Introduction

Tick-borne diseases are highly prevalent in domestic dogs, the monocytic ehrlichiosis (ME) being one of the most important by its gravity. The occurrence of myocarditis is known in affected animals; however, little is known about the effects of treatment in this disease.

Objectives

To evaluate the electrical activity of the heart by the conventional electrocardiogram of dogs affected by the ME before and after treatment with doxycycline.

Methods

Two groups were analyzed: one with 20 animals diagnosed with ME based on clinical and hematological changes found and positive PCR for Ehrlichia canis on blood (G1), and the second consisting of 10 healthy dogs as controls (G2). On the G1, an electrocardiographic evaluation was performed at the time of diagnosis (M1) and other after 28 days of treatment with 10 mg/kg each 24 hours of doxycycline (M2). In G2, there was only one examination.

Results

One among the 20 sick dogs (5%) featured arrhythmias in five minutes of recording, being 12 isolated junctional escapes, 93 isolated ventricular escapes and seven in pairs, six episodes of type II atrioventricular block (AVB), and 112 episodes of sinus arrest. After treatment, the arrhythmias regressed, there were two episodes of type II AVB and one junctional escape. The PR and QT intervals were statistically higher compared to M1, M2 and the control group, showing conduction delay in sick animals.

Conclusions

Treatment with doxycycline decreased arrhythmic events and improved conduction of the stimulus, presenting a possible positive effect on the heart of dogs with ME.