Plexus between Internal Mammary Graft and Pulmonary Vasculature after Minimally Invasive Coronary Surgery

Abstract

We report a complication associated with minimally invasive direct coronary artery bypass grafting surgery. The patient suffered a nonfatal anterior myocardial infarction 1 day after he underwent minimally invasive bypass grafting using the internal mammary artery. Two months later, coronary arteriography revealed a fistulous connection between the left internal mammary graft and the left pulmonary vasculature. To our knowledge, this particular complication has not been reported following minimally invasive coronary surgery.

Minimally invasive direct coronary artery bypass grafting (MIDCAB) is a new method for surgical revascularization of coronary arteries. The MIDCAB technique involves performing vessel grafting on the beating heart without cardiopulmonary bypass. However, potential risk exists when working through a small anterior thoracotomy. Here we report a complication associated with the MIDCAB procedure.

Case Report

In April 1998, a 56-year-old male presented with objective evidence of myocardial ischemia 2 months after single-vessel coronary artery bypass surgery (CABG). He had a history of exertional angina due to a high-grade lesion in the left anterior descending (LAD) artery. Prior to CABG, he had undergone 2 percutaneous coronary intervention procedures, initially by balloon angioplasty, and 3 months later by rotablation and stent placement. Both procedures had failed to maintain patency of the LAD artery because of restenosis. It had then been decided to refer him for single-vessel coronary bypass via the minimally invasive technique. Surgery was performed using a MIDCAB approach to graft the left internal mammary artery (LIMA) to the LAD, by means of a 6-mm end-to-side anastomosis. The patient remained stable throughout the operation. On the following day, he developed ST-segment elevation with new Q wave formation in leads V1-V3 and creatine kinase peaking at 1700 U/dL, which was consistent with an acute anterior-septal myocardial infarction. The patient otherwise recovered from surgery and no further anginal symptoms were reported. Two months after CABG surgery, a nuclear imaging study revealed anteroseptal anteroapical reversible perfusion defects, and echocardiography revealed anteroapical hypokinesis. These findings prompted repeat coronary angiography.

Physical examination was unremarkable. Electrocardiography revealed interval changes including loss of R waves and T-wave inversion in V1-V3. Left ventriculography showed abnormal wall motion in the anterior wall and an ejection fraction of 50% (from 60% before surgery). Coronary arteriography demonstrated that the previous high-grade stenosis in the mid LAD artery had become totally occluded. The mid and distal segments of the LAD were filling via collaterals from the right coronary and left circumflex arteries. Selective angiography of the LIMA graft showed that this conduit was patent, but the LAD artery was not visualized distal to the anastomosis. Instead, a plexus of small interconnecting vessels was seen above the pericardial shadow upon selective injection of contrast medium into the LIMA. This plexus of vessels was emptying into a vessel inside the left lung parenchyma, which was visualized in later frames as a large vascular structure in the left pulmonary hilum (Fig. 1). The findings suggested a sort of fistulous connection between the LIMA graft and the left pulmonary vasculature. The patient was managed conservatively. In our judgment, surgical correction was not indicated.

Fig. 1 Selective angiograms of the left internal mammary artery (LIMA) in left anterior oblique projection 2 months after minimally invasive direct coronary artery bypass grafting. Top Panel: Early phase of contrast injection reveals interconnecting vessels (black arrowhead) between the LIMA graft (white arrowhead) and vascular structures in the left pulmonary parenchyma. Bottom Panel: Late phase reveals a larger vascular structure (black arrowhead), probably a pulmonary vein.

Discussion

Fistulous communication between the internal mammary artery and pulmonary vasculature is uncommon and can be classified as congenital ^1,2 or acquired. Several cases of internal mammary artery–to–lung vessel fistulae have been reported as complications following conventional CABG surgery. ^3–9 To the best of our knowledge, the case we report here is the 1st associated with the MIDCAB technique. Several mechanisms have been postulated as the probable cause of this sort of fistulous connection after coronary bypass surgery. ^4–7 Inadvertent disruption of the visceral pleura could result in the exposure of pulmonary vessels and in direct contact with the dissected internal mammary artery, thereby promoting the formation of a fistula. Alternatively, the inflammatory process in the nearby myocardium or lung parenchyma after surgery could promote neovascularization via small interconnecting vessels.

Some surgical techniques have been developed to prevent mammary artery fistula formation after coronary surgery. ^10,11 One method is to separate the internal mammary artery pedicle from the lung by interposing a pericardial flap. Another is to clip rather than electrocoagulate the small side branches of the internal mammary artery. However, MIDCAB surgery, in which the thoracotomy field is small, hinders the surgeon from applying these techniques optimally. Previously reported patients who had internal mammary artery–to–lung vessel fistulae following coronary surgery presented with either recurrent angina or silent ischemia. Yet the patient in this case suffered a perioperative myocardial infarction. As his angiogram subsequently showed, the LIMA graft failed to establish a successful anastomosis beyond the diseased segment of the LAD artery. The original LAD lesion became totally occluded in the perioperative period, which likely led to acute myocardial infarction. We speculate that the inflammatory response from the myocardial infarction, and the occlusion of the LAD in the setting of a suboptimal surgical technique, stimulated the formation of interconnecting vessels between the LIMA graft and the pulmonary vasculature. Our patient was managed conservatively; however, in the event of refractory angina, ^3,5 growing fistula causing heart failure, ⁸ aneurysmal expansion of the fistula, ² or endarteritis, surgical correction would be indicated.

The MIDCAB procedure was developed to decrease operative-wound trauma and to eliminate the morbidity and mortality associated with use of the heart-lung machine. ^12,13 The 30-cm conventional median sternotomy is replaced by an 8-cm or smaller anterior thoracotomy. As with any new technique, there is a learning curve to this approach. There have been serious complications associated with MIDCAB, such as the avulsion of the LIMA graft ¹⁴ and cardiac tamponade. ¹⁵ Errors in anastomosis have also been reported, such as anastomosis of a LIMA graft to a small diagonal branch instead of the LAD artery. ¹⁶ Since patients with internal mammary artery–to–lung vessel fistula formation can remain asymptomatic for years, 3,5,7,9 the real incidence of this sequela may be higher than reported.

The MIDCAB approach has rapidly gained popularity among both physicians and patients. The 1st randomized study of patients (n = 62) who underwent isolated LIMA–to–LAD artery grafting on the beating heart reported significant reduction in systemic inflammatory responses, postoperative morbidity, and length of hospital stay, in comparison with patients who underwent conventional coronary surgery. ¹⁷ While concerns still exist, ¹⁸ it is likely that MIDCAB, along with another minimally invasive coronary bypass method, the port-access approach, may have a definite value for a selected group of patients.

In conclusion, minimally invasive coronary surgery, whatever its advantages, should not be allowed to jeopardize the ultimate goal of a successful and safe myocardial revascularization.