Biomedical subjects

S Moghe

Publications and source records attributed to S Moghe.

5 recordsLinked to original sources

PubMed2001

Correlation between defibrillation shock outcome and coherence in electrocardiograms.

Cycle periods in ECG during VF are correlated with periods of reentrant activation. The ECGs recorded from different locations on the thorax were contributed to from electrical activations within the heart in approximately inverse proportion of their distance from the recording sites. Similarity in cycle periods between ECGs recorded from two locations, therefore, can be used as an index of spatiotemporal similarity in the rate of activation. In the present study coherence was used, which is a mathematical function that measures the degree of similarity that two signals exhibit at specific cycle periods, to test if spatiotemporal similarity in cycle periods between pairs of orthogonal ECGs was correlated with defibrillation shock outcome. The authors estimated time-varying coherence from orthogonal ECGs during 10 seconds of electrically induced VF, which was terminated with a defibrillation shock with a 50% probability of successful outcome. Defibrillation shocks were delivered between a coil electrode placed at the right ventricular apex and a subdermal patch electrode. Time-varying coherencies between pairs of ECGs were estimated using an adaptive least mean square algorithm. Time-coherence surfaces were integrated within a frequency region centered at the dominant frequency. Data were collected from ten dogs during 206 (48%) successful and 221 (52%) unsuccessful trials. The results showed that coherencies between the sagittal-transverse pair were 10%-15% higher (P < 0.05) for successful than unsuccessful trials. The correlation between coherence and defibrillation outcome suggests that more defibrillation shocks occurred when the degree of spatial similarity in the rate of activations was higher terminated VF, than those that occurred at other times. These results are consistent with a hypothesis, recently proposed by others, that more uniform activation within regions of the heart that receive low potential gradients during shock may increase the probability of successful defibrillation.

Animals↗

PubMed2001

Novel feedback based stimulation protocol shows hysteresis in cardiac action potential duration restitution.

Short diastolic intervals (DI) produce short action potential durations (APD) due to restitution. Slope of restitution is hypothesized to be critical in initiation of VF. Importance of restitution in mechanisms of VF is recently debated, primarily because of a lack of consistent characterization of restitution. Currently used protocols, standard and dynamic, include pacing at constant S1-S1 intervals for a number of stimuli followed by an S2 or not. In these, DI are a function of both APD (memory effect) and pacing interval (DI = pacing interval--APD). Therefore, restitution functions obtained after variable number of S1 or variable S1-S1 intervals are different. We developed a novel feedback based protocol that permits selection of DI independent of pacing interval and APD. From the instant when transmembrane voltage drops below 90% of repolarization voltage, a stimulus is delivered after predetermined DI. We used DI that oscillated between 0 and 60 msec with periods ranging from 15 sec to 500 msec to quantify effects of short and long term memory on restitution. We used a Luo-Rudy dynamic model of cellular activation. Resulting restitution functions clearly showed multi-modal behavior and hysteresis. When DI increased following a period of decreasing intervals, the APD were shorter than when DI decreased following increasing intervals. Thus, same DI produce different APDs depending on past activation history. Such variation in APD may play a role in increased incidence of VF that is reported after large oscillations in heart rate, i.e. when episodes of bradycardia follow a tachycardic episode.

Action Potentials↗

PubMed2000

Frequency modulation within electrocardiograms during ventricular fibrillation.

Periods of reentrant activation and effective refractory periods are correlated with dominant frequency or reciprocal of cycle periods during ventricular fibrillation (VF). In the present study, we used an analysis technique based on Wigner transforms to quantify time-varying dominant frequencies in electrocardiograms (ECGs) during VF. We estimated dominant frequencies within orthogonal ECGs recorded in 10 dogs during trials of 10 s of VF and in 9 dogs during trials of 30 s of VF. In four additional dogs, we compared dominant frequencies during 10 s of VF before and after administration of amiodarone. Our results showed the following. 1) There was substantial frequency variation or modulation within the ECGs during 10 and 30 s of VF, the average variation being +/-15% from the mean frequency. Amiodarone decreased mean frequencies (P < 0.05) as expected; however, amiodarone also decreased the variation in frequencies (P < 0.05). 2) During 30 s of VF, the dominant frequencies increased continuously from 7.3 to 8.1 Hz (P < 0.05). The increase in frequency was almost linear with a rate of 0.022 Hz/s (r(2) = 0.93, P < 0.0005). 3) Modulation of frequencies during the first and the last one-half of 30 s of VF was not different. Average (in time) mean frequencies and modulation of frequencies were similar in all three ECGs. 4) Although the averages were similar, during any VF episode, dominant frequencies in ECGs recorded from different locations on the body surface were similar to each other at some times and markedly different from each other at other times. We conclude that during VF, 1) frequencies in ECGs vary considerably and continuously, and amiodarone decreases this variation; 2) mean frequencies increase linearly during first 30 s; 3) the variability in frequency does not change during 30 s; and 4) at any given time, the frequencies within spatially different body surface ECGs can be either similar or markedly different.

Amiodarone↗

PubMed1998

Relation between ventricular fibrillation voltage and probability of defibrillation shocks. Analysis using Hilbert transforms.

We used Hilbert transforms to re-evaluate the previously reported correlation between defibrillation shock outcome and absolute ventricular fibrillation voltage (AVFV). Previously in the literature, single values of AVFV acquired just prior to shock delivery were used to show a correlation between AVFV and shock outcome. In subsequent studies, a modified analysis procedure was used to show a correlation between shock outcome and moving average of AVFV. The use of single values of AVFV makes the AVFV sensitive to the local phase of the electrocardiographic (ECG) waveform, whereas moving averages are weighted by previous values of the ECG. The envelope is independent of the phase of the ECG and is not weighted by previous values of ECG as is the moving average. We explored, therefore, whether the AVFV computed from the envelopes of the ECG showed a stronger correlation with shock outcome than single values and moving averages of the AVFV. We estimated envelopes using the Hilbert transform. Orthogonal ECGs (sagittal, X; transverse, Y; and longitudinal, Z) were recorded from 11 dogs during 10 seconds of electrically induced ventricular fibrillation followed by a defibrillation shock with 50% probability of success. We used transvenous (right ventricular apex to subcutaneous patch) leads to deliver defibrillation shocks. Results from 236 successful and 249 unsuccessful trials showed, in contrast with the previously reported correlation, that moving average of AVFV was not higher for successful trials. In the Z direction, unsuccessful trials had higher voltage than successful trials (P < .05). Comparison of envelope voltages between successful and unsuccessful trials did not show any consistent and statistically significant differences. Although there were some methodological differences between ours and the previously reported studies, they are unlikely to have caused the discrepant observations. Our results suggest, therefore, that the absolute voltage of ECG during ventricular fibrillation is not robustly correlated with shock outcome.

Animals↗

PubMedDate not supplied

Bispectral energies within electrocardiograms during ventricular fibrillation are correlated with defibrillation shock outcome.

We investigated whether the degree of phase coupling among orthogonal electrocardiograms during ventricular fibrillation (VF) was correlated with defibrillation shock outcome. We used cross bispectrum to estimate the degree of phase coupling. In dogs, VF was electrically induced and terminated with a defibrillation shock with a 50% probability of success. The defibrillation shock was delivered between the right ventricular apex and a subcutaneous patch electrode. Bispectra were integrated within 8.7-11.7, 8.7-11.7 Hz bandwidths and compared between those trials for which the defibrillation shocks were successful (206 trials, 49%) and unsuccessful (221 trials, 51%) in terminating VF. Results showed that between 200 and 1000 ms before defibrillation shock, unsuccessful trials had greater bispectral energy than successful trials (p<0.05). Although correlations between degree of phase coupling and shock outcome do not indicate causal relationship or predictability, they provide further evidence of the organization during fibrillation. We discuss the nonstationary wavelet hypothesis, previously proposed in the literature by other investigators, as one of the possible mechanisms to explain the correlation between bispectral energy and shock outcome.

Animals↗