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J Thorac Cardiovasc Surg 2005;130:1212-1213
© 2005 The American Association for Thoracic Surgery
Brief Communication |
a Division of Cardiac Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA
b Division of Cardiology, Children's National Medical Center, Washington, DC.
c Department of Pediatric Cardiac Surgery, Children's National Medical Center, Washington, DC.
Received for publication April 13, 2005; accepted for publication April 21, 2005. * Address for reprints: Louis C. Benjamin, MD, Division of Cardiac Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA 15213. (Email: lcbenjamin03{at}comcast.net).
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Thorcopagus twins often have complex cardiac anomalies associated with other congenital defects.
1
This has precluded successful separation in the past.
We report a case in which a very small connecting bridge of myocardial tissue resulted in one ventricle pacing the other in thoracopagus-cardiopagus twins. This defect was not noted before the operation, despite extensive imaging. Surgical division and subsequent independent QRS complexes seen after separation of the myocardial bridge as in our case has not previously been reported.
Clinical Summary
Four-month-old infants born as conjoined twins were delivered at 34 weeks' gestational age by cesarean section. They were known to have a shared liver and were connected at the abdominal and thoracic cavities.
Cardiac evaluation included electrocardiography, echocardiography, cardiac catheterization, magnetic resonance imaging, and computed tomographic scanning. Both hearts were in the same pericardial sac but appeared structurally normal. The left ventricle of one twin was found to protrude into the thoracic cavity of the other, in direct contact with the other twin's right atrium and right ventricle. However, no communications or shared myocardial tissue between the twins' hearts could be visualized on any of the preoperative testing. Preoperative angiography demonstrated no shared coronary vessels according to the sequential and simultaneous aortic root angiograms, which clearly delineated the normal coronary arteries of each heart.
The twins were noted to have synchronous cardiac rhythms, despite the apparent absence of an anatomic source for shared conduction tissue. The preoperative tracing showing synchronous electrocardiographic activity between the twins is shown in Figure 1, A.
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The communication arose at the base of one left ventricle, adjacent to the origin of the posterior descending coronary artery. On the other heart, it attached near the atrioventricular groove, close to the right coronary artery. After test occlusion of the connection with a Dacron polyester tie and a tourniquet, two pledgeted sutures were placed, one at the base of each end of the myocardial bridge, and the tissue was divided. After separation, the two hearts immediately began to beat in an asynchronous fashion, in sinus rhythm, without any signs of arrhythmia. This is illustrated by the electrocardiographic tracings shown in Figure 1, B.
Discussion
The twins described in this case had no radiologic evidence of a congenital anomaly, despite exhaustive testing. The fact that the cardiac rhythms were synchronous was cause for concern, because synchronous heart rhythms in thoracopagus twins have been shown to be consistent with shared cardiac chambers.
2,3
An electrocardiogram demonstrating independent QRS complexes suggests isolated ventricles. We could not find any case in the literature where there was an isolated myocardial bridge that could be separated.
Although the ability of individual myocytes to sustain an electrical potential and go through the cardiac cycle has been well described, the ability of shared myocardial tissue to propagate a rhythm between two individual hearts has not. The potential for heart block or other fatal arrhythmias was entertained, because we could not predict the electrophysiologic consequences of separating this tissue. Since the operation, the children have shown no cardiac abnormalities and have remained in sinus rhythm.
References
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