Types of congenital abnormalities of the coronary arteries

Coronary artery anomalies have been reported in 1–2% of the population with some reports showing up to a 5.6% incidence.Reference Kayalar, Burkhart, Dearani, Cetta and Schaff^2, Reference Angelini³ The following is a brief description of the most common types of abnormal aortic origin of a coronary artery:

1. 1. Anomalous aortic origin of left coronary arterial branches from the right sinus of Valsalva. This is the most common anomaly accounting for about 40% of all major coronary anomalies. The types are as follows:

   • ∙ Left circumflex coronary artery from the right main coronary artery: passing to the patient’s right behind the aorta to reach its normal territory of blood supply. This anomaly typically has no clinical significance.

   • ∙ Left main coronary artery from the right sinus of Valsalva: occurs in up to 3% of all major coronary arterial anomalies. The left main coronary artery has at least 4 pathways after arising from the sinus:

     • ○ Posterior to the aorta: not typically associated with sudden cardiac death.

     • ○ Anterior to the right ventricular outflow tract: not typically associated with sudden cardiac death.

     • ○ Within the ventricular septum beneath the right ventricular infundibulum: this is the most common variant and is not associated with sudden cardiac death.

     • ○ Between the aorta and the right ventricular outflow tract: this variant is associated with sudden cardiac death during or immediately after vigorous exercise. Most patients with this variant have a slit-like ostium of the left main coronary artery, associated with an intramural course within the aortic root.Reference Law, DiBardino, Raviendren, Devaney and Davis⁴

   • ∙ Left anterior descending coronary artery from the right main coronary artery: very rare and typically associated with other forms of congenital heart disease. This variant may lead to significant myocardial ischaemia if obstruction occurs near the ostium of the common arterial trunk.

2. 2. Anomalous aortic origin of right coronary arterial branches from the left sinus of Valsalva. This anomaly accounts for about 35% of all major coronary artery anomalies. The course of the right coronary artery is between the aorta and the right ventricular outflow tract, with an angulated trajectory, intramural course, and slit-like ostium, which can lead to myocardial ischaemia and sudden cardiac death.Reference Taylor, Rogan and Virmani⁵

3. 3. Single coronary artery. This variant accounts for 20% of all major coronary arterial anomalies. Almost half of this anomaly is associated with other forms of congenital heart disease. The single coronary artery can arise from either the right or the left sinus of Valsalva and can have several different courses. The variant with the highest risk of sudden cardiac death occurs when a main coronary branch has an interarterial course – that is, between the aorta and the pulmonary artery.

4. 4. Left or right coronary arterial branches arising from the posterior sinus of Valsalva. This variant is exceedingly rare and has not been associated with sudden cardiac death.

Evaluation of coronary arteries

The evaluation of coronary arteries in paediatrics depends primarily on echocardiography. The American Society of Echocardiography recommends that routine coronary artery imaging should be included in the imaging protocol for children.Reference Lopez, Colan and Frommelt^6, Reference Lai, Geva and Shirali⁷ The imaging of coronary arteries in our institution in the acute critical-care setting after suspected sudden cardiac collapse or aborted sudden death is protocolised (Table 1). An echocardiogram is obtained within an hour of admission. In a previously healthy child who has had sudden cardiac collapse, the primary goals of the echocardiogram are to identify coronary artery origins and proximal courses as well as a complete functional assessment. The functional assessment includes measures of global systolic function such as ejection fraction and shortening fraction, as well as assessment for coronary-based segmental wall motion abnormalities.

Table 1 Aborted sudden cardiac arrest protocol.

CBC=complete blood count; CK-MB=creatinine kinase-myocardial binding; CMP=complete metabolic panel; CPB=Cardiopulmonary Bypass; CSR=critical safety risk; CTA=computed tomography angiogram; CV=cardiovascular; EKG=electrocardiogram; EP=electrophysiology; MR=magnetic resonance; BNP=brain natriuretic peptide

Coronary anatomy assessment by cross-sectional imaging and angiography

Echocardiography remains the main imaging modality for coronary assessment in paediatrics; however, computed tomography (CT) and magnetic resonance angiography provide excellent complementary imaging for high-risk patients.Reference Walsh, Nielsen and Ko⁸ Cross-sectional imaging is being increasingly utilised to confirm the origins of the coronary arteries as well as their proximal and distal courses after aborted sudden cardiac death. If abnormalities are detected, the cross-sectional imaging study is then available to guide surgical intervention.

At present, cardiac CT angiography is the most commonly used cross-sectional imaging modality, given the rapid acquisition of imaging data compared with magnetic resonance. This allows data acquisition from potentially high-risk infants or young children without subjecting them to sedation. Adequate coronary artery imaging is dependent on appropriate heart rate, patient cooperation, and sufficient contrast load. Prospective ECG-gated CT angiography with model-based iterative reconstruction often provides reliable assessment of coronary origins, branching, and distal courses. On the downside, CT imaging involves exposing patients to ionising radiation, a dose equivalent to between 150 and 1100 times that of a conventional X-ray. In addition, iodine-based contrast is required for adequate coronary artery assessment. If contrast allergy or renal clearance of contrast is a concern, other imaging modalities should be considered.

Cardiac magnetic resonance has become an increasingly useful cross-sectional imaging modality for coronary artery assessment in paediatrics.Reference Tangcharoen, Bell and Hegde⁹ Most programmes use a combination of standard magnetic resonance angiography and 3D whole-heart coronary angiography in order to obtain complete information about the coronary origins, branching pattern, and distal courses. The 3D whole-heart sequence has been quite successful at our institution in assessing coronary artery anatomy. The benefits of this technique are better resolution compared with standard magnetic resonance angiography as well as its ability to utilise respiratory gating, allowing the patient to breathe normally during data acquisition. The typical 3D whole-heart sequence lasts ~5–7 minutes, which is longer than CT acquisition, but equally effective without the added radiation exposure. On the other hand, one of the limitations in obtaining good coronary assessment is high resting heart rates. In addition, patients below 8 years of age may require sedation if it is felt that the patient will be uncooperative. Gadolinium-based contrast is usually well tolerated and has a lower allergic profile compared with the iodine-based contrasts used in CT. Cardiac magnetic resonance can also provide myocardial functional data and data on wall motion abnormalities in patients with aborted sudden cardiac death. Tissue characterisation, such as late gadolinium enhancement to assess myocardial fibrosis, is an added strength of magnetic resonance evaluation.

Echocardiography quality improvement initiative

Following an incident at our institution in which a coronary artery anomaly was not identified by echocardiogram in a patient after a sudden collapse, the coronary artery echocardiography imaging quality and protocol were reviewed. On review of the first-time studies, the coronary artery origins were determined to be definitively demonstrated only 45% of the time. Multiple interventions centered on image acquisition and reporting were then implemented. The most impactful intervention was the initiation of the coronary artery imaging protocol. After switching the machine to coronary artery pre-set settings, the screen was labelled right coronary artery or left coronary artery. Cine clips of dedicated 2D as well as colour Doppler images were then to be obtained of both the right and left coronary arteries. A still image was also to be obtained with colour compare showing the coronary artery in 2D as well as with colour fill for each – that is, the left and the right coronary artery (Fig 1). After implementation of the coronary protocol as well as other interventions, coronary artery origins were definitively identified in more than 80% of the studies.

Figure 1 Parasternal short-axis view demonstrating the LCA system. LCA=left coronary artery.

Critical care for patients undergoing elective repair of anomalous aortic origin of a coronary artery

The patient admitted to the cardiac critical care unit following elective coronary artery repair is expected to have been stable before surgery. These patients are often diagnosed incidentally and scheduled for elective surgery. The post-operative care for these patients should be straightforward. For a child with stable haemodynamics, early diuretic administration may be beneficial. Routine sedation and analgesia can be used to treat post-operative pain and anxiety. The majority of these patients are extubated in the operating room. These patients need to be monitored for post-operative ischaemia as their coronary arteries have been manipulated. ST-segment monitoring can be utilised as an early warning tool for ischaemia. Evidence of ischaemia confirmed by electrocardiogram should prompt evaluation with cardiac catheterisation to rule out dissection or embolic events. Unfortunately, in the immediate post-operative period, troponin-I cannot be utilised reliably to evaluate for ischaemia. In addition, in our institution, we utilise low-dose heparin followed by aspirin due to the rough surfaces caused by unroofing and re-shaping of the coronary ostia.

Critical care for patients presenting with aborted sudden cardiac death

Patients who present with aborted sudden cardiac death represent a unique group of ICU patients. Until the aetiology of their cardiac arrest is discovered, there is an unclear risk of recurrence. Upon admission, in addition to routine ICU care to manage the consequences of the arrest, a specific, goal-directed work-up must be carried out to determine the cause. At Cincinnati Children’s Hospital Medical Center, we have developed a protocol to streamline care for patients with aborted sudden cardiac arrest to arrive at the aetiology in the safest and the most expeditious way (Table 1). Although patients with anomalous aortic origin of a coronary artery are usually treated in an elective manner, those who present after an episode of aborted sudden cardiac death likely represent a different type of patient group, and therefore a more urgent approach is required. Patients monitored with bed rest in the ICU can experience recurrent cardiac arrest, and it may be challenging to resuscitate them after a second event.Reference Law, DiBardino, Raviendren, Devaney and Davis⁴ Medical management alone has not been demonstrated to improve outcome for patients with congenital abnormalities of the coronary arteries.Reference Brothers, Gaynor, Paridon, Lorber and Jacobs¹⁰ The goal of medical management is to stabilise and evaluate the patient in preparation for surgical intervention. Patients presenting with unstable haemodynamics constitute the highest-risk category. An aggressive approach should be taken as ischaemic injury is likely reversible. Likewise, the degree of multi-organ system injury, especially neurological, must be ascertained and treated to confirm surgical candidacy and timing of intervention. Given the unknown risk of recurrence and mechanism of provocation of cardiac arrest, it is challenging to recommend specific critical-care strategies.

These patients may receive mechanical ventilation upon presentation. Positive-pressure ventilation decreases left ventricular afterload and is beneficial in the setting of post-arrest ventricular dysfunction; however, careful monitoring is indicated to prevent an excessive rise in mean airway pressure and a reduction in venous return to the heart. Owing to the unpredictable potential for recurrent arrest, we have adopted the strategy of leaving these patients intubated until surgery. Vasoactive drugs may be needed to support cardiac output and systemic blood pressure. Milrinone and calcium chloride, which have the advantage of providing inotropic support without significant tachycardia or increase in myocardial oxygen consumption, are the preferred vasoactive infusions. If the diastolic blood pressure is inadequate to maintain coronary perfusion pressure, there may be a role for the short-term use of vasopressin. The goal of vasopressin titration is to raise diastolic blood pressure cautiously without producing excessive afterload to the heart. All these measures are temporary until surgery can be undertaken.

Post-operative care

Post-operative care is organised as with any other post-operative patient. In addition, careful attentiveness to any significant ECG changes will result in a decision to perform coronary angiography if there is evidence of ongoing myocardial ischaemia. It is debatable whether there is a role for the use of serum troponin levels in the post-operative management of these patients.Reference Law, DiBardino, Raviendren, Devaney and Davis⁴ Individuals with severe impairment of left ventricular function pre-operatively are expected to need some form of haemodynamic support. If the patient presented with mitral valve regurgitation pre-operatively, progressive improvement and resolution of mitral insufficiency can be expected if patients can be supported successfully during the peri-operative period. If vasoactive infusions are insufficient to maintain adequate haemodynamics, mechanical support devices including extracorporeal membrane oxygenation or temporary left ventricular assist device should be considered. As with elective coronary interventions, in our institution, we utilise low-dose heparin followed by aspirin therapy to prevent coronary thrombosis.