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Michael E Cain

Publications and source records attributed to Michael E Cain.

13 recordsLinked to original sources
PubMed2006

Relation of T-wave alternans to regional left ventricular dysfunction and eccentric hypertrophy secondary to coronary heart disease.

Left ventricular (LV) hypertrophy and structural disease are associated with exaggerated repolarization dispersion and risk for cardiac arrest. We hypothesized that T-wave alternans (TWA) from the electrocardiogram, reflecting proarrhythmic repolarization dispersion, would increase with extent of eccentric LV hypertrophy and vary spatially with the distribution of myocardial scar. We studied 28 patients with coronary disease, systolic dysfunction, and nonsustained ventricular tachycardia. On echocardiography, 21 patients had wall motion abnormalities and 20 had LV hypertrophy (mass index > or =100 g/m(2)). TWA magnitude (voltage of alternation), which was computed spectrally during ventricular stimulation, varied linearly with LV mass index (p = 0.003). Spatially, positive TWA (magnitude > or =1.9 microV) in orthogonal electrocardiographic axes overlaid scar or wall motion abnormalities in corresponding echocardiographic segments (p <0.05 in x and y axes). After a follow-up of 35 +/- 13 months, positive TWA predicted the combined end point of death or sustained ventricular arrhythmias in all patients (p = 0.025), with a trend for those with echocardiographic LV hypertrophy (p = 0.058). In conclusion, in patients with systolic dysfunction due to coronary artery disease, TWA may indicate arrhythmic contributions from regional myocardial scar and eccentric LV hypertrophy.

Aged↗
PubMed2005

T-wave alternans phase following ventricular extrasystoles predicts arrhythmia-free survival.

OBJECTIVE: The purpose of this study was to assess the value of T-wave alternans (TWA) following ventricular extrasystoles in predicting arrhythmia-free survival. BACKGROUND: Stratifying risk for sudden death in patients with coronary disease and moderate left ventricular (LV) dysfunction remains a challenge. We hypothesized that, in such patients, a discontinuity in beat-to-beat T-wave alternation (TWA phase reversal) following single ventricular extrasystoles reflects transiently exaggerated repolarization dispersion, and predicts spontaneous ventricular arrhythmias. METHODS: We studied 59 patients with ischemic LV dysfunction (mean LV ejection fraction 38.7 +/- 5.3%) and nonsustained ventricular tachycardia undergoing programmed stimulation. TWA was computed spectrally from the ECG during ventricular pacing, and TWA phase reversal was reflected by a discontinuity in T-wave oscillation after single ventricular extrasystoles. RESULTS: Patients induced into ventricular arrhythmias (n = 36) had greater TWA magnitude (V(alt): 6.60 +/- 6.46 microV vs 2.61 +/- 1.97 microV; P = .001) and more frequent TWA phase reversal (62.1% vs 44.4%; P = .02) than those who were not (n = 23). During a mean follow-up of 36 +/- 12 months, positive TWA (V(alt) > or =1.9 microV) and TWA phase reversal both (P < .05) predicted events (all-cause mortality, ventricular tachycardia, ventricular fibrillation). Univariate predictors of arrhythmia-free survival were TWA phase reversal (P < .005), positive TWA (P < .05), age (P = .008), and LV mass index (P = .043). On multivariate analysis, only TWA phase reversal and age predicted events; if TWA phase was excluded, only positive TWA and age predicted events. CONCLUSION: Phase reversal in TWA following ventricular extrasystoles predicts spontaneous ventricular arrhythmias and all-cause mortality in patients with moderate ischemic LV dysfunction and was a better predictor than positive TWA or programmed ventricular stimulation.

Aged↗
PubMed2003

Magnetic guidance system for cardiac electrophysiology: a prospective trial of safety and efficacy in humans.

OBJECTIVES: We evaluated in humans the safety and efficacy of a novel magnetic guidance system (MGS) for electrophysiological mapping, pacing, and ablation. BACKGROUND: Catheter ablation of atrial fibrillation and other complex arrhythmias requires precise catheter manipulation and stabilization. We have shown in animals that the MGS can precisely manipulate a mapping catheter within the heart with an external magnetic field rather than manual catheter control. METHODS: Thirty-one adults referred for diagnostic electrophysiology studies were enrolled in a prospective trial of the MGS. The magnetic catheter was navigated to preselected sites in the right atrium (RA) and right ventricle (RV) in the first 20 patients. Electrograms were recorded at each target site, and pacing thresholds were measured. In a subset of five patients, RA and RV electrograms and stimulation thresholds were recorded with both a standard ablation catheter and the magnetic catheter. Eleven additional patients were recruited for supraventricular tachycardia (SVT) mapping, and seven of these underwent ablation. RESULTS: Navigation was successful in 200 of 202 predetermined right-sided navigation targets and 13 of 13 targets in the left atria. Pacing thresholds and electrogram amplitudes in the RA and RV were not significantly different between the standard and magnetic catheters. The SVT mapping with the magnetic catheter was successful in 13 patients, including 4 with left-sided accessory pathways. The MGS was used for successful ablation of SVT in seven of seven patients. There were no procedural complications. CONCLUSIONS: These results demonstrate that the MGS can be used for intracardiac mapping, pacing, and ablation safely and effectively.

Adult↗
PubMed2003

Detection of the fingerprint of the electrophysiological abnormalities that increase vulnerability to life-threatening ventricular arrhythmias.

Reduction of sudden death requires accurate identification of patients at risk for ventricular tachycardia (VT) and effective therapies. The Multicenter Unsustained Tachycardia Trial and Multicenter Automatic Defibrillator Implantation Trials demonstrate that the implantable cardioverter defibrillator impacts favorably on the incidence of VT in patients with myocardial infarction, underscoring the need to detect the electrophysiologic abnormalities required for the development of VT. Methods used for this purpose include: Holter monitoring, ejection fraction, signal-averaged ECG, heart rate variability, T-wave alternans, baroreflex sensitivity, and programmed stimulation. Performance of each method alone has demonstrated high-negative but low-positive predictive values. Recent studies confirm that their use in combination augments performance.A second approach for improving performance has been to reexamine how well each method detects the electrophysiological derangements that lead to VT. Our recent work has focused on the signal-averaged ECG. Judging from transmural maps of ventricular activation during VT and sinus rhythm obtained from patients, late potentials fail to detect completely signals from myocardium responsible for VT. To obviate this limitation we developed an approach based on inferred epicardial potentials in the frequency domain from 190-surface ECGs using individualized heart-torso models. Torso geometry and electrode positions are measured with a 3-armed digitizer. The location of cardiac structures is determined using echocardiography. The pericardial surface is approximated by a sphere that encloses the heart. Epicardial potentials are inferred using the boundary element method with zero-order Tikhonov regularization and the Composite Residual Smoothing Operator over the QRS complex. Studies are underway to determine if analysis of bioelectrical signals enveloping arrhythmogenic tissue improves identification of patients vulnerable to VT.

Arrhythmias, Cardiac↗