Timolol 0.5% ophthalmic solution influences cardiac function in healthy cats

Area of Science:

• Veterinary Cardiology
• Ophthalmology
• Pharmacology

Background:

• Timolol is a beta-blocker commonly used in veterinary ophthalmology.
• Its effects on cardiac function, particularly systolic and diastolic parameters, require further investigation in feline models.
• Understanding these effects is crucial for assessing patient safety and potential therapeutic applications.

Purpose of the Study:

• To evaluate the impact of topical timolol 0.5% on left ventricular (LV) and left atrial (LA) systolic function in healthy cats.
• To determine if timolol facilitates diastolic function assessment by reducing heart rate (HR) and improving the separation of transmitral outflow waves on tissue Doppler imaging (TDI).

Main Methods:

• Two echocardiographic examinations were performed on 41 healthy cats, 20 minutes apart.
• The timolol group (33 cats) received topical timolol 0.5% after the initial echocardiogram.
• Standard and speckle-tracking echocardiography were utilized to assess LV and LA function.

Main Results:

• Timolol significantly reduced HR by 19% and decreased fractional shortening in both the LV (20.3%) and LA (16.6%).
• Septal and lateral S' velocities, indicators of systolic function, decreased substantially (51% and 43.1%, respectively).
• Despite HR reduction, timolol did not improve diastolic assessment, increasing isovolumic relaxation time and failing to separate mitral diastolic waves on TDI.

Conclusions:

• Topical timolol 0.5% negatively affects systolic function in cats, as evidenced by decreased echocardiographic variables.
• It does not aid in diastolic function assessment, contrary to expectations, and can increase isovolumic relaxation time.
• Common side effects include miosis, observed in over half of the treated cats.