REDUCED HEART-RATE RESPONSE TO EXERCISE IN ISCHEMIC-HEART-DISEASE - FALLACY OF THE TARGET HEART-RATE IN EXERCISE TESTING

  • 1 January 1979
    • journal article
    • research article
    • Vol. 11  (3) , 227-233
Abstract
When exercise testing 159 patients with prior myocardial infarction, 39 were limited by fatigue. This group was all in sinus rhythm; none were taking drugs likely to impair the chronotropic response of the heart; none experienced chest pain or developed ischemic ECG changes. In 18, maximal heart rate achieved with exercise was 2 SD or more below the age predicted value, and their heart rate response to exercise was reduced compared to the other 21 whose maximal exercise heart rates were within 2 SD of age predicted values. A subgroup of 8 subjects with reduced exercise heart rates was studied before and after vagal blockade. In the 4 subjects whose infarction was inferior, the reduction in heart rate response was more profound and persisted after vagal blockade, suggesting either reduced pacemaker responsiveness, due to ischemica or infarction, or autonomic imbalance as possible mechanisms. All 8 showed alinear increases in ventilation at higher power outputs and mean blood lactate postexercise was 7.5 mM/1 without vagal blockade. A reduced heart rate response to exercise, already shown to imply added coronary risk, may be subdivided etiologically and possibly prognostically. The use of a target heart rate in such patients offers no safety margin, and maximal exercise capacity will be grossly over-estimated if extrapolated from the submaximal heart rate response. A cardiovascular limitation to exercise may be detected by an alinear increase in ventilation.

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