T-wave amplitude and the P-Q interval: relationships to noninvasive indices of myocardial performance.

Abstract

ABSTRACTThis study examines the interrelationship of five noninvasive measures of cardiac performance: T‐wave amplitude (TWA), the P‐Q interval of the EKG (PQI), Pulse Transit Time (PTT), Carotid dP/dt, and heart rate or interbeat interval (IBI). These measures were manually derived from high‐speed recordings of EKG and carotid displacement pulse made as subjects performed a demanding mental arithmetic task. Within‐subject correlations between the measures were determined from 18 cardiac cycles sampled from baseline and task periods. Five of the median correlations were significant in the overall sample (N=19), most notably that between IBI and PQI. When subjects were partitioned into high and low PTT reactors, a larger number of significant correlations were observed in the more reactive group. PTT reactivity significantly enhanced the magnitude of three correlations: PTT vs IBI, PTT vs PQI, and PQI vs TWA.Comparing the two electrocardiographic indices, PQI displayed larger correlations with both IBI and PTT than did TWA. The pattern of correlations suggests that PQI measurement provides little information beyond that provided by HR alone and that TWA, although strongly related to PTT in a few subjects, is not consistently related to any measure except PQI. The results are discussed in light of reports suggesting that these indices might be used to assess beta‐adrenergic influences on the myocardium.