Baseline clinical characteristics of the participants are shown in . Participants who achieved target HR (n=10,194) were younger and had more favorable cardiac risk factor profile () as well as greater exercise capacity, larger HR increase and more brisk HR recovery than participants who stopped early ().
Baseline characteristics of the 12,555 men who performed exercise test in the Multiple Risk Factor Intervention Trial
Exercise test characteristics in the Multiple Risk Factor Intervention Trial
After an average 7 years of follow-up, 153 (1.2%) of the 12,555 study participants died suddenly (64% of the CHD deaths over 7 years) and 824 (7%) had fatal/non-fatal MI. After 25 years, 1,586 participants (13%) died of CHD and 4,642 (37%) died of all causes.
Not being able to achieve 85% of maximal HR during exercise test predicted an increased risk of death and MI (). After adjusting for baseline risk factors, men who stopped the exercise test early had an 80% higher risk of sudden death (p=0.001), a 40% higher risk of CHD death (p<0.001) and a 30% higher risk of all-cause death (p<0.001) than those who reached target HR (). Participants with chronotropic index < 0.8 also had an increased risk of all-cause death (hazard ratio 1.1, 95% CI 1.0 to 1.2; p<0.01). Of note, the risk of sudden death (hazard ratio 5.0, 95% CI 3.0 to 8.4) and all-cause mortality (hazard ratio 1.9, 95% CI 1.7 to 2.2) were particularly high in the 389 participants who stopped exercise test due to ST segment abnormalities.
Risk of death and myocardial infarction in relation to achieving target heart rate during exercise test
Higher resting HR predicted an increased risk of sudden death and all-cause mortality (). After adjustment for age, men with resting HR ≥80 beats/minute had 70% higher risk of sudden death (ptrend=0.02) and 25% higher risk of all-cause death (ptrend<0.0001) than men with resting HR <65 beats/minute. After adjusting for other cardiac risk factors, resting HR was independently associated with all-cause mortality (ptrend=0.001) ().
Risk of death and myocardial infarction in relation to the quartiles of resting heart rate
Delayed HR recovery predicted an increased risk of sudden death, MI, CHD death and all-cause death, after age adjustment only (ptrend<0.01 for all) (). Following adjustments for cardiac risk factors and exercise capacity, participants with HR recovery >65 beats (3 minutes after exercise) had a 10% lower risk of all-cause death than those with HR recovery <50 beats (ptrend=0.04) (). This association did not vary between age groups.
Risk of death and myocardial infarction in relation to the quartiles of heart rate recovery 3 minutes after exercise
Attenuated HR increase with exercise predicted an elevated risk of sudden death, CHD death, MI and all-cause death after age adjustment only (ptrend<0.01 for all). In multivariate analysis risk of all-cause death was lower (hazard ratio 0.87, 95% CI 0.79 to 0.96; ptrend=0.02) in those with HR increase ≥99 beats/min vs. <82 beats/min.
Exercise duration was inversely associated with sudden death, CHD death, fatal/nonfatal MI and all-cause mortality after adjustment for age. Each additional minute of exercise was associated with a 12% reduction in the risk of sudden death (ptrend=0.009) and a 5% reduction in the risks of CHD death, MI and all-cause mortality (ptrend<0.0001; ptrend=0.03 and ptrend<0.0001 respectively). After adjusting for other cardiac risk factors, men who exercised >8 minutes on standard Bruce protocol had a 15% lower risk of all-cause death than men who exercised <6 minutes (hazard ratio 0.85, 95% CI 0.7 to 0.9; ptrend<0.0001).
The relation of HR parameters with sudden death and all-cause mortality was examined in the subgroup (n=10,194) that exercised until reaching target HR (). In this subgroup, sudden death risk was higher (adjusted hazard ratio 2.0, 95% CI 1.0 to 3.8; ptrend=0.015) in men with resting HR ≥80 beats/minute vs. <65 beats/minute. Also, all-cause mortality was significantly different for those in the 4th quartile vs. the 1st quartile of resting HR (adjusted hazard ratio 1.15, 95% CI 1.0 to 1.3; ptrend=0.008), HR increase (adjusted hazard ratio 0.92, 95% CI 0.83 to 1.02; ptrend=0.03) and exercise duration (adjusted hazard ratio 0.86, 95% CI 0.78 to 0.94; ptrend<0.0001); whereas a trend of association was present for HR recovery (adjusted hazard ratio 0.92, 95% CI 0.8 to 1.0; ptrend=0.13) ().
Figure 2 Predictors of all-cause death among the 10,194 men who reached target heart rate during exercise test. Adjusted HR (95% CI) for the 4th quartile vs. the 1st quartile and regression coefficients were as follows: Resting HR hazard ratio 1.15, 95% CI 1.0 (more ...)