Pathophysiologic factors governing the variability of ischemic responses to treadmill and bicycle exercise

Comparison of myocardial ischemia on the ergocycle versus the treadmill in patients with coronary heart disease

We previously observed an attenuation of exercise-induced myocardial ischemia on the ergocycle during a ramp protocol compared to the standard Bruce protocol treadmill test in patients with coronary heart disease. However, it was uncertain whether decreased ischemia on the ergocycle resulted from the warm-up effect of the more gradual ramp protocol or from the mode of exercise itself (cycling vs running). Sixteen stable patients, aged 64 +/- 5 years, with documented coronary heart disease (> or =70% coronary artery stenosis and/or reversible myocardial perfusion defects) performed 3 symptom-limited exercise tests: the standard Bruce protocol treadmill test and 2 individualized ramp protocols (treadmill and ergocycle). We measured the ischemic threshold (heart rate x systolic blood pressure product at 1-mm ST-segment depression) and oxygen consumption (VO(2)). The ischemic threshold was higher during cycling (ergocycle ramp, 24,009 +/- 5,769 beats/min x mm Hg) compared to running (Bruce treadmill, 20,429 +/- 3,508 beats/min x mm Hg; and ramp treadmill, 19,451 +/- 3,392 beats/min x mm Hg; p <0.001), independently of exercise intensity (VO(2)). The peak VO(2) did not significantly differ among all tests (p = 0.25) despite a greater peak rate-pressure product achieved with the ergocycle (29,378 +/- 6,291 beats/min x mm Hg) compared to either treadmill protocol (Bruce, 26,202 +/- 5,831 beats/min x mm Hg; ramp, 25,654 +/- 6,492 beats/min x mm Hg; p <0.001). In conclusion, the mode of exercise (ergocycle vs treadmill), rather than the type of protocol (ramp vs Bruce), is associated with an attenuation of electrocardiographic parameters of myocardial ischemia, independently of exercise intensity (VO(2)) and myocardial demand (rate-pressure product).

Comparing stress testing methods. Available techniques and their use in CAD evaluation

Exercise stress testing remains one of the most widely used techniques in assessing functional capacity and in confirming a diagnosis of CAD. Its sensitivity and specificity are approximately 63% and 74%, respectively. The technique is safe when administered and supervised by qualified personnel who are trained to recognize contraindications and other reasons for termination of the test. More recently, echocardiography has been combined with exercise stress testing. It is a well-tolerated and valuable procedure for noninvasive evaluation of CAD. The sensitivity and specificity of stress echocardiography are higher than those of exercise stress testing and comparable to those of nuclear perfusion imaging. Continuing improvements in digital image analysis, cost, and the availability of contrast agents promise to make noninvasive stress testing even more useful in the years to come. Newer contrast and concomitant perfusion agents are on the horizon and may prove to be a reality in the echocardiographic laboratories of the future.

Advances in Exercise Echocardiography Can This Technique Still Thrive in the Era of Pharmacologic Stress Testing?

In the current literature, pharmacologic stress techniques are the focus of interest and excitement regarding new technologies and new indications such as the diagnosis of viable myocardium. In contrast, exercise echocardiography has evolved less and is less amenable to the introduction of new technologies. This article reviews the indications for exercise echocardiography (especially in contrast to pharmacologic stress), its accuracy relative to other testing, and application to clinical decision making. Exercise echocardiography remains to be well accepted as a diagnostic and risk-assessment technique, and in some clinical situations it provides valuable data that are not available during pharmacologic stress testing.