Response to Letter to the Editor by Dr. Jastrzebski

Abstract

Ann Noninvasive Electrocardiol 2011;16(4):416–417

We appreciate Dr. Jastrzebski's interest in our paper. He has a keen observation to note PR segment depression in our cases.

PR segment depression is the early part of atrial repolarization (Tp or also called Ta) wave. Just as ventricular myocardium, atrial myocardium also undergoes repolarization after depolarization. ¹ This Tp wave manifests as a gentle sagging wave beginning at the end of the P wave (PR segment depression), lasting up to about the beginning of the T wave (Fig. 1A). The reason why the Tp wave is directed opposite from the P wave while the T wave is directed to the same direction as the QRS complex is because the directions of propagation of depolarization and repolarization in atria are different from that of ventricles. In the ventricles, depolarization propagates from endocardium to epicardium while repolarization propagates from epicardium to endocardium, resulting in epicardium staying positively charged during both phases, so the QRS complex and the T wave are pointed in the same direction. In the atria, depolarization and repolarization propagate in the same direction which is parallel to atrial wall and the P wave and the Tp wave vectors are oppositely directed (a positive P wave accompanying a negative Tp wave). ¹

Figure 1.

(A) An easily recognizable Tp wave in a normal ECG. (B) An exaggerated Tp wave during the recovery phase of a treadmill test.

This Tp wave is often obscured by the QRS and ST segment especially when the PR interval is short. The Tp wave is more prominent in sinus tachycardia as often observed during treadmill exercise test (Fig. 1B). The Tp wave is observed to varying degrees in most ECG tracings including normals, early repolarization pattern (see Figs. 1A and 4 of the original article), and the entity described in our paper, more noticeably in the latter two perhaps because what causes ventricular repolarization to be unusual also causes atrial repolarization to be unusual. Besides, ST evaluation in these two conditions will certainly make the Tp wave more apparent.

The PR segment depression in pericarditis is the atrial counterpart of ST elevation, i.e., atrial injury pattern, and is usually more distinct and more sharply downsloping as seen in lead II of the last tracing of Figure 4 of the original article. However, not every case has typical manifestations as pointed out by Dr. Jastrzebski.

Only a few of the cases had more than one tracing (not systematically looked for) and the ECG findings persisted in some while they normalized in others as known to occur with early repolarization pattern.

Only several cases were managed by us. Other cases were identified only by meeting the ECG
inclusion criteria described in the paper when reviewing hospital ECGs. If some of them turned out to have pericarditis or myocardial infarction, we would not know.

According to our study, this entity is so rare in nonblacks (0%–0.7%) that when confronted with the ECG findings described in nonblacks, one should consider other diagnosis rather than this entity.