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

Abstract 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 (ATTRwt) 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 ATTRwt and determine the utility of CVR‐R for the detection of ATTRwt 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: ATTRwt, 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‐Rrest), CVR‐R with deep breaths (CVR‐Rbreath), and the change rate (CVR‐Rdiff rate). The relative change formula is as follows: CVR‐Rdiff rate = (CVR‐Rbreath − CVR‐Rrest)/CVR‐Rrest× 100 (%). Results There was no difference in the CVR‐Rrest levels among the three groups. The CVR‐Rdiff rate levels in the ATTRwt group were significantly lower (ATTRwt: −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 ATTRwt in HF, the best cut‐off value for the CVR‐Rdiff rate was 19.7 (area under the curve: 0.848). Conclusion Our data suggested autonomic dysfunction in patients with ATTRwt. Measurement of the CVR‐R in HF patients may be a convenient support tool for the detection of ATTRwt.