IVUS-Guided Evaluation and Percutaneous Intervention in an
Anomalous Left Main Coronary Artery

Case Report. A 42-year-old asymptomatic female with longstanding Type-1 diabetes and secondary chronic renal failure underwent evaluation for potential kidney-pancreas transplantation. A screening treadmill myocardial perfusion scintigraphy study revealed limiting exertional dyspnea and a medium-sized reversible anterior defect. She was referred for elective coronary angiography.

Angiography revealed an anomalous origin of the left main coronary artery (ALMCA) originating from the anterior aspect of the right sinus of Valsalva (Figure 1).

Catheter pressure dampening occurred on intubation, but ostial stenosis was not evident. Dynamic systolic compression was seen along the left main interarterial course, visibly accentuated by catheter intubation, as compared to nonselective cusp injections (Figures 2A and B). Additionally, the dominant right coronary artery had a severe, focal mid-vessel stenosis.

The patient was recommended for cardiac surgery, but after extensive discussion, declined this option and elected to undergo staged percutaneous coronary intervention (PCI). Given the patient’s tight angiographic stenosis, her submaximal stress test and the anticipation of a complex left main intervention, the right coronary lesion was stented with a 3.5 x 24 mm Taxus^®Liberté stent (Boston Scientific, Natick, Massachusetts). The patient returned 6 weeks later for stenting to the anomalous left main coronary artery under intravascular ultrasound (IVUS) guidance.

IVUS (0.5 mm/sec motorized pullback) was performed using the Galaxy system and the 40 MHz Atlantis Plus ultrasound catheter (Boston Scientific/Scimed). The images demonstrate several unique features of the ALMCA — the “slit-like” ostium with significant stenosis, baseline asymmetric distortion of the proximal lumen and superimposed dynamic systolic compression (Figures 2A–C; IVUS movie clip available from the Journal online [.avi format, 2.3 MB]). The ostial lumen cross-sectional area was 3.7 mm², a 62% reduction referenced to the distal left main artery. The eccentric nature of the aberrant segment luminal distortion is marked, predisposing to angiographic underestimation. PCI was undertaken with a 0.014 inch BMW guidewire (Guidant Corp., Indianapolis, Indiana) via an AL1 guide (Medtronic, Inc., Minneapolis, Minnesota). A 3.0 x 23 mm Cypher^™ stent (Cordis Corp., Miami, Florida) was placed with a small overhang into the aortic lumen and deployed to 16 atm. The stent was postdilated with a 3.25 mm Extensor balloon (Medtronic), including flaring of the ostium.

There was complete abolition of the ostial constriction and left main compression (Figure 4), providing an excellent final result. Follow up to 10 months has been uneventful, including a repeat perfusion scintigraphy study at 7 months that was normal. The patient remains on the active transplant list.

Discussion. ALMCA is a rare congenital defect with a prevalence of 0.024% in an angiographic series.¹ However, itis the second leading cause of sudden cardiac death in competitive athletes.² Death is typically exertional or immediately post-exertion. While fatality is most often reported in people younger than 30 years of age, ALMCA-attributed death has been described in older age groups as well.^3,4 Exertional chest discomfort and syncope are common premonitory symptoms, but in 55% of fatal cases, the first symptom is death.⁵ Stress testing can be positive for ischemia, but is not considered a reliable risk stratification tool.⁵

There are four potential anatomic pathways for an ALMCA to reach the usual anterior myocardial territory (Figure 5): (A) anterior-to-right ventricular outflow tract;

(B) “septal”, traveling an intramyocardial route through the subpulmonary infundibuluma above the interventricular septum;

(C) “interarterial”, with passage between the aorta and the main pulmonary trunk; and

(D) retroaortic. Of note, in most cases, the Type C ALMCA vessel travels an intramural course within the aorta, exiting the aortic wall near its normally anticipated left sinus origin (Figure 5). The Type C interarterial variant has been strongly associated with sudden cardiac death.^2,4 Types A and D are reported to have a benign prognosis in relation to sudden events, whereas Type B is uncertain, with some authors reporting adverse outcomes.^4,6

The mechanisms by which Type C ALMCA results in myocardial ischemia and sudden death are incompletely understood. A traditional explanation is exertion-exacerbated compression or “scissoring” between the aorta and main pulmonary trunk. The angiographic and IVUS images confirm that compression does occur. However, the superior arterial pressure in the coronary artery should logically protect against critical compression by the pulmonary trunk. This compression may instead be mediated exclusively by the aorta. During the aortic intramural segment, the anomalous coronary is susceptible to aortic wall tension. As wall tension is proportional to radius (Laplace’s law), it is possible that with exertion and arterial hypertension, the aortic wall tension may critically compress the anomalous coronary segment. Another possible mechanism is related to ostial compromise secondary to the acute takeoff. On its own, the ostial compromise evident in our case could precipitate ischemia or arrhythmia on maximal exertion. Exertion-mediated aortic distension may increase the acuity of takeoff and secondary ostial stenosis. The inner intramural wall that forms the ostium is a thin and relatively unsupported structure and may function as a flap,prolapsing into the lumen during aortic hypertension, further obstructing the lumen. Other proposed mechanisms include coronary vasospasm or accelerated focal atherosclerosis, but have little supportive documentation. In summary, it is likely that ALMCA ostial and proximal vessel abnormalities play a contributory or even synergistic role in pathophysiology, and that the intramural nature of the anomalous coronary segment and ostial stenosis are equally, or more, important than the fact of interarterial passage.

Diagnosis is typical during coronary angiography, but transesophageal echocardiography, electron beam computed tomography (CT), multislice CT and magnetic resonance imaging can be used to diagnose or define the anomalous course. Angiographically, the “dot and eye” method can be helpful in elucidating the relationship to the great vessels.⁷ It is important to note that ostial stenosis is frequently found during open surgical inspection, but not recognized during prior coronary angiography.⁸ Dampening of the catheter pressure trace on intubation may be the only indication of ostial stenosis. This paradox is likely due to the vertical orientation of the slit-like ovoid lumen, the oblique angle of takeoff and the unfamiliar arterial course. IVUS examination is recommended. A pressure wire could assist evaluation, as it may demonstrate a provocable pressure gradient,⁹ although the relationship between an absent (or present) pharmacologically-induced gradient to prognosis in ALMCA is unknown.

Management has been traditionally surgical. In the absence of a risk stratification tool, intervention is indicated in symptomatic patients, asymptomatic young patients and asymptomatic older patients considered at risk from exertional sudden death. Initial enthusiasm for coronary artery bypass grafting has fallen from favor, with concern that competitive flow in the native vessel results in early graft occlusion.¹⁰ Many surgeons have adopted a technique of “unroofing” the intramural segment, creating a wide gutter and neoostium for left coronary inflow.¹⁰ However, in doing so, it is often necessary to take down and then reattach the intercoronary commissure. This interruption of commissure integrity has resulted in late prolapse, aortic regurgitation and the need for aortic valve replacement.¹¹ Creation of a probe-guided neoostium avoids this complication, but subsequent stenosis can occur. There is little long-term data to guide decision making.

Experience with PCI to the interarterial ALMCA has been very limited: the largest case series involves 2 patients, supplemented by occasional reports of patients treated with primary PCI for myocardial infarction.^11,12 Immediate technical results have been excellent, with prognosis determined by the index presentation. Current stents are sufficiently flexible in order to permit accurate delivery to unusual anatomy and have high radial strength to obliterate ostial stenosis and lumen compression. In combination with low rates of restenosis with drugeluting technology, coronary stenting may be an acceptable alternative to surgery in good surgical candidates, in addition to the current indications for the percutaneous approach of high surgical risk, urgency or patient preference. It is relevant to note that drug-eluting stenting, in reasonable surgical candidates with congenitally-normal unprotected left main coronary stenoses, remains an unproven strategy. While generally considered contraindicated, several recent case series have demonstrated very promising outcomes and, as a result, several large, multicenter, randomized, controlled trials have been initiated, in particular the Synergy Between PCI with Taxus Drug-Eluting Stent and Cardiac Surgery (SYNTAX) trial and the Randomized Comparison of Bypass Surgery versus Angioplasty Using Sirolimus-Eluting Stent in Patients With Left Main Coronary Artery Disease (COMBAT) trial.¹³

We believe IVUS has an important role in both diagnostic evaluation and percutaneous treatment. It is essential to adequately evaluate the ostium. In addition, selection of stent length is greatly facilitated by IVUS imaging. Angiographically difficult to determine, IVUS can define the “normal”, noncompressed distal left main vessel. Selection of a relatively longer stent is necessary to achieve both adequate ostial coverage and extension into this normal distal vessel. In conclusion, the ALMCA has several unique features that can be best evaluated by IVUS. PCI is feasible in selected patients with good immediate and mid-term results.

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