TP segment is the isoelectric interval on the electrocardiogram (ECG). It is the region between the end of the T wave (ventricular repolarization or electrical inactivation) and the next P wave (atrial depolarization or electrical activation). It represents the time when the heart muscle cells are electrically silent. TP interval shortens when the heart rate increases and vice versa.
Ideally, elevation and depression of ST segment and PR segment are measured with reference to the TP segment. But when the heart rhythm is fast, a good TP segment may not be seen as the T wave of once cycle merges with the P wave of the succeeding cycle. This often occurs in the setting of an exercise test and in such situation, the E point which is at the beginning of the QRS complex can be taken as the reference.
Spodick’s sign is downsloping TP segment seen in stage I of acute pericarditis [1,2]. It is best seen in lead II and lateral leads. It has been mentioned that it can be seen in about 80% of cases of acute pericarditis. A good demonstration of Spodick’s sign is available in the article by Chaubey VK et al . They also quoted another article which had shown resolution of the Spodick’s sign in leads II, V4-V6 after treatment with non steroidal anti-inflammatory agents . Interestingly, authors of the cited article did not specifically mention about the sign.
Spodick’s sign is thought to be useful in differentiating acute coronary syndrome from acute pericarditis. In both conditions PR segment depression may be noted, but presence of Spodick’s sign will favour acute pericarditis [3,5].