In a recent study published in Europace, researchers have identified a simple marker to help in the early diagnosis of long QT syndrome (LQTS). The study aims on the presence of complete T and P wave fusion (TP-fusion) during peak exercise as a potential diagnostic tool.

A total of 578 individuals were studied, including 310 healthy athletes and 268 genotype-positive LQTS patients. All participants underwent a maximal exercise stress test while off medication. TP-fusion was deemed present only if it was complete in all precordial leads except V1. Individuals with incomplete TP-fusion were excluded. There were 246 athletes and 198 LQTS patients for analysis.

TP-fusion was observed in just 2% of healthy controls but was significantly more prevalent in 22% of LQTS patients (P < 0.001). Among individuals under 25 years old, the difference became even more pronounced, i.e., 3% of athletes versus 32% of LQTS patients showed TP-fusion. The study revealed that TP-fusion is a function of both QTc prolongation and high heart rate.

The appearance of TP-fusion at peak exercise was linked with an 88% probability of having LQTS. More than half (55%) of LQTS patients exhibiting TP-fusion had baseline QTc values within normal or borderline limits (<460 ms).