The ajmaline test as a method to disclose latent experimental Chagas' heart 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.