Scatterplots of RR and RT interval variability bring evidence for diverse non-linear dynamics of heart rate and ventricular repolarization duration in coronary heart disease

Objective QT interval prolongation and increased spatial QT dispersion are important factors increasing the risk in coronary heart disease. The author s studied the spontaneous beat-to-beat variability of ventricular repolariz ation (RT intervals) in normal subjects and in patients after myocardial in farction (MI) in order to define the determinants of abnormal temporal disp ersion. Methods Seventy-six patients with a history of MI (17 female, 59 male, aged 52 +/- 10 years) comprised the study group. Forty-seven patients had prese rved left ventricular ejection fraction (EF greater than or equal to 40%, M I-A) and 29 patients had left ventricular dysfunction (EF<40%, MI-B). Twent y healthy volunteers (6 female, 14 male, aged 25+/-5 years) were included a s the control group. An ECG signal of 512 heartbeats was recorded in the su pine position. After analogue-to-digital conversion (16 bit, 2 kHz), the fi ducial points of the R wave and T wave were determined. The RR and RT varia bility (V) assessed in the time domain as the standard deviations of RR and RT (ms), as well as the coefficients of scatterplots of RR and RT interval s. Results As expected, the standard deviation of RR was significantly reduced in MI patients. The magnitude of RTV in the time domain was similar in the controls and in both subgroups of MI patients. The complexity of heart rat e variability (HRV) was slightly, but significantly, reduced in the MI-B gr oup, but not significantly in the MI-A heart group. The complexity of RTV b ehaved in the opposite manner, being increased in both MI subgroups with th e lower mean in the MI-B patients. The different behaviour of HRV and RTV w as indicated by the increased ratio of RR/RT coefficients, which reached a significantly greater value in the MI-B group. Conclusion The authors have described different patterns of scatterplot of short-term HRV and RTV in normal subjects, which confirmed that RTV is a le ss complex phenomenon than HRV. In patients after MI, the complexity of HRV diminishes, while the complexity of RTV increases. These opposing changes are more pronounced in patients with left ventricular dysfunction. A possib le prognostic value of this feature is unknown and remains to be elucidated in future prospective studies. (Europace 2001; 3: 39-45) (C) 2001 The Euro pean Society of Cardiology.