The Different Types of Cardioplegia Explained

Cardioplegia is a chemical solution delivered to the heart during open-heart surgery to stop it from beating, giving surgeons a still, bloodless field to work on while protecting the muscle from damage. There is no single “best” cardioplegia. Instead, surgical teams choose from a range of solution types, temperatures, delivery routes, and dosing schedules, each with trade-offs that matter depending on the patient and the operation. The variety can seem bewildering, but the underlying logic is straightforward once you see how each variable affects the heart.

Why the Heart Needs Protection in the First Place

When a surgeon clamps the aorta to operate on the heart, blood flow to the heart muscle itself stops. Without intervention, the oxygen-starved muscle would suffer severe injury within minutes. Cardioplegia addresses this by doing two things at once: it arrests the heart electrically so it stops contracting (a beating heart burns through energy far faster than a still one), and it delivers ingredients meant to keep cells alive during the period of reduced or absent blood flow. The challenge is that the arrest itself can cause harm. For over four decades, the standard approach has used high concentrations of potassium to stop the heart, but that method has been linked to ionic imbalances, coronary spasm, arrhythmias, and a phenomenon called contractile stunning, where the heart struggles to regain normal pumping after surgery.¹ Much of the innovation in cardioplegia over the past few decades has been an effort to minimize those side effects.

Crystalloid Versus Blood Cardioplegia

The most fundamental distinction in cardioplegia is between crystalloid and blood-based solutions. Crystalloid cardioplegia is essentially an electrolyte solution, sometimes with added buffers or nutrients, mixed in a lab without any blood component. Blood cardioplegia mixes the patient’s own blood with a concentrated additive containing potassium and other agents. The blood acts as a carrier that delivers oxygen and nutrients to the arrested heart, which crystalloid solutions cannot do on their own.

A meta-analysis of randomized trials found that blood cardioplegia provides better myocardial protection than crystalloid, with lower rates of low-output syndrome and smaller early rises in markers of heart-muscle damage, though the rates of heart attack and death were similar between the two.² Despite that edge, crystalloid solutions remain widely used because they are simpler to prepare, less expensive, and in many routine operations the clinical outcomes end up comparable. One trial comparing warm blood cardioplegia and cold crystalloid cardioplegia in coronary bypass patients found that cardiac enzyme release and most clinical outcomes were similar between the groups.³ So the theoretical advantage of blood does not always translate into a measurable difference at the bedside, particularly for shorter, less complex operations.

Temperature Strategies

Cardioplegia can be delivered cold (typically around 4–10 °C), tepid (around 29 °C), or warm (close to body temperature at 37 °C). Cooling the heart slows its metabolism, which means it needs less oxygen while the clamp is on. Cold cardioplegia has been the traditional standard for exactly that reason: a colder heart tolerates longer periods without blood flow.

Warm blood cardioplegia took hold in the 1990s after proponents argued that maintaining normal temperature avoids the cellular stress of cooling and rewarming. Monitoring studies have shown that both warm and cold blood cardioplegia maintain aerobic metabolism in the arrested heart, with tissue oxygen levels rising and consumption falling during arrest, while tissue pH stays in the normal range.⁴ In practice, many surgeons use a hybrid approach: cold cardioplegia for most of the operation, then a warm “hot shot” of blood cardioplegia just before removing the aortic clamp to help the heart resume beating smoothly.

Where It Goes In

The route of delivery matters because the heart has to receive the solution evenly. There are two main paths. Antegrade delivery pumps cardioplegia into the aortic root, so it flows forward through the coronary arteries the same way blood normally travels. Retrograde delivery threads a catheter into the coronary sinus (a large vein on the back of the heart) and pushes the solution backward through the venous system.

Each route has blind spots. In an animal model simulating a blocked coronary artery, antegrade cardioplegia cooled the right ventricle well but failed to cool the territory downstream of the blockage, and functional recovery in that region was poor. Retrograde cardioplegia cooled the left ventricle more evenly but was inconsistent in the right ventricle.⁵ For patients with significant coronary artery disease, many surgeons now alternate between antegrade and retrograde delivery so that the entire heart muscle gets covered. A study comparing intermittent antegrade-only delivery with continuous combined antegrade-and-retrograde delivery concluded that the combined approach appeared to protect the heart better.⁶

Continuous Versus Intermittent Dosing

A separate decision is whether to keep cardioplegia flowing throughout the arrest period (continuous delivery) or to give it in repeated boluses every 15–20 minutes (intermittent delivery). Continuous delivery sounds ideal because the heart never goes without the protective solution, but it has a practical downside: the constant stream of fluid can obscure the surgical field, making delicate work harder. Intermittent delivery gives surgeons dry intervals to operate, then tops up the heart before ischemia accumulates.

When coronary arteries are severely blocked, continuous antegrade delivery loses much of its theoretical edge because the solution cannot reach the tissue behind the blockage anyway. One study found that in the presence of a coronary occlusion, continuous and intermittent antegrade cardioplegia produced nearly identical tissue temperatures and pH levels, with no meaningful difference in wall-motion recovery.⁷ So the choice often comes down to surgeon preference and the specific anatomy: if the coronaries are open and the surgeon wants maximum protection, continuous delivery has appeal; if blockages are present or the operation requires a clear field, intermittent dosing with retrograde supplementation is a common compromise.

Named Solutions and How They Differ

Several branded or widely recognized cardioplegia formulations have become shorthand in operating rooms around the world. Each reflects a different philosophy about what the arrested heart needs.

Del Nido Cardioplegia

Originally developed for pediatric heart surgery at Boston Children’s Hospital, del Nido cardioplegia has crossed over into adult practice. It is a blood-crystalloid mixture (typically a 1:4 ratio of blood to crystalloid) containing potassium, magnesium, mannitol, sodium bicarbonate, and lidocaine. A key selling point is that a single dose can keep the heart arrested for up to about 90 minutes, eliminating or reducing the need for repeated doses and allowing the surgeon to work uninterrupted.

A meta-analysis of ten randomized trials involving over 1,800 adult patients found that del Nido was associated with shorter aortic cross-clamp times by about nine minutes, a significantly lower rate of needing defibrillation after the clamp came off (around 15% versus 38% with conventional solutions), and a lower rate of postoperative stroke, with no difference in mortality.⁸ Another meta-analysis comparing del Nido specifically to cold blood cardioplegia confirmed the higher rate of spontaneous heartbeat return and lower cardioplegia volume, though most clinical endpoints like hospital stay and mortality were comparable.⁹

In pediatric patients, the advantage can be even more striking. A retrospective comparison of del Nido and St. Thomas solutions in children found that the rate of needing defibrillation after clamp removal was about 4% with del Nido versus nearly 27% with St. Thomas. In the smallest patients (under 6 kg), the gap was roughly 1% versus 18%.¹⁰

Custodiol (HTK Solution)

Custodiol, also known as histidine-tryptophan-ketoglutarate (HTK) solution, takes a different approach. It works by depleting extracellular sodium and calcium rather than flooding the heart with potassium. This mechanism arrests the heart through a process sometimes called hyperpolarization, which is closer to the cell’s natural resting state. Custodiol is also a single-dose solution, giving reliable arrest for extended periods, which makes it popular for long, complex operations and for minimally invasive surgery where re-dosing is technically awkward. One study found that single-dose Custodiol and single-dose St. Thomas cardioplegia provided comparable protection during minimally invasive mitral valve surgery through a small right-chest incision, even with ischemic arrest times exceeding one hour.¹¹ Similarly, a comparison in patients undergoing surgery through a right mini-thoracotomy found no significant differences in myocardial protection between Custodiol and cold blood cardioplegia.¹²

Custodiol has one well-known quirk that operating teams need to watch for: because it is a very low-sodium solution delivered in large volumes (often over a liter), it can cause a sharp drop in blood sodium levels. A retrospective study found that all patients receiving HTK solution developed hyponatremia, with serum sodium falling by an average of 15 mmol/L. The condition was isotonic, meaning overall blood concentration stayed stable, but the accompanying metabolic acidosis requires monitoring.¹³

St. Thomas Solution

St. Thomas solution is one of the earliest standardized crystalloid cardioplegias, developed at St. Thomas’ Hospital in London. It uses potassium, magnesium, and procaine to arrest and protect the heart. Multiple generations of the formula exist (St. Thomas I and II), and it remains a workhorse in many centers worldwide. Its long track record provides extensive safety data, but it typically requires repeat dosing every 20–30 minutes, which is one reason newer single-dose alternatives have gained ground for longer procedures.

Microplegia

Microplegia refers to a highly concentrated cardioplegia additive mixed with a very small volume of the patient’s own blood, essentially “all blood, minimal crystalloid.” The goal is to minimize the fluid load delivered to the patient, which can reduce hemodilution (thinning of the blood) and the need for blood transfusions. A systematic review and meta-analysis found that microplegia led to a significantly higher rate of spontaneous heartbeat return compared with conventional cardioplegia and a lower need for drugs to support heart function after surgery.¹⁴ Microplegia is especially attractive in smaller patients and in operations where surgeons want to keep fluid volumes low, such as minimally invasive procedures.

Metabolic Additives

Some centers enrich their cardioplegia with amino acids, particularly glutamate and aspartate, based on the idea that these molecules can serve as alternative fuel for heart cells when oxygen is scarce. Animal studies and limited clinical data have suggested that these amino acids have protective properties during ischemia.¹⁵ However, clinical results have been mixed. One study of patients with reduced heart function found that while glutamate and aspartate supported metabolic activity, they did not improve the heart’s functional recovery after surgery.¹⁶ An animal study looking at whether these amino acids could rescue already-stunned hearts found no improvement in high-energy phosphate recovery or oxygen consumption, raising questions about the practical benefit.¹⁷ The idea remains physiologically plausible, but the evidence has not coalesced enough to make amino acid enrichment a standard practice.

Other experimental additives are under investigation. A rat-heart study tested a PARP-1 inhibitor (a molecule that limits a specific cellular stress response) added to cardioplegia and found significantly better functional recovery and lower markers of oxidative damage during reperfusion.¹⁸ This is early-stage work, but it illustrates the direction the field is heading: tailoring cardioplegia chemistry to interrupt the specific molecular pathways that cause damage.

Hyperpolarizing Arrest

Standard potassium-based cardioplegia stops the heart by depolarizing it, essentially flooding the cells with potassium so they lock in an activated state. This works, but it leaves ion channels in an unnatural configuration that can promote calcium overload and other problems. Hyperpolarizing cardioplegia takes the opposite approach: it uses drugs that open certain potassium channels to push the cell membrane toward its natural resting potential, arresting the heart in a more relaxed state. Early laboratory work showed that a drug called aprikalim could produce predictable, sustainable hyperpolarized cardiac arrest that reversed cleanly when blood flow was restored.¹⁹ Despite decades of laboratory interest, hyperpolarizing cardioplegia has not yet entered routine clinical use, partly because the available drugs have systemic effects (like blood-pressure drops) that complicate their use in a patient on a heart-lung machine. Researchers continue to refine the pharmacology, and the concept remains one of the most intellectually appealing alternatives to the potassium-based status quo.

Pediatric Hearts Are Not Small Adult Hearts

Children’s hearts are structurally and metabolically different from adults’ in ways that change how cardioplegia should be handled. The immature myocardium is more sensitive to calcium overload during reperfusion, which is one of the main mechanisms of injury when the clamp comes off.²⁰ Pediatric-specific cardioplegia strategies address this by including calcium-buffering agents or by formulating solutions that reduce intracellular calcium buildup. In a laboratory comparison, cardiomyocytes exposed to a pediatric-specific formula had lower calcium levels during arrest and early reperfusion, and the cells were fully arrested rather than continuing to twitch as they did with adult formulations.²¹ Del Nido’s origins in pediatric surgery are no coincidence: its lidocaine and magnesium content address exactly this vulnerability. The broader lesson is that applying a one-size-fits-all cardioplegia strategy across all age groups overlooks real biological differences.

The Hypertrophied Heart

Patients with conditions like aortic valve disease often develop thickened heart walls. This hypertrophied muscle is harder to protect during surgery because the thicker wall means cardioplegia has to penetrate deeper, the oxygen demand is higher, and the subendocardial layers (the innermost part of the wall) are already at risk of being under-supplied even before the clamp goes on. Standard techniques are routinely applied regardless of pathology, but different cardiomyopathies respond differently to ischemia and reperfusion.²² One animal study comparing three types of cardioplegia in hypertrophied pig hearts found that an oxygenated fluorocarbon-based solution outperformed both blood and crystalloid cardioplegia during prolonged clamping.²³ Although fluorocarbon-based solutions never became mainstream, the study underscores a real clinical problem: the thicker the wall, the more carefully the team has to think about oxygen delivery, temperature control, and re-dosing intervals.

Cardioplegia Beyond the Operating Room

Cardioplegia chemistry also plays a role in organ transplantation. Donor hearts are currently preserved using static cold storage, where the heart is flushed with a cold preservation solution (often a cardioplegia-type formula) and packed on ice for transport. Custodiol, in fact, doubles as a transplant preservation fluid, which is one reason it was developed in the first place. The limitation of static cold storage is that prolonged cold ischemia raises the risk of early graft dysfunction once the heart is implanted. Newer machine-perfusion devices pump oxygenated solution or blood through the donor heart continuously during transport, keeping it metabolically active. Early evidence suggests that machine perfusion is comparable to cold cardioplegia for preservation and has the added advantage of allowing the transplant team to assess how well the heart is functioning before committing to implantation.²⁴ This technology could eventually expand the pool of usable donor hearts by salvaging organs that would have been discarded under older preservation methods.

How Surgeons Actually Choose

With so many variables (solution type, temperature, route, dosing schedule, and named formulation), you might wonder how a surgical team picks the right combination. In practice, most centers adopt a house protocol that reflects the lead surgeon’s training and the institution’s experience. A straightforward coronary bypass in a patient with normal heart function might use intermittent cold blood cardioplegia delivered antegrade, because it is well-studied and simple. A complex valve repair expected to take two or three hours might call for del Nido or Custodiol to avoid repeated interruptions for re-dosing. Minimally invasive surgery through a small incision often favors single-dose solutions because accessing the heart to re-dose is difficult. Pediatric operations lean toward del Nido or purpose-designed pediatric formulations. And in patients with thick, hypertrophied hearts, the team may combine retrograde delivery with shorter re-dosing intervals to ensure the inner wall layers stay protected.

The field continues to evolve. Modified del Nido formulations using different base fluids are already being tested in randomized trials, and researchers are exploring whether adjusting lactate levels or adding novel protective agents can squeeze out incremental gains.²⁵ The overarching trend is toward personalization: matching the cardioplegia strategy to the patient’s anatomy, the operation’s expected duration, and the specific vulnerabilities of the heart being protected, rather than relying on a single default recipe.