MEDIAN FIBRILLATION FREQUENCY IN CARDIAC-SURGERY - INFLUENCE OF TEMPERATURE AND GUIDE TO COUNTERSHOCK THERAPY

Objective: This study was designed (1) to investigate the effects of n ormothermic and hypothermic perfusion on the median frequency of the f ibrillating myocardium, and (2) to elucidate whether frequency-guided countershock therapy improves countershock success during the reperfus ion phase of cardiac surgery. Design: Prospective, randomized study. S etting: University hospital cardiac surgery room. Patients: Thirty pat ients (first part of the study) and 38 patients (second part of the st udy) scheduled for elective coronary artery by-pass surgery. Methods a nd results: During cardiopulmonary bypass, ventricular fibrillation (V F) was induced at a core body temperature of 34.1 +/- 0.2 degrees C (n ormothermia) (n = 15) or at a core body temperature of 29.8 +/- 0.2 de grees C (hypothermia) (n = 15). Using fast Fourier transformation of t he ECG signal, median fibrillation frequency was recorded continuously for a period of 120 s, At the end of surgery, countershock was perfor med as soon as VF was recognized on the ECG monitor (X Hz group; n = 1 9) or countershock was not performed until median fibrillation frequen cy had increased to the threshold of at least 5 Hz (5 Hz group; n = 19 ), Median fibrillation frequency in the normothermic fibrillation grou p was statistically higher than in the hypothermic group. In the X Hz and 5 Hz countershock group, median fibrillation frequency before the first countershock attempt was 3.6 +/- 0.2 Hz and 5.4 +/- 0.1 Hz (p < 0.0001), respectively. In the X Hz group, six countershocks resulted i n supraventricular rythm, 10 in VF, two in electromechanical dissociat ion, and one in asystole. In the 5 Hz group, 16 countershocks resulted in supraventricular rh)thm, two in VF, and one in as)stole (p = 0.008 ). Conclusions: During normothermia, median fibrillation frequency is significantly higher than during hypothermic perfusion conditions. Dur ing the reperfusion phase of cardiac surgery, countershock success rat e is significantly higher when a threshold of at least 5 Hz had been r eached before the first countershock attempt.