Coronary Artery Dissection Due to Atherosclerosis

Atherosclerotic coronary dissection is a tear in the intima and media of a diseased coronary artery. Blood enters the wall, forms a false lumen or intramural haematoma and narrows or occludes the true lumen.

Most cases are iatrogenic, caused by a catheter, wire, balloon, stent or atherectomy device. Catheter induced dissection complicates well under 1% of angiograms and interventions. Minor balloon related dissection is frequent and often not flow limiting.

Spontaneous dissection through a ruptured atherosclerotic plaque is rare and occurs mainly in older adults with multiple risk factors. It is a different disease from spontaneous coronary artery dissection, which affects non-atherosclerotic arteries, mostly in younger women.

Risk factors for iatrogenic dissection are heavy calcification, tortuosity, ostial lesions, deep intubation with a stiff or oversized guide catheter, hydrophilic wires, oversized or high pressure balloons, atherectomy and subintimal tracking in chronic occlusions.

Retrograde extension into the aortic root is a recognised complication, most often from the right coronary ostium. Left main dissection carries a high risk of shock and death.

Pathophysiology.

Mechanical stress fractures the plaque at its junction with normal wall. Blood tracks along the media, propagating antegrade or retrograde.

Dissection types by angiography: A (luminal radiolucency that clears with contrast), B (parallel tracts or double lumen that clear), C (extraluminal cap with persistent contrast after clearance), D (spiral filling defect), E (new persistent filling defect) and F (impaired flow or total occlusion). Types C to F carry the highest risk of closure.

An intramural haematoma compresses the true lumen without an intimal flap on angiography, so imaging is needed to show it.

Aortic root extension is graded by length along the ascending aorta: confined to the sinus, up to 40 mm, or more than 40 mm.

During or after a procedure: new chest pain, ST elevation, hypotension, bradycardia, ventricular fibrillation, or sudden loss of flow on injection. Spontaneous cases present as an acute coronary syndrome. Aortic extension may cause back pain, a new aortic regurgitation murmur or signs of tamponade.

• Angiography: haziness, a linear radiolucent flap, staining that persists after washout, a spiral filling defect, abrupt cut off or loss of flow. Grade flow with the TIMI flow scale.
• Intravascular ultrasound or optical coherence tomography confirms the true lumen, the entry tear, the extent of haematoma and the landing zones. Take care with the flush volume, which can extend a dissection.
• Aortogram or CT of the aorta when the dissection involves the ostium.
• ECG, troponin and bedside echocardiography for ventricular function, regional wall motion and pericardial effusion.

Differential diagnosis.

• Coronary spasm, air embolism and thrombus.
• Coronary perforation and no reflow.
• Spontaneous coronary artery dissection of a non-atherosclerotic artery.
• Primary aortic dissection involving a coronary ostium.

Immediate actions (first 5 minutes).

• Stop contrast injection and keep the wire in the true lumen.
• Heparin to an activated clotting time of 250 to 300 seconds (unfractionated heparin 70 to 100 units/kg intravenously, with further boluses by activated clotting time).
• Exclude spasm: nitroglycerin 100 to 200 microgram intracoronary, repeated up to 600 microgram while systolic pressure stays over 90 mmHg.
• Hypotension: noradrenaline 0.05 to 0.5 microgram/kg/min. Bradycardia: atropine 0.5 mg intravenously every 3 to 5 minutes to a maximum of 3 mg. Ventricular fibrillation: defibrillation at 200 J biphasic, adrenaline 1 mg every 3 to 5 minutes and amiodarone 300 mg.
• Shock from left main involvement: intra-aortic balloon pump, percutaneous ventricular assist device or veno arterial extracorporeal membrane oxygenation while the vessel is reopened.

Decide between observation and stenting.

• Types A and B with normal flow and no ischaemia: observe, with repeat angiography after 10 to 15 minutes and again before leaving the laboratory.
• Types C to F, any flow limitation, ongoing ischaemia, a long dissection or an ostial or left main location: stent.

Stenting technique.

• Confirm the true lumen with intravascular imaging. Cover the entry tear and extend to a normal reference segment, working from distal to proximal. Use drug eluting stents and avoid oversizing. Post-dilate at modest pressures.
• Ostial right coronary dissection: stent the ostium with 1 to 2 mm protruding into the aorta, which seals the entry and limits root extension.
• Aortic extension up to 40 mm: seal the ostium with a stent and observe with CT. Extension over 40 mm or into the ascending aorta, or any tamponade or aortic regurgitation: emergency surgery.
• Failed stenting, left main dissection with shock, or extensive multivessel involvement: emergency bypass grafting.

Antithrombotic therapy after stenting.

• Aspirin 150 to 300 mg loading dose, then 75 to 100 mg daily.
• Ticagrelor 180 mg loading dose, then 90 mg twice daily (or prasugrel 60 mg then 10 mg daily, 5 mg when weight is under 60 kg or age is 75 or over; or clopidogrel 600 mg then 75 mg daily). Continue 12 months after an acute coronary syndrome and 6 months in chronic coronary syndromes, shortening to 1 to 3 months when bleeding risk is high.
• Pantoprazole 40 mg once daily while on dual antiplatelet therapy.
• Atorvastatin 40 to 80 mg once daily for LDL cholesterol under 1.4 mmol/L.

Spontaneous atherosclerotic dissection. Treat as plaque rupture with an acute coronary syndrome: antithrombotic therapy, early angiography and stenting for flow limiting disease.

Monitoring. Continuous ECG for 48 to 72 hours, troponin every 6 hours until the peak, echocardiography at 24 to 48 hours, creatinine at 24 to 48 hours after contrast, CT of the aorta at 1 to 3 months when the root was involved.

Referral and escalation. Every dissection with flow limitation needs an operator with bail out capability and surgical back up in the same centre. Transfer at once if a left main or aortic extension is suspected and the centre has no surgical cover.

Special groups.

• Pregnancy: spontaneous coronary artery dissection is the usual cause of dissection, so treatment differs and specialist cardio obstetric care is needed.
• Kidney impairment: limit contrast volume and give isotonic saline hydration.
• Older adults: lower ticagrelor and prasugrel use by bleeding risk.