A comparison of heart rate variability in affected and unaffected members of families with progressive familial heart block type I
The presence of sinus bradycardia (less than 60/min) in patients affected by progressive familial heart block type I (PFHB1) and their inability to reach a target heart rate during exercise testing, prompted an investigation of the influence of the autonomic nervous system on cardiac conduction in these family members. Forty members of PFHB1 families, 20 affected and 20 not affected, were included in the study. All were subjected to 24-hour Holter monitoring and treadmill exercise testing (Bruce protocol). Spectral and non-spectral analyses of heart rate variability were performed to evaluate the autonomic nervous system. The results showed that there were no differences between the two groups and that they had normal autonomic nervous systems. It is therefore possible to conclude that the slow heart rate at rest of affected PFHB1 family members and their inability to reach a target heart rate during exercise testing is due to a primarily diseased heart conduction system.