Abstract 3642: Heart Rate Responses to Exercise for Assessment of Autonomic Function in Patients With Familial Amyloidotic Polyneuropathy
Background: The heart rate (HR) response to exercise measured by chronotropic index (CI) and the heart rate recovery (HRR) immediately after exercise reflect cardiac autonomic control. Familial amyloidotic polyneuropathy type I (FAP) is a hereditary form of amyloidosis characterized by polyneuropathy and progressive dysfunction of the autonomic nervous system. We sought to determine CI and HRR in FAP patients (pts) and to correlate the findings with I-123 metaiodobenzylguanidine (MIBG) myocardial imaging and heart rate variability (HRV) analysis.
Methods: 40 pts with the FAP mutation (22M/18F with a mean age of 40±14 years) presenting with different stages of the disease (22 with neurological involvement-group I and 18 asymptomatic carriers-group II) and 40 age-matched control subjects underwent exercise stress testing. CI was calculated as: (peak HR-resting HR)/(220-age-resting HR). A value of <0.8 was considered low. HRR was defined as the difference between peak HR and HR one minute later (HRR ≤18 bpm was abnormal). In addition FAP pts underwent heart-to-mediastinum MIBG uptake (normal=2.5±.3) and time and frequency domains HRV analysis from 24-h Holter recordings.
Results: FAP pts had significantly higher resting HR (92±16 bpm vs. 81±8 bpm, p=.0003), shorter exercise duration (547±150 sec vs. 666±105 sec, p<.0001) and lower CI (.7±.24 vs. .96±.1, p<.0001) and HRR (23±11 bpm vs. 37±12 bpm, p<.0001) than the healthy subjects. In FAP pts the HRR correlated with SDNN (r=.55, p=.0002), total power (r=.57, p=.0001), VLF (r=.56, p=.0002), LF (r=.55, p=.0003) and HF (r=.49, p=.001) while the CI correlated with LF/HF (r=.44, p=.005) and MIBG uptake (r=.49, p=.002). Group I differ from group II by significantly lower MIBG uptake (1.9±.5 vs. 2.2±.2, p=.03), CI (.61±.23 vs. .8±.21, p<.009) and HRR (19±10 bpm vs. 27±12 bpm, p<.02). CI was decreased in 17/22 group I pts and in 5/18 group II pts (χ2=7.9, p=.005) and the HRR was abnormal in 12/22 group I pts and in 3/18 group II pts (χ2=4.6, p=.03).
Conclusions: CI and HRR, which are easy to calculate from data contained in exercise testing, can be very useful to identify autonomic imbalance in FAP pts. The abnormal HRR seems to be related to the decreased vagal activity and the attenuated CI to the sympathetic denervation.