Lost P’s, but Not Yet Forgotten
A 30-year-old man presenting with 2 months of increasing cough and worsening dyspnea with minimal exertion was diagnosed with nonischemic dilated cardiomyopathy. An initial ECG revealed sinus tachycardia and left atrial enlargement. Despite maximal medical management, his symptoms and cardiac function did not improve. Orthotopic heart transplantation was performed using biatrial anastomosis from a 27-year-old donor. In this procedure, the donor atria are sutured to intact remnants of the native right and left atria, allowing for minimal interruption of blood flow from both vena cavae and all the recipient’s pulmonary veins while requiring fewer anastomotic connections. The recipient’s native right and left atrial remnants are physically and electrically intact and are sutured into and electrically isolated from the donor atria.
A postoperative ECG was performed (Figure 1), revealing both the dissociated (nonconducted) P waves (arrows) from the recipient’s native atria at a rate of 95 bpm, as well as conducting P waves from the donor’s atria (arrowheads) at a slower rate. Also of interest is the persistent juvenile pattern of the T-wave morphology (inverted in V1 and V2) noted from the transplanted heart, consistent with the young age of the donor.
Routine posttransplant surveillance tests included a transthoracic echocardiogram. M-mode tracing of the mitral valve revealed that a recipient P wave, if occurring during diastole, caused an additional opening deflection of the mitral valve, interposed between the standard E and A waves of early and late diastolic filling of the left ventricle (Figure 2). This indicated that the native left atrium had preserved electrical as well as some mechanical function. At the same visit, the patient underwent an endomyocardial biopsy of the right ventricle to assess for rejection. Right ventricle pressure tracing during cardiac catheterization (Figure 3) revealed extra elevations in pressure corresponding to recipient P waves when they occurred during the diastolic period of the transplanted heart. An echocardiogram of the patient’s right ventricle (Movie) demonstrated that during the third QRS cycle, a recipient P wave fell during diastole and was associated with an additional opening deflection of the tricuspid valve. The native right atrium, therefore, also retained its electrical and mechanical function.
Dissociation of recipient and donor atria has been observed in canines and humans.1,2 The recipient atria’s autonomic input is undisturbed by the transplant, whereas the donor heart’s nerve connections are severed during harvest. The recipient atrial rate has been demonstrated to increase in response to atropine, Valsalva maneuvers, muscular exercise, and hypotension, and, conversely, to decrease with carotid sinus massage. The donor atria, however, demonstrate blunted responses to exercise and hypotension, as is expected of a denervated heart.3 Quantitative echocardiography illustrates that donor atrial mechanical function contributes the majority of atrial emptying compared with the recipient atrium.4
Nineteen months after cardiac transplantation, the patient continued to feel well without symptoms and had no signs of organ rejection, but he continued to display his lost P waves.
The online-only Data Supplement, consisting of a movie, is available with this article at http://circ.ahajournals.org/cgi/content/full/115/3/e41/DC1.