Spectral analysis of heart rate variability in patients with paroxysmal supraventricular tachycardia

Background. During attacks of supraventricular tachycardia.(SVT) atria cont ract against closed atrio-ventricular valves and intra-atrial pressure subs tantially rises. Structures of sinus node are thus subjected to multiple me chanical overload. As a result there might emerge weakening of sinus pacema ker responses to cyclic changes of intensity of signals of autonomic nervou s system with subsequent lowering of heat rate variability (HRV) power. Aim and methods. To test this hypothesis we conducted spectral analysis of ECG tracings from 20 patients with SVT and 10 healthy subjects.. Patients with SVT were divided into 2 groups: 10 younger patients with age (mean 28.5 ye ars) similar to controls, and 10 older patients with mean age 55.6 years. M ean values obtained in the older group were compared with data by Craft and Schwartz for healthy elderly people. ECG was registered first in supine an d then in standing positions. Low frequency (LF) power of HRV was assessed in 0.05-0.15 Hz frequency band, while high frequency (HF) power - in both a ccepted band 0.15-0.4 Hz and in the band corresponding to the patients own respiratory rate. Results. The comparison showed that (1) in supine positio n mean LF and HF powers in both groups of patients were 30-80% lower than i n controls; (2) in upright position in younger patients HF power was simila r to that of controls while LF power was more than 50% lower; (3) both LF a nd HF powers were lowered in older patients in upright position (by 30 and 45%, respectively). Conclusion. The hypothesis that patients with SVT had l owered sensitivity of the sinus node to cyclic changes of intensity of symp athetic and parasympathetic signals was confirmed. Comparison with analogou s literature data from patients with hypertrophic cardiomyopathy, congestiv e heart failure and congenital inappropriate sinus tachycardia showed that decreased HRV power in patients with SVT could also be caused by excessive number of cardiac contractions.