Frequency modulation within electrocardiograms during ventricular fibrillation

Periods of reentrant activation and effective refractory periods are correl ated with dominant frequency or reciprocal of cycle periods during ventricu lar fibrillation (VF). In the present study, we used an analysis technique based on Wigner transforms to quantify time-varying dominant frequencies in electrocardiograms (ECGs) during VF. We estimated dominant frequencies wit hin orthogonal ECGs recorded in 10 dogs during trials of 10 s of VF and in 9 dogs during trials of 30 s of VF. In four additional dogs, we compared do minant frequencies during 10 s of VF before and after administration of ami odarone. Our results showed the following. 1) There was substantial frequen cy variation or modulation within the ECGs during 10 and 30 s of VF, the av erage variation being +/-15% from the mean frequency. Amiodarone decreased mean frequencies (P < 0.05) as expected; however, amiodarone also decreased the variation in frequencies (P < 0.05). 2) During 30 s of VF, the dominan t frequencies increased continuously from 7.3 to 8.1 Hz (P < 0.05). The inc rease in frequency was almost linear with a rate of 0.022 Hz/s (r(2) = 0.93 , P < 0.0005). 3) Modulation of frequencies during the first and the last o ne-half of 30 s of VF was not different. Average (in time) mean frequencies and modulation of frequencies were similar in all three ECGs. 4) Although the averages were similar, during any VF episode, dominant frequencies in E CGs recorded from different locations on the body surface were similar to e ach other at some times and markedly different from each other at other tim es. We conclude that during VF, 1) frequencies in ECGs vary considerably an d continuously, and amiodarone decreases this variation; 2) mean frequencie s increase linearly during first 30 s; 3) the variability in frequency does not change during 30 s; and 4) at any given time, the frequencies within s patially different body surface ECGs can be either similar or markedly diff erent.