Single Coronary Artery and Sick Sinus Syndrome

Single coronary artery has been noted as a rarity since the early 1960s, with an incidence of only 0.0024–0.4%.1,2,6,10 The true incidence of this congenital anomaly may be higher considering unreported cases. Is single coronary artery with sick sinus syndrome rare? It is! To our knowledge, these 2 patients are the first reported cases associating both disease entities. We present 2 cases of single coronary arteries both arising from the left sinus of Valsalva and both complicated with a right heart strain. This caused sinus node dysfunction, resulting in recurrent dizziness and syncope, which improved after pacemaker implantation. Case Report. Patient #1. A 49-year-old male was admitted because of recurrent dizziness and syncope for 2 weeks. He had been well when sudden episodes of “black-out” spells were noted. He would regain consciousness immediately. This was accompanied by chest tightness, dyspnea and palpitation at rest. Physical examination was unremarkable except for a grade 2/6 systolic murmur over the left lower sternal border and an engorged jugular vein. Arterial blood gas showed hypoxemia with a PaO2 of 67.5 mmHg at room air. Chest radiograph was negative. Cardiac ultrasound showed a dilated right atrium and ventricle with paradoxic septal wall motion but with adequate systolic function. There was also severe pulmonary hypertension with an estimated systolic pulmonary artery pressure of 90 mmHg and a moderate tricuspid regurgitation. Cardiac catheterization was performed and confirmed ultrasound findings. Hemodynamic profile showed the following: right atrium = 13/3 mmHg with a mean = 6 mmHg; right ventricle = 73/10 mmHg; pulmonary artery = 75/27 mmHg with a mean = 50 mmHg; left ventricle = 140/32 mmHg; aortic pressure = 140/60 mmHg; pulmonary capillary wedge pressure mean = 20 mmHg; and ejection fraction = 85%. Incidentally, there was only a single coronary artery arising from the left sinus of Valsalva with a normal course after repeated failure to cannulate the right coronary artery (RCA). The RCA arose from the left circumflex artery, coursing retrogradely and posterior to the aorta, through the atrioventricular groove and giving off branches (LII-P). No stenosis was noted over the coronary arteries. Pulmonary function test showed a restrictive ventilatory defect with moderate impairment of the diffusing capacity. Perfusion scan was normal. Patient was unresponsive to medications and syncope persisted. Electrophysiological studies showed sinus nodal dysfunction with a maximal corrected sinus node recovery time of 1,810 milliseconds. Implantation of a VVI 8086 pacemaker (Medtronic AVE, Santa Rosa, California) was performed and the patient improved. He has remained asymptomatic up to this date. Patient #2. A 65-year-old female was admitted because of dizziness, presyncope and exertional dyspnea for 1 month. A known hypertensive, she had remained well when she started having dizziness with presyncope, accompanied by dyspnea initially on exertion, progressing to dyspnea even at rest. Physical examination was unremarkable except for a slow heart rate of 40 beats/minute, but was regular in rhythm. There was also a grade 3/6 pansystolic murmur over the left sternal border. Laboratory examinations were within normal limits and chest radiograph showed cardiomegaly. Electrocardiogram showed sinus bradycardia, T-wave inversion over V1–V6, II, III and aVL, and a dilated left atrium. Cardiac ultrasound showed dilated left and right atria, asymmetrical concentric left ventricular hypertrophy, and right ventricular hypertrophy with adequate systolic function. There was severe asymmetric hypertrophy of the subpulmonic area, causing a right ventricular outflow tract obstruction with an estimated pressure gradient of 98 mmHg. The aortic valve was also thickened with moderate aortic regurgitation. A mild tricuspid regurgitation was also present. Cardiac catheterization was performed, but we failed to engage the RCA after repeated tries. The left coronary artery was easily engaged and later showed the RCA originating from the proximal left anterior descending artery, coursing anteriorly with respect to the pulmonary conus crossing and supplying blood to the right side (LII-A). Aside from this, right ventriculogram showed obstruction over the right ventricular outflow tract due to a muscular band, with a pressure gradient of 90 mmHg. Aortogram showed a dilated aortic root with moderate aortic regurgitation. Hemodynamic profile was as follows: right atrium = 16/6 mmHg with mean = 14 mmHg; right ventricle = 100/20 mmHg; pulmonary artery = 40/20 mmHg with mean = 26 mmHg; left ventricle = 160/24 mmHg; aorta = 180/80 mmHg; pulmonary capillary wedge pressure = 20/10 mmHg with mean = 15 mmHg; and ejection fraction = 81%. Electrophysiological studies showed sinus node dysfunction with a maximal corrected sinus node recovery time (SNRTC) of 1,080 milliseconds. A DDD 7866 pacemaker (Medtronic AVE) was implanted and symptoms improved. The patient would still have occasional exertional dyspnea after discharge and myomectomy was suggested. Patient refused. Discussion. Since most patients with single coronary artery are asymptomatic, they are usually diagnosed incidentally during angiography. Numerous classification schemes and revisions have been devised.1–4,7 Although usually asymptomatic, some subtypes, particularly R-3a, R-3b and R-5b6 using the Ogden and Goodyer classification and RII-B8 using the Lipton classification, are prone to sudden death during exercise and extreme stress.6,8,10 It was thought that because of the course of the coronary artery between the great vessels, compression during exercise resulted in ischemia and death.14 This was later replaced by a more plausible explanation as kinking of the artery from its angulated take off from its origin that was responsible for the ischemia during exercise.2 In symptomatic patients, chest pain, exertional dyspnea, syncope and palpitations are some of the subjective complaints. However, even when the course of the anomalous vessel was anterior or posterior to that of the great vessels and was significantly free of stenosis, cardiac ischemia does still occur.5 Single coronary artery is considered a benign condition by many, and usually compatible with a long and active life. Sharbaugh et al.,13 however, cautioned us not to overly consider patients with this diagnosis as “normal”, since 15% of patients still develop severe cardiac problems even without any additional cardiac anomalies and problems before the age of 40. Cardiac arrhythmias and infarctions have been associated with single coronary arteries,17 but have not been associated with sinus node dysfunction. Sinus node dysfunction, also known as sick sinus syndrome, is a common disease. Etiologies include intrinsic and extrinsic factors affecting the sinus node.18,19 It is a constellation of different arrhythmias that may occur singly or at the same time. Treatment is pacemaker implantation. The sinus node is supplied by the RCA in about 65% of cases, by the left circumflex branch in 25% and by both in 10% of cases, although some may originate from the aorta and the left main artery.19 Before, ischemia had been thought of as the major cause of this disease, of which coronary artery disease (CAD) was the prime suspect.9,11,15 This was later disproved after the dysfunction was noted only to be transient and recovered after the insult was removed. This was confirmed by autopsy findings in patients with sick sinus syndrome wherein degeneration and fibrosis were predominant findings, and ischemic damage was rarely found. Kyriakidis et al.12 also found that even though the sinus node arteries were atheromatous, no sinus node dysfunction was noted, with the exception of only 2 cases. In a patient with a single coronary artery, there may already be an unbalanced blood distribution over the entire myocardium making it already prone to ischemia during physical and emotional stress. In our 2 cases, the origins of the coronary arteries were both from the left sinus of Valsalva, making the right side “ischemia prone”. Since 60% of the blood supply of the cardiac conduction system comes from the RCA, an increase in the oxygen demand during stress in an already “ischemic prone” heart would disrupt the normal homeostatic environment of the conduction system. Instances wherein patients suddenly died after episodes of physical and emotional stressors were reported and attributed this to the disruption of the cardiac conducting system.10 In a study by Shaw et al.,16 chronic sinoatrial disorder was present even when blood supply to the sinus node was unobstructed. If CAD was not the cause of the ischemia, an artery with an anomalous origin affecting the opening of the coronary ostium could be responsible. It is therefore possible that “it is more of the ostial abnormality that is important”. Pulmonary hypertension and right ventricular outlet obstruction caused a strain over the right heart. The first patient had a moderate restrictive ventilatory defect, which resulted in a derangement in the diffusing capacity of the lung. This in turn increased pulmonary vascular resistance, furthering the alveolar hypoxia and resulting in pulmonary vasoconstriction and hypertension. In the second case, a vicious cycle ensued between the already existing right heart strain, the increase in the oxygen demand, and the already relative sinus node artery insufficiency from a single coronary artery. This dysfunction may have been initially transient as reports stressed, but the continuing and ongoing insult created a “wound-heal-wound” cycle that eventually led to irreversible damage. Although unproven, this is the most plausible explanation for what may have happened in our patients. While some reports may dispute the possibility of ischemia to the sinoatrial node because of the abundance of collateral flow, two factors need to be taken into account: 1) Their cases involved normal coronary anatomy and distribution as opposed to ours; and 2) a right heart strain was absent in their cases. Through this report, we can consider a single coronary artery with a right heart strain as a possible cause of sick sinus syndrome. At the same time, add sick sinus syndrome as one of the causes of unexplained syncope and dizziness in patients with single CAD. We conclude that single coronary artery without other congenital cardiac abnormalities, without acute angulations from its origin, with a course not lying between the great vessels, free from significant stenosis, and not involving conditions resulting in a right heart strain, may be considered to be normal and is compatible with a long and active life with no decrease in cardiac function, and less prone to sudden cardiac death.

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