Effects of 0.5% Timolol Maleate Ophthalmic Solution on Heart Rate and Selected Echocardiographic Indices in Apparently Healthy Cats

Abstract

BackgroundEchocardiographic assessment of diastolic function is challenging in cats, partially because of transmitral flow pattern fusion associated with high heart rates. With heart rate (HR) reduction, transmitral flow waveforms separate, allowing identification of diastolic dysfunction. Timolol, an ophthalmic, nonselective beta‐blocker used in glaucoma is safe and transiently decreases HR in clinical trials.HypothesisAdministration of timolol ophthalmic solution decreases HR and facilitates echocardiographic assessment of diastolic function in cats without inducing clinically relevant adverse effects.AnimalsTwenty‐five apparently healthy cats.MethodsElectrocardiograms and echocardiograms including transmitral flow patterns were evaluated before and 20 minutes after ocular administration of 1 drop of timolol 0.5% solution. Twenty cats underwent treatment with timolol, and 5 different cats served as untreated controls to evaluate the effects of acclimation to the hospital environment on HR.ResultsAcclimation to the hospital had no effect on HR in control cats. After timolol administration, a significant median HR reduction of 25 bpm was observed (P < .0001). Timolol had no effect on E/A ratio in cats without E/A fusion (7/20, P = .44). Of the 13 cats with E and A waves that were fused before timolol application, separation of these waves was identified in 8 cats (62%) after timolol treatment. No bradyarrhythmias were noted after timolol administration, but 2 cats had first‐degree atrioventricular block. Timolol resulted in resolution of dynamic outflow tract obstruction in 6 of 6 cats.Conclusions and clinical importanceOcular administration of timolol safely decreases HR in cats and could facilitate assessment of diastolic function.

Timolol 0.5% ophthalmic solution influences cardiac function in healthy cats

“…The timolol group was composed of 33 cats, including 18 females (mean age 6.1 years [range 1-13]; mean weight 5.1 kg [range 2. [1][2][3][4][5][6][7][8][9][10][11]). This group included Persian (n = 2), Maine Coon (n = 1), Siamese (n = 1) and mixed breed (n = 29) cats.…”

“…The mean decrease of 30 bpm was close to that previously reported (25 bpm). 11 Interestingly, another research group reported that a drop of timolol gel-forming solution did not affect HR 4 and 8 h later, 34 suggesting the bradycardic effect may not last long.…”

“…Hence, handling twice for echocardiography and the waiting period in a hospital environment did not stress the cats sufficiently to raise the HR and affect the indices. Although timolol has its maximum effect in cats between 6 and 12 h after administration, 12 we chose to repeat the echocardiogram 20 mins later to follow the same protocol for the diastolic assessment detailed previously, 11 which coincides with the onset of its action after topical administration. As previously mentioned, timolol applied topically to the eyes has systemic effects, with a reduction in HR being the easiest to observe.…”

“…Another option is to administer timolol ophthalmic solution to block the sympathetic tone and decrease the HR, separating the transmitral and TDI waves. 11 The topical application of timolol has a systemic absorption, 12,13 reducing the HR when administered alone in cats 11 or associated with topically applied carbonic anhydrase inhibitors, such as dorzolamide or brinzolamide. 14…”

The Feline Cardiomyopathies: 3. Cardiomyopathies other than HCM

“…30,41,42 If the E and A waves are summated, one can wait for the heart rate to come down as the cat relaxes over time, can apply a vagal maneuver, such as pressing on the nasal planum, or can administer a low dose of a beta blocker, such as ocular timolol, to slow the heart rate. 45,46 Tissue Doppler interrogation of the mitral valve annulus can also be performed and should show a reduced E' wave velocity. 47 Thoracic radiographs in dyspneic cats that have RCM show a higher occurrence of PLE (59%) than PE (25%) but both can be present (16%).…”