Impact of Baseline Heart Failure Burden on Post-ICD Mortality among Medicare Beneficiaries

Abstract

Objective

To assess the impact of baseline heart failure (HF) burden on survival with primary implantable cardioverter defibrillator (ICD) among Medicare recipients

Background

Survival after primary ICD implantation may differ between trial and Medicare populations

Methods

Linking data from the CMS ICD registry and the Medicare files (05–09), we identified primary ICD recipients ≥66 years with ejection fraction ≤35%. Number of prior HF hospitalizations (prior-HF-hosp) and length of hospitalization (hospital-day) prior to implantation were used to define HF burden. Crude all-cause mortality was estimated. Adjusted hazard ratios were derived from COX models.

Results

Of 66,974 ICD recipients (73% male, 88% white, mean age 75), 11,876 died (average follow-up=1.4 years), with three year mortality of 31%. Among patients with no prior-HF-hosp, three-year mortality was 27%, compared to 63% in those with ≥3 prior-HF-hosp (adjusted HR: 1.8). Among patients with same-day implantation, three-year mortality was 25%, compared to 53% in those with >1-week hospital-day prior to implantation (adjusted HR: 1.9). Mortality at three-year among the 31,685 ICD recipients with no prior-HF-hosp and same-day implantation (low HF burden) was similar to that in trials (22%).

Conclusion

Nearly one third of Medicare ICD recipients died within three years, reflecting a population with more advanced age and disease than seen in trial populations for primary prevention ICD. Nearly half of Medicare recipients had a low HF burden and had a survival similar to trial ICD recipients. Future research is warranted to understand the effectiveness of primary ICD implantation among Medicare beneficiaries with heavy HF burdens.

INTRODUCTION

Several landmark trials have demonstrated the efficacy of implantable cardioverter defibrillators (ICDs) in systolic heart failure (HF)(1–3). As a result, the Centers for Medicare & Medicaid Services (CMS) issued a National Coverage Determination in 2005 that expanded the ICD indication to include primary prevention of sudden cardiac death (SCD) among Medicare beneficiaries with prior myocardial infarction (MI) or chronic HF and left ventricular ejection fraction (EF) < 35% despite receipt of medical therapy(4). Data from the IMPROVE-HF registry has been extrapolated to project that ICD may be indicated to prolong survival for as many as 800,000 additional HF patients, most of whom are over 65 years old(5).

The demographics of patients currently receiving ICDs indicate that they are older with a higher prevalence of non-cardiac comorbidities than their counterparts enrolled in the landmark clinical trials(6). The survival benefit of ICDs is likely to attenuate with age(7–9), since increasing age has been associated with a decreased risk of SCD among HF populations(7–8) and non-cardiac death is more common in older ICD recipients(10). The survival benefit of ICDs also diminishes among patients with non-cardiac comorbidities, such as chronic kidney disease (9,11–12).

The efficacy of ICD implantation for primary prevention (primary ICDs) has been demonstrated among outpatient trial participants with stable mild-moderate HF symptoms, which have informed long-term cost-effectiveness estimates(1,13–14). It is not known how these benefits might translate to older patients with differing HF burdens, as reflected by multiple prior HF hospitalizations or prolonged current hospitalization for acute decompensation of chronic HF. In this study, we aimed to 1) describe long-term survival with primary ICDs in the Medicare population and 2) evaluate the impact of HF and comorbidity burden on survival with ICDs, using the number of previous HF hospitalizations and the length of hospitalization prior to ICD implantation as proxies for chronic and acute HF burden, respectively

METHODS

Data sources

We conducted a retrospective cohort study using the CMS-ICD registry and Medicare Provider Analysis and Review (MedPAR) files from January 1, 2005 through December 31, 2009.

CMS-ICD Registry

The CMS ICD registry is a subset of the American College of Cardiology (ACC)-National Cardiovascular Data Registry (NCDR) ICD Registry, which is the sole repository for ICD implantation data for Medicare beneficiaries(15–19). The registry was developed through a partnership of the Heart Rhythm Society and the American College of Cardiology Foundation, utilizing the expertise of the National Cardiovascular Data Registry. The data is entered by hospital personnel and is only included in the analytic file if hospitals achieve certain completeness on specific data elements(20). In addition, a subset of hospitals is randomly selected for quality control review to evaluate data accuracy. Currently, over 400,000 patients are included in the CMS-ICD registry, which contains 37 out of 170 data elements that the ACC-NCDR collects. These 37 elements include a patient’s identifying information, history and clinical characteristics, medications, facility information, provider information, ICD indications, device information, and in-hospital complications.

MedPAR file

The MedPAR file contains data from claims for services provided to fee-for-service beneficiaries admitted to Medicare-certified inpatient hospitals. It includes information on beneficiary demographics, diagnoses, procedures, and health resource utilization from hospitals or skilled nursing facilities, as well as detailed data on accommodation and departmental charges, days of care, and entitlement.

We linked the ICD registry to MedPAR files by four non-unique identifiers: gender, date of birth, admission date for ICD implantation, and provider ID, similarly to previously described methods(21–22). We validated this linkage by comparing to a linkage using a personal identifier (social security number cross-linked to beneficiary ID) among the subset of the data that had this identifier. We found that our linkage method had 95% specificity, 98% sensitivity, and 98% positive predictive value compared to the linkage method using personal identifiers.

Study population

The study population consisted of Medicare fee-for-service beneficiaries who had a reduced (≤35%) EF and received an ICD for the primary prevention of SCD. Patients who had a history of cardiac arrest or sustained ventricular tachycardia (VT) were excluded. We also required patients to be eligible for Medicare for at least one year prior to the index procedure and to be at least 66 years of age at the time of implantation. We censored patients in the analyses at the earliest occurrence of the following: death or the end of the study period.

Outcome

The study outcome was all-cause mortality. The date of death was obtained from the MedPAR file.

Measures of acute and chronic HF burden and subgroups

We used the number of previous HF hospitalizations and the length of hospitalization prior to ICD implantation as indicators of chronic and acute HF burden. We followed a previously validated algorithm with PPV of 94% to identify HF hospitalizations within one year prior to ICD implantation from MedPAR data(23), and then categorized the number of prior HF hospitalizations into four levels (Table 2). We also classified the interval from admission to ICD implantation to four levels (Table 3). Patient who had no prior HF hospitalization and received ICD on the admission date were considered to have low burden of HF.

Table 2.

Characteristics and outcomes by the number of prior HF hospitalizations

	0 hospitalizations	1 hospitalizations	2 hospitalizations	≥3 hospitalizations
N (% total population)	52,963(79)	10,247(15)	2,501(4)	1,263(1)
Age (y) §	75(71–80)	76(71–80)	76(71–81)	76(71–80)
Age ≤ 70y	13,005(25)	2,357(23)	564(23)	309(24)
Age ≥ 80y	14,025(26)	3,016(29)	733(29)	346(27)
Male	39,620(75)	6,906(67)	1,566(63)	761(60)
White	47,332(89)	8,682(85)	1,968(79)	934(74)
EF(%)§	25(20–30)	25(20–30)	25(20–30)	23(20–30)
≤20%	16,418(31)	4,406(43)	1,075(43)	610(48)
HF Duration	52,705	9,816	2,422	1238
New HF	7,965(15)	0(0)	0(0)	0(0)
0–3 months	7,297(14)	1,587(16)	348(14)	157(12)
3–9 months	6,317(12)	1,771(18)	398(16)	166(13)
>9 months	31,126(59)	6,458(66)	1,676(69)	915(74)
NYHA class	52,663	10,211	2489	1261
I	3,617(7)	253(2)	44(2)	12(1)
II	17,597(33)	2,386(23)	474(19)	189(15)
III	29,239(56)	6,824(67)	1,716(69)	882(70)
IV	2,210(4)	748(7)	255(10)	178(14)
QRS ≥ 120 msec	32,949(62)	6,817(67)	1,651(66)	852(67)
Ischemic cause HF	42,168(80)	7,995(78)	2,020(81)	1,049(83)
Unsustained VT	12,382(23)	2,273(22)	590(24)	309(24)
Prior Hospitalization for any cause§§	0·6(1)	2(1·3)	3·2(1·4)	5.5(2.6)
≥ 5	506(1)	498(5)	402(16)	720(57)
LOS of implantation§§	3·9(5·2)	4·2(5·5)	5(6)	5.9(6.2)
Charlson Score *§§	0·6(1·2)	1·8(1·6)	2·5(1·7)	3.1(1·8)
Outcomes
Death	8,135	2,449	769	523
Average follow-up(range)	1·4(0d-4y)	1·3(0d-4y)	1·3(0d-4y)	1·1(0d-4y)
Median survival(y) (IQR)	***	***	3(2·9–3·4)	2·9(1·7–2·1)
1-yr mortality risk(%) (95% CI)	10(10–11)	17(16–18)	24(23–26)	33(30–36)
2-yr mortality risk(%) (95% CI)	19(19–20)	30(29–31)	37(35–40)	51(48–55)
3-yr mortality risk(%) (95% CI)	27(27–28)	40(38–43)	52(46–57)	63(57–68)**
Hazard ratio (HR) for death	-	1·7(1·6–1·7)	2·2(2·1–2·4)	3·4(3.2–3·8)
Age, sex, race-adjusted HR	-	1·6(1·6–1·7)	2·2(2·0–2·3)	3.3(3.0–3.6)
Multivariable adjusted HR+	-	1·2(1·1–1·2)	1·3(1·2–1·5)	1.8(1·6–2·0)

^§Median(IQR);

^§§Mean (SD);

^*Without counting cardiac conditions (myocardial infarction and heart failure);

^**The marked survival times are censored observations

^***Follow-up was not long enough to observe median survival time

⁺Adjusted for age, gender, race, year of implantation, device type, time from admission to implantation, time from implantation to discharge, EF, ischemic HF, QRS duration, NYHA class, HF duration, Presence of unsustained VT, Non-dilated cardiomyopathy, cerebralvascular disease, diabetes, chronic kidney disease, COPD, osteoporosis, dementia, depression, mania, anxiety, psychotic disorder, delirium, metastatic cancer., MI in 40 days, CABG/PCI in 90 days. Prior use of flu vaccine, pneumococcal vaccine, pace maker, Number of prior hospitalizations for any cause, for mi or other cardiac disease, Charlson comorbidity score without counting MI and HF.

Table 3.

Characteristics and outcomes by the number of days from admission to ICD implantation

	0 days	1 day	2–7 days	≥8 days
N (% total population)	39,576(59)	5,636(8)	16,959(25)	4,803(6)
Age(y) §	75(70–80)	76(71–80)	76(71–81)	76(71–81)
Age ≤ 70y	10,005(25)	1,260(22)	3,877(23)	1,093(23)
Age ≥ 80y	9,982(25)	1,553(28)	5,151(30)	1,434(30)
Male	29,145(74)	4,269(76)	12,027(71)	3,412(71)
White	35,815(91)	5,023(89)	14,198(84)	3,880(81)
EF(%)§	25(20–30)	25(20–30)	25(20–30)	25(20–30)
EF ≤ 20%	11,845(30)	2,034(36)	6,743(40)	2,156(45)
HF Duration	39,071	5,570	16,766	4,774
New HF	4,919(13)	748(13)	1,898(11)	400(8)
0–3 months	4,007(10)	793(14)	3,379(20)	1,210(25)
3–9 months	5,533(14)	658(12)	1,928(12)	533(11)
>9 months	24,612(63)	3,371(61)	9,561(57)	2,631(55)
NYHA class	39,398	5,605	16,852	4,769
I	2,555(6)	348(6)	866(5)	157(3)
II	13,510(34)	1,662(30)	4,449(26)	1026(21)
III	22,286(57)	3,321(59)	10,089(60)	2,971(62)
IV	1,047(3)	274(5)	1,448(9)	615(13)
QRS ≥120 msec	25,363(64)	3,752(67)	10,365(61)	2,789(58)
Ischemic cause HF	31,111(79)	4,452(79)	13,662(81)	4,007(83)
Unsustained VT	6,384(16)	1,436(26)	5,578(33)	2,156(45)
Prior Hospitalization for any cause§§	0.9(1.3)	1.1(1.5)	1.1(1.6)	1.4(1.8)
≥ 5	919(2)	202(4)	738(4)	267(6)
Time from Implantation to discharge (days)§§	1.4(1.7)	2.1(2.7)	2.8(3.2)	4.4(5)
Charlson Score*§§	0.8(1.3)	1(1.4)	1.1(1.6)	1.3(1.7)
Outcome
Death	5,245	972	3,999	1,660
Average follow-up(range)	1.5(0d-4y)	1.4(0d-4y)	1.3(0d-4y)	1.2(0d-4y)
Median survival(y) (IQR)	***	***	3.8(3.8-.)	2.7(2.6–3.3)
1-yr mortality risk(%) (95% CI)	8(8–8)	12(11–13)	18(18–19)	29(28–31)
2-yr mortality risk(%) (95% CI)	16(16–17)	22(21–23)	30(29–31)	43(41–44)
3-yr mortality risk(%) (95% CI)	25(24–25)	32(29–35)	41(39–42)	53(50–57)
Hazard ratio(HR) for death	-	1.4(1·3–1·5)	2.1(2.0–2.2)	3.4(3.2–3.6)
Age, sex, race-adjusted HR	-	1.4(1·3–1·5)	2.0(1.9–2.1)	3.2(3.1–3.4)
Multivariable adjusted HR+	-	1.1(1·0–1·2)	1.4(1.4–1.5)	1.9(1.8–2.0)

^§Median(IQR);

^§§Mean (SD);

^*Without cardiac conditions: myocardial infarction and heart failure;

^**The marked survival times are censored observations;

^***Follow-up was not long enough to observe median survival time

⁺Adjusted for age, gender, race, year of implantation, device type, time from implantation to discharge, EF, ischemic HF, QRS duration, NYHA class, HF duration, Presence of unsustained VT, Non-dilated cardiomyopathy, cerebralvascular disease, diabetes, chronic kidney disease, COPD, osteoporosis, dementia, depression, mania, anxiety, psychotic disorder, delirium, metastatic cancer., MI in 40 days, CABG/PCI in 90 days. Prior use of flu vaccine, pneumococcal vaccine, pace maker, Number of prior hospitalizations for any cause, for hf, mi or other cardiac disease, Charlson comorbidity score without counting MI and HF.

Statistical analysis

Baseline characteristics of the overall study population and each subgroup were characterized by percentages for categorical variables and using medians and interquartile ranges or means and standard deviations for continuous variables.

We graphed cumulative mortality over time using Kaplan-Meier estimators for the entire study population and for each subgroup. Differences among subgroups were tested using log-rank tests. We used proportional hazards regression models to derive crude, demographic (age, gender, and race), and multivariable-adjusted HRs among the subgroups. We attempted to account for the impact of other measures of HF severity (such as HF duration and NYHA class) and of comorbidities (such as CAD, un-sustained VT, Non-dilated cardiomyopathy, cerebrovascular disease, diabetes, chronic kidney disease, COPD, osteoporosis, mental disorders, metastatic cancer) on post-implantation mortality in the multivariable-adjusted model (see footnotes for Table 2 and 3 for the complete list of covariates in the model).

All analyses were conducted using SAS for Windows, release 9.2 (SAS Institute Inc., Cary, NC). The study was approved by the Institutional Review Board of Brigham and Women's Hospital.

RESULTS

Characteristics and survival of overall Medicare patients with ICD

The final study cohort consisted of 66,974 Medicare HF patients who underwent ICD implantation for primary prevention of SCD (Appendix I for the description of the final study patients). The median age was 75 years and the majority were male (73%) and white (88%) (Table 1). More than half of the patients (61%) had known HF for more than nine months, with 79% having HF due to an ischemic cause. The median EF was 25%. Over a quarter (28%) of the patients were hospitalized at least once for any cause within one year prior to implantation, among which, 14% had more than five hospitalizations. During the average follow-up of 1·4 years, 11,876 patients died. One-, two-, and three- year mortality after ICD implantation was 12%, 22%, and 31%, respectively (Table 1).

Table 1.

Main characteristic and outcomes among Medicare beneficiaries receiving primary ICD implantations (N=66,974)

Median Age (y) (IQR)	75(71–80)
Male	48,853(73)
White	58,916(88)
Median EF % (IQR)	25(20–30)
HF Duration
New HF	7,965(12)
0–3 months	9,389(14)
3–9 months	8,652(13)
>9 months	40,175(61)
Missing (N)	793
NYHA class
I	3,926(6)
II	20,647(31)
III	38,667(58)
IV	3,384(5)
Missing (N)	350
QRS ≥ 120 msec	42,269(63)
Ischemic cause HF	53,232(79)
≥1 Prior hospitalization for any cause	18,752 (28)
≥5 Prior hospitalization for any cause	2,624 (4)
Cardiac Resynchronization Therapy - Defibrillators	32,201(48)
Outcomes
Death (N)	11,876
In-hospital death (N)	327
In hospital death risk(%) (95% CI)	0·49 (0·45–0·55)
Average follow-up(range)	1·4 (0 day–4 yrs)
Mortality rate (per 1,000 person-year)	128
1-yr mortality risk(%) (95% CI)	12 (12–13)
2-yr mortality risk(%) (95% CI)	22 (22–23)
3-yr mortality risk(%) (95% CI)	31 (30–32)

Chronic HF burden: number of prior HF hospitalizations

At least one prior hospitalization for HF had occurred in the year preceding ICD implantation for 14,011 patients (21%). Of these, 27% had two or more hospitalizations attributed to HF (Table 2). A higher number of prior HF hospitalizations was associated with lower EF: 31% had EF ≤ 20% among patients with no prior HF hospitalization versus 48% among patients with three or more prior HF hospitalizations). Prior HF hospitalization was also associated with higher NYHA class at time of implant: 59% of patients no prior HF hospitalization had NYHA class III/IV symptoms at implantation compared to 84% among patients with three or more prior HF hospitalizations. Chronic HF burden was also associated with more frequent comorbidities, as reflected by the number of prior all-cause hospitalizations and the Charlson comorbidity score. (Table 2)

Mortality by the number of prior HF hospitalizations

After ICD placement, mortality at three years increased from 27% in patients without prior HF hospitalization to 63% in those with three or more prior HF hospitalizations (Table 2, Figure 1). Among patient who had more than three prior HF hospitalizations, more than half died by two years of implantation (Figure 1). Compared to patients without a prior hospitalization, the crude HR for mortality ranged from 1.7 for patients with one prior HF hospitalization to 3.4 for patients with three or more prior HF hospitalizations. The pattern of HRs across levels of chronic HF burden remained similar after adjusting for demographics. The impact of number of hospitalizations on all-cause mortality suggests that the number of hospitalizations may serve as a surrogate for HF severity and comorbidities, because its effect diminished substantially after adjusting for these variables in multivariable analyses. (Table 2) Although close to a half (48%, Table 1) of the patients received a CRT-D device, the impact of the number of prior HF hospitalization on post-implantation mortality did not vary by device type (data available upon request).

Figure 1. Kaplan-Meier cumulative crude mortality by the number of prior HF hospitalizations.

After ICD placement, mortality at three years increased from 27% in patients without prior HF hospitalization to 63% in those with three or more prior HF hospitalizations. Among patient who had more than three prior HF hospitalizations, more than half died by two years of implantation.

Acute HF burden: number of days from admission to ICD implantation

Of 27,398 patients who had at least one hospital day between the admission day and ICD implantation, 62% had been hospitalized for two to seven days prior to the procedure. Similar to the impact of the number of prior HF hospitalizations, a longer duration from admission to ICD implantation was associated with lower EF, higher NYHA class, and higher comorbidity burden. It was also associated with greater proportion of HF of ischemic origin (79% in the same-day implantation patients versus 83% in those who hospitalized for eight or more days before implantation). (Table 3)

Mortality by the number of days from admission to ICD implantation

Mortality at three years was more than twice as high, from 25% in patients with same-day implantation to 53% in the patients hospitalized for eight or more days before implantation (Table 3, Figure 2). Among patients who had more than eight hospital-days before implantation, more than half died by three years (Figure 2). Compared to the same-day implantation group, the crude HR for mortality ranged from 1.4 in the same-day implantation group to 3.4 in the eight or more days group. The pattern of elevated HRs remained similar after adjusting for demographics. After adjusting for HF severity and comorbidities, the impact of the hospitalization duration on mortality was attenuated, indicating that duration of hospitalization, like number of HF hospitalizations, likely serves as a surrogate for overall disease severity. (Table 3) The impact of the hospitalization duration on post-implantation mortality was also the same between patients received CRT-D and simple ICD (data available upon request).

Figure 2. Kaplan-Meier cumulative crude mortality by the number of days from admission to ICD implantation.

Mortality at three years was more than twice as high, from 25% in patients with same-day implantation to 53% in the patients hospitalized for eight or more days before implantation. Among patients who had more than eight hospital-days before implantation, more than half died by three years.

A Subgroup with Low HF burden

Accumulating acute and chronic HF burden is associated with escalating mortality risk. Conversely, patients who had no HF hospitalization in the year before ICD implantation and received the device on the admission day (47%, N=31, 685) had the lowest risk of mortality. (Table 4) In fact, these patient without a high burden of HF had similar mortality after ICD implantation as those in the major trials (Figure 3). By contrast, a higher mortality was seen for primary ICD recipients was seen in those with both chronic and acute burdens of HF at the time of implantation (N=6,120, three-year mortality=50–69%). (Table 4)

Table 4.

Mortality at three years after ICD implantation among subgroups categorized by acute and chronic HF burdens

Acute HF burden	0 Hospital days from admission to implantation	1–7 Hospital days from admission to implantation	8+ Hospital days from admission to implantation
Chronic HF burden
0 Prior HF hospitalizations	22% (N=31,685)	34% (N=17,581)	50% (N=3,697)
1–2 Prior HF hospitalizations	35% (N=7,332)	50% (N=4,459)	59% (N=957)
3+ Prior HF hospitalizations	54% (N=559)	69% (N=555)	61% * (N=149)

^*The survival times are censored observations

Figure 3. Post-implantation Mortality among Medicare Populations with Low Burden of HF (N=31, 685).

Patient who had no HF hospitalization in the year before ICD implantation and received the device on the admission day (47%, N=31, 685) had similar mortality after ICD implantation as those in the major trials (Mortality at three-year in patients with low HF burden=22% versus 16–22% in SCD-HeFT and MADIT II).

DISCUSSION

We assessed mortality after ICD implantation in a large population of Medicare beneficiaries using a national ICD registry linked to Medicare inpatient claims data. Approximately one in three Medicare patients died within three years of implantation in our study. We observed higher mortality among patients with a higher number of prior HF hospitalizations (measure of chronic HF burden) and a longer duration between admission and ICD implantation (measure of acute HF burden). Both measures may be surrogates not only for HF severity but also for other comorbidities, and they have additive effect on post-ICD mortality. Although our analyses did not include a comparison group of non-ICD recipients and could not estimate the relative effect of ICDs in these subgroups, they provided insights on the sub-populations less likely to experience a competing risk of mortality that cannot be prevented by ICD therapy. Specifically, we observed nearly half of the Medicare ICD recipients had low burden of HF at the time of implantation and their survival was similar to what had been demonstrated in the landmark trials.

Saxon and colleagues assessed the long-term mortality after ICD implantation for primary and secondary prevention during the post-ICD coverage expansion period,(24) 21% died at three years for patients receiving an ICD (N=108, 027) and 29% for those receiving CRT-D (N=77, 751). The overall survival after primary ICD implantation appears to be shorter among our Medicare population given that mortality in the Saxon study is likely to have been elevated by including patients receiving the devices for secondary prevention. The shorter survival after ICD implantation among our Medicare patients could reflect more severe HF or comorbidities associated with older age. Compared to primary ICD recipients in a nationwide ICD registry(25), which includes patients younger than 66 years of age, our Medicare ICD recipients had worse HF symptoms by NYHA class.

We attempted to quantify the chronic burden of HF by the number of prior HF hospitalizations, which has been shown to be an independent predictor of mortality among HF patients(26–28). Patients with repeated HF hospitalizations are more likely to die from non-arrhythmic causes of death such as pump failure or non-cardiac causes(29–30). Moreover, previous HF hospitalization has been shown to predict early HF death and lower ICD efficacy in the MADIT-II trial(31), The decision to implant an ICD in patients with prior HF hospitalizations should be made cautiously and with appropriately calibrated expectations of HF survival.

To describe the burden of a prolonged exacerbation of HF, we used the duration from admission to ICD implantation, assuming that prior to implantation patients were likely undergoing evaluation or treatment either for HF or for other serious comorbidities. Increasing the number of days during a HF hospitalization suggests that decompensation is more complicated, more severe, or more refractory to interventions. Although we were not able to investigate what happened during the prolonged hospitalization before the procedure in our study population, our assumption was supported by the observation that those who received an elective ICD procedure had shorter time from admission to implantation (mean=0.3 days, SD=1) than those who received ICDs during an admission for HF, other cardiac conditions or non-cardiac conditions (mean=5 days, SD=4). Indications for HF admission generally include symptoms at rest, which meet the definition of Class IV HF, for which ICD are generally considered to be contra-indicated. Evidence to support ICD use among patients with ongoing Class IV symptoms is limited, as these patients were not included in pivotal trials of ICD efficacy among HF populations (1, 3), although the use of ICD with CRT has been shown to be beneficial in ongoing Class IV patients in COMPANION (2). Prevention of SCD would be expected to have less impact on overall mortality than preventing death due to HF after HF decompensation since the major cause of death among trial patients hospitalized for worsening HF is progressive HF rather than SCD(32), and HF hospitalization is a major risk factor for death in ICD recipients(31). Our findings indicate research is needed on whether ICD implantation during an admission for HF decompensation will have a survival benefit due to competing mortality. This may be particularly important for patients requiring a prolonged hospitalization given our finding that length of hospitalization prior to implantation was associated with shorter survival.

Lastly, the post-implantation mortality among our Medicare primary ICD recipients is higher than that of the patients included in the major primary ICD trials(1,3)—16% in SCD-HeFT and 22% in MADIT II (at three-year), However, we observed the mortality was similar to that of the landmark trials (1, 3) when ICDs were implanted among Medicare patients who had no prior HF hospitalizations and can receive ICDs on the admission day (Table 4), despite the underlying age difference. It is encouraging that we identified this sub-population by using the rough proxies of HF burdens. It is also worth noting that a substantial proportion of the Medicare ICD recipients were in the “low HF burden” category at the time of implantation, which reflects an appropriate selection of Medicare ICD recipients in the current practice. Nevertheless, future research is warranted to refine our measures of baseline HF burden to support clinical decisions on who should receive the device.

Our results should be interpreted in light of inherent limitations. As mentioned earlier, our analyses did not include a comparison group of non-ICD recipients, and could not estimate the relative effect of ICDs by underlying HF burdens. The registry and Medicare data were not always in agreement. For example, 6% of patients who received ICDs with a primary prevention indication were also noted in the registry to have sustained VT noted (suggesting secondary prevention). We excluded these patients in order to avoid mixing primary and secondary ICDs. A review of a tertiary care center’s ICD registry found incomplete coding for indication, further supporting our decision to exclude patients with discrepant indication data(33).

We linked 64% (N=122, 562) of registry records to MedPAR file. The MedPAR file does not contain claims for the majority of non-fee-for-service Medicare beneficiaries, unless those beneficiaries enrolled in a cost-based managed care plan and the plan elects to have CMS to process and pay for the service provided(34). Given the prevalence of Medicare beneficiaries under a non-cost-based managed care arrangement, which ranges from 14% to 22% during the study time frame(34), our matched records represent approximately 79% of the implantations recorded in the registry that would be for fee-for-service Medicare beneficiaries. Incomplete linkage may have also been due to data entry errors or inconsistencies in the information collection policy between the registry and Medicare files on the fields that were used for linkage. For example, when gender is unknown to Medicare, “Female” value is automatically assigned for that claim(35). Also, if arrival to the emergency department is recorded as the patient’s admission date in the registry, it would differ from the date recorded in the claims data. Nevertheless, these errors are likely to be random and unlikely to compromise the validity of our findings.

CONCLUSIONS

Approximately one in three Medicare primary ICD recipients died within three years of implantation. Medicare patients with a low cumulative burden of HF had similar mortality to those in the landmark trials. Further studies are needed to assess effectiveness of primary ICD implantation among patients with heavy burdens of HF and other comorbidities to guide clinical strategies and policy decisions among Medicare beneficiaries.

Abbreviations List

CRT

Cardiac resynchronization therapy

CRT-D

Cardiac resynchronization therapy-Defibrillator

EF

Ejection fraction

HF

Heart failure

ICD

Implantable cardioverter defibrillator