EXERCISE RESPONSE OF THE RECIPIENT ATRIAL REMNANT AFTER ORTHOTOPIC CARDIAC TRANSPLANTATION - IMPLICATIONS FOR RECIPIENT ATRIAL TRIGGERED PACING

The assumption that the recipient atrial remnant in the cardiac transp lant recipient is normal has led to the suggestion that it is an appro priate trigger for permanent pacing in transplant recipients who need pacing or to restore chronotropic competence and/or mechanical synchro ny of the composite atrium. We examined the chronotropic response to e xercise in 12 orthotopic cardiac transplant recipients (mean age 49 ye ars) at a mean time of 17 months posttransplantation. Recipient and do nor atrial rates were noted and compared and chronotropic competence d etermined. Two of 12 recipient atrial remnants were in atrial fibrilla tion. Only six of the remaining 10 recipient atria exhibited chronotro pic competence. Seven of 10 recipient atria had rates higher than that of the donor. Only four often recipient atria in sinus rhythm satisfi ed both criteria. Two of these had abnormally high atrial responses ea rly into exercise. Of the remaining two, only one recipient atrial rem nant demonstrated a greater than or equal to 20% increase in heart rat e above that of the donor at peak exercise. Hence only 1 of 12 (8.3%) transplant recipients potentially could benefit from recipient atrial triggered pacing. While recipient atrial triggered pacing is an attrac tive theoretical concept for restoring chronotropic competence followi ng orthotopic cardiac transplantation, it may rarely be practical beca use the recipient atrial remnant displays rhythm abnormalities, chrono tropic incompetence, and abnormalities in its exercise response.