J.Desmond Allen

Effects of lignocaine, propranolol and bretylium on ventricular fibrillation threshold

Abstract The threshold for electrically induced ventricular fibrillation was measured by external transthoracic shocks in dogs weighing from 18 to 35 kg, anesthetized with morphine and pentobarbitone. The duration of the vulnerable period was determined for shocks of 10 joules. The administration of lignocaine, 10 mg/kg followed by an intravenous infusion of 1 mg/kg per min, raised the ventricular fibrillation threshold; smaller doses did not. Neither propranolol nor bretylium in the doses used raised the ventricular fibrillation threshold. None of the drugs affected the duration of the vulnerable period.

Waveform Optimization for Internal Atrial Defibrillation: Effects of Waveform Rounding, Phase Duration, and Voltage Swing

KIDWAI, B.J., et al.: Waveform Optimization for Internal Atrial Defibrillation: Effects of Waveform Rounding, Phase Duration, and Voltage Swing. The aim of this study was to compare the efficacy of internal atrial defibrillation by conventional truncated exponential biphasic waveforms with and without waveform rounding (1–2 phases) and to determine optimal duration for this novel double rounded waveform. Atrial fibrillation, induced by rapid electrical stimulation, was converted by internal shocks through defibrillation catheters (lateral right atrium and coronary sinus) in anesthetised sheep. Rounding the leading edges of the conventional biphasic waveform (Ventritex HVS‐02; settings 100/–50 V, 150/–70 V, and 200/–100 V; n = 8) reduced delivered peak and trough voltages, currents, and energy (by ≥ 21%, P < 0.001; for double (both phases) rounded) without decreasing cardioversion success. At 100/–50 V the efficacy of single (first phase) rounded (53 ± 13%; mean ± SEM) and double rounded (59 ± 11%) shocks was similar to the conventional waveform (56 ± 14%). Double rounded waveform (phase durations 1–20 ms) efficacy was optimum at 6–10 ms phase duration (100% success at 10–ms phase duration; 1.52 ± 0.04 J delivered energy; n = 6). Successful cardioversion by conventional, single rounded, and double rounded biphasic waveforms (duration 6 ms each phase), conventional monophasic, rounded monophasic (duration 12 ms), and a damped sine waveform correlated strongly with peak‐to‐trough voltage swing within the waveform (r = 0.882; P < 0.01; n = 8). For internal atrial defibrillation, rounding both phases of the conventional biphasic waveforms, the double rounded waveform, permits similar efficacy to the conventional truncated exponential biphasic waveform at reduced peak voltage, current, and delivered energy. Optimum phase duration is 6–10 ms (tested range 1–20 ms).

The effects of bretylium on experimental cardiac dysrhythmias.

Abstract Bretylium produced ventricular dysrhythmias in anesthetized normal dogs. It abolished ventricular dysrhythmias induced by adrenaline in dogs respired with halothane and room air, or by ouabain, but only after an initial aggravation of the dysrhythmia. Bretylium aggravated the ventricular dysrhythmias occurring in conscious dogs 20 to 24 hours after coronary artery ligation. These results cast doubt on the rationale of bretylium therapy in the treatment of ventricular dysrhythmias in man.

Low‐Tilt Monophasic and Biphasic Waveforms Compared with Standard Biphasic Waveforms in the Transvenous Defibrillation of Ventricular Fibrillation

Commercially available implantable defibrillators utilize a high‐tilt waveform. Studies in atrial fibrillation and transthoracic defibrillation of ventricular fibrillation (VF) have shown improved defibrillation efficacy using low‐tilt (LT) waveforms. We investigated the feasibility, efficacy, and safety of a LT waveform in the transvenous defibrillation of VF and hypothesized that it would be more efficacious than standard tilted biphasic (STB) waveforms.

The effects of potassium-ATP channel modulation on ventricular fibrillation and defibrillation in the pig heart

BACKGROUND Drugs acting on the cardiac ATP-sensitive potassium (K-ATP) channels may modulate responses to ischaemia and arrhythmogenesis. We investigated the effects of K-ATP channel modulation on frequency patterns of ventricular fibrillation (VF) and on defibrillation threshold (DFT). METHODS AND RESULTS Each group of 24 pigs randomly received intravenous levcromakalim (LKM) 40 microgram/kg (K-ATP agonist), glibenclamide (Glib) 20 mg/kg (K-ATP antagonist), saline or vehicle. Firstly, QTc interval was measured before and after drug. VF was then induced by endocardial stimulation and its power spectra and dominant frequencies over 15 min determined by fast Fourier transformation. Secondly, transthoracic DFT was determined (step-up/step-down protocol) before and after each drug. LKM reduced QTc interval (e.g., lead II, 354-321 ms, P<0.05) and increased the dominant VF frequency between 6 and 8 min (9.5+/-0.5 Hz at 6.5 min compared with 7.2+/-0.6 Hz (saline), 7.4+/-0.8 Hz (vehicle), 6.8+/-0.5 Hz (Glib), P=0.03). LKM reduced (to 57.2+/-2.1 mmHg) and Glib increased (to 107.8+/-6.1) mean arterial BP compared with saline (80.3+/-5.6) and vehicle (87. 6+/-7.1; P<0.01). There was no significant difference in defibrillation threshold energy, current or voltage, after any drug. CONCLUSIONS Activation of K-ATP channels reduced blood pressure and QTc interval. The lack of major effect on VF dominant frequency and DFT of either LKM or Glib suggests that prior administration of similar drugs to patients should not prejudice outcome from VF cardiac arrest.

Electrocardiographic recording, atrial pacing, and defibrillation in the course of electrophysiologic studies using the esophagus

BackgroundThe purpose of this study was to evaluate the use of a new quadripolar esophageal electrode system during electrophysiologic studies, with regard to transesophageal ECG recording, atrial pacing, and countershock of induced sustained ventricular tachyarrhythmias. MethodsThe esophageal system was electively positioned in 29 patients undergoing electrophysiological studies for investigation of life-threatening ventricular arrhythmias. ResultsOne patient was unable to tolerate the esophageal system after its initial successful placement and the electrode was withdrawn. High-quality esophageal ECG recordings were obtained in the remaining 28 patients. Transesophageal atrial pacing was attempted in four patients and successful capture was achieved in all four patients. During programmed ventricular stimulation, electric countershock was required for termination of five episodes of induced ventricular tachycardia and 10 episodes of induced ventricular fibrillation. Successful transesophageal countershock of the five episodes of ventricular tachycardia and of nine of 10 episodes of ventricular fibrillation were effected, with minimal delay, using a maximal delivered transesophageal energy of 100 J. In one patient with induced ventricular fibrillation, successful transthoracic defibrillation was achieved with a single shock of 200 J delivered energy, transesophageal countershock was not attempted. ConclusionsThis esophageal system provides high-quality ECG recordings with the facility for atrial pacing. It also permits low-energy transesophageal defibrillation of ventricular tachyarrhythmias and should prove to be a useful adjunct in electrophysiologic studies and resuscitation.