Coefficient of R‐R interval variations under deep breathing load in patients with wild‐type transthyretin amyloid cardiomyopathy: A case‐control study

BACKGROUND AND AIMS: An autonomic nervous disorder is an important characteristic of cardiac amyloidosis; however, the prevalence of autonomic dysfunction in wild‐type transthyretin amyloidosis (ATTR(wt)) has not been established. Analysis of the R‐R interval coefficient of variation (CVR‐R) is a noninvasive method to measure parasympathetic activity. We aimed to assess autonomic dysfunction of ATTR(wt) and determine the utility of CVR‐R for the detection of ATTR(wt) in other cardiac diseases. METHODS: This is a single‐center, retrospective, case‐control study. Fifty patients with heart failure (HF) were studied. The etiologies of HF were as follows: ATTR(wt), n = 10; previous myocardial infarction (MI), n = 20; and left ventricular hypertrophy (LVH) due to other disease processes (e.g., aortic stenosis), n = 20. We measured the CVR‐R at rest (CVR‐R(rest)), CVR‐R with deep breaths (CVR‐R(breath)), and the change rate (CVR‐R(diff rate)). The relative change formula is as follows: CVR‐R(diff rate) = (CVR‐R(breath) − CVR‐R(rest))/CVR‐R(rest) [Formula: see text] 100 (%). RESULTS: There was no difference in the CVR‐R(rest) levels among the three groups. The CVR‐R(diff rate) levels in the ATTR(wt) group were significantly lower (ATTR(wt): −8.77 [−43.8 to 10.9]; LVH: 67.4 [38.7 to 89.4]; MI: 83.7 [60.4 to 142.9]). Based on the receiver operative characteristic curve analysis to identify ATTR(wt) in HF, the best cut‐off value for the CVR‐R(diff rate) was 19.7 (area under the curve: 0.848). CONCLUSION: Our data suggested autonomic dysfunction in patients with ATTR(wt). Measurement of the CVR‐R in HF patients may be a convenient support tool for the detection of ATTR(wt).