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Anaesthesia for repair of anomalous origin of left coronary artery from pulmonary artery

Sir, 
 
Anomalous origin of left coronary artery from pulmonary artery (ALCAPA) is a rare congenital heart defect (1 in 3,00,000 live births), in which left coronary artery arises from pulmonary artery, instead of branching from the aorta.[1,2,3] A 35-year-old, 47 kg female was scheduled for corrective surgical repair of ALCAPA. For the previous 2 years, she had progressively increasing breathlessness and anginal attacks on exertion. The 12 lead electrocardiograms (ECG) revealed sinus rhythm, without any ST or T wave changes. Transthoracic echocardiography revealed mild left ventricular enlargement and normal ejection fraction of 55%, without any regional wall motion abnormalities. The coronary angiography revealed ALCAPA. Her medications included enalapril, digoxin and furosemide. 
 
In the operation theatre, after securing a 16 gauge intravenous (IV) cannula, monitoring with ECG, non-invasive blood pressure (BP), cardiac output (CO) and oxygen saturation (SpO2) was started. The left femoral artery and left radial artery were cannulated for invasive BP monitoring. General anaesthesia was induced and trachea intubated using fentanyl 100 μg, morphine 6 mg, midazolam 2 mg, etomidate 6 mg and vecuronium 8 mg (all administered IV). Right internal jugular vein was cannulated, and anaesthesia was maintained using oxygen/air/isoflurane, with infusions of rocuronium and fentanyl. 
 
The ventilatory settings were aimed to prevent hypocarbia, hyperoxia and alkalosis. A low FiO2 of 0.4 was used to maintain a high pulmonary vascular resistance (PVR). The end-tidal CO2 was maintained between 40 and 42 mmHg, and partial pressure of oxygen was monitored. The surgery was performed under cardiopulmonary bypass (CPB). Dopamine (5 μg/kg/min) was used during weaning of the patient from CPB. Intra-operatively and post-operatively, patient remained haemodynamically stable. 
 
The survival of neonates with ALCAPA varies with the adequacy of left ventricular perfusion. This depends on the inflow of blood to left coronary artery via collaterals from right coronary artery (RCA) and the proportion of coronary steal from left coronary artery to the pulmonary artery. Only 10-20% of these neonates survive till adulthood.[4] In the post-natal period, there is a decrease in pulmonary vascular resistance (PVR) and oxygen content of the pulmonary blood. This can reverse the direction of blood flow from left coronary artery to the pulmonary artery (coronary steal phenomenon). This causes hypo-perfusion of the left ventricular myocardium by relatively de-saturated blood, leading to myocardial ischaemia. This can lead to mitral valve insufficiency.[5,6] Patients might have accompanying atrial septal defect, ventricular septal defect, patent ductus arteriosus, tetralogy of Fallot or coarctation of the aorta. All these factors precipitate congestive heart failure in 80–90% of these infants. These neonates present with tachypnoea, tachycardia, poor feeding, irritability and diaphoresis. They can survive till adulthood, due to well-developed collaterals from RCA, which provides adequate perfusion to the left ventricle. The RCA was dilated and tortuous in this patient [Figure 1]. The coronary angiogram is the gold standard investigation for diagnosis of ALCAPA. The adults present with exertional dyspnoea, angina and cardiac arrhythmias.[2] Diuretics and inotropes are used for the management of congestive heart failure. 
 
 
 
Figure 1 
 
Dilated and tortuous right coronary artery 
 
 
 
The anaesthetic goals are to (1) maintain optimum preload, (2) prevent a decrease in PVR, (3) maintain myocardial contractility, (4) maintain low or normal systemic vascular resistance (SVR) and (5) prevent tachycardia. The preload is optimized to ensure an adequate CO. In these patients, the stroke volume is monitored instead of CO, because CO varies with heart rate. The laryngoscopy/intubation should be smooth and rapid. Swings in heart rate and BP are avoided. Tachycardia is detrimental, as it can alter the myocardial oxygen supply/demand ratio and predispose to myocardial ischaemia. Etomidate being haemodynamically stable is preferred for induction of anaesthesia. Isoflurane is the inhalational agent of choice, as it causes less myocardial depression, compared with halothane or sevoflurane and is a better myocardial protective agent. 
 
Low PVR will accentuate the coronary steal phenomenon. The presence of hypocarbia, hyperoxia or alkalosis decreases PVR and is detrimental. They are ventilated using oxygen/air mixture, and partial pressure of oxygen is not allowed to rise very high. A higher end-tidal CO2 is maintained to achieve a higher PVR. A low afterload SVR is maintained, for an adequate stroke volume. Aggressive reduction of afterload may also be deleterious, as it attenuates the perfusion of RCA, thus decreasing the blood flow to left coronary artery. Inotropes such as dopamine, dobutamine or milrinone should be used cautiously, as they increase the consumption of myocardial oxygen, which may accentuate myocardial ischemia. Thus, patients with ALCAPA repair can be managed successfully, after understanding the pathophysiological changes.