One heart, two bodies: insight from the transplanted heart and its new electrocardiogram.

Cardiac transplantation provides a unique opportunity to record the electric field generated by a human heart in a new somatic environment. By examining pre- and posttransplantation electrocardiograms (ECGs), it is possible to address questions on the effect of rotation of the heart on its long axis on the surface ECG, the effect of thoracic anatomy on ECG voltage and predisposing factors for conduction defects observed after transplant surgery. To examine these questions, we reviewed a series of 35 matched donor and recipient ECGs. There were no differences in the mean height of the donors and recipients, but age, weight and body surface area were higher in the recipients (p less than 0.025). We found no significant differences in the mean heart rate or precordial voltage but the PR and QT intervals were shorter (p less than 0.025), and the precordial transitional zone was more to the left after transplantation (p less than 0.0005). New evidence of right bundle branch delay was found in 11 recipients and this was not related to pretransplantation hemodynamic factors or the period of ischemic arrest. Thus, there is indeed an anatomic basis for the ECG determination of clockwise rotation of the heart when the precordial transition zone is to the left. Age and body habitus, per se, do not appear to affect precordial voltage and evidence of right bundle delay in the transplant recipient appears to be related to the altered position of the heart and not to injury or changes in right ventricular hemodynamics.