Normal scores of deep breathing tests: beware of dysrhythmia in transthyretin amyloidosis.

BACKGROUND: The heart rate (HR) response to paced deep breathing (DB) is a common test of cardiac autonomic function, where high heart rate variability (HRV) is considered to reflect normal autonomic function. We evaluated the DB test in patients with hereditary transthyretin amyloid (ATTRm) amyloidosis, where autonomic dysregulation and atrial arrhythmias are common.

METHODS: Paced DB was performed during one minute (six breaths/min) in 165 recordings in adult ATTRm amyloidosis patients with the TTR Val30Met mutation, 42 hypertrophic cardiomyopathy (HCM) patients and 211 healthy subjects. HRV was scored by traditional DB indices and by a novel regularity index, estimating the fraction of the HRV that was coherent with the breathing pattern.

RESULTS: Twenty per cent of ATTRm amyloidosis patients presented with age-adjusted HRV scores within normal limits but poor regularity due to subtle atrial arrhythmias and cardiac conduction disturbances. Forty-seven per cent of ATTRm amyloidosis patients presented with HRV scores below normal limits, whereas HCM patients presented with higher HRV than ATTRm amyloidosis patients.

CONCLUSIONS: Reduced HRV is common in ATTRm amyloidosis patients during DB, however, autonomic function cannot be evaluated in patients presenting with the combination of "normal" scores and low regularity, since their HR responses often reflects dysrhythmias.