QT interval instability and QRS interval dispersion in healthy cats and cats with a hypertrophic cardiomyopathy phenotype.

OBJECTIVES: Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats. Electrocardiographic (ECG) analysis can help with the diagnosis of HCM and also in the investigation of the secondary consequences of the disease. This study investigated ECG markers of QT interval variability (total instability [TI], short-term instability [STI], long-term instability [LTI], QT variance [QTv]), mean QT interval (QTa) and QT interval corrected for heart rate (QTac), as well as the duration (QRSd) and dispersion (QRSv) of the QRS interval in healthy cats and in those with HCM. METHODS: Data were collected from 63 domestic cats: 40 in the control group and 23 in the HCM group. Fifty consecutive QT intervals were recorded for all cats and then QTa, QTac, QTv, TI, LTI and STI were calculated. QRSd and QRSv were also obtained for all animals. A Mann-Whitney U-test was used for group comparison. Receiver operating characteristic curves were plotted to evaluate the sensitivity and specificity of all markers for HCM. Logistic regression analysis was performed to assess the risks of cats having HCM, based on the studied indexes. RESULTS: QTa (P <0.01), QTac (P <0.01), QRSd (P <0.01) and STI (P = 0.02) were higher in the HCM group. QTa >158.8 ms, QTac >27.4 ms and QRSd >0.045 s had an accuracy of 77.4%, 68.2% and 80.9%, respectively, in detecting HCM. Logistic regression showed that cats with QTa >158 ms, QTac >27.4 ms and QRSd >0.045 s had a 1.58-, 1,23- and 6.5-fold higher risk, respectively, of developing HCM. CONCLUSIONS AND RELEVANCE: Cats with HCM had higher ventricular instability as assessed by STI and showed a prolongation of the QT and QRS intervals via the QTa, QTac and QRSd markers. These markers show potential as ancillary screening tools for identifying the presence of HCM.

Timolol 0.5% ophthalmic solution influences cardiac function in healthy cats.

OBJECTIVES: 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). METHODS: 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. RESULTS: 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%). CONCLUSIONS AND RELEVANCE: 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.