cardiac stress ECG testing

see also:

• Mx of possible acute coronary syndrome without ST elevation (NSTEACS)
• cardiac stress testing

• the low sensitivity and specificity of stress ECG testing for detection of significant coronary artery disease has resulted in it largely being displaced by other methods of cardiac stress testing

• see diagnostic tests - sens, spec, PPV, NPV, etc
• the positive predictive value is generally low (<10% for cardiac death and < 20% for cardiac death or AMI), and thus, they should only be performed on patients with a reasonable pre-test probability - ie. not on 30yr olds who are worried they might have heart disease but do not have clinical features to suggest cardiac disease.

• probably should be considered for invasive investigation rather than stress testing as even a negative test result will not lower the probability of ACS sufficiently to warrant avoiding an invasive test.
• clinical risk markers are perhaps more reliable than stress testing in determining who should have invasive investigation such as coronary angiography.

• these patients are most likely to benefit from stress testing

• these patients probably should be counseled before embarking on stress testing as they are much more likely to have a false positive result than a true positive result and thus may end up having unnecessary and risky invasive testing.
• for instance if sensitivity is 50% and specificity is 90% and the pre-test probability is only 5%, then of 1000 patients tested, 125 will have a positive result, but of these, 95 will have a false positive result.

• patients are usually deemed safe for stress ECG testing if:
  • there have not been symptoms of heart failure or recurrent angina for 12 to 24 hours
  • the electrocardiogram has been stable for 12 to 24 hours
• women:
  • Exercise ECG testing is associated with a higher false-positive rate in women than men, due at least in part to a lower pretest probability, however, among patients with a non-ST elevation ACS, exercise ECG risk scores appear to be as helpful for predicting prognosis in women as in men and recommendations for stress testing in women in this setting are generally similar to those in men¹⁾.
  • exercise ECG test sensitivity 61% and specificity 70% for women.
  • stress testing for diagnosis is warranted only in women with an intermediate (10 to 90 percent) pretest probability of CHD
  • among women at intermediate risk, exercise electrocardiography should be performed, assuming that the patient can exercise and has no baseline ECG abnormalities that would interfere with interpretation of the test, otherwise they should have stress echo or stress MIBI performed.
  • no further evaluation is necessary if the maximum stress test is negative and the patient can achieve an adequate work level, although risk factor modification with or without antiischemic therapy is warranted if the clinical history strongly suggests classic angina
  • women with a moderate to severely abnormal test should go on to coronary angiography if they are a candidate for percutaneous coronary intervention or coronary artery bypass grafting
  • the treadmill score was of much less value for predicting 2 year mortality in women than for men.
  • premenopausal women have a much lower incidence of CHD than men and thus a much lower pre-test probability, although a negative stress ECG result is therefore helpful in excluding CHD in women.
  • women have much greater incidence of false-positive ST segment depression during exercise presumably, partly related to mitral valve prolapse and to microvascular disease.
  • women are much more likely to have angina pain with normal coronary angiography (presumably due to microvascular disease rather than large vessel disease).
  • many prefer to perform stress echocardiography or stress MIBI scans rather than stress ECG in women.

• accurate stress ECG interpretation cannot be achieved in patients with baseline ECG abnormalities such as digoxin Rx, Left Bundle Branch Block (LBBB), left ventricular hypertrophy with ST-T wave changes, ventricular pre-excitation (eg. WPW), or ventricular pacing.
• angina type pain or ECG changes within past 12-24 hours.