Heart Rate Dependency and Inter-Lead Variability of the T Peak – T End Intervals

The electrocardiographic (ECG) assessment of the T peak – T end (Tpe) intervals has been used in many clinical studies but several related physiologic aspects have not been reported. Specifically, the sources of the Tpe differences between different ECG leads have not been researched, relationship of Tpe duration to underlying heart rate has not been established, and little is known about the correspondence of Tpe intervals in different ECG leads. This study evaluated 796,620 10-second 12-lead ECGs obtained from long-term Holters recorded in 639 healthy subjects (311 females) aged 33.8±9.4 years. For each ECG, transformation to orthogonal XYZ lead was used to measure Tpe in the orthogonal vector magnitude (used as a reference for lead-to-lead comparisons) and to construct a 3-dimensional T wave loop. The loop roundness was expressed by a ratio between its circumference and length. These ratios were significantly related to the standard deviation of Tpe in different ECG leads. At heart rate of 60 beats per minute, Tpe intervals were shorter in females than in males (82.5±5.6 vs 90.0±6.5 ms, p<0.0001). When studying linear slopes between Tpe intervals measured in different leads and the underlying heart rate, we found only minimal heart rate dependency which was not systematic across the ECG leads and/or across the population. For any ECG lead, positive Tpe/RR slope was found in some subjects (e.g. 79% and 25% of subjects for V2 and V4 measurements, respectively) and a negative Tpe/RR slope in other subjects (e.g. 40% and 65% for V6 and V5, respectively). The steepest positive and negative Tpe/RR slopes were found for measurements in lead V2 and V4, respectively. In all leads, the Tpe/RR slope values were close to zero indicating, on average, Tpe changes well below 2 ms for RR interval changes of 100 ms. On average, longest Tpe intervals were measured in lead V2, the shortest in lead III. The study concludes that the Tpe intervals measured in different leads cannot be combined. Irrespective of the measured ECG lead, the Tpe interval is not systematically heart rate dependent and no heart rate correction should be used in clinical Tpe investigations.