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

Abstract

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.

Guidelines for Diagnosis and Treatment of Chagas Disease

“…About 20-30% of those infected will go on to develop the chronic form of the disease up to 10 or 30 years after they first contracted it. The ajmaline test and the endomyocardial biopsy are, probably, the most sensitive methods to unmask latent forms of chagasic myocarditis during the indeterminate stage [8] CHRONIC PHASE: The chronic phase begins 2-3 months after the initial infection when the clinical manifestations (if any) of the acute phase disappear, and parasitemia falls to undetectable levels. In most cases, the chronic phase presents as an indeterminate form, which may evolve to the cardiac, digestive, or cardiodigestive forms after years or decades.…”