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 ( <0.01), QTac ( <0.01), QRSd ( <0.01) and STI ( = 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.