Abstract 7: Direction of Signal Recording Affects Amplitude Based Measures of Ventricular Fibrillation in Humans Undergoing Defibrillation Testing During ICD Implantation
Introduction: A shock applied to prolonged ventricular fibrillation (VF) is less likely to result in a perfusing rhythm than if applied early. Waveform analysis may indicate the duration of VF and the likelihood of defibrillation success, and if such analysis is to be relied upon, we need to understand the errors that may result from variations in AED patch placement. We analyzed VF from patients undergoing implantable cardioverter-defibrillator implantation.
Methods: VF was induced in 26 patients with ischemic cardiomyopathy and 19 patients with dilated cardiomyopathy and recorded in six limb leads. Frequency characteristics (mean, median, dominant and bandwidth) were computed as well as amplitude-based measures of slope (median of absolute difference of voltage every 5 ms) and AMSA (summed product of frequency and amplitude). Characteristics were compared by ANOVA, with repeated measures by lead.
Results: Frequency characteristics were similar in all leads. However, slope and AMSA were significantly affected (p<0.001) by lead for both cardiomyopathy groups. In particular, for ischemic cardiomyopathy patients between leads I and II (a change in the frontal plane of 60 degrees), slope varied from 0.008± 0.001 mV to 0.012 ± 0.001 mV (mean ± SEM, p<0.001) and AMSA varied from 29.4 ± 3.2 to 49.3± 4.6 mV Hz (p<0.001). There were no significant differences between ischemic and dilated cardiomyopathy patients.
Conclusion: Amplitude based measures of VF are significantly affected by recording direction. This investigation implies that AED patches must be consistently and correctly placed if amplitude-based measures are used to decide whether to deliver a defibrillatory shock.