Frequency and amplitude structure of ventricular fibrillation of canine heart during ischemia and reperfusion: an experimental study

Introduction: Ventricular fibrillation (VF) is a fatal arrhythmia that causes sudden cardiac death in the overwhelming majority of cases (> 80%). Objective: The study was aimed to examine frequency and amplitude structure of VF upon canine heart reperfusion after ischemia within 30–240 s. Methods: Six experiments were conducted on 12 dogs. In each experiment the isolated heart of the one dog was perfused with the blood of the other (supporting) dog. Nine episodes of heart ischemia, lasting 30, 60, 90, 120, 150, 180, 210 and 240 s, were examined in six experiments (72 episodes of heart ischemia at VF in total). Before and after each ischemia episode, ten-minute perfusion and reperfusion were performed at VF, and heart electrograms were recorded. Spectral analysis of electrograms was conducted using Fast Fourier Transform in the range of 0.5–15 Hz. The frequency and proportions of the 1st through the 3rd oscillations of the most powerful frequencies were determined during perfusion, ischemia and reperfusion of the heart at VF (frequency (Hz) — mode; proportions (%) — M±SD; n = 270). Results: The frequency and proportions of the dominant oscillations were stable at perfusion and amounted to 9–10 Hz and 39–41%, respectively, without significant changes after 30-second ischemia (P = 0.09; P = 0.07) and 10-minute reperfusion (from P = 0.07 to P = 0.23; from P = 0.09 to P = 0.21). At the 2nd min of ischemia, the frequency of dominant oscillations decreased to 8.5–9.0  Hz (P = 0.009) but their proportions did not change significantly (P = 0.06). At the 3-4th min of ischemia, the frequency of dominant oscillations decreased to 5.0-7.5 Hz (P = 0.002), and their proportions reduced to 32-33% (P = 0.001). During reperfusion, after 1–2-minute ischemia, the frequency of the dominant oscillations increased to 10.5–12.0 Hz (P = 0.03 and P = 0.002) at the 1st min and decreased to 9.5–10.5 Hz (P = 0.01 and P = 0.009) at the 2nd min of reperfusion processes. After 3–4 minute ischemia, the frequency of dominant oscillations increased to 12.5–14.0 Hz (P = 0.001) at the 1st min and decreased to 10–11 Hz (P = 0.005 and P = 0.007) at the 2nd min of reperfusion processes. Further, the proportions of dominant oscillations after 1–2-minute ischemia decreased to 33–36% (P = 0.003 and P = 0.002) at the 1st min and increased to 39% (P = 0.005 and P = 0.001) at the 2nd min of reperfusion. After 3–4-minute ischemia, the proportion of dominant oscillations remained reduced (32–34%) at the 1st min but increased to 36–40% (P = 0.005 and P = 0.007) at the 2nd min during reperfusion. Conclusion: The organized VF activity was more sensitive to reperfusion than to ischemia, as evidenced by more significant changes in the VF frequency and amplitude structure at reperfusion relative to ischemia. VF was specified by explosive (impulse) destabilization of the organized activity at reperfusion, which manifested itself by an increase in the frequency of dominant FV oscillations at the 1st min and their decrease at 2–3th min of reperfusion process, as well as by a decrease in the proportions of dominant VF oscillations at the 1st min and their increase at 2–3th min at reperfusion. The severity of destabilization of the organized VF activity at reperfusion positively associated with the ischemia duration.