Intravascular Ultrasound and Pharmacological Stress Test to Evaluate the Anomalous Origin of the Right Coronary Artery

ABSTRACT: The anomalous origin of the right coronary artery is a common finding. With its origin in the left coronary sinus, the right coronary artery can have a route between the aorta and pulmonary artery trunk and can cause myocardial ischemia and sudden death. The anomalous origin of the artery and its route may be diagnosed by coronary angiography or multislice computed tomography. Intravascular ultrasound provides high-resolution images and a precise evaluation of coronary anomalies. The role of intravascular ultrasound was recently demonstrated in the diagnosis of extrinsic compression of the anomalous right coronary artery. We describe 3 cases of anomalous right coronary artery originating in the left coronary sinus. The intravascular ultrasound detected a reduction of the coronary lumen from anomalous course, even when the luminal reduction was not evident by angiography. We suggest that a pharmacological stress test should be used, with a vasoactive drug that simulates physical effort, to determine the reduction of the arterial lumen.

J INVASIVE CARDIOL 2012;24(6):E131-E134

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The anomalous origin of the right coronary artery (RCA) affects approximately 1.1% of people subjected to coronary angiography.¹ When the RCA originates from the contralateral coronary sinus, its course is between the aorta and pulmonary trunk and may cause myocardial ischemia and sudden death.^1,2 Symptoms may be triggered by physical effort, as there is greater hemodynamic stress from the increased extrinsic compression and distortion of the coronary course associated with the increased need for myocardial perfusion.

The diagnosis of anomalous origin and the course between the aorta and pulmonary trunk may be performed by coronary angiography or multislice computed tomography (multislice-CT). Intravascular ultrasound (IVUS) provides high-resolution images that can be used to evaluate coronary anomalies. Recently, the role of IVUS was demonstrated in the diagnosis of extrinsic compression of the anomalous RCA.³

We report 3 cases of anomalous origin of the RCA from the left coronary sinus. We used IVUS to identify the reduction of the coronary lumen that was determined by the artery route between the aorta and pulmonary trunk. The luminal reduction of the RCA was identifiable even when it was not evident by angiography. We propose a pharmacological stress test, with a vasoactive drug that simulates physical activity, to determine the reduction of the arterial lumen. All patients signed informed consent forms that used easily understood terminology.

Case Report 1. The first patient was a 69-year-old male who was seen at the emergency room for angina chest pain that lasted 15 minutes. The electrocardiogram showed a T-wave inversion in the inferior wall. There was no increase in myocardial injury markers. The patient underwent stress myocardial scintigraphy, which showed reversible perfusion deficit in the inferior wall. The anomalous origin of the RCA, arising from the left coronary sinus, was observed by angiography. A constriction of the ostium and the proximal segment of the artery were also observed. The left coronary artery was normal. There was no atherosclerosis by coronary angiography. IVUS confirmed a significant stenosis in the medial segment, with a luminal area of 4.34 mm² and without the presence of atherosclerotic plaques. There was no observed asymmetry of the coronary ostium (Figure 1, Table 1), and significant atherosclerosis was not identified. The patient underwent coronary artery bypass surgery involving an implantation of the right internal thoracic artery to the RCA and proximal coronary artery ligation. The patient recovered favorably and was discharged in good clinical condition and without angina on the seventh postoperative day.

Case Report 2. The second patient was a 56-year-old female who had received outpatient treatment for class III-IV angina in the previous 3 months. A functional evaluation with a cardiac stress test (treadmill test) was positive for myocardial ischemia with a low load of the Bruce protocol. The patient was referred for coronary angiography, which showed an anomalous origin of the RCA from the left coronary sinus. It was not possible to demonstrate the presence of extrinsic compression. The left coronary artery was normal, and the coronary angiography showed no atherosclerosis. The presence of significant extrinsic compression of the proximal segment of the artery and an absence of atherosclerotic plaque material was determined by IVUS. A significant worsening of coronary stenosis was observed during systole, with a minimal lumen area of 4.38 mm² (Figure 2, Table 1). No relevant atherosclerosis was identified in the IVUS. The patient underwent an artery bypass surgery using the left internal thoracic artery to the RCA, which relieved the symptoms.

Case Report 3. The third patient was a 50-year-old male who was previously asymptomatic but required treatment after presenting syncope during physical effort. After regaining consciousness, the patient complained of chest pain, which was relieved by sublingual nitrate. The electrocardiogram and physical examination in the emergency room were normal, except for high blood pressure, although cardiac enzymes were elevated. A coronary angiography revealed the dominant origin of the RCA from the left sinus of Valsalva and coursing between the aorta and pulmonary trunk.

There was a mild constriction of the RCA (Figure 3). The left coronary artery was normal, and there was no significant atherosclerosis by coronary angiography. Coronary angiography showed extrinsic compression of the proximal segment of the RCA.

The patient underwent IVUS, which showed extrinsic compression of the proximal segment of the RCA by the aorta and pulmonary trunk. The minimal luminal area was 5.67 mm². No significant atherosclerosis was observed by IVUS. As the extrinsic compression did not indicate a critical reduction of the lumen area, a pharmacological stress test was performed using norepinephrine. After 3 minutes with a 0.01 μg/kg/min infusion, the patient showed typical angina. The IVUS showed coronary compression with an expressive reduction of the luminal area to 3.14 mm² (Figure 3). The infusion of norepinephrine was suspended and nitroglycerin was administered; there was an immediate reduction in symptoms.

A right coronary artery bypass was performed using the right internal thoracic artery. The patient exhibited good progression after surgery and remained asymptomatic.

Discussion. For these 3 patients, the main findings from the IVUS were the absence of significant atherosclerotic disease, a marked reduction in the luminal area at systole, and an asymmetry of the ostium lumen and the proximal segment of the RCA (Table 1). The pharmacological stress test showed a reduction of the coronary lumen that was associated with the development of symptoms.

Coronary anomalies are divided into the “significant or major” and “non-significant or minor” forms. The significant form of coronary anomaly causes disorders of myocardial perfusion, and the non-significant form is associated with normal coronary flow. The significant anomalies have a low incidence, corresponding to only 0.25%-0.90% of congenital heart diseases.

Thus, the clinical significance of these anomalies and the associated changes in coronary flow remain unclear. Despite the low incidence, coronary anomalies show a high risk of sudden death. The high risk is likely related to cumulative episodes of myocardial ischemia that result in scattered areas of myocardial fibrosis and create an electrically unstable myocardial substrate, which predisposes patients to lethal ventricular arrhythmias.^4-6

Pathophysiological mechanisms have been proposed for these adverse events, including acute angle origin or occlusion at the emergence of the coronary arteries, coronary spasms from a twisting motion, and mechanical compression of the anomalous artery between the aorta and pulmonary trunk during physical effort. The initial portion of the artery may be intramural (within the tunica media of the aorta), which can further aggravate the coronary obstruction, especially with aortic expansion during physical effort.⁷

The clinical presentation of this anomaly is usually the occurrence of angina during physical effort, dyspnea, dizziness or syncope, cardiac arrhythmias, and sudden death. These symptoms may vary according to patient age; for example, symptoms may manifest as excessive irritability in infants. The physical examination and the electrocardiogram at rest are usually normal. The stress test may show ischemia with exercise.⁸

Nuclear magnetic resonance and coronary computed tomography angiography can confirm the diagnosis of coronary malformations. Although NMR and computed tomography detect morphological changes and the artery course, they are limited in determining the degree of coronary artery obstruction that is caused by the extrinsic compression of the aorta and pulmonary trunk. IVUS has advantages in this regard because it can objectively demonstrate dynamic vessel changes and the occurrence of extrinsic compression. This application of IVUS was only recently described in the literature.³ In the present study, significant reductions in lumen area were observed in all cases even when angiography did not indicate reductions.

The use of pharmacological stress during the intravascular assessment can allow for a functional diagnosis. The significant reduction in luminal area after the administration of vasoactive drugs was well documented in case 3, which confirmed the diagnosis of extrinsic compression of the coronary artery. We used norepinephrine to reproduce the physiological changes that occur during physical effort. Norepinephrine has vasoconstrictive effects that cause an increase in blood pressure, but there is no vasodilation of large vessels and pulmonary circulation is retained. Unlike dobutamine, norepinephrine has no significant inotropic effect and does not cause significant tachycardia. Norepinephrine simulates the conditions that determine the reduction of arterial caliber from aortopulmonary extrinsic constriction.⁹

In these cases, IVUS showed a reduction of the coronary lumen and there was evidence of arterial compression and asymmetry. In case 3, we tested the effects of the infusion of norepinephrine on the extrinsic compression and luminal area. The infusion of norepinephrine was associated with the development of symptoms and the reduction of the minimal lumen area that was detected with IVUS.

The 3 cases were managed with coronary artery bypass surgery. There are reports of the use of stents to correct this anomaly; however, we opted for surgery, as the literature was unclear on whether the radial force of a coronary stent would support the extrinsic compression associated with repetitive hemodynamic stresses through a patient's life.

Conclusion

We reported 3 cases of anomalous origin of the RCA from the left coronary sinus. The diagnoses were performed by coronary angiography. The IVUS demonstrated the reduction of the coronary lumen and arterial asymmetry, and it accurately identified the extrinsic compression and quantified the lumen area reduction. In uncertain cases, the infusion of norepinephrine allows for evaluation of the behavior of the RCA lumen under stress conditions.

The reported cases demonstrate that IVUS can play an important role in the proper evaluation of the impact of the course between the aorta and pulmonary artery in cases of anomalous origin of the RCA. IVUS should be considered in patients who show signs of extrinsic luminal compression that is not demonstrated by coronary angiography.

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From the Center for Cardiovascular Research, Hospital Sao Lucas - Catholic University of Rio Grande do Sul, Brasil, Porto Alegre, Brazil.
Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.
Manuscript submitted January 16, 2012 and accepted January 30, 2012.
Address for correspondence: Dr. Paulo Caramori, MD, PhD, FSCAI, FACC, Director, The Center for Cardiovascular Research, Hospital Sao Lucas , Catholic University of Rio Grande do Sul, Av. Ipiranga 6690, sala 300, Porto Alegre, RS  90610-000  Brazil. Email: dennizmo@yahoo.com.br