Exercise testing after myocardial infarction: how soon, what protocol, how should results be acted upon?

Risk stratification in acute myocardial infarction aims to identify patients at greatest risk of recurrent ischaemic events who might benefit prognostically from further investigation and treatment. Risk, however, is not a linear function of time, more than 60% of all major events during the first year occurring in the first 30 days after hospital admission.1 Recognition of this fact has rendered obsolete old arguments about the appropriate timing of stress testing and other non-invasive tests which must be performed as early as possible (certainly before discharge) to be of significant value. Not all patients need a stress test, which is unlikely to provide significant incremental information when unrelieved chest pain or severe heart failure, for example, confirm a high level of risk.

However, there remains a group that makes a largely uncomplicated early recovery for whom pre-discharge stress testing is recommended as a means of detecting residual myocardial ischaemia. A symptom limited test using the Bruce protocol is recommended for most patients although for some, particularly the elderly, modified protocols may be more suitable. An abnormal stress test with regional ST depression may be predictive of recurrent ischaemic events and provides grounds for coronary arteriography with a view to revascularisation. Other markers of risk include low exercise tolerance (<7 mets), failure of the blood pressure to rise normally during exercise and exertional arrhythmias. Unfortunately, recent meta-analysis has shown that inducible ischaemia during treadmill testing has a low positive predictive value for death and myocardial infarction in the first year, falling below 10% in patients who have received thrombolytic therapy.3 Nevertheless, when “non-ischaemic” risk criteria are considered, the treadmill may provide added clinical value, inability to perform a stress test and low exercise tolerance both being independently predictive of recurrent events.4 Moreover, the negative predictive accuracy of pre-discharge stress testing is high, those with a normal test usually having a good prognosis without need for additional investigation.5 Finally, it should be noted that the diagnostic value of exertional ST depression and reversible thallium perfusion defects is equivalent, making the treadmill a more cost effective strategy for risk stratification than the gamma camera.