Morbidity and mortality after palliative surgery for patients with the hypoplastic left heart syndrome is continually improving.1–5 The highest mortality occurs after the first palliative stage, be this the first stage of the Norwood sequence or the so-called Sano modification, with a much lower surgical mortality from the second and third stages, these comprising first the construction of a superior cavopulmonary connection, and then the total cavopulmonary connection. After successful initial palliation, and before the second stage of surgery, there is a risk of unexpected sudden death said to vary from 4 to 20%. This has been attributed to blockage of shunts, obstruction of the aortic arch, ventricular dysfunction, pulmonary venous obstruction, and to non-cardiac causes such as infection.6 Post mortem studies are not always conclusive as to the cause.
Formation of thrombus in the native aortic root is a complication that has only rarely been reported, and has invariably been fatal.7, 8 This is due to the critical role of the aortic root as a conduit for retrograde flow to supply the coronary arterial circulation. We report a patient who was investigated for impaired ventricular function and electrocardiographic changes three months after the second stage of the Norwood palliation for hypoplastic left heart syndrome. A small adherent clot was demonstrated in the non coronary sinus of Valsalva during cardiac catheterisation. We postulate that such small undetected thrombus may be the cause for some unexplained inter stage deaths.
Case report
After an antenatal diagnosis of hypoplastic left heart syndrome, a 3.2 kilogram neonate was found to have aortic atresia and critical mitral stenosis, with the ascending aorta measuring 5 millimetres. The infant underwent a modified first stage of the Norwood sequence on the second day her of life, inserting a 3.5 millimetres polytetrafluoroethylene (Gore-Tex; WL Gore & Associates, Inc. Flagstaff, Arizona, USA) shunt from the right subclavian artery to the right pulmonary artery. The second stage of the Norwood sequence, a Hemifontan operation, was performed at five months of age when she weighed 5.7 kilograms. The child was discharged home ten days later on oral aspirin with an unremarkable electrocardiogram, and good cardiac function as revealed by the echocardiogram (Fig. 1a).
Figure 1. The pre discharge electrocardiogram (a) after the Hemifontan operation shows narrow QRS complexes with right axis deviation. The current electrocardiogram (b), in contrast, shows broad QRS complexes, a superior axis, and widespread inversion of the T waves.
During follow-up, the infant was noted to be growing and developing normally, but when she was 8 months old, her cardiac function was found to have deteriorated on echocardiography, and she was admitted for further investigations. An electrocardiogram showed left axis deviation and broadening of the QRS complexes of new onset, with changes in the ST–T waves in all the limb leads and leads V1 to V3 (Fig. 1b). Cardiac magnetic resonance imaging showed regionally impaired function in the right ventricular free wall superiorly, with an ejection fraction of 22%, but no obstruction to the origin of the main coronary arteries. Cardiac catheterisation with coronary angiography was then performed, which showed normal calibre of the epicardial coronary arteries and a small filling defect measuring 2 millimetres by 3.4 millimetres in the non coronary sinus of Valsalva (Fig. 2). The patient was anticoagulated with warfarin, and enoximone and lisinopril were commenced. The infant remains clinically well two months later, albeit with little change in her ventricular function
Figure 2. The arrow indicates the filling defect in the non coronary sinus of Valsalva of the native aortic root as seen in the left anterior oblique projection.
Discussion
Coronary arterial insufficiency is a major cause of morbidity and mortality after the first stage of the Norwood reconstruction for hypoplastic left heart syndrome. In a post-mortem study of 122 patients, it was demonstrated to be the commonest cause of acute death in the postoperative period, being found in over one-quarter of patients, of whom one-third had died of chronic myocardial failure due to coronary insufficiency.9 The initial high mortality after the first stage of the Norwood palliative strategy has improved markedly with improvements in surgical technique and postoperative intensive care.1–5, 10
A major challenge to those looking after these infants is the small incidence of sudden death after an ostensibly good initial palliation. This happening has been attributed to a number of causes, including blockage of shunts, obstruction of the aorticarch, ventricular dysfunction, and pulmonary venous obstruction.6 Late thrombotic occlusion of the native aortic root has been infrequently reported, and in all the reported cases resulted in sudden death.7, 8 In most of these patients, the thrombus has been identified by routine transthoracic or transoesophageal echocardiography when the patients have presented in a collapsed state. In our patient, multiple transthoracic, and even transoesophageal, echocardiographic interrogations failed to detect the clot, as did magnetic resonance imaging.
The presence of clot in the non coronary sinus of Valsalva suggests that intermittent coronary thrombo-embolism caused impairment of myocardial function in our patient. The location of the thrombus away from the main coronary arterial orifices, and not obstructing the aortic root, may explain why this did not cause sudden death. The cause for the thrombus might be related to relatively low velocity of flow in the native aorta, which might be more of a problem in patients with native aortas of relatively large diameter. Conversely, in patients with diminutive ascending aortas, there may be a lower risk of thrombosis, as the size of the ascending aorta matches the calibre of the coronary arteries, and there is no blind-ending sac providing a nidus for stasis. The state of the aortic root is always carefully interrogated with routine echocardiography during follow-up of patients after staged palliation of hypoplastic left heart syndrome. It may not be possible, however, to visualize small intraaortic thrombus even when this is specifically sought. Even coronary angiography may have failed to visualise this if the clot had embolised before or during the procedure. We proceeded to coronary angiography because although magnetic resonance imaging scan had shown no obstruction to the proximal coronary arteries, the regional changes in function and the electrocardiographic changes were suggestive of a regional problem with myocardial blood flow.
We acknowledge that we have not seen any distal emboluses in the patient presented but given the outcome of previously reported cases, and the ability of thrombus to embolise before being detected, it is possible that this is one of the mechanisms of late unexplained deaths in patients undergoing Norwood palliation. Formal anticoagulation, in those units where it is not routine, should be considered in the patient with a relatively large native aortic root. A careful search should be performed for clot in the aortic root in patients with otherwise unexplained deterioration, ventricular dysfunction, or changes in the electrocardiogram.
