Ultrastructural changes in cardiac myocytes from Boxer dogs with arrhythmogenic right ventricular cardiomyopathy.

Objectives: We sought to quantify the number and length of desmosomes, gap junctions, and adherens junctions in arrhythmogenic right ventricular cardiomyopathy (ARVC) and non-ARVC dogs, and to determine if ultrastructural changes existed.

Animals: Hearts from 8 Boxer dogs afflicted with histopathologically confirmed ARVC and 6 dogs without ARVC were studied.

Methods: Quantitative transmission electron microscopy (TEM) and Western blot semi-quantification of α-actinin were used to study the intercalated disc and sarcomere of the right and left ventricles.

Poincaré plots and tachograms reveal beat patterning in sick sinus syndrome with supraventricular tachycardia and varying AV nodal block.

Using 24-h ambulatory electrocardiography, the RR intervals of all beats were determined in a West Highland white terrier with sick sinus syndrome characterized by long sinus pauses, bradycardia, supraventricular tachycardia (SVT) and varying degrees of atrioventricular (AV) heart block. Distinctive patterns of bradycardia and 1:1, 2:1, 3:1, 4:1 and 5:1 AV block associated with SVT were evident in the tachogram (RR interval distribution over time) and Poincaré plots (short-term heart rate variability plots of RRn versus RRn+1). These patterns differed from those of abrupt alteration in cycle length during long sinus pauses or bursts of supraventricular tachycardia.

"Zone of avoidance": RR interval distribution in tachograms, histograms, and Poincaré plots of a Boxer dog.

The RR intervals of sinus and ventricular beats were determined by analysis of a 24-h ambulatory electrocardiogram in a Boxer before and after treatment with sotalol. These RR intervals were plotted using tachograms, histograms, and Poincaré plots. The tachogram demonstrated a 'band' wherein a range of RR intervals was infrequent, the histogram did not take the form of a single Gaussian distribution of RR intervals, and the Poincaré plot showed nonhomogeneous beat-to-beat variability.

Combination therapy with mexiletine and sotalol suppresses inherited ventricular arrhythmias in German shepherd dogs better than mexiletine or sotalol monotherapy: a randomized cross-over study.

Objectives: To determine the spontaneous variability of ventricular arrhythmias (VA) and evaluate anti-arrhythmic efficacy of mexiletine, sotalol, and a mexiletine-sotalol combination in German shepherd dogs (GSD) with inherited arrhythmias.

Animals, Materials And Methods: 12 affected GSD, median age 20 weeks, received mexiletine (8 mg/kg PO q8 h), sotalol (2.5 mg/kg PO q12 h), and combination therapy for 6 days in random order.

Evaluation of atrial fibrillation induced during anesthesia with fentanyl and pentobarbital in German Shepherd Dogs with inherited arrhythmias.

Objective: To determine the type of atrial fibrillation induced by use of 2 pacing protocols during fentanyl and pentobarbital anesthesia before and after administration of atropine and to determine the organization of electrical activity in the left and right atria during atrial fibrillation in German Shepherd Dogs.

Animals: 7 German Shepherd Dogs.

Procedures: Extrastimulus and pacedown protocols were performed before and after atropine administration.