hospital volume was associated with a lower risk of MAE and higher likelihood of successful deployment with a leak of <5mm when analyzed as separate endpoints on the overall and FLX only populations (Tables S1 & S2)
Annual Physician Volume and Outcomes
The median annual physician volume was 30 (30) and the distribution of annual hospital volumes is depicted in Figure S1B The median number of procedures across physician volume quartiles (with interquartile range) was: Q1, 8 (3); Q2, 14 (3); Q3, 22 (5); and Q4, 45 (32). Table 3 summarizes patient and hospital characteristics stratified by physician volume quartiles. Higher volume physicians tended to more frequently implant Watchman in patients with ischemic stroke and increased thromboembolic risk as the indication for occlusion but were less likely to implant devices for a history of major bleeding and in Black, Asian, and Hispanic patients.
Table 3.
Patient and hospital characteristics stratified by implanting physician volume quartiles.
| Characteristic | Physician Volume Q1 | Physician Volume Q2 | Physician Volume Q3 | Physician Volume Q4 | p-value |
|---|---|---|---|---|---|
| Annual Physician Volume | 7.84(3.0) | 13.71(3.2) | 21.60(4.9) | 45.09(32.4) | <.0001 |
| Age | 76.0(8.0) | 76.2(7.9) | 76.1(7.9) | 76.3(8.0) | 0.0181 |
| Sex | 3646(59.9%) | 6253(58.5%) | 11992(58.6%) | 29510(58.8%) | 0.2787 |
| Race | |||||
| White | 5501(90.2%) | 9804(91.7%) | 19017(92.8%) | 47112(93.9%) | <.0001 |
| Black | 356(5.8%) | 570(5.3%) | 961(4.7%) | 2014(4.0%) | <.0001 |
| Asian | 120(2.0%) | 177(1.7%) | 284(1.4%) | 475(0.9%) | <.0001 |
| Other | 51(0.8%) | 49(0.5%) | 103(0.5%) | 168(0.3%) | <.0001 |
| Hispanic | 318(5.3%) | 397(3.7%) | 789(3.9%) | 1266(2.5%) | <.0001 |
| Insurance payer | |||||
| Private | 3430(56.2%) | 5671(53.0%) | 11239(54.9%) | 28924(57.6%) | <.0001 |
| Medicare | 4775(78.3%) | 8315(77.7%) | 15932(77.8%) | 39110(77.9%) | 0.8127 |
| Medicaid | 373(6.1%) | 627(5.9%) | 1010(4.9%) | 2330(4.6%) | <.0001 |
| State-Specific plan | 79(1.3%) | 61(0.6%) | 164(0.8%) | 378(0.8%) | <.0001 |
| Other | 266(4.4%) | 495(4.6%) | 1080(5.3%) | 2639(5.3%) | 0.0015 |
| Admitted for LAAO procedure | 5896(97.2%) | 10403(97.7%) | 19901(97.4%) | 48638(97.1%) | 0.0073 |
| Patient History and Risk Factors | |||||
| CHA2DS2-VASc Score | 4.9(1.5) | 4.9(1.5) | 4.8(1.5) | 4.8(1.5) | 0.003 |
| Congestive heart failure | 2326(38.2%) | 3979(37.3%) | 7856(38.4%) | 19555(39.0%) | 0.0082 |
| NYHA Class I | 705(11.6%) | 1270(11.9%) | 2333(11.4%) | 5618(11.2%) | 0.2156 |
| NYHA Class II | 1048(17.2%) | 1593(14.9%) | 3519(17.2%) | 8918(17.8%) | <.0001 |
| NYHA Class III | 439(7.2%) | 812(7.6%) | 1491(7.3%) | 3814(7.6%) | 0.3795 |
| NYHA Class IV | 23(0.4%) | 55(0.5%) | 89(0.4%) | 246(0.5%) | 0.4686 |
| Hypertension | 5596(91.8%) | 9837(92.0%) | 18825(91.9%) | 46127(91.9%) | 0.9637 |
| Diabetes | 2365(38.8%) | 4058(38.0%) | 7646(37.3%) | 17952(35.8%) | <.0001 |
| Stroke | 1486(24.4%) | 2518(23.6%) | 4747(23.2%) | 11054(22.0%) | <.0001 |
| TIA | 825(13.5%) | 1324(12.4%) | 2610(12.7%) | 6045(12.0%) | 0.0017 |
| Prior thromboembolism | 914(15.0%) | 1662(15.6%) | 3024(14.8%) | 7968(15.9%) | 0.0018 |
| Vascular disease | 3240(53.2%) | 5864(54.9%) | 10948(53.5%) | 27356(54.5%) | 0.0104 |
| Prior MI | 994(16.3%) | 1671(15.6%) | 3195(15.6%) | 8058(16.1%) | 0.303 |
| PAD | 726(11.9%) | 1223(11.4%) | 2334(11.4%) | 5390(10.7%) | 0.0036 |
| Known aortic plaque | 146(2.4%) | 253(2.4%) | 497(2.4%) | 1270(2.5%) | 0.6752 |
| HAS-BLED Score | 3.0(1.2) | 2.9(1.2) | 2.9(1.1) | 2.9(1.1) | <.0001 |
| Ischemic stroke | 872(55.9%) | 1548(60.0%) | 2977(60.7%) | 7391(63.9%) | <.0001 |
| Hemorrhagic stroke | 412(26.4%) | 601(23.2%) | 1115(22.7%) | 2397(20.7%) | <.0001 |
| Undetermined stroke | 329(21.1%) | 574(22.3%) | 1037(21.1%) | 2283(19.7%) | 0.0131 |
| Labile INR | 457(7.5%) | 799(7.5%) | 1540(7.5%) | 3054(6.1%) | <.0001 |
| Alcohol use | 333(5.5%) | 550(5.2%) | 1050(5.1%) | 2549(5.1%) | 0.6368 |
| Antiplatelet medication use | 1793(29.4%) | 3410(31.9%) | 6286(30.7%) | 16377(32.6%) | <.0001 |
| NSAID | 1062(17.4%) | 1850(17.3%) | 3849(18.8%) | 10416(20.8%) | <.0001 |
| Other History and Risk Factors | |||||
| Clinically relevant prior bleeding | 4336(71.2%) | 7319(68.6%) | 13386(65.4%) | 30145(60.1%) | <.0001 |
| Intracranial | 703(11.5%) | 1139(10.6%) | 2082(10.2%) | 4773(9.5%) | <.0001 |
| Epistaxis | 394(6.5%) | 628(5.9%) | 1303(6.4%) | 2935(5.8%) | 0.0249 |
| Gastrointestinal | 2619(42.9%) | 4452(41.6%) | 8061(39.3%) | 17662(35.2%) | <.0001 |
| Other | 1010(16.6%) | 1687(15.8%) | 3057(14.9%) | 7216(14.4%) | <.0001 |
| Indication for occlusion | |||||
| Increased thromboembolic risk | 3508(57.5%) | 5942(55.6%) | 12142(59.3%) | 32790(65.3%) | <.0001 |
| History of major bleeding | 4081(66.9%) | 6858(64.1%) | 12537(61.2%) | 28282(56.3%) | <.0001 |
| High fall risk | 2147(35.2%) | 4016(37.5%) | 7420(36.2%) | 18985(37.8%) | <.0001 |
| Labile INR | 342(5.6%) | 592(5.5%) | 1153(5.6%) | 2492(5.0%) | 0.0006 |
| Patient preference | 2110(34.6%) | 3660(34.2%) | 7753(37.8%) | 20508(40.9%) | <.0001 |
| Non-compliance with anticoagulation therapy | 265(4.3%) | 341(3.2%) | 619(3.0%) | 1618(3.2%) | <.0001 |
| Fall risk | 2434(40.0%) | 4526(42.4%) | 8366(40.9%) | 20726(41.4%) | 0.0116 |
| Genetic coagulopathy | 42(0.7%) | 75(0.7%) | 148(0.7%) | 344(0.7%) | 0.9604 |
| LVEF | 54.3(10.2) | 54.1(9.8) | 54.0(10.0) | 53.8(10.0) | 0.0022 |
| Chronic Lung Disease | 1247(20.5%) | 2281(21.4%) | 4450(21.7%) | 10372(20.7%) | 0.0083 |
| CAD | 2859(46.9%) | 5070(47.5%) | 9587(46.8%) | 23038(45.9%) | 0.0093 |
| OSA | 1663(27.3%) | 2924(27.4%) | 6040(29.5%) | 14605(29.1%) | <.0001 |
| Atrial fibrillation calssification | |||||
| Paroxysmal | 3538(58.0%) | 6241(58.3%) | 12279(59.9%) | 30225(60.2%) | 0.0001 |
| Persistent | 1205(19.8%) | 2163(20.2%) | 4083(19.9%) | 10391(20.7%) | 0.0622 |
| Long standing persistent | 452(7.4%) | 781(7.3%) | 1344(6.6%) | 2771(5.5%) | <.0001 |
| Permanent | 830(13.6%) | 1398(13.1%) | 2624(12.8%) | 6500(12.9%) | 0.4219 |
| Physical Exam and Laboratory Results | |||||
| Body Mass Index | 30.1( 9.7) | 30.1(8.5) | 30.2(10.9) | 30.0(9.2) | 0.0111 |
| Hemoglobin | 12.5(2.1) | 12.6(2.1) | 12.7(2.0) | 12.7(2.0) | <.0001 |
| Creatinine | 1.4(1.2) | 1.3(1.1) | 1.3(1.1) | 1.3(1.0) | <.0001 |
| Albumin | 3.9(0.5) | 3.8(0.5) | 3.9(0.5) | 3.9(0.5) | <.0001 |
| Platelet count <50,000 | 220(3.6%) | 299(2.8%) | 625(3.1%) | 1331(2.7%) | <.0001 |
| Hospital Characteristics | |||||
| Rural | 429(7.0%) | 845(7.9%) | 2295(11.2%) | 4670(9.3%) | <.0001 |
| Suburban | 2029(33.3%) | 3517(32.9%) | 6458(31.5%) | 13241(26.4%) | <.0001 |
| Urban | 3640(59.7%) | 6334(59.2%) | 11735(57.3%) | 32287(64.3%) | <.0001 |
| U.S. Region | |||||
| Northeast | 1333(21.9%) | 1978(18.5%) | 3288(16.0%) | 7455(14.9%) | <.0001 |
| West | 1225(20.1%) | 1418(13.3%) | 3847(18.8%) | 10771(21.5%) | <.0001 |
| Midwest | 1236(20.3%) | 3049(28.5%) | 6024(29.4%) | 10643( 21.2%) | <.0001 |
| South | 2287(37.5%) | 4249(39.7%) | 7253(35.4%) | 21329(42.5%) | <.0001 |
| Type of facility | |||||
| Government | 107(1.8%) | 116(1.1%) | 275(1.3%) | 1032(2.1%) | <.0001 |
| Private | 4450(73.0%) | 8651(80.9%) | 17276(84.3%) | 41180(82.0%) | <.0001 |
| University | 1541(25.3%) | 1929(18.0%) | 2937(14.3%) | 7986(15.9%) | <.0001 |
| Teaching hospital | 4113(67.4%) | 6518(60.9%) | 11835(57.8%) | 29703(59.2%) | <.0001 |
| Hospital beds | 545.7(317.3) | 492.1(255.5) | 483.1(262.2) | 520.3(269.6) | <.0001 |
CAD = coronary artery disease, INR = international normalized ratio, LAAO = left atrial appendage occlusion, LVEF = left ventricular ejection fraction, MI = myocardial infarction, NSAIDS = nonsteroidal anti-inflammatory drugs, NYHA = New York Heart Association, OSA = obstructive sleep apnea, PAD = peripheral arterial disease, TIA = transient ischemic attack
Continuous variables are displayed as median and interquartile ranges
The unadjusted procedural success rate increased across volume quartiles: Q1 92.4%, Q2 93.2%, Q3 93.8%, Q4 94.7%. With Q4 as the reference, the adjusted likelihood of procedural success was significantly less among Q1 (0.72, CI 0.63–0.82), Q2 (0.79, CI 0.71–0.89), and Q3 (0.88, CI 0.79–0.97) (Figure 1 & Table 4). In a sensitivity analysis of Watchman FLX procedures, the unadjusted procedural success rate increased across physician volume quartiles: Q1 94.7%, Q2 94.8%, Q3 95.5%, Q4 95.4%. The likelihood of procedural success among FLX procedures, with Q4 as the reference, was significantly less among Q2 (0.82, CI 0.68–0.98), trended towards being less among Q1 (0.81, CI 0.65–1.01), and was similar among Q3 (0.97, CI 0.83–1.13) (Figure 1 & Table 4). Figure 2 depicts the unadjusted and adjusted linear relationship between physician volume and procedural success among all procedures (C) and FLX procedures (D). While an adjusted 95% procedural success rate (depicted by the dotted orange line) is achieved with an average physician volume of ~60 or more annual cases in the overall cohort, 95% success rate was achieved, on average, with an annual procedure volume of ~15 with the FLX device. However, the variability in outcomes was greater among lower volume physicians.
Table 4.
Adjusted relationship between annual physician volume quartile and procedural success
| Overall Cohort | FLX Procedures | |||||||
|---|---|---|---|---|---|---|---|---|
| Volume Quartile | Odds Ratio | Lower 95% confidence bound | Upper 95% confidence bound | p-value | Odds Ratio | Lower 95% confidence bound | Upper 95% confidence bound | p-value |
| I vs. IV | 0.717 | 0.63 | 0.815 | <0.0001 | 0.809 | 0.649 | 1.009 | 0.0593 |
| II vs. IV | 0.794 | 0.707 | 0.891 | 0.0001 | 0.817 | 0.681 | 0.979 | 0.0288 |
| III vs. IV | 0.875 | 0.792 | 0.968 | 0.0091 | 0.965 | 0.825 | 1.128 | 0.6683 |
Additional analyses demonstrated increased physician volume was associated with a lower risk of MAE and higher likelihood of successful deployment with a leak of <5mm when analyzed as separate endpoints (Tables S3 & S4). The only exception was that in the FLX cohort, Q2 physicians had the lowest likelihood of successful deployment without significant leak, while Q1 and Q3 physicians had outcomes similar to Q4.
Low volume (Q1) physicians at high volume (Q4) hospitals had higher procedure success rates compared to low volume physicians at low volume hospitals (93.2% vs. 91.0%, p=0.0221). A trend towards lower rates of MAE were observed among low volume physicians at high volume (versus low volume) hospitals (2.8% vs 3.9%, p=0.0708).
There was no interaction between physician specialty, annual physician procedure volume, and Watchman procedural success (adjusted p=0.73).
DISCUSSION
This analysis of over 87,000 Watchman LAAO procedures performed at 693 sites has several clinically relevant findings. Consistent with prior studies investigating the volume-outcome relationship of percutaneous and surgical procedures, we noted increased annual hospital and physician Watchman volumes were associated with an increased likelihood of procedural success. With transition to the newer generation Watchman FLX device, the volume outcome curves flattened such that the absolute differences in mean procedural success rates among the highest and lowest volume quartiles (at both physician and the hospital level) were ~1%; however, variability in rates of procedural success were greater among lower volume physicians and hospitals. Taken together, these data suggest that while there is a volume-outcome relationship with LAAO, the newer-generation Watchman FLX device, with a higher overall procedural success rates, may allow lower volume physicians and hospitals to achieve high quality outcomes. To our knowledge, this is the first study to show that the procedure volume-outcome relationship varies by device type, and can be attenuated by iterative improvements in device design.
The first-generation Watchman device was FDA approved in 201513 after intense regulatory scrutiny and responding to the FDA mandate to perform a second pivotal trial14 to demonstrate improved periprocedural safety. In this context, the Watchman device was gradually introduced across hospitals and physicians using a detailed physician training and education program with continuous FDA oversight. This approach resulted in a very good safety profile among early commercial Watchman implants9 and likely attenuated the volume-outcome relationships enumerated in this manuscript.
Some have advocated for considering related procedures when assessing a volume-outcome relationship.3 For example, giving a surgeon or hospital credit for all related cardiac surgeries (e.g. combining valve surgeries and CABG) when calculating annual surgical volume for assessment of the relationship between procedural volume and outcomes with a single procedure (i.e. CABG), rather than solely considering annual CABG volume.3 Future research will be required to assess if there is an impact of annual volume of other left atrial (e.g. AF catheter ablation or percutaneous mitral valve repair) on the relationship between annual LAAO implant volume and LAAO outcomes. However, we did not observe an interaction between physician specialty, annual physician volume, and outcomes, which is notable since electrophysiologists are performing increasing numbers of left atrial procedures due to the increasing utilization of AF catheter ablation.
The current study demonstrates that the introduction of the newer-generation Watchman FLX device was associated with an increase in procedural success and a “flattening” of the hospital and physician volume-outcome relationship. This could be interpreted as an example of a gradual attenuation of the volume-outcome relationship over time, which has been reported with PCI and CABG1, rather than transition to a newer-generation Watchman device. Indeed, the gradual improvements in procedure safety and implant success over time were emphasized by a recent analysis15 comparing commercial Watchman 2.5 procedures (across a variety of hospitals) matched to patients enrolled in the pivotal PROTECT-AF16 and PREVAIL14 trials (from highly selected centers). However, the rapid transition from the first-generation Watchman 2.5 device to the newer generation Watchman FLX device (occurring over ~1 month at each site) allowed for the conduct of a unique experimental design comparing the outcomes of the first 27,013 FLX implants at 637 sites with the same number of Watchman 2.5 implants immediately before the transition to the new FLX device.17 The results from this study, which were also consistent in a secondary analysis using conventional 2:1 propensity score matching, demonstrated that the FLX transition was associated with a decline in the risk of pericardial tamponade, death, and a composite of MAE. Taken together, these findings suggest that “flattening” of the volume outcome relationship observed with the transition to the newer-generation FLX device is more strongly tied to the device itself rather than gradual improvements due to cumulative experience across operators and hospitals.
Although the field of LAAO is rapidly growing, the Watchman devices were the only FDA approved, commercially available devices for endocardial LAAO during the study period in the US. More recently, the Amulet device was FDA approved based on the results of the randomized Amplatzer Amulet Left Atrial Appendage Occluder Versus Watchman Device for Stroke Prophylaxis (Amulet IDE) trial.18 The Amulet IDE trial randomized patients to the Amulet device or the first-generation Watchman 2.5 device, and demonstrated similar long-term rates of stroke or systemic embolism, major bleeding, and cardiovascular death at 18 months. However, periprocedural complications were higher with Amulet, driven by significant differences in pericardial effusion and device embolism, which decreased with operator experience.18 Although there are certainly similarities between the Watchman and Amulet implant procedures (e.g. transseptal approach, cannulation of the left atrial appendage with a pigtail catheter) the extent to which procedural experience with the Watchman device translates to safety and efficacy with the Amulet device is unclear; in light of our study’s findings of device specific differences in the volume outcomes relationship across Watchman devices, this question merits further study. Additional study will also be required to determine how experience with commercially available LAAO devices impacts the safety and effectiveness of LAAO devices currently under investigation, including the WaveCrest and Conformal LAAO19 devices.
Limitations
This is a retrospective analysis of the NCDR LAAO Registry that contains several limitations associated with registry-based research. Patient and procedure characteristics (including adverse outcomes) are site reported and could be subject to inaccuracies and underreporting compared to the clinical trial setting. However, the NCDR has a longstanding data quality program to ensure submissions are valid, complete, and accurate, and this includes annual audits of 5% of participating sites.10 Device leaks were site determined and not centrally adjudicated. This analysis includes only Watchman LAAO devices. While this homogeneity increases the validity of the findings, it makes generalizability of these findings uncertain to other LAAO devices with different safety profiles and different physician education and device roll-out paradigms. While the LAAO Registry is a rich database for many applications, there are insufficient variables that would allow for the determination whether the association between procedure volume and race and ethnicity was directly related to race and ethnicity, or due to their associations between socioeconomics, health literacy, access to care, among other factors. This topic requires future study.
CONCLUSIONS
In this large US study of over 87,000 attempted LAAO implants, we demonstrated that higher physician and hospital procedure volumes were associated with a greater likelihood of procedural success. However, introduction of the newer generation Watchman FLX device resulted in a flattening of the volume curve such that even lower volume physicians and hospitals often achieved outcomes commensurate with higher volume physicians and hospitals. Our findings that the procedure volume-outcome relationship varies by device type, and can be markedly attenuated by iterative improvements in device design that improve procedural success and safety, have important implications for the commercial release, roll-out, and iteration of new LAAO and other devices.
Supplementary Material
What is Known
Procedure volumes are associated with outcomes for many cardiovascular procedures but the relationship between procedure volume and outcomes for Watchman LAAO remains poorly understood
What the Study Adds
Increasing physician and hospital volume was associated with increased likelihood of Watchman procedure success.
In analyses restricted to newer generation Watchman FLX procedures, there was significant attenuation in the volume-outcome relationship.
The LAAO volume-outcome relationship varies by device type and this relationship may require evaluation for each device type.
Acknowledgements
We wish to acknowledge Bonnie Garmisa, MAT, (Yale New Haven Hospital Center for Outcomes Research and Evaluation), for her longitudinal project leadership and Zhuokai Li, PhD, (formerly employed at Duke Clinical Research Institute), for sharing coding from a previous project.
Sources of Funding:
This study was funded by the American College of Cardiology (ACC) National Cardiovascular Data Registry (NCDR) and the National Heart, Lung and Blood Institute (NHLBI) grants R56HL142765 and R01HL142765.
Role of the Funder/Sponsor:
The sponsors/funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication. Sponsors/funders also had no right to veto publication nor to control the decision regarding to which journal the article was submitted.
This research was supported by the American College of Cardiology Foundation’s National Cardiovascular Data Registry (NCDR). The views expressed in this presentation represent those of the author(s), and do not necessarily represent the official views of the NCDR or its associated professional societies identified at CVQuality.ACC.org/
Disclosures
DJF has received: research grants from the Abbott, American Heart Association, Biosense Webster, Boston Scientific, Medtronic, Merit Medical, National Cardiovascular Data Registry, and National Institutes of Health, and consulting fees from Abbott, AtriCure, NI Medical, Microport, and Sanofi. JVF reported receiving consulting fees from Medtronic, Boston Scientific, Pacemate, and Biosense Webster, equity from Pacemate, and funding from the NIH. JPC reported an institutional contract with the American College of Cardiology for his role as Senior Scientific Advisor of the NCDR and equity interest in Medtronic. JPP is supported by R01AG074185 from the National Institutes of Aging. He also receives grants for clinical research from Abbott, the American Heart Association, the Association for the Advancement of Medical Instrumentation, Bayer, Boston Scientific, iRhythm, and Philips and serves as a consultant to Abbott, Abbvie, ARCA biopharma, Bayer, Boston Scientific, Bristol Myers Squibb (Myokardia), Element Science, Itamar Medical, LivaNova, Medtronic, Milestone, ElectroPhysiology Frontiers, ReCor, Sanofi, Philips, and Up-to-Date. FAM reported an institutional contract with the American College of Cardiology for his role as Chief Scientific Advisor of the NCDR. SV has received grants from American College of Cardiology, Society of Thoracic Surgeons, Cytokinetics, Abbott Vascular, Boston Scientific, National Institutes of Health (R01 and SBIR) and Food and Drug Administration (NEST cc) and serves as a consultant for Medtronic, Edwards Lifesciences, Total CME, American College of Physicians. The other authors report no relevant disclosures.
NON-STANDARD ABBREVIATIONS AND ACRONYMS
- AF
atrial fibrillation
- CABG
coronary artery bypass grafting
- CI
confidence interval
- IDE
investigational device exeption
- LAAO
left atrial appendage occlusion
- NCDR
National Cardiovascular Data Registry
- PCI
percutaneous coronary intervention
- SD
standard deviation
Footnotes
For more information go to CVQuality.ACC.org/. or ncdrresearch@acc.org
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