Electrocardiographic findings in experimental myocarditis in DBA/2 mice: complete atrioventricular block in the acute stage, low voltage of the QRS complex in the subacute stage and arrhythmias in the chronic stage.

To determine whether arrhythmias persist in the chronic stage of myocarditis, serial electrocardiograms were studied in DBA/2 mice with experimentally induced myocarditis. After baseline electrocardiograms with standard limb and two precordial leads were recorded, 52 mice were inoculated intraperitoneally with 0.1 ml of the myocardiotropic variant of encephalomyocarditis in a viral suspension containing 10(2) TCD50 (50% tissue culture infective dose). Electrocardiograms were recorded every day on days 3 to 18 and, thereafter, once every 10 to 20 days until day 220. The cumulative incidence rate of myocarditis was 90.4% (47 of 52). No arrhythmias were found on baseline electrocardiograms. Serial electrocardiograms showed atrial and ventricular premature complexes and complete atrioventricular (AV) block, respectively, in 6 (12.8%), 8 (17.0%) and 25 (53.2%) of 47 mice with myocarditis. Myocardial lesions were found in the heart of mice with these ectopic complexes. Mononuclear cell infiltrations into the His bundle were noted in the conduction system of mice with complete AV block. Heart rate began to increase after day 11 (638 +/- 105 beats/min, n = 16 versus control rate 557 +/- 57 beats/min, n = 47, mean +/- standard deviation, p less than 0.01) and reached a maximum on day 15 (40 +/- 22 beats/min, n = 8, p less than 0.01). The sum of QRS voltage in eight leads began to decrease after day 6 (62.1 +/- 18.8 mm, n = 24 versus control value 80.0 +/- 14.7 mm, n = 47, p less than 0.01) and reached a minimum on day 13 (32.5 +/- 7.5 mm, n = 8, p less than 0.01) when myocardial necrosis and congestion of the lungs and liver were most prominent.(ABSTRACT TRUNCATED AT 250 WORDS)