Avaliação eletrocardiográfica de cães clinicamente hígidos sob tratamento com solução oftálmica de maleato de timolol 0,5%: estudo preliminar

Abstract

sinusal e bradicardia sinusal. Os intervalos RR e PR prolongaram significativamente (p < 0,05) desde o primeiro dia de instilação de timolol, sendo o prolongamento mais expressivo no décimo quarto dia de tratamento. O intervalo QT demonstrou pouca variação, apenas prolongando significativamente (p < 0,05) no décimo quarto dia de aplicação de timolol. O intervalo QTc não demonstrou alteração significativa (p > 0,05). Apesar das alterações encontradas, não foram observadas manifestações clínicas relacionadas ao timolol nos animais estudados. Deve-se considerar, porém, que os animais em questão eram hígidos e, portanto, as alterações decorrentes do uso do timolol em animais com cardiopatias preexistentes poderiam promover sinais clínicos, sendo recomendada a avaliação cardíaca de pacientes previamente à prescrição do timolol oftálmico.Palavras-chave: Glaucoma. Caninos. Eletrocardiograma. AbstractTimolol maleate 0.5% is a drug recommended for glaucoma treatment in dogs. After administration, it is absorbed to systemic circulation and being an antagonist of beta adrenergic receptors it has important systemic side effects on cardiac electrical conduction. The present study evaluated the modification caused by ophthalmic timolol 0.5% in the electrocardiogram. Six clinically normal dogs were selected to participate in two different ophthalmic treatments: in the first one, a placebo (hypromellose 0.5%) was used and in the second one, timolol 0.5% was administered. Each solution was applied twice a day, for 14 days. The electrocardiographic parameters were measured in times: zero, 10, 60, 120, 240, 360 and 720 min after ocular solution instillation in first, seventh and 14th days of each treatment. The differences found in electrocardiogram were more evident between 120 and 240 min after instillation of timolol 0.5% when compared with placebo treatment. The rhythm was irregular, with sinus arrhythmia and sinus bradycardia moments. The RR and PR intervals lengthen notoriously (p < 0.05) from the first day of timolol administration, and are more expressive in the 14th day of treatment. The QT interval demonstrated a few changes, just lengthening noticeably (p < 0.05) in the 14th day of timolol application. The QTc interval did not show expressive change. Despite the changes in the electrocardiogram, no clinical manifestation related to beta-adrenoceptor antagonists were observed. One must consider, however, that the animals studied were healthy and thus, clinical signs could result from the changes implied by the use of timolol in animals with pre-existing heart disease. Therefore, cardiac assessment of patients prior to prescription of ophthalmic timolol is recommended. Keywords