QUANTIFICATION OF THE MODIFICATIONS IN THE DOMINANT FREQUENCY OF VENTRICULAR-FIBRILLATION UNDER CONDITIONS OF ISCHEMIA AND REPERFUSION - ANEXPERIMENTAL-STUDY

The characteristics of ventricular fibrillatory signals vary as a func tion of the time elapsed from the onset of arrhythmia and the maneuver s used to maintain coronary perfusion. The dominant frequency (FrD) of the power spectrum of ventricular fibrillation (VF) is known to decre ase after interrupting coronary perfusion, though the corresponding re covery process upon reestablishing coronary flow has not been quantifi ed to date. With the aim of investigating the recovery of the Fro duri ng reperfusion after a brief ischemic period, 11 isolated and perfused rabbit heart preparations were used to analyze the signals obtained w ith three unipolar epicardial electrodes (E1-E3) and a bipolar electro de immersed in the thermostatized organ bath (E4), following the elect rical induction of VF. Recordings were made under conditions of mainta ined coronary perfusion (5 min), upon interrupting perfusion (15 min), and after reperfusion (5 min). FrD was determined using Welch's metho d. The variations in Fro were quantified during both ischemia and repe rfusion, based on an exponential model Delta FrD = A exp (-t/C). Durin g ischemia Delta FrD is the difference between FrD and the minimum val ue, while t is the time elapsed from the interruption of coronary perf usion. During reperfusion Delta FrD is the difference between the maxi m um value and Fro, while t is the time elapsed from the restoration o f perfusion. A is one of the constants of the model, and C is the time constant. Fro exhibited respective initial values of 16.20 +/- 1.67, 16.03 +/- 1.38, and 16.03 +/- 1.80 Hz in the epicardial leads, and 15. 09 +/- 1.07 Hz in the bipolar lead within the bath. No significant var iations were observed during maintained coronary perfusion. The fit of the Fro variations to the model during ischemia and reperfusion prove d significant in nine experiments. The mean time constants C obtained on fitting to the model during ischemia were as follows: E1 = 294.4 +/ - 75.6, E2 = 225.7 +/- 48.5, E3 = 327.4 +/- 79.7, and E4 = 298.7 +/- 4 3.9 seconds. The mean values of C obtained during reperfusion, and the significance of the differences with respect to the ischemic period w ere: E1 = 57.5 +/- 8.4 (P < 0.01), E2 = 64.5 +/- 11.2 (P < 0.01), E3 = 80.7 +/- 13.3 (P < 0.01), and E4 = 74.9 +/- 13.6 (P < 0.0001). The ti me course variations of the Fro of the VF power spectrum fit an expone ntial model during ischemia and reperfusion. The time constants of the model during reperfusion after a brief ischemic period are significan tly shorter than those obtained during ischemia.