Ventricular Arrhythmia

The presents of T wave alternans (TWA) in surface ECG signals has been recognized as a marker of electrical instability, and is hypothesized to be related with patients at increased risk for ventricular arrhythmias. In this paper we present a TWA simulation study. TWA phenomenon was simulated by change of the ventricular heart cells action potential time duration. The magnitude was calculated in surface ECG with use of time domain method. Spatially concordant TWA, where during one heart beat all ventricular cells have short and during next beat long action potential duration and discordant where at least one region is out of phase were simulated. Vectocardiographic representation was employed. Obtained results shows high level of the T loop pattern and location disturbances connected to discordant TWA simulation in opposite to concordant simulation. This result may be explained by spatial heterogeneity of the ventricular repolarization process which is significantly higher in case of discordant than concordant TWA.

ABSTRACT PURPOSE To assess by cardiac-MR the prevalence of myocardial morphologic and/or functional alterations in arrhythmic patients. METHOD AND MATERIALS We examined 43 patients with non ischemic ventricular arrhythmias. Premature ventricular complexes had left bundle branch block morphology(LBBB) in 29 cases, in 7 a right bundle branch block contour(RBBB) and 7 had polymorphic patterns(PV). US was negative in 78.4% of patients, while CMR was negative in only 13% of patients. Studies were performed on a 1.5 MR scanner with Cine sequences (FIESTA), bb-FSE and IR-prep FGRE 15 minutes after injection of 0,2 mmol/Kg of Gd-DTPA. RESULTS CMR found a high prevalence of morphological, signal intensity and functional myocardial abnormalities. RV dilatation was found in 85% of patients with PV arrhytmias, 48.3% of patients with LBBB morphology, 12.5% of patients with RBBB morphology. LV dilatation was present in 28.6%, 25% and 24.1 % of patients with LBBB, PV and RBBB type arrhytmias respectively. RV wall motion abnormalities were identified in 50% and 36.7 % of patients with PV and LBBB pattern respectively; LV wall motion abnormalities in 25% and 10.3% of patients with PV and LBBB pattern respectively. Free wall RV signal/thickness abnormalities were found in 23,3% of patients(18.6% with LBBB pattern and 4.7 with PV pattern); LV signal abnormalities were found in 11.6% of patients(9.3% with LBBB pattern and 2.3% with PV pattern). Seven patients underwent myocardial biopsy: 5 were positive for myocarditis, 1 was positive for ARVD, one had a negative biopsy. CONCLUSION In patients with primary ventricular arrhythmias CMR documented high prevalence (87%) of morphological, signal intensity and wall motion abnormalities even with negative echocardiogram. CLINICAL RELEVANCE/APPLICATION CMR sholud be considered first choice technique in patients with high grade non ischemic ventricular arrythmias, to select candidates for endomyocardial byopsies and to guide the site of the byopsy.

Deletion of amino-acid residues 1505-1507 (KPQ) in the cardiac SCN5A Na(+) channel causes autosomal dominant prolongation of the electrocardiographic QT interval (long-QT syndrome type 3 or LQT3). Excessive prolongation of the action potential at low heart rates predisposes individuals with LQT3 to fatal arrhythmias, typically at rest or during sleep. Here we report that mice heterozygous for a knock-in KPQ-deletion (SCN5A(Delta/+)) show the essential LQT3 features and spontaneously develop life-threatening polymorphous ventricular arrhythmias. Unexpectedly, sudden accelerations in heart rate or premature beats caused lengthening of the action potential with early afterdepolarization and triggered arrhythmias in Scn5a(Delta/+) mice. Adrenergic agonists normalized the response to rate acceleration in vitro and suppressed arrhythmias upon premature stimulation in vivo. These results show the possible risk of sudden heart-rate accelerations. The Scn5a(Delta/+) mouse with its predisposi...