DESCRIPTION OF TIME-DOMAIN-BASED AND FREQUENCY-DOMAIN-BASED MEASURES OF HEART-RATE-VARIABILITY IN INDIVIDUALS TAKING ANTIARRHYTHMICS, BETA-BLOCKERS, CALCIUM-CHANNEL BLOCKERS, AND OR ANTIHYPERTENSIVE DRUGS AFTER SUDDEN CARDIAC-ARREST

Concomitant drug therapies after sudden cardiac arrest and their poten tial effect of altering heart rate variability (HRV) represent confoun ding factors in interpreting the outcome of nonpharmacologic therapies on HRV. The purpose of this study is to describe a broad spectrum of time-domain and frequency-domain measurements of HRV in 50 individuals after sudden cardiac arrest. Some of the individuals were taking anti arrhythmics (n = 9), beta blockers (n = 13), calcium channel blockers (n = 10), nitrates (n = 8), cardiac glycosides (n = 10), and/or antihy pertensives (n = 12). Heart rate variability was measured using a Holt er recorder for 24 hours and the SpaceLabs FT2000 Monitoring System (R edmond, WA). In those individuals taking antiarrhythmic drugs, the pow er density within the low-frequency range (.016-.04 Hz) was significan tly decreased (P = .001) compared to those not taking antiarrhythmics (n = 41). However, 78% of the people taking antiarrhythmics also had c ongestive heart failure (New York Heart Association functional classes II and III), which also decreased HRV. Those individuals taking beta blockers tended to have slower heart rates (P < .01). The association between beta blocker use and HRV was positive, but not statistically s ignificant except for the increased power density in the low-frequency range (P < .05). In general, the relationships between HRV and drug t herapy-calcium channel blockers, antihypertensives, cardiac glycosides , or nitrates-were not statistically significant.