Cardioplegia: Stopping the Heart Safely

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Cardioplegia: Stopping the Heart Safely

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Forty minutes into an aortic valve replacement, the cross-clamp is on and the heart is arrested. Then a little electrical activity starts creeping back on the ECG. What do you do? Tell the surgeon — out loud, straight away — because that heart is waking up while it's still ischaemic. The anaesthetist is part of myocardial protection, even though the solution runs through the perfusionist's pump. This episode is cardioplegia from the top end of the table. We start with why it exists: the moment the aorta is clamped, the heart has no coronary flow, and a warm, beating, ischaemic heart runs out of energy in minutes. Cardioplegia makes planned ischaemia survivable in five ways — arrest, cool, empty, feed and buffer, and limit reperfusion injury — and arrest does most of the work. Then what's in the bag, grouped the way examiners like it: an arresting agent, buffers, osmotic agents and substrate. How potassium produces a depolarised arrest by inactivating fast sodium channels, and why that isn't quite a resting membrane. Why the commonest solution is 4:1 blood cardioplegia, and what blood adds over crystalloid. Warm versus cold as a real trade-off — and the hot shot that gets the heart ready before the clamp comes off. Delivery routes next. Antegrade into the aortic root as standard, direct into the ostia, or down the vein grafts. Retrograde through the coronary sinus for aortic regurgitation, aortic and root surgery, and severe coronary disease — with the 40 mmHg limit on coronary sinus pressure, why retrograde protects the right ventricle less well, and how to confirm the cannula on TOE. And why antegrade into a regurgitant root distends the ventricle instead of perfusing it. Then the seven complications — trauma, air, oedema, bleeding, difficulty restarting, electrolyte disturbance and inadequate protection — and how the last one really shows up: as a heart that comes off badly. del Nido, with its single long-acting dose, lidocaine and low calcium. Custodiol (HTK), which arrests the heart by taking the sodium away rather than adding potassium, and the price you pay in volume and dilution. And Laplace's law, which explains why a distended ventricle is dangerous and why we vent — during surgery, with a balloon pump, and on VA-ECMO. We finish with the anaesthetist's checklist during the cross-clamp, and what to be ready for when it comes off. Chapters (00:00) Cold open — the ECG wakes up during the cross-clamp(01:00) Why we need cardioplegia, and the five mechanisms(01:50) How much oxygen arrest and cooling save(02:30) What's in the bag(02:40) Potassium and the depolarised arrest(04:10) Buffers, osmotic agents and substrate(04:50) Blood versus crystalloid(05:40) Warm versus cold(06:30) The hot shot(07:00) Antegrade delivery(07:40) Retrograde delivery, and when you need it(08:00) Why antegrade fails with aortic regurgitation(08:40) The coronary sinus pressure limit, and the right ventricle(09:20) Confirming the retrograde cannula on TOE(10:00) The seven complications(12:20) del Nido(13:30) Custodiol (HTK)(15:00) Laplace's law, and why we vent(16:00) The anaesthetist's checklist during the cross-clamp(16:30) Wrap-up Key takeaways If electrical activity returns on the ECG during the cross-clamp, tell the surgeon straight away — the heart is working while ischaemicCardioplegia protects the heart in five ways: arrest, cool, empty, deliver substrate and buffering, and limit reperfusion injury — arrest does the heavy liftingContents fall into four groups: an arresting agent (usually potassium, with magnesium), buffers, osmotic agents and substrateHigh potassium raises the resting membrane potential and inactivates fast sodium channels — a depolarised arrest in diastoleBlood cardioplegia (4:1) adds oxygen carriage, buffering, free-radical scavenging and better microvascular flow, with less oedemaCold maximises metabolic suppression; warm supports aerobic metabolism; a warm "hot shot" before clamp removal prepares the heart for reperfusionRetrograde delivery via the coronary sinus is used for significant aortic regurgitation, aortic valve and root surgery, and severe coronary disease — keep sinus pressure below 40 mmHgRetrograde protects the right ventricle less well, so it's often combined with antegradeIn aortic regurgitation, antegrade root delivery distends the left ventricle — watch the LV on TOE and say if it's getting biggerComplications: trauma, air, myocardial oedema, bleeding, difficulty restarting, systemic electrolyte disturbance and inadequate protectiondel Nido (1 part blood to 4 crystalloid, with lidocaine and low calcium) gives a single dose lasting up to around 90 minutesCustodiol (HTK) arrests by sodium depletion — a hyperpolarised arrest — with long protection, but large volumes cause haemodilution and hyponatraemiaLaplace: wall tension rises with pressure and radius — which is why distension is dangerous and why we ventSolutions, doses and protocols are ...

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