Surgery chapters
Preoperative assessment for cardiac surgery, cardiopulmonary bypass, incisions, conduits and valve options
How patients are assessed and investigated before heart surgery, how the heart-lung machine works and how the heart is protected, the incisions used, the grafts chosen for coronary bypass, and how surgeons choose between valve repair, mechanical and tissue valves.
- Before heart surgery, assess symptoms, LV function, coronary anatomy (angiography is the gold standard) and comorbidity, and score risk with EuroSCORE II.
- Cardiopulmonary bypass drains venous blood from the right atrium, oxygenates and pumps it into the ascending aorta; the heart is protected by potassium cardioplegia (arrest in diastole) and hypothermia; heparin is reversed with protamine.
- LIMA to LAD is the best graft; the long saphenous vein is the commonest; valves are repaired where possible (mitral, tricuspid), otherwise replaced with a mechanical (durable, lifelong warfarin) or tissue valve (no lifelong warfarin, wears out).
On this page
Overview
Cardiac surgery covers coronary bypass, valve surgery, congenital repairs and aortic surgery. Most operations need the heart to be still and bloodless, which became possible when cardiopulmonary bypass (CPB) was first used successfully by Gibbon in 1953.
For the exam you need four things: how a patient is assessed and investigated before surgery, how bypass and myocardial protection work, which incision is used for which operation, and how conduits and valves are chosen.
Preoperative assessment
Clinical assessment
- Symptoms: angina, breathlessness, fatigue, palpitations, swelling and syncope, and how much they limit daily life.
- Risk factors for ischaemic heart disease: age, male sex, smoking, hypertension, diabetes, raised lipids, family history, obesity and inactivity.
- Coexisting disease that changes risk or plan: carotid disease, peripheral arterial disease, lung function, diabetic control and complications, renal impairment and bleeding disorders.
- Conduit check: look at the legs for varicose veins (poor vein grafts) and do an Allen's test if the radial artery may be used.
Drugs before surgery
| Drug | Usual plan |
|---|---|
| Antiplatelets (including aspirin) and anticoagulants | Usually stopped before surgery to limit bleeding (unless the surgeon decides otherwise, e.g. recent stent) |
| Oral hypoglycaemics | Stopped |
| Diuretics, ACE inhibitors | Stopped at the surgeon's discretion |
| Other cardiac and antihypertensive drugs (e.g. beta-blockers) | Continued |
Risk scoring
- EuroSCORE II (widely used in the UK) and the STS score predict operative mortality.
- No score predicts what happens to one individual. The decision is made by the Heart Team (cardiologist, surgeon, anaesthetist) using the score as a guide.
Investigations
| Test | What it adds |
|---|---|
| Resting ECG | Baseline; Q waves of old infarction. Can be normal even with severe multivessel disease |
| Troponin, CK-MB | Diagnosis and prognosis in acute coronary syndrome |
| Exercise tolerance test | Inducible ischaemia; neither a positive nor a negative result is absolute |
| Echocardiography (transthoracic or transoesophageal) | LV function, regional wall motion, valve lesions. Stress echo (exercise or dobutamine) shows viable, recoverable muscle |
| Myocardial perfusion scan (e.g. thallium-201) | Significance of a stenosis and viability |
| Cardiac MRI (with gadolinium) | Ischaemic burden, viability, masses, pericardium |
| PET | Perfusion and metabolism; finds injured but viable myocardium |
| CT coronary angiography and calcium score | Non-invasive look at proximal disease; selects who needs invasive angiography |
| Coronary angiography | Gold standard. Site, severity and extent of stenoses, quality of distal vessels, LV function |
| FFR, IVUS | Whether a stenosis limits flow; detail of left main stem disease |
On angiography a stenosis of more than 70% of the diameter (about 90% of the cross-sectional area) is called severe. Angiography shows anatomy only; it does not prove ischaemia.
Patients over 40 years having valve surgery usually have coronary angiography first, so that coexisting coronary disease can be grafted at the same operation.
When is coronary bypass (CABG) indicated?
Revascularisation is offered for symptoms (angina despite optimal medical treatment) or for prognosis in certain anatomical patterns:
- Left main stem stenosis over 50% ("critical left main") – worst outlook without surgery.
- Proximal LAD stenosis over 50%.
- Two- or three-vessel disease.
- Poor LV function with multivessel disease.
- CABG is favoured over PCI especially in diabetics and high-risk multivessel disease.
Coronary anatomy you need: the LAD is the most often diseased and most often grafted artery. The posterior descending artery comes from the right coronary artery in about 90% (right dominance).
Surgery is also needed for mechanical complications of infarction: ventricular septal rupture (typically 3–7 days after MI, new pansystolic murmur, pulmonary oedema; patch repair), papillary muscle rupture (acute mitral regurgitation; usually valve replacement) and LV aneurysm.
Cardiopulmonary bypass
Setting up
- Median sternotomy, pericardium opened.
- Full heparinisation before any cannula goes in.
- Arterial cannula in the ascending aorta (purse-string). Alternatives: femoral or axillary artery (axillary gives forward flow and allows selective brain perfusion in aortic surgery). Used when the aorta is dissected, diseased or hard to reach.
- Venous cannula: a single two-stage cannula through the right atrial appendage (tip in the IVC, side holes in the right atrium), or separate SVC and IVC cannulae (bicaval) when the right atrium must be opened. The femoral vein is an alternative.
The circuit
| Part | Job |
|---|---|
| Venous reservoir | Collects blood by gravity (siphon); sits well below the heart |
| Oxygenator (membrane) | Gas exchange (does the lungs' job) |
| Heat exchanger | Cools or rewarms the blood |
| Pump | Returns blood to the aorta at a flow set by body surface area |
| Arterial filter | Removes particles and air |
| Suckers and vents | Clear the field and decompress the heart |
Once full flow is reached, the ventilator is stopped.
Protecting the heart
When the aorta is cross-clamped, coronary flow stops and the heart becomes ischaemic. Permanent damage can begin within about 15–20 minutes, so the myocardium must be protected.
- Cardioplegia: a solution given into the aortic root/coronary arteries (antegrade) or through the coronary sinus (retrograde). Most contain potassium, which depolarises the cell membrane and arrests the heart in diastole.
- Cold solutions (about 4–10°C) cut oxygen demand.
- Warm solutions may help recovery after reperfusion.
- Intermittent cross-clamp fibrillation: short periods (about 10–20 min) of induced VF with the clamp on; the heart is still but not bloodless.
- Deep hypothermic circulatory arrest: body cooled to 15–18°C and the circulation stopped for up to about 20–30 minutes (arch surgery, some paediatric repairs). Metabolic rate halves for every 7°C fall.
"K+ keeps it Kalm in diastole" – potassium cardioplegia stops the heart relaxed.
Coming off bypass
Remove all air from the heart → release the cross-clamp → defibrillate if in VF → place epicardial pacing wires → rewarm, correct acidosis and low potassium, restart ventilation → reduce pump flow as the heart takes over → remove cannulae → give protamine to reverse heparin.
Heparin is reversed with protamine, not vitamin K. Vitamin K reverses warfarin.
Complications of bypass
- Systemic inflammatory response (SIRS) from blood contact with the circuit, which can lead to multiorgan failure.
- Bleeding (coagulopathy), air embolism, microemboli, stroke and cognitive change, myocardial depression, lung injury, renal and gut ischaemia, pancreatitis, infection, vascular injury, postcardiotomy syndrome.
- Problems at cannulation (aortic dissection, atrial injury) or at the start (oxygenator failure).
Ways to reduce the insult: "mini" bypass circuits and off-pump CABG (OPCAB) on the beating heart using a stabiliser.
Other uses of bypass
Rewarming from profound hypothermia, severe respiratory failure, pulmonary embolectomy, lung transplantation, major chest trauma and removal of tumours invading great vessels.
Incisions
| Incision | Used for |
|---|---|
| Median sternotomy (suprasternal notch to xiphisternum) | Most cardiac operations: CABG, valves, ascending aorta, anterior mediastinum |
| Right thoracotomy / right mini-thoracotomy | Some mitral and minimally invasive operations |
| Left anterior (submammary) mini-thoracotomy | MIDCAB (LIMA to LAD without sternotomy); transapical TAVI |
| Left posterolateral thoracotomy | PDA ligation, coarctation repair, descending thoracic aorta |
| Left anterior thoracotomy or clamshell | Emergency access to the heart in trauma |
| Subxiphoid approach | Pericardial aspiration or window |
The mitral valve is reached through the left atrium (interatrial groove), through the right atrium and septum, or through the left atrial appendage. The aortic valve is reached through an aortotomy.
Conduits for coronary bypass
| Conduit | Key facts |
|---|---|
| Left internal mammary (internal thoracic) artery | Conduit of choice for the LAD. Left attached to the subclavian artery (pedicled). Reported long-term patency above 98%; improves survival and fewer reoperations |
| Bilateral internal mammary arteries | More arterial grafting, but more sternal wound problems in obese diabetics |
| Radial artery | Second arterial graft; Allen's test first |
| Gastroepiploic, inferior epigastric arteries | Other arterial options |
| Long saphenous vein | Most commonly used. Easy to harvest, long, easy to handle. Historic patency about 50–60% at 10 years; better with aspirin and statins. Harvested starting in front of the medial malleolus |
| Short saphenous, cephalic veins | Back-up; poorer patency |
Patient clenches the fist; examiner presses on both radial and ulnar arteries.
Hand opens (pale); pressure on the ulnar artery is released.
Colour returns within about 5–7 seconds → ulnar collateral flow adequate → radial artery can be taken.
Slow or no return → do not harvest the radial artery.
Outcomes and complications of CABG
- Operative mortality about 1–3%.
- Atrial fibrillation in about 30% (keep potassium above 4.5 mmol/L; beta-blocker, amiodarone, digoxin or cardioversion).
- Significant bleeding about 2–3%; may need re-sternotomy for tamponade.
- Stroke about 2%.
- Deep sternal wound infection / mediastinitis about 0.5–2%, more common in diabetics, obese and dialysis patients; carries high mortality.
- Angina relief: over 90% at 1 year, falling to about 60% at 10 years as grafts and native vessels progress.
Valve options
Mitral and aortic valves are the usual targets. Repair is preferred for the mitral (especially degenerative regurgitation) and tricuspid valves. The aortic valve is usually replaced in adults.
| Option | For | Against |
|---|---|---|
| Repair | Keeps the patient's own structures, better ventricular function, no long-term anticoagulation, fewer valve complications | Technically demanding; may fail (recurrent regurgitation) |
| Mechanical valve | Any age, any position; very durable (lifelong) | Lifelong warfarin: bleeding and thromboembolism risk, regular blood tests |
| Stented tissue (xenograft, e.g. porcine) | Readily available; short anticoagulation only | Limited lifespan (about 10–15 years); calcific degeneration, faster in the young |
| Stentless tissue valve | Better flow, less outflow obstruction | Harder to insert |
| Homograft (cadaver) | No anticoagulation, good flow, lowest endocarditis risk (with autograft) | Hard to obtain; technically difficult |
Choosing a valve
- Mechanical: younger patients who can take warfarin safely.
- Tissue: usually over about 60 years, women who want pregnancy (warfarin is teratogenic), people with bleeding tendency or poor compliance, and those likely to need other major surgery.
All mechanical valves need lifelong warfarin, usually begun on day 1 or 2 after surgery. Tissue valves need short-term or no anticoagulation depending on rhythm.
Prosthetic valve complications
- Thrombosis and thromboembolism – the commonest complication; higher in the mitral than the aortic position.
- Structural failure – mainly tissue valves; rare in those over 70.
- Paravalvular leak – early from technique, late from endocarditis; can cause haemolytic anaemia.
- Prosthetic valve endocarditis – about 2–4%, highest in the first 3 months. Early: Staph. epidermidis; overall Staph. aureus is commonest; also viridans streptococci. Diagnose with blood cultures and echo; mortality over 20%.
UK NICE advice is that dental antibiotic prophylaxis is not routinely needed for prosthetic valves, but other guidelines (e.g. American) still advise it. Follow the current local policy.
Percutaneous options
- TAVI (transcatheter aortic valve implantation): for aortic stenosis in patients too old, frail or high-risk for open surgery, or with a porcelain aorta. Routes: transfemoral/subclavian (retrograde) or transapical (via a small left anterolateral thoracotomy). Complications include paravalvular regurgitation, stroke, vascular injury and heart block.
- Percutaneous mitral balloon valvotomy – main intervention for suitable rheumatic mitral stenosis.
- MitraClip – clips the mitral leaflets together in selected high-risk regurgitation.
Typical surgical indications for valve disease
- Aortic stenosis: severe and symptomatic (mean gradient over 40 mmHg, peak velocity over 4 m/s, valve area under 1 cm²), or severe with falling LV function, or when other cardiac surgery is planned.
- Aortic regurgitation: symptomatic severe AR, or asymptomatic with LV dysfunction or an LV end-systolic diameter over 50 mm.
- Mitral regurgitation: severe and symptomatic, or severe with LV changes.
Expect: the gold-standard investigation before CABG (coronary angiography) and what counts as a severe stenosis; tests of myocardial viability (dobutamine stress echo, thallium, PET, MRI); anatomical indications for CABG (left main, proximal LAD, triple-vessel disease with poor LV); components of the bypass circuit; how potassium cardioplegia arrests the heart in diastole; protamine reversal of heparin; median sternotomy as the standard incision and left thoracotomy for PDA and coarctation; LIMA to LAD as the best graft and long saphenous vein as the commonest; Allen's test; mechanical versus tissue valve choice and warfarin; the commonest prosthetic valve complication; and TAVI indications.
Quick revision
- Angiography is the gold standard; more than 70% diameter narrowing is severe.
- CABG for left main over 50%, proximal LAD, two/three-vessel disease with poor LV, and diabetics with multivessel disease.
- CPB: venous blood from the right atrium → reservoir → oxygenator → pump → ascending aorta.
- Cardioplegia: potassium, cold, antegrade or retrograde; diastolic arrest.
- Off bypass: de-air, defibrillate, pace, rewarm, protamine.
- LIMA to LAD best; long saphenous vein commonest; Allen's test before radial harvest.
- Mitral and tricuspid: repair if possible; aortic: replace; TAVI for high-risk.
- Mechanical = durable + lifelong warfarin; tissue = no lifelong warfarin + wears out.
Written by The House Job from standard references (Bailey & Love).
FAQ
Why does cardioplegia contain potassium?
A high potassium level depolarises the heart muscle membrane, so the heart stops in diastole and uses much less oxygen while the aorta is clamped.
Why is the internal mammary artery preferred to vein for the LAD?
It resists atherosclerosis and stays open far longer than vein grafts, which improves long-term survival and reduces reoperation.
What reverses heparin at the end of bypass?
Protamine, which binds heparin and neutralises it once the cannulae are removed.
Which valve would suit a young woman planning pregnancy?
Usually a repair or a tissue valve, because a mechanical valve needs lifelong warfarin, which harms the fetus and raises bleeding risk.