Diagnostic Electrocardiographic Sequences in Acute Pericarditis

Diagnostic electrocardiographic patterns were analyzed in 50 consecutive patients who had unequivocal clinical evidence of acute pericarditis. Distributions of P and QRS, and of P-R segment, ST-segment and T wave changes were plotted by lead and by mean frontal vector (Â). Transient gross deviations of P-R segments, mainly in Stages 1 and/or 2, occurred in 41 patients (82%) and could produce an optical illusion of ST elevations when the J-points were actually on the baseline.  P-R was close to 180° opposite to  P and was not related to P wave or heart rate changes. In Stage 1,  ST tended to be concordant with  QRS and  T. T wave inversions in Stage 3 produced an  T which was distributed over an arc of 210° with no range of predilection. Transient increase in magnitude of a normally oriented PR vector was consistent with the subepicardial atrial injury of acute pericarditis. It is the analogue of the classic Stage 1 ST-segment abnormalities of subepicardial ventricular injury and was equally as widespread in the electorcardiogram and almost as prevalent. P-R segment deviations were always depressions for leads of "epicardial" patterns. ST-segment deviations departed from the classic elevation pattern in 10 patients: 7 patients in whom ST was depressed in Lead III, 5 of whom had a horizontal QRS axis; and 3 patients in whom ST was depressed in aVL, two of whom had a vertical QRS axis. In Stage 3, the much wider range for  T as compared with the relatively concentrated early injury vectors,  P-R and  ST, is ascribed to greater inhomogeneity of post-injury ventricular repolarization.