Background:
Cardiac repolarization is a complex phenomenon that depends on heart rate (HR), autonomic nervous system (ANS) activity, age, gender and diseases/pathological conditions etc. Cardiovascular events in LQT1 mutation carriers are also typically related to age, gender, and QT interval, and are triggered by physical exercise. We studied the repolarization response to heavy exercise in healthy subjects.
Material and methods:
Vectorcardiography (VCG) was recorded with the Coronet II system (Ortivus AB, Danderyd, Sweden) using the Frank orthogonal leads (X, Y and Z) at supine rest before and after a maximal cycle ergometer test in 42 healthy subjects. They were of different age and gender, 21 old (64-79 years) and 21 young (20-32 years), 23 were women and 19 men. Maximum T-vector amplitude and direction were assessed as well as T-area, QTc-interval and other VCG parameters.
Results:
At baseline most parameters differed between old and young subjects, but only QRS-duration, QRS-area and T-amplitude between women and men. Younger subjects had lower HR (59 vs 72 bpm; p<0.01), higher T-amplitude (530 vs 395 μV; p<0.01), larger T-area (73 vs 48 μVs; p<0.001), shorter QTc (417 vs 430 ms; p<0.01) and a narrower QT-angle (25 vs 59°; p<0.01).
The response to strenuous exercise was much more pronounced in the younger subjects with an increase in resting HR by 35 bpm compared with 17 bpm for the old subjects (p<0.001). This was accompanied by a more pronounced decrease in T-amplitude (-138 vs -27 μV; p<0.01) and T-area (-20 vs -7 μVs; p<0.01) but a larger prolongation of QTc (54 vs 10 ms; p<0.001).
Conclusion:
Young people seem to have a more active ANS, which results in a more pronounced repolarization response to heavy exercise. This might explain why patients with LQT1 more likely suffer from malignant arrhythmias at ages below 40 years.
2012.