Background: Existence of a relationship between the electrocardiographic QRS interval duration and the diurnally varying heart rate, of consistent sign and magnitude, is controversial and the relationship has not been fully characterized in normal populations.
Methods And Results: We analyzed the QRS-RR interval relationship in 884 Holter recordings in 410 normal subjects participating in 5 clinical trials. The slope of the linear regression of QRS on RR was positive in 93% of subjects with an average slope of 0.0125, which indicates an increase in QRS duration of 1.25msec for an increase in RR interval of 100msec. The increase was 15% larger in women than in men. Age had no significant effect on the slope.
Conclusions: In two populations of normal subjects we observed a robust, direct relationship between the spontaneously changing RR interval and intraventricular conduction time represented by the duration of the QRS interval. As heart rate increases, QRS duration decreases. The change is larger in women. These observations have important physiological and clinical implications.
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