In Emergency Department Patients with Acute Chest Pain, Stress Cardiac MRI Observation Unit Care Reduces 1- year Cardiac-Related Health Care Expenditures: A Randomized Trial

Abstract

Objective

To compare the direct cost of medical care and clinical events during the first year after patients with intermediate risk acute chest pain were randomized to stress cardiovascular magnetic resonance (CMR) observation unit (OU) testing, versus inpatient care.

Background

In a recent study, randomization to OU-CMR reduced median index hospitalization cost compared to inpatient care in patients presenting to the emergency department with intermediate risk acute chest pain.

Methods

Emergency department patients with intermediate risk chest pain were randomized to OU-CMR (OU care, cardiac markers, stress CMR) or inpatient care (admission, care per admitting provider). This analysis reports the direct cost of cardiac-related care and clinical outcomes (MI, revascularization, cardiovascular death) during the first year of follow-up subsequent to discharge. Consistent with health economics literature, provider cost was calculated from work-related relative value units using the Medicare conversion factor; facility charges were converted to cost using departmental specific cost-to-charge ratios. Linear models were used to compare cost accumulation among study groups.

Results

One-hundred nine (109) randomized subjects were included in this analysis (52 OU-CMR, 57 inpatient care). The median age was 56 years; baseline characteristics were similar in both groups. At 1 year, 6% of OU-CMR and 9% of inpatient care participants experienced a major cardiac event (p=0.72) with 1 patient in each group experiencing a cardiac event after discharge. First-year cardiac-related costs were significantly lower for participants randomized to OU-CMR compared to participants receiving inpatient care (geometric mean = $3101 vs $4742 including the index visit (p = .004) and $29 vs $152 following discharge (p = .012)). During the year following randomization, 6% of OU-CMR and 9% of inpatient care participants experienced a major cardiac event (p=0.72).

Conclusions

An OU-CMR strategy reduces cardiac-related cost of medical care during the index visit and over the first year subsequent to discharge, without an observed increase in major cardiac events.

Introduction

Chest pain observation units reduce costs of the index hospital visits for patients with chest pain (1,2) and are recommended for use in the ACC/AHA guidelines.(3) However, patients with intermediate risk chest pain and no definite evidence for acute coronary syndrome (ACS) are commonly admitted for inpatient care due to the difficulty of managing patients with prior coronary heart events, and the higher acuity of their presenting illness.

A recent randomized clinical trial in emergency department (ED) patients with intermediate risk chest pain demonstrated that observation unit care coupled with stress cardiovascular magnetic resonance testing (OU-CMR) was associated with a median reduction in cost of $588 during the index hospitalization compared to inpatient hospital care.(4) However, the cost of an index hospitalization may not adequately reflect resource consumption for a particular illness; also, the care delivered during the index hospitalization may impact downstream care patterns.

The objective of this study was to compare the cost of medical care, measures of resource utilization, and report the clinical outcomes in ED patients with intermediate risk acute chest pain in the year following randomization to either inpatient care or OU-CMR. We anticipated that the reduction in index hospital visit cost seen with OU-CMR would be followed by similar utilization patterns among groups after hospital discharge. We suspected that reductions seen with OU-CMR would occur without an increase in the rates of major cardiac events.

Methods

Study Design

As previously described(4), we conducted a single center randomized clinical trial. All participants provided written informed consent. The study was approved by the Institutional Review Board of Wake Forest University School of Medicine, and was HIPAA compliant.

Participants were recruited from the ED of a tertiary care referral center from January 2008 through April 2009 that has an annual volume of 96,000 visits per year and is a level 1 trauma center. The ED is staffed by board prepared / board certified emergency physicians supervising care provided by residents in training. The observation unit is under the direction of the ED and is staffed by nurse practitioners and physician assistants with care provided jointly with emergency physicians. Cardiovascular medicine consultation is available at the discretion of the emergency physicians.

We enrolled individuals presenting to the ED with intermediate risk acute chest pain. Intermediate risk was defined as at least an intermediate probability that the patient’s symptoms were related to acute coronary syndrome or a TIMI risk score ≥2 calculated in the ED. Care providers were encouraged to use the ACC/AHA framework to formulate their clinical impression. Additional inclusion criteria were age ≥18 years, care provider impression that an inpatient assessment was indicated, and care provider assessment that the patient could be discharged if cardiac disease was excluded. Exclusion criteria were an initial Troponin I above the diagnostic threshold for MI, ST-segment elevation (≥1mV) or depression (≥2mV), contraindications to CMR, systolic blood pressure <90 mm Hg, inability to lie flat, refusal of follow-up procedures, <3 months life expectancy, pregnancy, renal insufficiency (such that the estimated glomerular filtration rate was <45 cc/minute), chronic liver disease, or solid organ transplant.

To find eligible participants, study staff screened ED patients with chest pain or related symptoms from 8am–11pm Monday through Thursday and 8am–11am on Friday. Consented participants were then randomized to one of two study arms: OU-CMR or inpatient care. OU-CMR participants were placed into the observation unit, received serial cardiac markers at 4 hours and 8 hours from the initial marker, and had orders placed for a stress CMR study. One OU-CMR participant left against medical advice prior to observation unit placement. Inpatient care participants were consulted for admission following standard admission practices at the study institution. Study patients were admitted to the services of cardiologists [n=29], internists [n=17], family medicine physicians [n=8], with 3 leaving against medical advice prior to admission.

OU-CMR imaging protocol

Imaging in OU-CMR participants has been previously described(4) and was similar to imaging used for clinical care at the study institution. In general, imaging was conducted with a 1.5 Tesla Siemens Magnetom Avanto system (Siemens Medical Solutions, Munich, Germany). Initial orders were placed for an adenosine CMR, which included the imaging sequences noted in Table 1. Dobutamine stress was available as an alternative in the event adenosine was contraindicated. Images were interpreted by board certified cardiology or radiology faculty with at least level II training in CMR.(5)

Table 1.

Typical imaging sequences for OU-CMR participants

Scan	Views	Pulse Sequence	Imaging Matrix	FOV (mm)	Slice Thickness (mm)	TE (ms)	TR (ms)	Flip Angle (deg)	Band-width (Hz/pix)
Resting wall motion	2, 3, 4 chamber and 3 LV short axis views	Cine SSFP	192×156	360	7	1.2	40	80	930
T2 dark blood (body coil)	2, 3, 4 chamber and 3 LV short axis views	IR turboSE (2RR, no fatsat)	256×162	360	8	74	658	60/200	150
Contrast and Stress Agent Injection gadopentetate dimeglumine 0.1 mmol/kg) and stress agent: adenosine or dobutamine
Stress perfusion	3 LV short axis views	Turbo-GRE	192×108	360	8	1.1	170	12	650
Contrast Injection gadopentetate dimeglumine 0.1 mmol/kg
Rest perfusion	3 LV short axis views	Turbo-GRE	192×108	360	8	1.1	170	12	650
Delayed enhancement	2, 3, 4 chamber and 10 short axis views	IR GRE 300 TI	192×140	320	8	3.3	800	25	130

FOV = Field of view, TR = Repetition time, TE = Echo time, LV = Left ventricle, IR = Inversion recovery, TI = Inversion time, SSFP = Steady state free precession, SE = Spin echo, GRE = Gradient echo, FS = Fat saturation

Outcomes and definitions

The primary outcome of this analysis is the direct cost of cardiac-related healthcare through 1 year after randomization. Utilization measures used to calculate cost were cardiac-related hospital admissions, cardiac procedures, and cardiac-related office visits, further defined in Table 2. If a hospitalization or office visit met the definition of cardiac-related, the entire cost of the visit was considered cardiac-related. The secondary outcome is major cardiac events, comprised of myocardial infarction, revascularization, and cardiovascular death.

Table 2.

Definition of cardiac-related healthcare utilization

Cardiac Related ED Visits

Signs or symptoms of chest pain or dyspnea associated with either: an ECG and cardiac markers being performed; or discharge or admitting diagnosis related to cardiac disease (if provided)

Cardiac Related Hospitalizations

One of the following cardiac procedures performed: Cardiac imaging / stress testing (excluding resting echo as a sole test) Revascularization Pacemaker / defibrillator placement

Primary reason for admission is concern for ACS

Discharge diagnosis related to chest pain, MI, ACS, heart failure, or other cardiac disease

Cardiac related outpatient visits

Cardiology Appointment

Appointment associated with or leading to cardiac testing or procedure (imaging, catheterization, or revascularization)

Follow-up related to an ED visit for chest pain, a hospitalization for chest pain, or other cardiac hospitalization

Appointment due to chest pain

Appointment related to diagnosis or treatment of heart disease; except routine follow-up or visits with the primary care physician to follow a stable cardiac condition

Outpatient Cardiac Related Procedures

Cardiac imaging / stress testing

Cardiac rhythm monitoring (ex. Holter monitor)

Revascularization

Pacemaker / defibrillator placement

Myocardial infarction occurring at the study institution was defined as a troponin I > 1.0 ng/ml in the presence of ischemic symptoms. Troponin I was measured in the central lab using either the TnI-Ultra™ assay using the ADVIA Centaur platform (Siemens) or the Access® AccuTnI™ Troponin I Assay using the dxi800s platform (Beckman Coulter). Patients reporting major cardiac events outside the study institution were considered to have had the event.

Data Collection and outcome measurement

After randomization, patients were followed during their index hospitalization by record review. Study staff then conducted a structured record review and telephone follow-up at approximately 30 days, 3 months, 6 months, and 1 year after randomization. Participants reporting hospitalizations occurring at another facility that were possibly cardiac-related had those records requested from the facility and reviewed.

During each telephone follow-up, a modified version of a previously described script was used to identify potential cardiac events.(6) Participants were then asked to identify all health care encounters during the follow-up interval which were then categorized as an office visit, emergency department visit, hospitalization, or procedure. These patient reports were cross referenced to those found in the medical record at the time of the phone contact. After completion of follow-up, itemized physician and facility billing records were obtained for each participant for the year following enrollment. Billing information was then manually paired with the encounters previously identified by record review and telephone follow-up. Encounters discovered through any of the three methods of identifying utilization (phone, medical record review, and billing record review) and classified as cardiac-related (Table 2) were included in the primary analysis. When available, exact dates were used for each component of resource consumption. If the date was not available, the date between the last contact and event reporting was used.

Follow up was conducted with medical record and billing record review on all participants through 1 year. In addition, telephone attempts continued through the patient’s enrollment in the study regardless of the success of the prior attempt. Follow up time was included through one year for those patients with more than one year of follow-up. For those patients who could not be contacted at 1 year, we used data through the longer of either the last telephone contact or when telephone and medical records (including billing records) no longer demonstrated accumulation of cardiac-related services.

Cost was comprised of two elements, provider and facility cost. Provider cost was calculated by obtaining work-related relative value units associated with each charge and converting to dollars using the Medicare conversion factor. Facility cost was determined by applying to each charge the departmental-specific cost to charge ratios used to file cost reports with Centers for Medicare and Medicaid Services annually. Cost for events occurring at other institutions (8/246 events) was calculated using the mean cost for similar services consumed among other study participants at the study institution.

The sample size for this study was determined to provide adequate power for assessing the effect of OU-CMR on the cost of the index hospital visit, which was the primary objective of this trial.(4) A cost model was constructed to assist in estimating the possible treatment effect and the variance of the index cost was estimated from pilot data. Based on this information, it was calculated that 110 participants would provide 90% power to detect a $2000 difference in the index hospital visit cost between study groups, allowing for an 8% attrition rate.

Data analysis

Baseline demographics and clinical outcomes were compared using Fisher exact tests for proportions; medians of continuous variables were compared using Wilcoxon rank sum tests. The primary analysis compared the first-year cardiac-related costs for patients randomized to OU-CMR to those costs for patients randomized to usual inpatient care. A year was defined as the first 360 days following discharge, allowing us to look at costs accrued over 12 equal ‘months’ of 30 days. Linear regression was used to assess group differences in total costs and costs following discharge, unadjusted and adjusted for patient characteristics. Covariates included the two stratification variables (known coronary disease (Y/N) and time of day of presentation (6a–3p or 3p–6a)), age at enrollment, gender, confirmed prior heart failure, confirmed prior MI, confirmed prior coronary revascularization, and chest pain at ED arrival. The cost data were highly skewed so log transformations were used to reduce the skewness and to stabilize the variances between groups. A small constant of 1 was added to follow-up costs so that log transformations could be used when the costs were zero. P-values for group differences in cost are based on analyses of the log-transformed data. We then divided costs up into 12 monthly periods of 30 days and repeated measures models were used to assess changes over time and to determine if the changes over time varied by group. An unstructured covariance matrix was used to account for the within patient correlation in costs over time.

Results

Study population, study intervention and follow up

Enrollment was conducted over 15 months during which 180 patients appearing to meet inclusion and exclusion criteria were approached to consent for participation in the study. Twenty-five exhibited unrecognized exclusion criteria, and 46 refused to participate in the randomization process. The remaining 109 formed the study population accounting for 110 participant encounters. One participant was enrolled twice and the second encounter was excluded from this analysis, although the costs of the second encounter are included along with the costs associated with the initial counter for that participant. This analysis included 57 participants randomized to inpatient care and 52 randomized to OU-CMR. The baseline characteristics of study participants are shown in Table 3 and are not statistically different between groups.

Table 3.

Baseline Characteristics of the Study Population – n (%)

	Inpatient care N = 57	OU-CMR N = 52	p value
Age (years, median [Q1, Q3])*	57 (47, 64)	55 (48, 62)	0.54
Male	30 (53)	24 (46)	0.57
Caucasian	40 (70)	35 (67)	0.84
Hypertension	43 (75)	35 (67)	0.40
Diabetes mellitus	23 (40)*	19 (37)	0.32
Current smoking	18 (32)	18 (35)	0.84
Hyperlipidemia	44 (77)	38 (73)*	0.66
Prior Heart Failure	3 (5)	2 (4)	1.00
Established CAD†	16 (29)	11 (21)	0.51
Prior MI‡	15 (26)	8 (15)	0.24
Prior PCI§	15 (26)	7 (13)	0.15
Prior CABG||	3 (5)	2 (4)	1.00

^*1 participant with unknown diabetes status and 2 participants with unknown hyperlipidemia status and were considered to not have these conditions; Categorical variables compared with fisher exact tests, medians compared with Wilcoxon rank sum test.

^*Q1, Q3 = first and third quartiles;

^†CAD = coronary artery disease,

^‡MI, myocardial infarction;

^§PCI, percutaneous coronary intervention;

^||CABG = coronary artery bypass graft

Of the 52 OU-CMR participants, 51 were managed in the observation unit and 1 left against medical advice. Stress CMR testing was conducted in 48/52 participants over a median scan time of 53 minutes. Hospital admission was avoided in 41 OU-CMR participants. In the inpatient care group, 3/57 left against medical advice prior to admission and the remaining 54 were admitted. Once admitted, 9 inpatient participants received stress CMR as part of their clinical evaluation, 31 received stress echocardiography, 9 received cardiac catheterization, and 10 received no stress testing or catheterization. Several patients in both groups received multiple procedures. All patients were followed through 360 days using medical record review and billing record analysis. Follow up information after discharge was obtained in 98% of participants through review of medical and billing records, and phone interviews designed to identify or confirm the absence of events. Phone contact at 1 year or beyond was established in 81%, each of whom contributed 360 days of information. Remaining participants contributed follow up data up to the last date of known consumption of cardiac-related services or the last date of phone follow up. The mean follow-up time was 320.5 days for the inpatient care participants and 309.0 for the OU-CMR participants.

Cardiac-related healthcare utilization

After discharge from the index hospital visit, 15% of OU-CMR participants experienced at least 1 cardiac-related ED visit during the subsequent year compared to 37% in the inpatient care group (p=0.02) (Table 4). Similarly, cardiac-related hospital admissions were significantly lower in the OU-CMR group (12%) compared to 35% in the inpatient care group (p=0.01). No differences were seen in the number of cardiac-related outpatient visits per group (p=0.30) with 83% of participants having between 0 and 2 visits over the year.

Table 4.

Cardiac-related healthcare utilization and clinical events – n (%)

	Index visit		After discharge through 1 year follow-up period		Cumulative		p-value*
	Inpatient care	OU-CMR	Inpatient care	OU-CMR	Inpatient care	OU-CMR
Stress testing	40 (70)	50 (96)	9 (16)	5 (10)	45 (79)	50 (96)	0.01
Cardiac catheterization	9 (16)	7 (13)	11 (19)	1 (2)	19 (33)	8 (15)	0.04
Cardiac catheterization or stress testing	47 (82)	51 (98)	18 (32)	6 (12)	53 (93)	51 (98)	0.37
Cardiac-related ED visits	-NA-	-NA-	-NA-	-NA-			0.02
0					36 (63)	44 (85)
1					14 (25)	7 (13)
≥2					7 (12)	1 (2)
Cardiac-related hospital admissions	-NA-	-NA-	-NA-	-NA-			0.01
0					37 (65)	46 (88)
1					15 (26)	5 (10)
≥2					5 (9)	1 (2)
Outpatient cardiac-related visits	-NA-	-NA-	-NA-	-NA-			0.30
0					19 (33)	24 (46)
1–2					26 (46)	21 (40)
3–4					9 (16)	7 (13)
≥5					3 (5)	0 (0)
Major Cardiac Events†	5 (9)	2 (4)	1 (2)	1 (2)	5 (9)	3 (6)	0.72
Cardiovascular death	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	0 (0)	-
MI‡	1 (2)	1 (2)	0 (0)	1 (2)	1 (2)	2 (4)	0.60
Coronary	5 (9)	2 (4)	1 (2)	0 (0)	5 (9)	2 (4)	0.44
Revascularization
PCI§	5 (9)	1 (2)	1 (2)	0 (0)	5 (9)	1 (2)	0.21
CABG||	0 (0)	1 (2)	0 (0)	0 (0)	0 (0)	1 (2)	0.48

^*Comparison between OU-CMR and inpatient care for cumulative events was conducted with Fisher exact tests;

^†Data represents the number of participants experiencing each event. Some participants experienced more than 1 event.

^‡MI, myocardial infarction;

^§PCI, percutaneous coronary intervention;

^||CABG = coronary artery bypass graft

Cardiac testing procedures by study group are displayed in Table 4. During the index visit, cardiac catheterizations were performed in 13% of the OU-CMR group compared to 16% of the inpatient care group (p=0.79). After discharge, no difference in the rates of stress testing were detected (OU-CMR 10% vs inpatient care 16%, p=0.40) but the inpatient care group had a higher rate of cardiac catheterization (19% versus 2%) in the OU-CMR group (p=0.01). During the incident visit and the subsequent 1-year follow-up, more OU-CMR participants received stress testing (96% vs 79%, p=0.01), while fewer received cardiac catheterization (15% vs 33%, p=0.04).

Clinical Outcomes

From randomization to completion of follow up, eight participants experienced nine major cardiac events. In the OU-CMR group, two participants had major cardiac events during the index visit: one experienced an MI before CMR testing and had a PCI; one had inducible ischemia on CMR testing and received coronary artery bypass graft surgery. At follow up, one additional patient had MI without revascularization. In the inpatient group, five participants had major cardiac events during the index hospitalization; all had PCI, one had MI. At follow up, one of these patients had an additional PCI. There were no statistical differences among groups in the occurrence of major cardiac events.

Cardiac-related healthcare cost

The distributions of cost by study group from enrollment through 1 year are shown in Figure 1, the cumulative accrual of cost after discharge is shown in Figure 2, and the data are summarized in Table 5. Costs were remarkably variable, with overall costs ranging from $616 to $34084 and follow-up costs ranging from $0 to $17698. Considering all cardiac related costs from enrollment through 360 days, the geometric mean (95% confidence interval) cost was $3101 ($2519, $3817) among OU-CMR participants and $4742 ($3888, $5783) among inpatient care participants (p = .004). The difference remains significant once adjustment is made for covariates (p=.018). In the adjusted model, prior coronary artery disease (p=.047), prior heart failure (p=.049), no prior revascularization (p=.029), and pain at ED arrival (p=.046) were associated with higher costs. When only considering the cost of care after discharge from the index hospital visit, the geometric mean cost was $29 ($11, $74) for OU-CMR participants and $152 ($63, $366) among inpatient care participants (p = .012). This difference remains significant after adjustment is made for covariates (p=.049). In the adjusted model, only pain at ED arrival (p=.024) was associated with higher costs.

Figure 1. Cardiac-related cost from randomization through 1 year.

This figure shows the cumulative distribution of cost by study group over 1 year. It is obtained by calculating the percentage of patients with total cost (including the index visit and follow-up cost) less than or equal to the cost specified on the x-axis. In the observation unit cardiac magnetic resonance (OUCMR) group, 79% had total costs less than $5000 compared to 58% of the inpatient care group, suggesting OUCMR is a cost-reducing care strategy.

Figure 2. Cost accumulation by month following discharge among study groups, excluding the index hospital visit cost.

Mean cumulative cost by study group after hospital discharge (y-axis) is displayed by month of follow up (x-axis). Mean cumulative cost for a month is calculated as the sum of the costs across all patients up to and including that month divided by the number of patients. Observation unit cardiac magnetic resonance (OUCMR) participants had lower cost of care in the year after discharge from the index hospital visit (p=0.012). Reduced cost was the result of fewer cardiac-related emergency department visits and cardiac-related hospitalizations suggesting that an OUCMR strategy impacts care utilization after discharge.

Table 5.

Cardiac-related costs overall and just during the follow-up period

Type of Cost	Inpatient Care							OU-GMR							p value
	N	GM*	Median	Min ‡	Q1||	Q3**	Max§	N	GM	Median	Min	Q1	Q3	Max	Unadjusted	Adjusted
Overall†	57	4742	3850	616	2669	9710	26610	52	3101	2186	1020	1957	4308	34084	0.004	0.018
Follow-up	57	152	187	0	32	3777	17698	50	29	32	0	0	559	11637	0.012	0.049

^*GM = geometric mean;

^†Overall includes index visit and follow-up charges;

^‡Min = minimum;

^§ Max= maximum;

^|| First quartile;

^**Third quartile; Unadjusted p value from t-test on log-transformed data; adjusted p value from regression analysis of log data.

We then looked at the cardiac-related costs over time in both groups. The repeated measures ANCOVA models showed a significant time (p < .001) and group (p = .012) effect with the costs for first month being significantly higher than for the other months and the average costs for the inpatient group being higher than for the OU-CMR group. While it appears that the biggest difference between the two groups occurs in the first few months following the discharge, the group*time interaction was nonsignificant (p = .388). The only covariate that was significantly associated with higher cost in this model was having prior heart failure (p = .001).

Discussion

The results of this study indicate that a CMR imaging strategy can be used in an OU to reduce the cost of care for patients typically managed in the inpatient setting. The reduction in cost seen with OUCMR during the index visit was not associated with a “rebound” increase in consumption after discharge, as would be seen if testing or interventions were being deferred from the index visit. In contrast, the OUCMR group continued to accumulate cost at a lower rate, due to fewer cardiac-related ED visits, hospitalizations, and catheterizations. In this study, one-year cost is lower in those randomized to OU-CMR versus an inpatient admission at the time of their presentation to the ED.

Importance of considering care after hospital discharge

Within the 1-year period of time after the original ED visit, one can detect health-related expenditures that may be deferred from the index visit to the outpatient arena, account for changes in behavior resulting from the care pathway, and assess differences in clinical outcomes. This has particular importance in cardiac care as a previous study has shown that percutaneous coronary interventions are associated with an increase in subsequent care utilization(7). Our results suggest that OU-CMR reduces follow-up costs. The source of reduced cost relates to procedures and recidivism. Both groups had similar patterns of cardiac-related outpatient visits. However, the inpatient care group experienced higher rates of cardiac-related ED visits, re-hospitalizations, and cardiac catheterizations. Nearly one-third of the inpatient care group received a cardiac catheterization by the trial’s end, compared to only 15% of the OU-CMR group. These findings are consistent with those reported by Farkouh and colleagues who also reported a reduction in cardiac related utilization associated with OU care through 6 months of follow-up.(1)

Observation unit care in patients with non-low risk chest pain

Observation unit care is common for patients with chest pain, but is mostly used in patients with low pretest probability for ACS. OU care is not commonly implemented in patients with non-low risk chest pain and the utility of OU care in this population is not well understood. Only 1 other trial included patients with prior coronary events and randomized patients to OU care versus inpatient care.(1) That trial by Farkouh and colleagues allowed a variety of testing modalities in the OU group, including exercise ECG testing, stress echo, and stress nuclear imaging. They found that the cost savings associated with OU care at 6 months was dependent on using stress ECG testing without imaging; among the patients receiving stress imaging, there was no cost benefit to OU care.(8) Our findings contradict their findings in that we demonstrated cost savings with OU-CMR care through the first year after presentation. This could mean that the cost reduction results from using stress CMR rather than OU care, or perhaps it is the combination of using CMR as an imaging modality within an OU that is lowering 1-year follow-up costs.

Despite a class I endorsement by the ACC/AHA guidelines(3), the safety of OU care is not well investigated in patients with non-low risk chest pain. In the OU arm of Farkouh’s trial, 3/214 patients from the OU group died within 6 months of randomization compared to none in the inpatient group (p=ns). The OU group also experienced a total of 6 cardiac events between 30 days and 6 months from randomization compared to 1 in the inpatient group (p=ns). In our trial, 1 patient in each group had a major cardiac event, both between 6 months and 1 year following randomization. For OU-CMR participants, this is consistent with previous analyses demonstrating the excellent long-term prognosis after a negative stress CMR.(9,10) The low event rates support our underlying assertion that an OU-CMR pathway should have similar safety to inpatient care since both pathways typically incorporate serial cardiac markers and objective cardiac testing. However, a larger trial should address the safety of OU care in this population.

Mechanisms for OU-CMR reducing cost

We propose several mechanisms that could, in part, contribute to the observed differences in costs between the treatment pathways. First, patients in the OU-CMR group could have been more stringently selected for revascularization during the index visit. As a result, the increase in post-revascularization cardiac-related care occurred less often. Second, patients in the OU-CMR group may have felt more reassured reducing their likelihood of returning to the ED. Similarly, a recent CMR exam could have impacted physician behavior after discharge when deciding whether to pursue a patient’s complaint of chest pain. This mechanism could also potentially account for the dramatic difference in catheterizations after discharge. Finally, it could be that inpatient care participants established relationships with subspecialists which in turn increased the likelihood that a subspecialist procedure would be performed.

Rationale for cardiac MRI use in observation unit care

Cardiac MRI was felt by this study team to be the ideal imaging modality for OU implementation. The strength of CMR rests in its ability to provide a comprehensive evaluation without ionizing radiation. The comprehensive assessment in this protocol included a T2-weighted assessment for myocardial edema that often accompanies ACS, resting left ventricular wall motion, resting and stress perfusion to identify ischemia, and delayed enhancement to identify infarcts. Through this comprehensive assessment, clinicians are readily able to distinguish new infarcts or ischemia in the setting of pre-existing infarcts, left ventricular dilation, or hypertrophy. In addition, other causes of chest pain, such as myocarditis, or other processes that simulate infarcts (e.g. Takotsubo cardiomyopathy) can be readily identified.

Limitations

Our study has some limitations. First, the data were collected from a single center and contained a modest number of participants. Future work will require a larger sample size from other sites to determine if these findings remain valid across healthcare systems and diverse patient populations. Second, the results were obtained in the tightly controlled setting of a clinical trial. The OU-CMR intervention may have a different effect when examined outside the clinical trial context. Third, the classification of healthcare encounters as cardiac related or not cardiac related was conducted without the immediate knowledge of subjects’ study group assignments. However, the study group assignment could have been obtained as this step required a record review. Objective definitions were used to standardize these assessments and minimize bias, however, this represents a potential threat to internal validity. Fourth, extensive medical and financial record reviews were performed to identify events after discharge, and further, most patients were contacted at 1 year to identify additional events. However, some participants did not contribute complete information. Follow up did not differ by group and we feel it is unlikely that this introduced systematic error. Finally, there is the possibility that patient groups were unbalanced despite randomization. We stratified the randomization scheme based on prior coronary disease to prevent this from occurring, no statistical differences in baseline data were seen among study groups, and the findings remained significant after adjusting for covariates in our cost models. However, we cannot entirely exclude the possibility that differences in study groups contributed to our results.

Conclusion

Early findings demonstrate that an OU-CMR strategy is an efficient management strategy for emergency department patients with intermediate risk chest pain, but without definite ACS. In addition to reducing the index hospital visit cost, an OU-CMR strategy continues to reduce cost after hospital discharge leading to lower total cost at 1 year compared to inpatient care. The reduction in cost after discharge was the result of fewer cardiac catheterizations, cardiac-related ED visits, and cardiac-related hospitalizations.

Abbreviations

ACC

American College of Cardiology

AHA

American Heart Association

ACS

acute coronary syndrome

MI

myocardial infarction

PCI

percutaneous coronary intervention

CMR

cardiac magnetic resonance imaging

OU

observation unit

ED

emergency department

TIMI

Thrombolysis in Myocardial Infarction