Dissociation of heart rate and ECG morphology

The authors studied thirteen healthy subjects in which identical heart rates (ΔHR<1%) could be obtained under different autonomous conditions: by increasing the angle of the legs with the horizontal plane, with tilt angles ranging from 0 till 60° and back, or by performing a handgrip maneuver. During all measurements the thorax was kept at a 700 angle. Heart rate increased from 65.2a±9.0 (control) to 72.1±8. 7 (tilt) and 72.1±8.8 (handgrip) bpm. A number of vector cardiographic parameters differed significantly (P<0.05) between tilt and handgrip, e.g. QRS azimuth (-33.5±15.0 vs. -22.4±22.5°), QRS duration (103±10 vs. 107±13 ms), maximal T vector (646±200 vs. 703±184 μV), T azimuth (45.3±14.5 vs. 38.6±13.6°) and the heart rate corrected QT interval (418±15 vs. 435±21 ms). This study demonstrates that tilt and handgrip dissociate heart rate and ventricular depolarization and repolarization