An Unusual Cause of Right Ventricular Myocardial Infarction

The extent of myocardial injury and subsequent complications of ST-segment elevation myocardial infarction (STEMI) are dependent on the territory supplied by the occluded coronary artery. The culprit vessel of STEMI can often be predicted by review of the surface 12-lead electrocardiograph (ECG) and the patient's clinical presentation. Interventional cardiologists use this information to plan their diagnostic and therapeutic strategies in patients with STEMI.

The current medical literature states that 100% of patients with hemodynamically significant right ventricular myocardial infarction have an occlusion of the proximal right coronary artery.^6,28 We describe a previously unreported finding of right ventricular myocardial infarction in a patient with unusual coronary anatomy involving a single coronary artery.

Case Report. A 76-year-old Caucasian female with a remote history of a non-ST segment elevation myocardial infarction (NSTEMI) and hypertension presented to our emergency room with substernal chest pain of 2 hours of duration. On admission, she was anxious and in obvious discomfort. Her skin was pale and diaphoretic. Vital signs showed a blood pressure of 70/48 mmHg, pulse of 46 beats per minute, and a respiratory rate of 16 per minute. Carotid impulses were normal and mild jugular venous distention was noted. The lung fields were clear. Cardiac examination revealed normal first and second heart sounds, and there were no appreciable cardiac murmurs or ventricular heaves. Extremities were cool, but showed no clubbing, cyanosis, or edema. Standard 12-lead ECG showed 3-4 mm of ST segment elevation in leads II, III, aVF and V6, and marked ST- segment depression in the anterior and lateral leads consistent with an acute inferior posterior lateral myocardial infarction (Figure 1). A right-sided ECG revealed > 1 mm ST segment elevation in lead RV4, consistent with right ventricular myocardial infarction (RVI) (Figure 2). Resuscitation measures were initiated with volume expansion and intravenous pressors. The patient was sent for emergent cardiac catheterization, coronary angiography and possible coronary intervention.

Nonselective injection in the right sinus of Valsalva during coronary angiography revealed the right coronary artery (RCA) to be congenitally absent (Figure 3). A single coronary artery arose from the left coronary sinus. The left main coronary artery bifurcated into the left anterior descending (LAD) and left circumflex arteries. The LAD had mild proximal calcified stenosis of less than 50%. A 75% lesion in a small caliber first diagonal branch was noted. A critical (> 90%) narrowing in the proximal portion of the left circumflex artery (LCX) was present. This lesion demonstrated a large, hazy filling defect consistent with intracoronary thrombus. Angiographic cutoff of the posterior-lateral vessel suggested distal embolization of thrombus (Figures 4 and 5). The LCX continued along the atrioventricular groove, giving off posterior left ventricular and posterior descending (PDA) branches. The vessel then continued beyond the PDA, following the course of the right atrioventricular groove in the typical distribution of the right coronary artery (RCA) and provided multiple right ventricular marginal branches.

The patient was administered 325 mg of oral aspirin and intravenous (IV) unfractionated heparin (50 IV/kg bolus) and intravenous abciximab (0.25 mg/kg bolus and IV infusion of 0.125/kg/min). A 6-French EBU guide catheter (Medtronic Vascular Inc., Minneapolis, Minnesota) engaged the left coronary artery and a 0.014 BMW wire (Abbott Vascular, Santa Clara, California) was advanced across the lesion without difficulty. Manual aspiration thrombectomy was performed using an Export catheter (Medtronic Vascular Inc.). This yielded a large amount of red and white thrombotic material, associated with improvement in the subsequent angiographic appearance of the vessel. No additional macrovascular embolization was identified. Stenting was performed using a 3.5 x 23 mm Cypher stent (Cordis Corp., Miami Lakes, Florida). The successful final angiographic result is shown in Figure 6. Prior to sheath removal, left ventriculography demonstrated an ejection fraction of 40% with a moderate area of inferior basal hypokenesia. She was discharged on aspirin, clopidogrel, carvedilol, ramipril and atorvastatin. A nuclear myocardial perfusion scan performed one month after the acute event revealed a fixed defect without ischemia and an improvement in left ventricular ejection fraction to 50%. The patient remained free of major adverse cardiovascular events during three years of follow-up.

Discussion. We describe a previously unreported finding of a hemodynamically significant right ventricular myocardial infarction (RVI) due to a thrombotic occlusion of a left circumflex coronary (LCX) artery in the setting of a congenital single left coronary artery. Our patient presented with the classic clinical and electrocardiographic (ECG) findings of RVI complicating an acute inferior-posterior STEMI. Emergent angiography demonstrated the unexpected finding of an anomalous coronary artery and percutaneous coronary intervention resulted in relief of the coronary obstruction, resolution of symptoms, and rapid recovery of the patient.

Rapid recognition of RVI is critical because this syndrome is associated with a considerable immediate morbidity and mortality and has a well-delineated set of priorities for management. Although, isolated RVI is a rare event,¹ right ventricular involvement in the setting of an acute inferior wall MI is quite common, occurring in up to 35% of instances.^1,4 The RVI is hemodynamically significant in 10-15%¹⁰ of patients with an acute inferior myocardial infarction.^1–5 In such patients, the infarction typically involves the left ventricular inferior-posterior wall, septum, and posterior right ventricular free wall.^1,2 When right ventricular dysfunction does occur, the right ventricle loses its ability to maintain cardiac output across the pulmonary circuit, resulting in decreased left ventricular filling pressures and a drop in systemic cardiac output and ultimately, systemic hypotension. The right ventricle may become dilated and displace the interventricular septum to the left, further reducing left ventricular filling and cardiac output.³ Thus, patients with RVI demonstrate clinical signs of elevated right-heart pressure, but the left ventricular filling and systolic function may be normal. The clinical triad of hypotension, clear lung fields, and elevated jugular venous pressure in a patient with an inferior infarction is considered a specific, virtually pathognomonic sign of right ventricular infarction.^4,5 Caution must be exercised in relying solely on such findings, however, since they are may be masked by volume depletion. The physical and hemodynamic signs of right ventricular infarction may only emerge after volume resuscitation.^4,5 Cardiac auscultation may reveal a right-sided S3 and S4. Auscultation of tricuspid regurgitation, which may be severe, suggests papillary muscle dysfunction or right ventricular chamber dilation. Jugular venous distention with prominent V-waves may also be seen with significant tricuspid regurgitation.

The standard surface 12-lead ECG can also suggest right ventricular infarction in the setting of acute inferior wall myocardial infarction. ST-segment elevation disproportionally greater in lead III relative to the other inferior leads should alert the clinician to consider the presence of RV infarction (i.e., ST elevation in lead III is greater than lead II).¹¹ Additionally, the ECG finding of ST segment elevation in lead V1 in association with ST depression in lead V2 is suggestive of RVI. One author describes the finding of ST segment depression in lead V2, ≤ 50% of the magnitude of ST elevation in aVF to be sensitive and specific ECG finding for right ventricular infarction.¹² The most frequent conduction abnormalities associated with RVI are right bundle-branch block and complete heart block.^4,12

The right-sided ECG is an important diagnosis tool in the assessment of right ventricular infarction. Several investigators have reported that ST-segment elevation in lead V4R > 1.0 mm is a sensitive and specific marker of RV infarction and this ECG pattern correlates closely with occlusion of the proximal right coronary artery.^13,14 Robalino et al found that ST-segment elevation in lead V4R > 1 mm was 87% specific and 100% sensitive for occlusion of the RCA proximal to the first ventricular (RV marginal) branch.¹²

It is important to recognize the transient nature of right-sided ST-segment elevation. In one series, 48% of patients had resolution of ST segment changes in RV4 within 10 hours of the onset of symptoms,¹³ thus emphasizing the importance of obtaining a right-sided ECG as early as possible in patients with evidence of acute inferior ST-elevation MI. The clinician must be cognizant of other potential causes of ST segment elevation in the right-sided precordial leads including pulmonary embolism, pericarditis, and anteroseptal MI. The coronary angiography of RVI has been described by Bowers et al. They reported that 100% of right ventricular myocardial infarction resulted from occlusion of the proximal right coronary artery.^5,17 The most common anatomic substrate resulting in RV ischemic dysfunction is occlusion of the proximal RCA. This compromises flow to the major RV marginal branches whereas more distal right coronary occlusions spare the dominant RV marginal vessels and rarely compromise RV performance.^5,17

Coronary anomalies, as seen in our patient, may alter the perfusion pattern of the myocardium, including the right ventricle. Isolated coronary artery anomalies are rare in the adults, estimated to be present in 0.3–1.3% of the general population.¹⁸ They are usually incidentally detected during routine coronary angiography performed to evaluate coronary artery disease.¹⁸ By definition, an isolated single coronary artery (SCA) arises from the aortic trunk by a single coronary ostium, and supplies the entire heart regardless of its pattern. The incidence of SCA is 0.024–0.066% in a general population undergoing coronary angiography.¹⁹ According to Banchi, the first case of single coronary artery was reported by Thebesius in 1716 and the first antemortem diagnosis was made in 1967 by means of coronary angiography.¹⁹ In 1979, Lipton et al proposed an angiographic classification for single coronary artery anomalies, which was further modified in 1990 by Yamanaka and Hobbs.¹⁸ Using the Lipton classification, our patient demonstrates the “L-1” variant of single left coronary artery. The “L-1” artery arises in the left sinus of Valsalva and gives rise to a normal LAD and a markedly dominant left circumflex artery, which supplies the typical territory of the right coronary artery. There is no coronary artery ostium arising from the right sinus of Valsalva.^19,20

Early reperfusion, either with primary percutaneous coronary intervention (PCI) or fibrinolytic therapy, is imperative in patients with RVI and can preserve both right and left ventricular function and reduce mortality and morbidity.^5,16 Several studies document that complete reperfusion of the culprit coronary artery by PCI enhances the recovery of RV performance and improves the clinical course and survival of patients with ischemic RV dysfunction.^5,6,17 In contrast, unsuccessful reperfusion is associated with impaired recovery of right ventricular function, persistent hemodynamic compromise, and a high mortality rate of up to 58%.¹⁷

Conclusion. We report the first case of right ventricular myocardial infarction caused by obstruction of the left circumflex coronary artery in a patient with a congenital single left coronary artery. In this “L-1” anomaly, the left circumflex coronary artery supplies the myocardium typically served by the right coronary artery. Emergent angiography revealed the unexpected anatomical finding and successful intervention resulted in an excellent patient outcome. Interventional cardiologists should be prepared to respond appropriately when unexpected coronary anomalies are encountered during emergent procedures in patients with acute STEMI.

References

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