Three-dimensional return map: a new tool for quantification of heart rate variability

Several methods are used to study heart rate variability, but they have limitations, which might be overcome by the use of a three-dimensional return map.

To evaluate the performance of three-dimensional return map-derived indices to detect (1) sympathetic and parasympathetic modulation to the sinus node and (2) autonomic dysfunction in diabetic patients.

Six healthy subjects underwent partial and total pharmacological autonomic blockade in a protocol that incorporated vagal and sympathetic predominance. Twenty-two patients with type 2 diabetes mellitus and 12 normal controls participated in the subsequent validation experiment. Three-dimensional return maps were constructed by plotting RRn intervals versus the difference between adjacent RR intervals [(RRn+1)-(RRn)] versus the number of counts, and four derived indices (P1, P2, P3, MN) were created for quantification.

Both indices P1 and MN were significantly increased after sympathetic blockade with propranolol, while all indices except P1 were modified after parasympathetic blockade (P < 0.05). During the validation experiments, P1 and MN detected differences between normal controls, and diabetic patients with and without autonomic neuropathy. The overall accuracy of most three-dimensional indices to detect autonomic dysfunction, estimated by the area under the ROC curve, was significantly better than traditional time domain indices. Three-dimensional return map-derived indices also showed adequate reproducibility on two different recording days (intra-class correlation coefficients of 0.69 to 0.82; P < 0.001).

Three-dimensional return map-derived indices are reproducible, quantify parasympathetic as well as sympathetic modulation to the sinus node, and are capable of detecting autonomic dysfunction in diabetic patients.