Myocardial ischaemia

Stress testing

Patients with ongoing symptomatic ischaemia early after acute coronary syndromes are usually regarded as a high risk group requiring urgent angiographic investigation. However, many patients who make an uncomplicated early recovery have inducible ischaemia (with or without symptoms) that is variably predictive of recurrent ischaemic events. Thus stress testing has a time honoured role for predischarge risk stratification, particularly in uncomplicated myocardial infarction. 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 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 (fig 4.4), falling below 10% in patients who have received thrombolytic treatment.10 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.11 Moreover, the negative predictive accuracy of predischarge stress testing is high, those with a normal test usually having a good prognosis without the need for additional investigation. 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 after myocardial infarction than the gamma camera.10 Predis-charge stress testing has also been recommended in unstable angina, but although an ischaemic response at low work load has been associated with an increased risk, the positive predictive value of an abnormal test is low.

Holter ST monitoring

Ambulatory ischaemia during predischarge Holter monitoring also identifies patients at

Figure 4.4. Positive predictive value (PPV) of non-invasive tests in non-thrombolytic and thrombolytic treated patients for cardiac death or reinfarction rates, and rates of abnormal tests. EF, ejection fraction. Reproduced from Shaw et al° with permission.

Treadmill stress testing for predischarge risk stratification

• Positive predictive accuracy of ST depression < 10% after thrombolytic treatment

• Inability to perform a stress test and low exercise tolerance are most useful predictors of recurrent events

• Negative predictive accuracy is high

• Diagnostic value of exertional ST depression and thallium perfusion defects are equivalent, making the treadmill more cost effective than the gamma camera risk of recurrent ischaemic events. In unstable angina its use is well documented; although it provides prognostic information additional to that available from the admission ECG, its incremental value relative to stress testing is not clear. In myocardial infarction ischaemic ST shift during predischarge Holter monitoring has a positive predictive value for recurrent infarction and death of 20%, and provides prognostic information that is additional to and independent of that obtained from stress testing and clinical assessment.12 Preliminary evidence suggests therefore that ambulatory ischaemia during Holter monitoring may be more useful than stress testing for risk stratification in acute coronary syndromes. It can certainly be applied earlier after admission when risk is greatest, but it is unlikely to become more widely used until further studies are available defining its role.

Run for Your Life The Health Benefits Of Treadmills

Run for Your Life The Health Benefits Of Treadmills

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