Abstract 147: β-Blockade Causes a Reduction in the Frequency Spectrum of Ventricular Fibrillation but Improves Resuscitation Outcome: A Potential Limitation of Quantitative Waveform Measures
Background: Quantitative waveform measures (QWM), can predict defibrillation and restoration of spontaneous circulation (ROSC) in drug-naïve animal models with normal coronary arteries. However, patients at risk for sudden death are often treated with medications affecting adrenergic activity prior to arrest. The purpose of this study was to determine if pretreatment with adrenergic agents alters QWM measures and prediction of ROSC.
Methods: Thirty swine were randomized to three pre-arrest treatment groups: control, IV labetalol, or IV metoprolol. After drug treatment, VF was induced by balloon occlusion of the LAD. The VF ECG waveform was recorded at 1000 Hz over 7 min of untreated VF. After 7 min, resuscitation was begun and continued for 15 minutes or until ROSC. The Fourier frequency spectra, the amplitude spectrum area (AMSA), and detrended fluctuation analysis (DFA) were calculated from VF onset to initiation of resuscitation.
Results: The frequency spectrum in metoprolol and labetalol treated animals demonstrated a reduction in mean frequencies from 1 to 3 min and from 3 to 7 min. The decline in AMSA was similar in all three groups over the first 3 minutes. From 3 to 7 min the metoprolol group was significantly lower than the control group (p<0.001) and the labetalol group was lower still (p <0.001). The DFA demonstrated little difference between the control and metoprolol groups, but showed a linear increase over 7 minutes in the labetalol group. The relative risk of ROSC of was 4.4 when comparing metoprolol to control and 1.4 comparing labetalol to control animals.
Conclusion: Adrenergic blockade prior to VF reduces frequencies in the Fourier spectrum of VF to values predictive of poor outcome. Adrenergic blockade prior to VF induction affects quantitative measures of the VF waveform and may limit the ability of such measures to predict downtime or defibrillation outcome. Despite the prediction of poor outcome based on QWM, metoprolol treated animals had an increase in ROSC rates compared to control and labetalol treated animals.
- © 2011 by American Heart Association, Inc.