EFFICACY AND SAFETY OF TEN DEFIBRILLATOR WAVEFORMS USING AN ISOLATED CANINE HEART MODEL
Abstract
The efficacy and safety of 10 defibrillator waveforms were studied in 25 isolated canine heart preparations. The coronary arteries of the isolated heart are constantly perfused with oxygenated blood from a second dog. The heart exhibits a regular, rhythmic contraction and responds to changes in diastolic loading according to Starling's law. The heart can also demonstrate true ventricular fibrillation and defibrillation. The absence of autonomic reflexes and tissue ischemia allows for determination of defibrillator shock effects on cardiac contractility. First, defibrillation threshold was established for each waveform. Then, suprathreshold shocks of 3 to 9 times threshold current were applied and cardiac depression recorded. This depression was, dose-related, transient and did not affect the response of the heart to subsequent shocks. From these data, the shock strength required to produce a 50% depression was obtained for each waveform. The waveform safety factor was the shock strength required to produce a 50% depression divided by the defibrillation threshold. The threshold average current densities for the 2 msec, 5 msec, 10 msec, and 20 msec rectangular waveforms, the 5 msec damped sine, three 10 msec trapezoidal waveforms (45%, 65%, and 80% tilt), the 10 msec dual pulse, and 10 msec reciprocal pulse waveforms were 81, 55, 41, 35, 59, 38, 38, 34, 36, and 32 mA/cm('2). The corresponding mean threshold energy densities were 3.1, 3.2, 3.6, 6.1, 2.8, 3.9, 3.3, 2.7, 2.9, and 3.1 mJ/cm('3). The 2 msec waveform had significantly lower safety factors (3.9 and 15 for current and energy, respectively) than all other waveforms (p < 0.05). The 45%, 65%, and 80% tilt trapezoidal waveforms had significantly lower (p < 0.05) safety factors (approximately 4.5 and 20) than all other 5, 10, and 20 msec waveforms (approximately 5.3 and 26).
Degree
Ph.D.
Subject Area
Anatomy & physiology|Animals
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