Morphological and Functional Assessment of the Septal Course of a Left Coronary Artery Originating from the Right Sinus of Valsa

Key words: coronary anomaly, intracoronary pressure, intravascular ultrasound, multislice computed tomography Origin of the left main coronary artery (LMCA) from the right aortic sinus is a rare coronary anomaly.^1–11 When coursing interarterially, the risk of sudden death probably caused by myocardial ischemia due to compression of the LMCA between the great vessels during systole is significantly elevated.^{5,6,9,13–15} When coursing intraseptally, the clinical significance of this condition is not established. Exertional myocardial ischemia of clinical significance demonstrated by perfusion scintigraphy has been anecdotally reported,^16,17 while other authors did not find an association between the anomalous septal course of the LMCA and clinical symptoms.¹⁸ We report on the hemodynamic and morphological findings of a septal course of the LMCA originating from the right aortic sinus diagnosed at routine follow-up coronary angiography in an asymptomatic 53-year-old patient who previously underwent orthotopic heart transplantation. Case Report Diagnosis of ischemic cardiomyopathy was made in a 53-year-old man. The patient had been in New York Heart Association Class IV. Orthotopic heart transplantation was undertaken in May 2000. The donor was a 19-year-old male who died of suicide leaping from a bridge. To our knowledge, the donor never had any cardiac symptoms. An electrocardiogram before organ explantation was unremarkable. The post-operative course was completely uneventful. Physical examination was inconspicuous; in particular, the heart sounds were unremarkable and cardiac murmurs were not detectable. The resting electrocardiogram showed sinus rhythm, the heart rate was 72 beats/minute, QRS axis was indifferent, there were unspecific T-inversions in leads I, aVL and V1 to V5. The heart size was normal on chest x-ray and no pulmonary congestion or pleural effusion were present. Echocardiography did not show any peculiarities. Routine dobutamine stress echocardiography and Tc-99m myocardial perfusion SPECT imaging did not reveal myocardial ischemia. Follow-up coronary angiography after transplantation showed an unremarkable right coronary artery. Origin of the LMCA from a common right ostium was noted. Septal course of the LMCA between the aorta (AO) and the right ventricular outflow tract (RVOT) was suspected and confirmed by simultaneous right ventricular injection and coronary arteriography and by volume-rendered reconstruction of an electrocardiogram-gated multislice computed tomography (Figures 1A and 1B). Significant compression of the LMCA during systole could be demonstrated by angiography as well as by intravascular ultrasound. Only very mild atherosclerosis with no relevant plaque formation was present at the site of the dynamic stenosis (Figure 2). Determination of the fractional flow reserve (FFR) by intracoronary pressure recordings during maximal hyperemia induced by 90 µg of intracoronary adenosine was 0.98 (normal, > 0.75). A pressure drop was not noted in systole or in diastole. Discussion Primary congenital anomalies of the coronary arteries are detected in about 1% of adult patients undergoing coronary arteriography. An anomalous origin of the LMCA from the right sinus of Valsalva occurs in 0.02–0.3% of patients.^1–11 Anatomic classification of the origin of the LMCA from the right sinus of Valsalva itself is complex. The LMCA may arise from either behind the right sinus of Valsalva or from a common ostium with the RCA straddling the right-left commissure and the left sinus of Valsalva. The ostium of the anomalously arising LMCA is frequently slit-like, likely compromising flow reserve.6 In this case, the LMCA shared a common ostium with the RCA; as assessed by angiography, multislice computed tomography and intravascular ultrasound, it did not reveal a slit-like ostium. According to the course of the LMCA in relation to the AO and the RVOT or the pulmonary trunk (PT) en route to the left side of the heart, the anomaly can be further classified into four major groups. A course anteriorly (of the PT), posteriorly (of the AO), intraseptally (between the AO and RVOT) and interarterially (between the AO and PT) can be distinguished. While the anterior and posterior course does not influence long-term outcome, the interarterial course has been associated with a significant risk of sudden death.^{5,6,9,13–15} In a necropsy analysis of 32 patients with an interarterial course, the LMCA arose abnormally from the contralateral sinus in 7 cases. In 5 patients, the anomaly was considered the cause of death, since all of these patients had signs or symptoms of cardiac disease during life. The other 2 patients died from trauma and renal disease, respectively.⁵ The mechanism of sudden death is believed to be episodic myocardial ischemia due to transient occlusion of the anomalous LMCA caused by an increase in blood flow through the AO and PT that occurs during exercise and creates compression of the interarterial tunnel.^6,13,14 Dominance of either the right or left circumflex coronary artery has been hypothesized as a predictor for fatal outcome.⁵ A septal course of the LMCA, as in our case, seems to be more benign in nature, although the clinical relevance and resulting consequences of this anomaly are not yet defined. While some authors demonstrated exertional myocardial ischemia to be of clinical significance by means of perfusion scintigraphy,^16,17 other authors did not find an association between an anomalous septal course of the left coronary artery and clinical symptoms.¹⁸ Since angina pectoris is not a reliable clinical symptom in heart transplant patients, perfusion scintigraphy as well as a dobutamine stress echocardiogram were performed; they were unremarkable. Routine coronary angiography and intravascular ultrasound revealed no relevant atherosclerotic disease, but did show systolic compression of the intraseptal portion of the LMCA. The FFR served as a complementary invasive test for myocardial ischemia and was found to be entirely normal. Whether the measurement of FFR by adenosine-induced maximal hyperemia for the assessment of a dynamic stenosis caused by myocardial compression is an adequate diagnostic approach is questionable. It is a widely used and reliable method, but has been validated only in atherosclerotic coronary disease. Provocation with catecholamines to increase contractility might have been a more suitable stimulus to evaluate the significance of the obstruction. If necessary, wrong sinus coronary artery anomalies are surgically correctable in most cases. Coronary artery bypass graft surgery remains the standard procedure for restoring normal distal coronary flow, with good long-term results.^{4,6,8,9,19–21} In light of missing hemodynamic significance, surgical correction was deferred in our patient.

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