Abstract 9968: Reduced Heart Rate Recovery after Exercise is Associated with Mortality After an ICD

Abstract

Background and purpose: The period of recovery in heart rate (HRR) after exercise is thought to be mediated by parasympathetic reactivation. Abnormal heart rate recovery (<12 bpm during the 1st minute or < 25 bpm at 5 minutes) after exercise, has been shown to be a powerful predictor of mortality in those with coronary artery disease or heart failure (HF). HRR has not been studied in persons with an ICD. The purpose of this study was to examine the relationship between 1 and 5 minute HRR and 1 year mortality in patients undergoing exercise testing who have an ICD for either primary or secondary prevention of sudden cardiac arrest.

Methods: 149 patients who had a previous ICD implant (39% primary indication, 61% secondary indication, mean age 54+12.5 years, 76% male, 3.7+4.3 years since implant, 100% taking beta blockers) entered a clinical trial of exercise after an ICD. At baseline study entry, they completed a cardiopulmonary exercise test using a modified Balke treadmill protocol. HRR was calculated as the difference between peak exercise HR and 1 and 5 minutes into the recovery period using 12 lead EKG recordings. Analysis of variance was used to determine if HRR was significantly related to 1 year mortality after study entry.

Results: There were 4 deaths within the 1st year after study entry (2.6%), all had a history of HF. Three deaths were due to HF and 1 was due to cancer. HRR was significantly reduced in those who died at both 1 minute (mean+SD; 7.5+6.2 bpm vs. 18.3+8.1 bpm, F=2.64, p=0.009) and at 5 minutes (19.2+6.0 bpm vs 38.7+13.9 bpm, F=2.76, p=0.006) when compared to those who did not. At baseline, there was statistically higher HRR in secondary prevention (19.4 bpm vs. 16.3 bpm at 1min (p=0.42) compared to primary prevention (40.7 bpm vs. 33.8 bpm at 5min (p=0.007). HRR was not related to ICD shocks.

Conclusions: Those who have an ICD for primary prevention with a history of HF had lower HRR after exercise testing and higher 1 year mortality than those with a secondary prevention ICD. HRR is a useful marker of autonomic dysregulation and risk for mortality in those with HF who have an ICD.