Nondominant Right Coronary Artery Occlusion Leading to an Anterior ST-Segment Elevation Myocardial Infarction

Abstract

Background

A nondominant right coronary artery supplies a small portion of the myocardium. Albeit rare, an acute occlusion of a nondominant right coronary artery is believed to be inconsequential with minimal clinical relevance.

Case Presentation

We present a case of a middle-aged man who presented with chest pain and an electrocardiogram demonstrating anterior ST-segment elevation. An emergent coronary angiogram revealed acute thrombotic occlusion of the proximal nondominant right coronary artery with no significant obstructive atherosclerotic disease in the dominant left coronary circulation. Balloon angioplasty of the occluded vessel followed by implantation of a drug-eluting stent resulted in the resolution of the chest pain and ST-segment elevation.

Conclusion

While electrocardiographic ST-segment elevations in the anterior precordial leads are highly suggestive of a left anterior descending artery occlusion, herein, we present a rare case of an acute anterior ST-segment elevation myocardial infarction secondary to a nondominant right coronary artery occlusion.

Introduction

Dominance of a coronary artery has been traditionally defined by the artery reaching the crux of the heart and supplying both the posterior descending artery and posterolateral system.¹ In approximately 85% of patients, the right coronary artery (RCA) is the dominant vessel, while 8% are left coronary artery dominant, and 7% are reported as codominant.¹ A nondominant RCA supplies a small territory of myocardium, and its role in ischemic heart disease is poorly defined.^2,3 We present a rare case of an anterior ST-segment elevation myocardial infarction (STEMI) secondary to an acute occlusion of a nondominant RCA.

Case Presentation

A 57-year-old man with a prior history of hypertension and hyperlipidemia presented to the emergency department for evaluation of acute-onset chest pain, which started an hour prior while performing yard work. Upon arrival, vitals showed he was normotensive, with a normal heart rate, and he was saturating well without the need for supplemental oxygen. His physical examination was unremarkable except for mild chest-pain-related distress. An electrocardiogram (ECG) on presentation revealed greater than 1 mm ST-segment elevations in the anterior precordial leads (V1–V4) and T-wave inversions in the lateral leads (I, aVL) (Figure 1). The patient’s past medical history is significant only for hyperlipidaemia, and he had been recently started on a moderate intensity statin. He was a nonsmoker.

Figure 1.

A prepercutaneous coronary intervention electrocardiogram revealed ST-segment elevations in leads V1-V4 (blue arrows).

Given the diagnosis of an acute anterior STEMI, the patient was administered aspirin (324 mg) and ticagrelor (180 mg), and he was then emergently transferred to the cardiac catheterization laboratory. Coronary angiography revealed a 100% acute thrombotic occlusion of a proximal nondominant RCA with thrombolysis in myocardial infarction (TIMI) 0 flow (Figure 2A). There was no angiographic evidence of obstructive atherosclerotic disease in the dominant left coronary circulation (Figure 2B–C).

Figure 2.

A coronary angiography demonstrated (A) 100% occlusion of nondominant proximal right coronary artery (orange arrow), no significant obstructive disease in the left main, left anterior descending, and left circumflex coronary arteries in (B) the right anterior oblique caudal view and (C) the left anterior oblique cranial view.

In the setting of active signs and symptoms of ischemia with no other identifiable coronary culprit lesion, percutaneous coronary intervention (PCI) of the nondominant RCA was pursued. Balloon angioplasty with a 2.0 mm compliant balloon restored flow and revealed 2 large right ventricular (RV) marginal branches. Then, a 2.5 x 22 mm Onyx Frontier drug-eluting stent (DES) was placed in the proximal RCA. This resulted in TIMI 3 flow in the vessel (Figure 3A–B), with subsequent resolution of chest pain as well as ST-segment changes on postprocedure ECG (Figure 3C). The patient was transferred to the coronary care unit, and a transthoracic echocardiography revealed overall preserved biventricular systolic function (left ventricular ejection fraction of 60%) with normal RV function, absence of RV dilation, and mild tricuspid regurgitation. The patient remained chest pain-free, had an uneventful clinical course thereafter, and was discharged on hospital day 2 with close follow-up and outpatient cardiac rehabilitation referral.

Figure 3.

A post-percutaneous coronary intervention coronary angiography demonstrated normalized blood flow in the right coronary artery in (A) the left anterior oblique and (B) the shallow right anterior oblique views, which supplies 2 large right ventricular marginal branches. (C) An electrocardiogram showed resolution of the ST-segment changes.and left circumflex coronary arteries.

Follow-Up

At the 1-month follow-up, the patient was doing well from a clinical standpoint and denied any complaints of angina. He had been compliant with his high-intensity statin, dual antiplatelet and beta-blocker medications, and had resumed all his daily activities with no functional limitations.

Discussion

Epidemiology

While the true incidence of acute occlusions of a nondominant RCA remains unknown, data on its clinical implications have been limited to a few case reports. Devitt et al described 2 such cases where RV infarction manifested by hypotension and arrhythmias (atrial fibrillation, ventricular tachycardia, ventricular fibrillation, and junctional bradycardia) was the predominant presentation.³ Zheng et al described a case of a patient who suffered from a resuscitated ventricular fibrillation arrest with no significant resultant cardiomyopathy from a nondominant RCA occlusion, but he was noted to have mild RV dilation on subsequent imaging, presumably due to ischemia.⁴ Lin et al described a patient, similar to the patient mentioned in our case study, with ST-segment elevations in leads V1–V3 from a nondominant RCA occlusion that was uncomplicated without significant resultant cardiomyopathy, shock, or arrhythmias.⁵ Ismail et al also presented their experience on a nondominant RCA stenosis resulting in anterior ST-segment elevations with resolution of ST-elevations after PCI.⁶

Clinical Features

Angiographically significant nondominant RCA lesions are frequently ignored on routine coronary angiography as they are thought to be clinically irrelevant. While uncommon, acute occlusions of a nondominant RCA leading to angina, arrhythmias, shock, and even cardiac arrest have been described in the medical literature.² On the other hand, it is well known that anterior ST-segment elevations are commonly seen following acute occlusions of the left anterior descending coronary artery.

Anatomically, a dominant RCA gives rise to the posterior descending artery, which supplies the posterior one-third of the interventricular septum.¹ Hence, acute occlusions of a dominant RCA usually result in ischemia of the inferior wall that manifests as ST-segment elevations in the inferior leads with reciprocal anterior ST-segment depressions. Right ventricular myocardial infarction can be seen in up to 50% of inferior myocardial infarctions due to occlusion of the RV marginal branches from the proximal RCA.¹ In a nondominant RCA occlusion, inferior ischemia is absent, and, thus, the predominant changes evident on ECG are in the anterior precordial leads from involvement of the RV marginal branches.

Case Analysis

In this report, we discussed a 57-year-old man who presented with an acute anterior STEMI that was found to be due to occlusion of a nondominant RCA. Following PCI, the artery was noted to supply 2 large RV marginal branches that wrapped around the anterior surface of the RV. Ischemia from these 2 large RV marginal branches was the reason why the proximal nondominant RCA occlusion manifested as ST-segment elevations in the anterior precordial leads V1–V4. Given the relatively smaller territory of myocardium supplied by the nondominant RCA, we saw minimal impact on overall myocardial function. The patient maintained preserved biventricular function, and his clinical course was free from any significant arrhythmias or clinical heart failure.

Conclusion

This case report highlights the importance of considering a nondominant RCA occlusion as a rare cause of anterior STEMI. The mainstay of treatment remains prompt coronary angiography with urgent revascularization of the culprit vessel. Further large-scale studies are needed to better understand the incidence, and the short- and long-term clinical implications of acute nondominant RCA occlusions.