Non-invasive Wedensky modulation within the QRS complex
To investigate non-invasively induced Wedensky modulation, 2ms pulses of 5, 20 and 40 mA were delivered between precordial and subscapular patches synchronously with the QRS complex. Wavelet vector magnitude was obtained for averaged modulated and non-modulated complexes. The surface area of a 3D-envelope of their difference (WSR) was compared in 59 patients with an uncomplicated follow-up after myocardial infarction (MI) (42 men, 64.3+/-9.1 years), in 30 patients with ischaemic heart disease and a history of ventricular tachycardial fibrillation (VT/VF) (29 men, 63.1+/-9.8 years), and in 53 healthy subjects (control) (22 men, 56.6+/-10.1 years). Reproducibility of the assessment was tested by computing relative errors in a sub-population of 30 VT/VF patients and 47 controls. Wedensky modulation parameters differed significantly between control, MI and VT/VF subjects. In 10ms post-modulation windows, the following WSR values were obtained: controls: 1184 496 (5mA), 1553 +/- 838 (20mA) and 2092 1488 (40 mA); VT/VF: 861 +/- 412 (5 mA), 1134 +/- 636 (20 mA) and 1320 1036 (40 mA); MI: 1305=885 (5mA) and 1779 1169 (20mA). With all modulating energies used, the VT/VF patients differed significantly from both the controls and MI patients; control patients against VT/VF patients: p<0.004 (5mA), p<0.01 (20mA) and p<0.001 (40 mA); VT/VF patients against MI patients: p<0.02 (5 mA), p<0.01 (20 mA); control patients against MI patients: all p = NS. The reproducibility assessment showed an acceptable stability of Wedensky modulation parameters. This study demonstrated that wavelet decomposition detects non-invasive Wedensky modulation within the QRS complex, and VT/VF patients are less sensitive to Wedensky modulation than control and MI patients.
wedensky modulation myocardial infarction wavelet decomposition ventricular tachycardia signal averaged electrocardiogram