Cats with Hypertrophic Phenotype Cardiomyopathy - P-wave Electrical Axis

Abstract

Background:  Hypertrophic phenotype cardiomyopathy is the most common heart disease in cats. Although the echocardiogram is the gold standard test for diagnosing fHCM, patients with the disease may have electrocardiographic changes. Despite being reported in most 12-lead electrocardiograms, the P wave axis generally receives little attention when compared to other wave parameters. We performed a Doppler echocardiographic and electrocardiographic study in cats, in order to verify the presence of correlation between the electrical axis average P wave and the presence of fCMH, aiming to investigate the possibility of its aid in the early diagnosis of cardiac disorders.

Material, Methods & Results: One hundred cats of different breeds, ages, males and females were evaluated. Those animals with a history of previous disease other than hypertrophic cardiomyopathy were excluded from the study. The groups were formed after obtaining the results of the echocardiographic examination. Eight of the 100 cats did not allow echocardiographic evaluation, and the remaining 92 were divided into 2 groups (control group, n = 64 and heart disease group, n = 28) after the examination. Of these 92 animals, 28 cats had the hypertrophic cardiomyopathy phenotype. The electrocardiographic examination was performed after the allocation of animals into groups lasting 5 min with the recording of tracings for later interpretation. To calculate the axis of the P wave, leads D1 and D3 were used, measuring the amplitude of the P wave in these leads and calculating the resulting amplitude. All cats studied had mean electrical axis of the P wave within the normal range for the species (0º to 90º). Based on mean electrical axis P wave values, there was no significant difference between groups. The control group had a median of 63.7° with a maximum value of 80°, a minimum value of 60° and a mean of 65.1°. The fCMH group had a median of 68.7° with a maximum value of 85.3°, a minimum value of 56.3° and a mean of 68.8°. Of the fCMH group, three cats had increased P wave duration (50.33 ± 5.77 ms), suggesting left atrial overload, and 13 cats had increased QRS complex duration (66.30 ± 11.23 ms). Also, 18 cats (Control group: 11; fCMH group: 7) showed T wave amplitude greater than 25% of R, suggesting the presence of myocardial hypoxia and/or electrolyte disturbance. One cat had a prolonged PR interval (from the fCMH group). As for the QT interval, 6 cats had an interval < 120 (2 from the control group and 4 from the affected group) and 3 had an interval > 180 (1 from the control group and 2 from the affected group). The ST segment remained isoelectric in all segments. As for the mean electrical axis of the QRS complex, 5 cats (10.42%) had axis deviation to the right (control: 1; fCMH: 4) suggesting right ventricular overload; 7 cats (14.58%) had left axis deviation (control: 5; fCMH: 2), suggestive of left ventricular overload; and 36 cats (75%) had a normal mean electrical axis.

Discussion: Based on the results obtained in the present study, it can be concluded that screening studies in asymptomatic felines should be increasingly implemented in the veterinary clinical routine, since the frequency found was high (30.44%) and that patients may remain asymptomatic for years until the development of signs. It should be concluded that there was no correlation between the mean electric axis of P-wave and the presence of subclinical phenotype hypertrophic cardiomyopathy. Therefore, more studies are needed, with felines at different stages of the disease, to evaluate whether this electrocardiographic measurement allows us to assist in its diagnosis, since it is a feasible measure in cats. Furthermore, it is concluded that the electrocardiogram should be used as an aid method in the diagnosis of the disease and not as a screening test. 

Keywords: cats, cardiomyopathy, P wave.

Título: Felinos portadores de cardiomiopatia fenótipo hipertrófica - eixo elétrico da onda P

Descritores: gatos, cardiomiopatia, onda P.