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RESEARCH PRODUCT

P-Wave Indices: Derivation of Reference Values from the Framingham Heart Study

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P wave indices constitute an intermediate, phenotype reflecting the impact of ischemic, metabolic and inflammatory insults on atrial electrophysiology and morphology. Measured from the surface electrocardiogram (ECG), they reflect dimensions of atrial depolarization and are modified by conditions that alter atrial conduction, atrial refractoriness, or may result in a proarrhythmic substrate. The P wave indices of duration and dispersion have most commonly been measured. An array of studies have utilized these P wave indices to distinguish subjects with diverse cardiovascular and non-cardiovascular conditions and diseases from healthy reference groups.(1) Computerized software has more recently facilitated measurement of P wave indices reflecting atrial area and terminal force. The range of P wave indices has had considerable variability in the literature, limiting the establishment of reference values. For example, the largest (n=15,429) identified study to date utilized digitized ECGs and computer software to report a maximum P wave duration of 112.3±12.3 ms in African-American and 107.0±12.2 ms in white subjects in a middle-aged cohort (mean age 54.2±5.8 years).(2) A younger cohort (mean age 24 years) of army recruits reported a maximum P wave duration of 96 msec.(3) In other samples, assessment of P wave duration in referent groups has been similarly variable.(1) Using cut-points of a normal P wave duration as <120 msec, studies have reported 41%(4) to 47%(5) of hospitalized patients as having prolonged measurements. Consequently, we undertook this study to define reference values of P wave indices in the Framingham Heart Study (FHS). We had two major objectives for the study. First, we sought to examine our hypothesis that reference P wave indices would vary between men and women and would increase with advanced age. Second, we sought to identify the clinical correlates associated with P wave indices in the reference range. We calculated P wave indices in a healthy referent cohort identified as a subset within the FHS and without prevalent atrial fibrillation (AF), cardiovascular disease or select cardiovascular risk factors such as hypertension, diabetes and obesity. For our measures of interest, we identified the maximum and mean P wave durations; mean duration in lead II; P wave dispersion, calculated as the difference between maximum and minimum duration between two leads; standard deviation of mean duration; and the PR interval from a prior assessment. (6)