Converting Enzyme Inhibition Normalizes QT Interval in Spontaneously Hypertensive Rats

Abstract

Abstract-We quantified the repolarization time (so-called QT interval) in a rat, an animal species that does not show a well-characterized T wave on surface ECG. We used spontaneously hypertensive rats (SHR) and converting enzyme inhibition to demonstrate a reversible increase in QT interval in pressure-overloaded hearts in the absence of ischemia. An implanted telemetry system recording ECG data in freely moving rats was used to automatically calculate the RR interval. The QT duration was manually determined by use of a calibrated gauge, and a time-frequency domain analysis was used to evaluate heart rate variability. Left ventricular mass was sequentially assessed by echocardiography. Before treatment, 12-month-old SHR had higher left ventricular mass, QT and RR intervals, and unchanged heart rate variability compared with age-matched Wistar rats. A 2-month converting enzyme inhibition treatment with trandolapril reduces systolic blood pressure, left ventricular mass, and QT interval. The RR interval and heart rate variability remains unchanged. There is a positive correlation between the QT interval and left ventricular mass. The SHR is suitable for longitudinal studies on the QT interval. Thus, the detection of the QT interval reflects the phenotypic changes that occur during mechanical overload and, on the basis of these criteria, allows an in vivo determination of the adaptational process. Key Words: hypertrophy Ⅲ hypertension, arterial Ⅲ electrocardiography Ⅲ converting enzyme inhibition Ⅲ QT interval S everal ECG indexes have been proposed for identifying patients at risk of sudden death, including an increased QT-interval dispersion. [1][2][3] Clinical trials had demonstrated that this index is specifically altered in chronic cardiac hypertrophy and/or during myocardial ischemia and is reversible under therapy. Nevertheless, the meaning of the QTinterval dispersion is a complex issue that includes at least 2 different phenomena, namely, a lengthening of the average duration of the action potential (AP) and myocardial heterogeneity; indeed, in clinical conditions, the QT interval is both prolonged and dispersed, because hypertensive cardiopathy usually associates cardiac hypertrophy with myocardial fibrosis. 4 -7 There is a need for models of pure mechanical overload without any ischemia, a condition that is nearly impossible to observe in clinical situations, and experimental animal models would help to resolve this issue. Among different animal species, the rat may be an ideal model because it never suffers from atherosclerosis. In addition, there exists a welldocumented rat strain, the spontaneously hypertensive rat (SHR), which complies with the above criteria and has been extensively used for pharmacological research and particularly in experimental testing of most of the available antihypertensive drugs.The QT interval represents repolarization time. It is not easy to measure in humans, despite a well-characterized T wave. In rats, the situation is still more difficult because the T wave is not c...

Contactless magnetocardiographic mapping in anesthetized Wistar rats: evidence of age-related changes of cardiac electrical activity

“…Such an anomaly might introduce significant errors in a quantitative estimate of MF strength and orientation. Absolute values of cardiac intervals were consistent with those reported in previous ECG and MCG studies (6,13,24,25). Clear-cut age-related changes in the duration of PR, QRS, QT peak , QT end , JT peak , JT end, and T peak-end were found.…”

“…It is well known that aging is associated with morphological and electrical remodeling of the myocardium (3, 34, 45, 58), leading to a higher incidence of life-threatening arrhythmias and sudden death (33,55), especially in the presence of ventricular hypertrophy or other cardiomyopathy (6,25,26,59,67,68). Therefore, the primary aim of this research was to evaluate age-related changes in cardiac intervals and VR parameters calculated from MCG maps, with the influence of sex taken into account (10,13,73).…”

Chronic converting enzyme inhibition normalizes QT interval in aging rats

“…At the cellular level, ventricular repolarization is prolonged in a number of cardiac disturbances such as myocardial hypertrophy, ischemia or congestive heart failure (1,2,5). Changes of the QT interval have also been described in experimental models of hypertension (28). The other parameters examined in the present study were found to be unchanged by aging.…”

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