title: Median fibrillation frequency in cardiac surgery: influence of temperature and guide to countershock therapy.
abstract: OBJECTIVE
  This study was designed (1) to investigate the effects of normothermic and hypothermic perfusion on the median frequency of the fibrillating myocardium, and (2) to elucidate whether frequency-guided countershock therapy improves countershock success during the reperfusion phase of cardiac surgery.
  
  
  METHODS
  Prospective, randomized study.
  
  
  METHODS
  University hospital cardiac surgery room.
  
  
  METHODS
  Thirty patients (first part of the study) and 38 patients (second part of the study) scheduled for elective coronary artery bypass surgery.
  
  
  RESULTS
  During cardiopulmonary bypass, ventricular fibrillation (VF) was induced at a core body temperature of 34.1+/-0.2 degrees C (normothermia) (n=15) or at a core body temperature of 29.8+/-0.2 degrees C (hypothermia) (n=15). Using fast Fourier transformation of the ECG signal, median fibrillation frequency was recorded continuously for a period of 120 s. At the end of surgery, countershock was performed as soon as VF was recognized on the ECG monitor (X Hz group; n=19) or countershock was not performed until median fibrillation frequency had increased to the threshold of at least 5 Hz (5 Hz group; n=19). Median fibrillation frequency in the normothermic fibrillation group 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 in supraventricular rhythm, 10 in VF, two in electromechanical dissociation, and one in asystole. In the 5 Hz group, 16 countershocks resulted in supraventricular rhythm, two in VF, and one in asystole (p=0.008).
  
  
  CONCLUSIONS
  During normothermia, median fibrillation frequency is significantly higher than during hypothermic perfusion conditions. During the reperfusion phase of cardiac surgery, countershock success rate is significantly higher when a threshold of at least 5 Hz had been reached before the first countershock attempt.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, University of Ulm, Germany.
authors.forename: H U
authors.initials: HU
authors.lastname: Strohmenger
authors.forename: W
authors.initials: W
authors.lastname: Hemmer
authors.forename: K H
authors.initials: KH
authors.lastname: Lindner
authors.forename: J
authors.initials: J
authors.lastname: Schickling
authors.forename: C G
authors.initials: CG
authors.lastname: Brown
mesh_terms: D001026:Coronary Artery Bypass / Q000379:methods / Q000706:statistics & numerical data; D017558:Elective Surgical Procedures / Q000706:statistics & numerical data; D004554:Electric Countershock / Q000379:methods / Q000706:statistics & numerical data; D004562:Electrocardiography / Q000295:instrumentation / Q000379:methods / Q000706:statistics & numerical data; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007036:Hypothermia, Induced / Q000706:statistics & numerical data; D007431:Intraoperative Complications / Q000503:physiopathology / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D015425:Myocardial Reperfusion / Q000706:statistics & numerical data; D011446:Prospective Studies; D013696:Temperature; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy*