Exercise Stress Testing

The cardiopulmonary exercise test represents the gold standard for assessment of the aerobic exercise capacity and cardiopulmonary responses to dynamic exercise.

The VO2max describes an individuals exercise capacity relative to age and sex matched healthy peers.

May include echocardiography or nuclear imaging.

During exercise the myocardium becomes ischemic.

The stress test is useful in assessing residual ischemia after an acute myocardial infarction or in cases of incomplete revascularization or when treating symptomatic patients who have had previous revascularization.

Pharmacologic stress tests were developed as an alternative to exercise testing for patient unable to perform exercise protocols, and that has been continued growth in its use.

Pharmacological stress test use is increasing because of the aging population, increasing obesity and associated comorbidities including musculoskeletal or neurologic conditions that may preclude the use of exercise testing because of an inability to achieve an adequate workload.

Exercise testing has a preference over pharmacologic methods demonstrating prognostic importance of information of symptom limited exercise, including functional capacity, exercise duration, heart rate, heart rhythm, and blood pressure responses.

An individuals functional capacity, frequently estimated in units of oxygen uptake as metabolic units from treadmill speed and grade is a powerful prognostic factor predictive of clinical events such as myocardio perfusion.

Estimates show that such screening accounts for 45% of cardiac stress imaging, and evidence does not show that this results in better outcomes for patients.

 

 

Most health agencies  do not recommend stress exercise testing test as a routine procedure.

 

 

Unless high-risk markers are present: diabetes in patients aged over 40, peripheral arterial disease; or a risk of coronary heart disease greater than 2 percent yearly.

Prediction of cardiac events and mortality strongly associated with workload achieved, heart rate recovery, information from exercise testing.

 

A stress test may use an echocardiogram for ultrasonic imaging of the heart, in which case the test is called an echocardiography stress test or stress echo, or a gamma camera to image radioisotopes injected into the bloodstream called a nuclear stress test.

 

The American Heart Association recommends ECG treadmill testing as the first choice for patients with medium risk of coronary heart disease according to risk factors of smoking, family history of coronary artery stenosis, hypertension, diabetes and high cholesterol. 

Perfusion stress test (with 99mTc labelled sestamibi) is appropriate for select patients, especially those with an abnormal resting electrocardiogram.

Treadmill test: sensitivity 73-90%, specificity 50-74% (Modified Bruce protocol)

Nuclear test: sensitivity 81%, specificity 85-95%

According to American Heart Association data, about 65% of men and 47% of women present with a heart attack or sudden cardiac arrest as their first symptom of cardiovascular disease. 

Stress cardiac imaging is not recommended for asymptomatic, low-risk patients as part of their routine care.

 

Nuclear stress test uses myocardial perfusion imaging. 

Typically, a radiotracer (Tc-99 sestamibi, or thalium  chloride may be injected during the test. 

Scans are acquired with a gamma camera to capture images of the blood flow. 

Scans acquired before and after exercise are examined to assess the state of the coronary arteries of the patient.

The nuclear stress tests more accurately identify regional areas of reduced blood flow.

Pharmacological stimulation from vasodilators such as dipyridamole or adenosine, or positive chronotropic agents such as dobutamine can be used. 

The typical dose of radiation received during nuclear cardiac stress test  procedure can range from 9.4 millisieverts to 40.7 millisieverts.

 

The radionuclide tracers used are carcinogenic, so frequent use of these tests carries a small risk of cancer.

Adenosine and dipyridamole used during cardiac stress tests to dilate blood vessels can cause mild hypotension.

Adenosine and dipyridamole pharmacologic stress testing relies on coronary steal. 

These vasodilators are used to dilate coronary vessels increase blood velocity and flow rate in normal vessels and less of a response in stenotic vessels. 

This difference in vascular response leads to a steal of flow and perfusion defects appear in cardiac nuclear scans or as ST-segment changes.

Adenosine, Lexiscan (Regadenoson), or dipyridamole are generally used when a patient cannot achieve adequate work level with treadmill exercise.

An exercise stress test may provide more information about exercise tolerance than a pharmacologic stress test.

Agents used in stress testing: 

Vasodilators acting as adenosine receptor agonists, such as adenosine itself, and dipyridamole

Regadenoson which acts specifically at the adenosine A2A receptor, thus affecting the heart more than the lung.

 

Caffeine is is a competitive antagonist of the A2A adenosine receptor and can attenuate the vasodilatory effects of adenosine.

Persistent adverse reactions to Adenosine and Lexiscan can be ameliorated by aminophylline.

Dobutamine

Lexiscan or Dobutamine are often used in patients with severe asthma or COPD as adenosine and dipyridamole can cause acute exacerbation of these conditions. 

 

 

The echocardiography may be performed both before and after the exercise so that structural differences can be compared.

Patients ideally exert themselves to a near maximal or maximal level insuring that myocardial tissue is assessed across the spectrum of aerobic capacity.

Cardiac events 1 to 3 years after normal exercise echocardiogram is lower than when compared with the normal dobutamine stress echocardio gram.

Exercise stress testing compared to pharmacological stress testing has more information and is more accurate predictor of cardiovascular health.

The American Heart Association recommends ECG treadmill testing as the first choice for patients with medium risk of coronary heart disease according to risk factors of smoking, family history of coronary artery stenosis, hypertension, diabetes and high cholesterol. 

Sub maximal exertion is one of the mechanisms for a false negative exercise stress test.

Left ventricular dysfunction during exercise allows for the earliest detection of ischemia.

Ventricular imaging added to exercise testing increases sensitivity, specificity and prognostic abilities.

With an ischemic response is a potent predictor of coronary events.

Stroke volume decreases at workloads above ischemic threshold, reducing the rate of increase in oxygen uptake relative to the increase in work rate with a concomitant steepening of the heart rate. up

Exercise stress testing-≥1mm ST depression sensitivity 23% and specificity 89%, ≥1.5

Exercise treadmill testing provides information about the prognosis in patients with stable coronary artery disease.

Exercise treadmill testing (ETT) is used to evaluate symptomatic patients with an intermediate pretest probability of coronary artery disease who can exercise and have normal resting ST segments.

ETT with imaging is appropriate when pretest probability of coronary artery disease is high or the baseline ST. abnormalities are present with the resting depression of 1 mm equal or greater, or left ventricular hypertrophy with repolarization abnormalities, pre-excitation or digoxin therapy.

Pharmacologic stress testing for coronary CT angiograms are often preferred in the presence of left bundle branch block and ventricular pacing because both increase the likelihood of false positive perfusion defect with exercise.

Sensitivity of exercise treadmill testing for obstructive coronary artery disease is approximately 68% and then 61% and women with the specificity of approximately 77% of men and 70% in women.

>1mm ST depression sensitivity 23% and specificity 89%, >1.5 mm ST depression 88% sensitivity and 98% specificity.

Pooled data suggests a sensitivity of 68% and a specificity of 77%.

Less sensitive in women and may be less specific than in men.

In patients without a high risk of extensive coronary artery disease the sensitivity may be as low as 45%.

Complication rate about 1 in 2500 tests.

Rate of acute myocardial infarction or death is 1 per 2500 tests.

Mortality <1 in 50,000.

Exercise electrocardiography provides incremental information in patients greater than 65 years as compared with clinical and rest echocardiographic variables.

Exercise testing can identify women with impaired fasting glucose levels who are at high risk for all cause mortality (Lyerly GW).

In a study of 1747 diabetic veterans showed that exercise induced ST-segment depression is associated with more cardiovascular events than patients without ST-depression over a 2 year follow-up (Callahan PR).

In 45 patients with exercise induced silent ischemia, diabetic patients had worse cardiovascular disease outcomes than non diabetics (Weiner DA).

In subjects with histories of ventricular tachycardia or fibrillation serious arrhythmias occur during 2.3% of tests.

5% to 11% of patients with abnormal responses only display such findings during the recovery period.

Heart rate recovery of less than 12 beats per minute in the first minute following exercise predicts all-cause mortality in patients undergoing exercise stress testing.

Very rapid heart rate recovery immediately after exercise is associated with a lower risk of coronary heart disease and cardiovascular events.

Heart rate recovery a powerful prognostic predictor of coronary disease.

The peak exercise heart rate is often blunted by the presence of B-blockers and such testing has lower accuracy than in patients not receiving such agents.

Drugs that can influence results include digoxin, beta-blockers, vasodilators, and hypertensive agents that alter hemodynamic responses.

Is not recommended for testing healthy asymptomatic patients.

May be of value in patients with an intermediate risk of cardiovascular disease.

Most useful for predicting fatal rather than nonfatal events.

Routine use of periodic stress testing postrevascularization procedures without specific clinical indication is not recommended as it is associated with high rates of resource utilization and high rates of false positive results.

In a retrospective study of 2105 asymptomatic patients status post CABG or PCI exercise echocardiography founf only 13% of patients with ischemia, only 34% of those underwent subsequent revascularization and those patients did not have improved survival (Harb et al).