Electrocardiograms (ECGs) obtained on transplant recipients should demonstrate normal sinus rhythm. The donor heart is implanted with its sinus node intact to preserve normal atrioventricular conduction. The technique of cardiac transplantation also results in the preservation of the recipient's sinus node at the superior cavoatrial junction. The atrial suture line renders the two sinus nodes electrically isolated from each other. Thus, ECGs will frequently have two distinct P waves ( Fig. 56-1). The sinus node of the donor heart is easily identified by its constant 1:1 relationship to the QRS complex, while the native P wave marches through the donor heart rhythm independently. The presence of the two separate P waves may lead to confusion about the patient's rhythm. The ECGs may be interpreted erroneously as showing atrial fibrillation, atrial flutter, or frequent premature atrial complexes. The use of calipers aids in the definition of the two distinct P waves. Sinus node dysfunction in the posttransplant heart occurs in approximately 4 to 5 percent of patients and is manifest by either sinus brachycardia with heart rates of equal to or less than 50 beats per minute or sinus standstill with a junctional escape rhythm with heart rates of 60 to 70 beats per minute. This dysfunction occurs in the early postoperative period and resolves spontaneously in most patients. For patients in whom sinus node dysfunction persists, treatment consists of either theophylline, which accelerates the sinus bradycardia in some patients, or implantation of a permanent transvenous pacemaker. The type of pacemaker implanted varies depending on institutional preference but generally is either an atrial pacemaker programmed in the AAIR mode or a ventricular pacemaker programmed in the VVIR mode. Use of an atrial rate-responsive pacemaker preserves atrioventricular conduction in addition to providing physiologic rate responsiveness.
FIG. 56-1. Electrocardiogram demonstrating donor and recipient P waves. N donor P wave; T recipient P wave.
Posttransplant chest radiographs show evidence of a prior sternotomy but otherwise are generally normal. Some patients may have evidence of "cardiomegaly" related to the transplantation of a heart from a donor who was larger than the recipient ( Fig 56-2).
Echocardiography is a useful tool for evaluating cardiac function post-transplantation. Interpretation of the echocardiogram is routine with the exception of the evaluation of the atrial size. Because the atrial anastomoses incorporate the posterior walls of the recipient's native atria, echocardiography will show atrial enlargement, but this has no significant effect on cardiac function. Early rejection results in diastolic dysfunction, although the echocardiographic indices may be subtle and difficult to detect. Severe rejection will be accompanied by signs of biventricular enlargement with global hypocontractility and significant atrioventricular valve regurgitation.
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