Minimally invasive direct coronary artery bypass (MIDCAB) is a novel method for bypassing diseased coronary arteries that can replace open coronary artery bypass grafts (CABG) in certain situations, most commonly when bypassing the left anterior descending artery (LAD) with a left internal thoracic artery (LITA) graft. The main difference from traditional CABG is that sternotomy is avoided. The procedure is often performed without placing the patient on cardiopulmonary bypass (CPB) ("off-pump" procedure).
The procedure can be performed for multivessel disease as part of a hybrid procedure that includes percutaneous coronary intervention (PCI).
Coronary surgery that circumvents sternotomy and/or CPB results in lower perioperative morbidity and mortality rates compared to "traditional" CABG. 2 Patient selection criteria can thus be expanded to include older patients with significant comorbidities.
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Indications
- proximal occlusion/stenosis unsuitable for PTCA
- failed PTCA
- prior CABG with occluded vein grafts and patent internal thoracic artery
- multivessel disease in patients with associated risk factors who are at high risk for cardiopulmonary bypass, i.e. patients with COPD, CRF, aortic atheroma, diffuse vasculopathy)
- ischemic cardiomyopathy with anterior wall ischemia
- as part of a hybrid procedure for multivessel disease (i.e., MIDCAB and concomitant PTCA)
- as an adjunct to major noncardiac procedure, e.g. abdominal aortic aneurysm repair 2
Contraindications
Contraindications are all relative and are becoming obsolete as the technique is constantly being refined:
- myocardial bridge
- small, diffusely diseased coronary artery
Technique
The internal thoracic artery is dissected using three ports, similar to abdominal laparoscopic technique, then grafted to the coronary vessel through a 5 cm-wide left intercostal incision.
Nowadays, there are centers where minimally invasive cardiac surgery is being performed with the assistance of robotic arms, to further minimize damage to thoracic and cardiac tissue 3.
Radiographic features
Plain radiograph
Since sternotomy is avoided, surgical clips around the heart borders are the only telltale sign of previous coronary surgery.
If the patient's medical history is unavailable, the differential diagnosis for surgical clips projected over the mediastinal border includes:
- partial pneumonectomy
- in some cases, additional signs of pulmonary surgery will be absent, depending on the extent of surgery (segmentectomy vs lobectomy) and chronicity, i.e. whether the remaining lung has had ample time for compensatory hypertrophy
- clipping of a patent ductus arteriosus (PDA): single metal clip in the aortopulmonary window
CT
High-resolution CT (HRCT) with coronary CT angiography (cCTA) is an invaluable "one-stop shop" for surgery planning. Thin-slice ECG-gated CT with reformations and 3D reconstructions afford the cardiac surgeon the ability to 4-6:
- identify patients suitable for MIDCAB, based on native artery anatomy and calcium score, as well as potential graft anatomy
- plan the approach
- visualize the exact locations of previously performed bypass grafts to avoid damaging them during the procedure
MRI
As yet, CT is superior to cardiac MRI, as most MR machines in use today have lower spatial resolution and therefore cannot visualize small coronary artery anatomy as accurately as CT. In addition, MRI cannot be used to perform calcium scoring.
Angiography
Preoperative and postoperative coronary angiography has been mostly eschewed in favor of coronary CT angiography. Catheter angiography is invasive in itself and suffers from limitations such as non-visualization of occluded grafts, inability to perform calcium scoring. It cannot reveal any relevant anatomy outside the vessel lumen, either, such as myocardial or epicardial fat bridging 6.
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