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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.

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Hypercortisolism is one of the most common endocrine diseases in dogs. In humans, it is clearly associated with a higher risk of cardiovascular events, but studies in dogs are scarce. To investigate the arrhythmogenic risk of dogs with naturally-occurring hypercortisolism (NOHC), indices of variability and instability of the QT interval were retrospectively studied in 38 dogs with NOHC and prospectively studied in 12 healthy dogs: variance (QTv), total instability (TI), short-term (STI) and long-term (LTI), and mean (QTm). Except for QTm, all parameters studied were higher in the NOHC group than in the control group. In addition, STI and QTv showed moderate positive correlation with left ventricle wall thickness. The NOHC group was subdivided according to cortisol suppression pattern in the low-dose dexamethasone suppression test. All electrocardiographic indices of partial and absent suppression patterns were numerically higher than healthy dogs. QTv and TI were lower in the control group than in both NOHC subgroups. LTI and STI were lower in the CG than in the group with the partial suppression pattern. There was no statistical difference between sex groups in any of the electrocardiographic parameters studied. This result might indicate that the etiology of NOHC, and its consequent influence on hypothalamus-pituitary-adrenal axis could interfere on the heterogeneity of ventricular repolarization parameters in different ways, especially in the short-term and the long-term stability; however further studies are necessary to understand the role of cortisol on electrical instability in dogs.

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El propósito fue investigar si la naturaleza de la respuesta compensatoria de la masa ventricular izquierda (MVI) es un factor determinante del grado de labilidad temporal de la repolarización miocárdica. Se evaluaron 263 pacientes hipertensos y 52 sujetos controles normotensos mediante ecocardiografía y electrocardiografía de alta resolución. Se definió MVI inapropiada como un índice de compensación de la MVI (ICMVI) > 128%. El grado de labilidad temporal de la repolarización miocárdica se evaluó a través del índice de variabilidad del intervalo OT (IVQT) determinado en forma automatizada. Pacientes hipertensos con MVI inapropiada presentaron valores significativamente más altos del IVQT (-0,92 ± 0,25) en comparación con sujetos normotensos (-1,53 ± 0,21) y pacientes hipertensos con MVI apropiada (-1,24 2410,18) (P<0,001). El ICMVI se correlacionó en forma dirtecta con el IVQT (r=0,49, P<0,001). en el análisis multivariante de regresión lineal, el nivel de MVI inapropiada. medido a través del ICMVI, se comportó como un predictor independiente del grado de labilidad temporal de la repolarización miocárdica (ß=0,007; P<0,001). Los resultados de este estudio indican que, en pacientes con HTA-E, la presencia de MVI inapropiadamente alta para el estímulo hemodinámico del ventrículo izquierdo se relaciona con aumento de la variabilidad temporal del intervalo QT.

The goal of this study was to investigate whether the compensatory nature of left ventricular mass (LVM) is a determinant factor of the temporal lability of the myocardial repolarization. Two hundred and sixty three hypertensive patients and 52 normotensive control subjects were studied by Doppler echocardiography and high resolution electrocardiography. A compensatory index of LVM (CILVM) > 128% defined inapropiate LVM. The degree of myocardial repolarization lability was evaluated by the QT interval variability index (QTVI). Hypertensive patients with inapropiate LVM had QTVI values significantly higher (-0,92 ± 0,25) than those with appropriate MVI (-1.24 ± 0.18) and normotensive control subjects (-1.53 ± 0.21) (P<0.001). The CILVM was positively correlated with QTVI (r=0.49; P<0.001). A stepwise multivariate linear regtession analysis showed that the level of inappropriate LVM was an independent predictor of QTVI (ß=0.007; P<0.001). Our result indicate that inappropriately high LVM for hemodynamic stimuli are associated with increased QT temporal variability.

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