ajmaline and Chagas-Disease

Forty-one chronically T. cruzi-infected male adult albino rats with normal resting ECG were submitted to the ajmaline test (1 mg/kg body weight injected into the dorsal vein of the penis). Twenty-one similar noninfected animals served as controls. Ajmaline induced the following ECG alterations in control rats: A decrease in heart rate, an increase in heart rate, an increase in P-wave duration, an increase in PR interval, lengthening of the QRS complex, and left axis deviation in 33%, 28%, 14%, 90%, 100%, and 33% of the animals, respectively. Ajmaline evoked similar alterations in 29 of 41 (71%) T. cruzi-infected rats. However, 12 of 41 (29%) infected rats showed ECG changes of a magnitude not seen in controls: P-wave enlargement, first-degree AV block, lengthened QRS complex, and first-degree AV block plus lengthened QRS complex in 7%, 12%, 14%, and 4% of the animals, respectively. Microscopical lesions were not found in control rats. However, 22 of 41 (53%) infected rats were found to have the following pathological lesions: mononuclear cell infiltrate, necrosis, myocyte vacuolization, and interstitial fibrosis in 56%, 39%, 29%, and 7% of the animals, respectively. By comparing the ECG changes evoked by ajmaline not seen in controls with the concomitant pathological lesions, the ajmaline test was found to have 54% sensitivity, 100% specificity, and 100% positive predictive value. Thus, the ajmaline test appears to be useful for unmasking myocardial disease and therefore may be considered a potential method for the full characterization of the indeterminate form of Chagas' disease in experimental animals.

Topics: Ajmaline; Animals; Chagas Cardiomyopathy; Chagas Disease; Electrocardiography; Heart Rate; Male; Myocardium; Rats; Trypanosoma cruzi

In the present study, the ajmaline test was applied to T. cruzi-infected rats and evaluated for the ability to reveal ECG disturbances. The test consists of intravenous injection of ajmaline (2 mg/kg body-weight) under ether anaesthesia, and continuous ECG monitoring (right precordial lead: V1 or V2, 100 mm/sec paper speed). The animals used for the test (n = 30) had been experimentally infected with the Colombia strain of T. cruzi (1,000 parasites/g body-weight, newly weaned rats) one year before the experiments. Control non-infected rats (n = 21) were similarly maintained and treated. The ECGs were analysed under baseline conditions, i.e., before ajmaline, and 15, 30, 60 and 180 seconds after completion of ajmaline injection through the dorsal vein of the penis. The following parameters were studied: heart rate, PR interval, QRS and Qat duration. Morphological changes of the QRS complex and ST-T segment were also recorded. Under baseline conditions, the two groups had comparable values for all parameters, except for the PR interval, which was significantly increased in infected rats. No changes in wave rhythm or morphology were detected under baseline conditions. The PR and QaT intervals and QRS duration were significantly longer in both groups after ajmaline injection, at all periods studied. When the two groups were compared for relative variations, consistently and significantly higher alterations (p less than 0.05) were observed in the T. cruzi-infected group, except for the QaT interval at 180 seconds. However, the severe rhythm and ventricular conduction disturbances detected in 30% of the infected rats represented clear-cut discriminative alterations.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Ajmaline; Animals; Chagas Cardiomyopathy; Chagas Disease; Electrocardiography; Heart Rate; Male; Rats; Rats, Inbred Strains