Abstract
Introduction: Clinically in ventricular fibrillation (VF), ECG amplitude, and frequency decrease as ischemia progresses and predict defibrillation success. In vitro ECG amplitude declines without ischemia, independent of VF frequencies. This study examines the contribution of cellular electrical activity and global organization to ECG amplitude changes during VF. Methods and Results: Rabbit hearts were Langendorff-perfused (40 mL/min, Tyrode’s solution) and loaded with RH237. During VF, ECG, and epicardial optical action potentials were recorded (photodiode array; 256 sites, 15 mm × 15 mm). After 60 s of VF, perfusion was either maintained, global ischemia produced by low-flow (6 mL/min), or solution [K+]o raised to 8 mM. Peak-to-peak amplitude was determined for all signals. During VF, in control, ECG amplitude decreased to a steady-state (∼57% baseline), whereas in low-flow steady-state was not reached with the amplitude continuing to fall to 33% of baseline by 600 s. Optically, LV amplitude declined more than RV, reaching significance in control (LV vs. RV; 33 ± 5 vs. 63 ± 8%, p < 0.01). During VF in 8 mM [K+]o, amplitude changes were more complex; ECG amplitude increased with time (105 ± 13%), whilst LV amplitude decreased (60 ± 15%, p < 0.001). Microelectrode studies showed amplitude reduction in control and 8 mM [K+]o (to ∼79 and ∼93% baseline, respectively). Evaluation of electrical coordination by cross-correlation of optical signals showed as VF progressed coordination reduced in control (baseline 0.36 ± 0.02 to 0.28 ± 0.003, p < 0.01), maintained in low-flow (0.41 ± 0.03 to 0.37 ± 0.005, p = NS) and increased in 8 mM [K+]o (0.36 ± 0.02 to 0.53 ± 0.08, p < 0.05). Conclusion: ECG amplitude decline in VF is due to a combination of decreased systolic activation at the cellular level and increased desynchronization of inter-cellular electrical activity.
Highlights
In ventricular fibrillation (VF), ECG amplitude, and frequency decrease as ischemia progresses and predict defibrillation success
This study examines the contribution of cellular electrical activity and global organization to ECG amplitude changes during VF
Rather microelectrode studies demonstrated significant depolarization of the diastolic membrane potential during VF in raised [K+]o and reduction of CONCLUSION This study documents for the first time that during VF in control conditions ECG activation amplitude reduces with time
Summary
In ventricular fibrillation (VF), ECG amplitude, and frequency decrease as ischemia progresses and predict defibrillation success. Many clinical (Weaver et al, 1985; Strohmenger et al, 1997, 2001; Eftestol et al, 2004) and animal (Noc et al, 1994; Achleitner et al, 2000, 2001; Kolarova et al, 2003) studies have shown that the amplitude of ECG oscillation in VF just prior to defibrillation can predict the likelihood of defibrillation success and may be the most useful ECG parameter to assess optimal timing of defibrillation in out-of-hospital arrests (Strohmenger et al, 2001).
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