Singularities of the heart beat as demonstrated by recurrence quantification analysis

Deterministic, chaotic, nonlinear dynamics have enjoyed considerable popularity in the analysis of physiological systems. Many models, however, fail to incorporate some basic features of the involved physiology. The authors´ research using experimental data from ECGs analyzed by recurrence quantification analysis (RQA) suggest that some of these dynamics can be better modeled by singularities of differential equations, alternating with oscillations which result in multi-choice responses to excitations. ECGs of 34 healthy volunteers were recorded for 512 consecutive beats. Recurrence plots suggested discontinuities at the T-P interval, and the durations of the T-P and P-T intervals were manually calculated. Although the distributions of these two intervals were found to be similar (KS two sample test, p=NS), RQA demonstrated that the T-P Interval approached the embedding limit of pseudo random numbers [pseudo random=4; T-P=4; (95% CI=3.64.3)]. This suggests the primary stochastic process of ECGs is located In the T-P interval and represents a singularity of the dynamics alternating with the determinism of the P-T interval. The dynamics are thus discontinuous and poorly represented by FFT and other, nonlinear transform techniques