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The exercise treadmill test: Estimating cardiovascular prognosis

Cleveland Clinic Journal of Medicine. 2008 June;75(6):424-430
June 1, 2008|Cleveland Clinic Journal of Medicine
Todd D. Miller, MD
Author and Disclosure Information

Todd D. Miller, MD
Professor of Medicine, Co-Director, Nuclear Cardiology Laboratory, Department of Cardiovascular Diseases, Mayo Clinic, Rochester, MN

Address: Todd D. Miller, MD, Mayo Clinic, Gonda 5, 200 First Street SW, Rochester, MN 55905; e-mail miller.todd@mayo.edu

Dr. Miller has disclosed that he has financial relationships with the Bristol Myers Squibb, KAI Pharmaceuticals, King Pharmaceuticals, Radiant Medical, TargeGen, and TherOx corporations.

ABSTRACTAbnormal hemodynamic responses to exercise treadmill testing may indicate an increased risk of coronary events and death, even if evidence of ischemia is absent. Exercise duration and the blood pressure, heart rate, and heart rhythm responses to exercise have prognostic significance.

 

KEY POINTS

  • Of the prognostic factors, exercise duration is the one most strongly associated with risk of coronary events and death, independent of age, sex, or known presence and severity of coronary artery disease.
  • A decrease in blood pressure with exercise can reflect severe coronary artery disease or left ventricular systolic dysfunction.
  • A heart rate that does not increase adequately during exercise or does not recover rapidly after exercise is associated with an increased risk of death.
  • Exercise training may help to improve the prognosis of patients with an abnormal hemodynamic response to exercise caused by poor general health.

Blood pressure during and after exercise

During exercise testing, blood pressure is usually measured by cuff sphygmomanometry. However, motion during exercise and background noise from the treadmill machine can reduce the accuracy of this measurement.

Several studies have compared blood pressures measured by cuff sphygmomanometry vs intra-arterial measurements,15 and most have found that systolic pressures are lower as measured by cuff sphygmomanometry, with smaller differences between methods at higher exercise intensity. The diastolic pressure is significantly lower as measured by cuff sphygmomanometry than by intra-arterial measurements at rest and during exercise; error increases with exercise intensity.

Hypotensive and hypertensive blood pressure responses to exercise have been defined in various ways.

Exercise hypotension is best defined as systolic blood pressure that is lower during exercise than while standing at rest before exercise.16 It reflects a failure of cardiac output to increase during exercise and is associated with severe coronary artery disease (eg, left main coronary artery or three-vessel involvement), left ventricular systolic dysfunction, or both.17,18

Dubach et al,16 in a study of 2,036 patients who underwent exercise treadmill testing to evaluate chronic coronary artery disease, found that exercise hypotension was associated with a threefold higher risk of cardiac events over 2 years.

In a large meta-analysis of exercise testing following myocardial infarction, the only independent predictors of risk were limited exercise workload and exercise hypotension.19

Exercise hypertension is defined as a rise in systolic blood pressure during exercise above a threshold, usually between 190 and 220 mm Hg.20 Some studies suggest that exercise hypertension predicts future arterial hypertension in people with normal resting blood pressure.21,22

Whether exercise hypertension predicts future cardiovascular events has not been extensively investigated. A Mayo Clinic study reported that exercise hypertension was significantly associated (P = .03) with cardiovascular events in people without symptoms or clinically evident cardiovascular disease during a mean follow-up of 7.7 years.23 On the other hand, a study from Cleveland Clinic showed that patients being evaluated for coronary artery disease who had a hypertensive response to exercise had a lower prevalence of severe angiographic coronary disease (P = .004) and a lower risk of death over the next 2 years (P = .03) compared with the rest of the study population.24

An abnormal systolic blood pressure recovery ratio, defined as an increase (rather than the expected decrease) in systolic blood pressure in the early postexercise recovery period has been shown to be a marker of underlying coronary artery disease,25 but has not consistently been associated with an adverse prognosis.26

Chronotropic incompetence

The heart rate normally increases with exercise and decreases as soon as exercise stops. Failure of the heart rate to increase as expected during exercise is termed chronotropic incompetence. Chronotropic incompetence predicts all-cause and cardiovascular death.27–30

Different criteria for defining chronotropic incompetence were used in different studies, based on resting heart rate, exercise protocol, patient age, and medications (especially beta-blockers).

The predicted chronotropic response can be calculated by a suggested formula31: (peak heart rate minus resting heart rate) ÷ (220 minus age minus resting heart rate). The difference between peak heart rate and resting heart rate is known as the heart rate reserve.

Chronotropic incompetence is defined as less than 80% of the predicted value and as less than 62% for patients taking beta-blockers.31,32

Heart rate recovery

Cole CR, et al. Heart-rate recovery immediately after exercise as a predictor of mortality. N Engl J Med 1999; 341:1351–1357. Copyright © 1999, Massachusetts Medical Society. All rights reserved.
Figure 3. Estimates of the relative risk of death within 6 years according to heart rate recovery 1 minute after cessation of exercise. Circles represent the relative risk of death for each of the quintiles as compared with the quintile with the greatest reduction (5th). Blue and red lines represent the 95% confidence intervals.
When exercise stops, the heart rate returns to the pre-exercise rate over several minutes to hours, with the most marked reduction in the first few minutes. Impaired heart rate recovery (failure of the heart rate to decrease normally) predicts all-cause mortality and cardiovascular events, including sudden death, in healthy populations and in patients with coronary artery disease (Figure 3).5,30,33–36

Several variables influence heart rate recovery, including activity (eg, complete cessation of exercise or cool-down) and position (supine, sitting, standing). Suggested thresholds for abnormal responses are31:

  • Upright: the heart rate should slow down by at least 12 beats/minute at 1 minute
  • Supine: at least 18 beats/minute at 1 minute
  • Sitting: at least 22 beats/minute at 2 minutes.

Heart rate variability

Heart rate variability, ie, differences in the beat-to-beat interval among successive heart cycles, can be quantified by spectral analysis, although this is not routinely available clinically. Dewey et al37 measured heart rate variability during the first and last 2 minutes of exercise and during the first 2 minutes of recovery in 1,335 subjects (95% men, mean age 58 years). Markers of impaired heart rate variability measured during exercise and in recovery were independent predictors of all-cause and cardiovascular death during a mean follow-up of 5 years.

Ventricular ectopy

Uncommon types of ventricular arrhythmias can occur during exercise testing:

  • Sustained ventricular tachycardia or ventricular fibrillation due to coronary artery disease or left ventricular dysfunction occurs rarely but is life-threatening.
  • Ventricular tachycardia in healthy young adults without structural heart disease may arise from the right ventricular outflow tract. It is benign.38
  • Arrhythmogenic right ventricular dysplasia, a cardiomyopathy involving the right ventricle, can also occur in healthy young adults and has a poor prognosis. It must be distinguished from the benign form.

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