Coronary Artery Disease
Prognostic Contribution of Exercise Capacity, Heart Rate Recovery, Chronotropic Incompetence, and Myocardial Perfusion Single-Photon Emission Computerized Tomography in the Prediction of Cardiac Death and All-Cause Mortality

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Chronotropic incompetence, measured by the percentage (%) of heart rate (HR) reserve achieved (%HR reserve), abnormal HR recovery, reduced exercise capacity (EC), and myocardial perfusion single-photon emission computerized tomography (SPECT MPS) abnormalities are known predictors of all-cause mortality (ACM) and cardiac death (CD). The aim of this study was to determine if EC, %HR reserve, and HR recovery add incremental value to MPS in the prediction of ACM and CD. A total of 11,218 patients without valvular disease and not on β blockers underwent symptom-limited exercise MPS. %HR reserve was (peak HR − rest HR)/(220 − age − rest HR) × 100, with %HR reserve <80 defined as low. HR recovery was peak HR − recovery HR. An HR recovery <22 beats/min at 2 minutes after peak exercise was considered abnormal. Poor EC was defined as exercise duration ≤6 minutes (7 metabolic equivalents). Summed stress scores (SSSs) were calculated using a 20-segment, 5-point MPS model. Statistical analysis was performed using Cox regression models. There were 445 deaths (148 CD) during a mean follow-up of 3.2 ± 2.5 years. In multivariate analysis, the independent predictors of ACM were age, χ2 = 154.81; EC, χ2 = 74.00; SSS, χ2 = 32.99; %HR reserve, χ2 = 24.74; abnormal electrocardiogram at rest, χ2 = 23.13; HR recovery, χ2 = 18.45; diabetes, χ2 = 17.75; and previous coronary artery disease, χ2 = 11.85 (p ≤0.0006). The independent predictors of CD were SSS, χ2 = 54.25; EC, χ2 = 49.34; age, χ2 = 46.45; abnormal electrocardiogram at rest, χ2 = 30.60; previous coronary artery disease, χ2 = 20.69; Duke treadmill score, χ2 = 19.50; %HR reserve, χ2 = 11.43; diabetes, χ2 = 10.23 (all p ≤0.0014); and HR recovery, χ2 = 5.30 (p = 0.0214). The exercise variables showed increases in Harrell's C static and net improvement reclassification, with EC showing the strongest incremental improvement in predicting ACM and CD (respective C-index 76.5% and 83.3% and net reclassification index 0.3201 and 0.4996). In conclusion, EC, %HR reserve, and HR recovery are independent predictors of ACM and CD and add incremental prognostic value to extent and severity of MPS.

Section snippets

Methods

We identified 11,218 consecutive patients who underwent exercise MPS from 1991 to 1999 at Cedars-Sinai Medical Center, had no history of valvular heart disease, were not under the influence of β blockers at the time of the exercise study, and did not undergo early revascularization, defined as revascularization <90 days after exercise testing. Institutional review board approval was obtained for the performance of this research. Data regarding the presence of hypertension, diabetes mellitus,

Results

The baseline and stress test characteristics of the 11,218 patients enrolled in this study are summarized on the basis of EC in Tables 1 and 2. The most common reason for testing was abnormal treadmill exercise test (35%), followed by reported presence of CAD by primary physician (22.5%), unstable angina (16.6%), abnormal ECG at rest (15%), preoperative evaluation (5.9%), and history of arrhythmia (5.4%). Patients with poor exercise tolerance had greater SSS, SRS, and SDS (all p <0.001). Women

Discussion

In this study, we have demonstrated for the first time that EC, CI as assessed by %HR reserve, and abnormal HR recovery are independent predictors of and add incremental value in the prediction of ACM and CD over traditional cardiovascular risk factors and comprehensive assessment MPS abnormalities. Previously, EC, %HR reserve, and HR recovery have shown incremental value over dichotomized MPS (normal/abnormal) in ACM prediction10; however, added value has not been examined regarding extent and

Disclosures

The authors have no conflicts of interest to disclose.

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