Diastolic micro-signals preceding ventricular tachyarrhythmias: evaluation of potential association with muscle activity

The presence of small electrical activities, preceding the spontaneous onset of malignant ventricular tachyarrhythmias (VT), is sometimes observed during diastolic phases of intracardiac electrograms (EGMs) recorded from patients with implantable cardioverter defibrillators (ICDs). Aim of this paper is to investigate if similar electrical activities could be determined by myopotentials or diaphragmatic activityies, and to characterize them in the frequency domain. Ten EGMs obtained from 8 ICD recipients implanted with Boston Scientific ICDs are considered. EGMs are recorded while the patient was asked to cough or to do mild isometric abdominal contraction. Signal analysis examines the overall EGMs (to monitor rate and beat morphology) and the diastolic activity by: (i) blanking QRS waves; (ii) filtering each diastolic interval in the bandwidth 15-80 Hz; (iii) computing spectral analysis (PSD) of each diastolic interval. Overall EGM analysis shows a slight increase of heart rate during isometric contraction. Micro-signals extracted during diastole, when visible, have small amplitude compared to those observed before the VT-onset, and PSD peaks in the range 20-40 Hz, not due to power line interferences. Conclusion: results suggest that diastolic micro-signals observed immediately before VT-onset should be associated to mechanisms different from myopotentials or diaphragmatic activity recorded from within the heart.