‘Warm-up Angina’: Harnessing the Benefits of Exercise and Myocardial Ischaemia
The following are 10 points to remember about warm-up angina:
1. The phenomenon of warm-up angina was first noted over 200 years ago. It describes the curious observation whereby exercise-induced ischemia on second effort is significantly reduced or even abolished if separated from first effort by a brief rest period.
2. Warm-up angina is objectively defined by reduced ischemia (ST-segment depression) or a raised ‘ischemic threshold’ on second, compared to first, exertion. A raised ‘ischemic threshold’ is defined by an increase in the rate pressure product (RPP) at which a pre-stated amount of ST-segment depression occurs.
3. Rather than cardiac work (RPP), an ‘ischemic threshold’ can also be defined by external work achieved (watts on cycle ergometer or METs/minute on treadmill).
4. A warm-up period of exercise may enable higher intensity exercise training to be carried out safely, which in turn may offer prognostic benefit. Although only 20% of patients describe warm-up symptoms, approximately 80% of coronary artery disease (CAD) patients have been shown to objectively demonstrate warm-up angina.
5. American cardiac rehabilitation guidelines recommend for CAD patients to exercise at ‘low aerobic intensities,’ namely, below their ischemic threshold; reflecting a concern for triggering an acute myocardial infarction with sudden physical exertion, and an increased arrhythmia risk.
6. Subsequently, it was shown that it was safe to exercise to a moderate intensity that precipitated angina or ischemia, which prolonged the time to ischemia and time to angina on second effort. A delay in rest periods of >15 minutes reduced the benefits of warm-up effects.
7. Exercise is capable of triggering systemic arterial vasodilation and left ventricular afterload reduction, resulting in a decrease in myocardial oxygen consumption.
8. Ischemia may activate contributory myocardial protective mechanisms, possibly through the opening of KATP channels.
9. Warm-up angina harnesses the beneficial cardioprotective effects of both exercise and ischemia, and in both the systemic and coronary circulations.
10. The mechanism of reduction in ischemia following a first initial stimulus is likely to be progressive coronary and systemic vasodilatation, which through enhanced ventricular–vascular coupling and cardiac–coronary interaction, enhance diastolic relaxation, reduced microvascular resistance, and hence, augmented coronary blood flow.
Keywords: Rest, Coronary Artery Disease, Myocardial Ischemia, Exercise
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