Timolol 0.5% ophthalmic solution influences cardiac function in healthy cats

The aim of this study was to ascertain the effect of a drop of timolol 0.5% ophthalmic solution on the systolic function of the left ventricle (LV) and left atrium (LA), and to confirm if timolol helped appraisal of diastolic function by reducing heart rate (HR) and separating the transmitral outflow waves from tissue Doppler imaging (TDI).

A total of 41 client-owned healthy cats underwent two echocardiograms 20 mins apart. The timolol group (33 cats) received a drop of timolol solution after the first examination. Standard and speckle-tracking echocardiography evaluated the LV and LA function of both groups at the two time points evaluated.

Timolol reduced HR (19%), and fractional shortening from LV (20.3%) and LA (16.6%). Septal S' decreased by 51% (from 7.7 to 5.2 cm/s) and lateral S' dropped by 43.1% (7.3 to 5.1 cm/s). Most longitudinal techniques did not change after timolol, including the mitral annular plane systolic excursion from the interventricular annulus, tricuspid annular plane systolic excursion, LV longitudinal strain and LV tissue motion annular displacement. The isovolumic relaxation time increased by 15.2% (from 54 to 64.6 ms), with most cats presenting this variable above the reference (>60 ms). Timolol did not support diastolic assessment, enabling evaluation in only 2/11 cats when using lateral TDI and 1/9 cats using septal TDI. Regarding side effects, miosis occurred in 18 cats (54.5%).

Timolol reduced systolic function, decreasing standard echocardiographic variables. Regarding diastolic evaluation, although timolol decreased HR, it did not separate the mitral diastolic waves, as expected.