ECG alterations with progressive left ventricular hypertrophy in spontaneous hypertension.

Although many ECG criteria exist for diagnosis of left ventricular hypertrophy (LVH) in hypertensive man, little is known of which specific ECG changes accompany progression of LVH with duration of hypertension. The spontaneously hypertensive rat (SHR) provides the best animal model thus far developed for studying this process since these animals demonstrate a progressive increase in left ventricular/body weight ratio with age. Electrocardiograms were performed under light ether anesthesia in four age groups of SHR and two normotensive Wistar strains (NR and WKY). Analysis of variance for two factors (rat strain and age) revealed progressively increased QRS and P-wave duration and delay in intrinsicoid deflection in SHR (p less than 0.001). Bipeak P-wave notching was also noted in SHR similar to left atrial abnormality in hypertensive man. Thus, specific ECG indices can be identified in association with the known progressive increase in left ventricular mass in SHR and should provide a better means to understand evolving ECG changes in LVH.