Prognostic Value of Peak Stress Cardiac Power in Stress Echocardiography

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  • In this retrospective study of nearly 25,000 patients, higher cardiac power at peak exercise and higher power reserve were independently associated with reduced risk of all-cause mortality and development of heart failure.

Study Questions:

What is the prognostic value of peak exercise cardiac power and power reserve in patients with normal left ventricular ejection fraction (LVEF) undergoing stress echocardiography?

Methods:

This single-center retrospective analysis included patients with EF ≥50% who underwent treadmill or bicycle exercise stress echocardiography from 2004-2018. Exclusion criteria were moderate or greater right ventricular dysfunction and significant valvular disease. Cardiac power was calculated as a function of blood pressure and cardiac output (heart rate x stroke volume, with the latter derived from 2D images, using the modified Quinones method) and was normalized to LV mass. Power reserve was defined as the difference between power/mass at stress and power/mass at rest. The primary clinical endpoint was all-cause mortality, and the secondary endpoint was the diagnosis of heart failure (HF).

Results:

The cohort included 24,885 patients (mean age 59 ± 13 years, 44.6% female, 47.6% with hypertension, 11.6% with diabetes, 6.1% with prior myocardial infarction). Mean power/mass at rest was 0.8 ± 0.2 W/100 g myocardium, increasing to 2.1 ± 0.7 W/100 g at peak stress. Patients were divided into quartiles of power/mass at peak stress, and higher quartiles included younger patients, more women, and fewer patients with diabetes, hypertension, previously known coronary artery disease, and inducible ischemia.

Over a median 3.9 years of follow-up, 929 patients died, and 1,312 developed HF. In multivariable analyses, power/mass at peak stress was were independently associated with mortality (adjusted hazard ratio [HR] for highest vs. lowest quartile, 0.5; 95% confidence interval [CI], 0.4-0.6; p < 0.001) and development of HF (adjusted HR, 0.4; 95% CI, 0.3-0.5; p < 0.001), with similar findings for power reserve. Power/mass at rest was independently associated with development of HF (adjusted HR for highest vs. lowest quartile, 0.6; 95% CI, 0.5-0.8; p < 0.001), but not with mortality. Other multivariable predictors of both mortality and HF included advanced age, diabetes, lower peak METs achieved during stress, and resting wall motion abnormalities.

Conclusions:

In exercise stress echocardiography, LV power/mass at peak stress and power reserve provide incremental prognostic value beyond exercise parameters and evidence of myocardial ischemia.

Perspective:

The prognostic value of cardiac power among patients with HF with reduced EF (HFrEF) has previously been described, and this manuscript is the first to illustrate its potential for use among patients with normal EF. EF measurement in this study was based on the modified Quinones method, which is no longer recommended by the American Society of Echocardiography because it is based on linear measurements and relies more heavily on geometric assumptions than Simpson’s method of discs. However, the modified Quinones method does offer the advantage of rapid measurement, and it may be more practical for use with post-stress images, which can be technically limited by respiratory motion. Moreover, no special equipment or software would be required to obtain the data needed for cardiac power measurements with this method. A major strength of the study is its very large sample size. Because the study was retrospective, there was likely a bias toward symptomatic patients referred for clinical stress testing, and it remains to be seen whether noninvasively measured cardiac power would have similar prognostic value in asymptomatic individuals.

Clinical Topics: Diabetes and Cardiometabolic Disease, Heart Failure and Cardiomyopathies, Noninvasive Imaging, Prevention, Sports and Exercise Cardiology, Valvular Heart Disease, Atherosclerotic Disease (CAD/PAD), Acute Heart Failure, Echocardiography/Ultrasound, Hypertension, Sports and Exercise and ECG and Stress Testing, Sports and Exercise and Imaging

Keywords: Bicycling, Blood Pressure, Cardiac Output, Coronary Artery Disease, Diabetes Mellitus, Diagnostic Imaging, Echocardiography, Echocardiography, Stress, Exercise Test, Heart Failure, Heart Valve Diseases, Hypertension, Metabolic Syndrome X, Myocardial Infarction, Myocardial Ischemia, Myocardium, Secondary Prevention, Stroke Volume, Ventricular Function, Left


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