Introduction

Myocardial protection is a key component of successful cardiac surgery. Universal method of cardioplegia for prevention of ischemic myocardial damage has been searched since the 1950s of the 20th century. Despite certain diversity of data on cardioplegia, there is no clear consensus on solutions and technique of perfusion in different groups of patients [1, 2].

Types of cardioplegia differ depending on the presence of blood (blood or crystalloid) and temperature of solution (warm or cold). Warm cardioplegia always contains blood. Moreover, there are types of cardioplegia with different duration of cardiac protective effect. Short-term protection (up to 30 min) is usually ensured by warm blood cardioplegia. The choice of cardioplegia solutions with long-term safe cardiac arrest (≥ 90 min) is still limited. Bretschneider solution (“Custodiol”) is used for this purpose in Europe and Russia.

Cardioplegic solutions are divided into intracellular and extracellular ones depending on concentration of sodium and potassium. Extracellular solutions have high concentrations of potassium, magnesium and sodium, while intracellular solutions are characterized by low levels of electrolytes. In particular, concentration of sodium corresponds to its content in cellular cytoplasm. Sodium concentration in extracellular solutions is close to its level in interstitial fluid. Intracellular solutions often require rarer infusions and have high protective properties. However, there is a significant drawback: recovery of cardiac contractility is slow and requires additional period of cardiopulmonary bypass after myocardial reperfusion. Most likely, this is due to slow restoration of ionic composition in myocardial interstitium and cytoplasm of cardiomyocytes.

Custodiol as intracellular solution reduces concentration of sodium and calcium causing cardiac arrest by preventing depolarization of cell membranes. Histidine is a buffer increasing efficiency of anaerobic glycolysis. Ketoglutarate supplies ATP during reperfusion. Tryptophan stabilizes cell membranes. Mannitol as osmotic diuretic reduces cellular edema and promotes scavenging of free radicals reducing ischemic damage. Custodiol is successfully used for preservation of the heart and other organs after their harvesting for subsequent transplantation, as well as in pediatric cardiac surgery for congenital heart defects. It is a “standard” of conservation providing long-term and safe period of anoxia. Importantly, this is not always advisable in surgical practice because the vast majority of interventions can be performed within 1.5-2 hours of aortic cross-clamping.

Blood cardioplegia with potassium is still the most popular in adults. The advantages of blood cardioplegia include high oncotic properties preventing intracellular edema, buffering capacity, rapid cardiac arrest in oxygen enriched environment, periodic re-oxygenation with elimination of metabolites and high energy phosphate retention. The reverse side is a short period of safe anoxia (up to 20-30 min). Repeated or even multiple infusions are required that creates certain inconvenience for surgeon and can cause injury of coronary ostia.

In 1995, the researchers from the University of Pittsburgh presented a new solution for cardioplegia [3]. The technique implied a single injection of a modified depolarizing solution. Solution of autologous blood and crystalloids (Del Nido cardioplegia) provided long-term safe myocardial anoxia. It is believed that this solution promotes preservation of intracellular high-energy phosphates and maintenance of intracellular pH, as well as reduces calcium flow inside the cells during and after ischemia [4, 5].

Del Nido solution was created for neonatal and pediatric cardiac surgery. Basic solution is enriched with potassium and does not contain calcium. Solution also includes electrolyte composition similar to extracellular fluid, lidocaine (sodium channel blocker inhibiting negative effects of hyperkalemic depolarization), mannitol (reduces post-ischemic myocardial edema and eliminates free radicals) and other additives such as magnesium sulfate (calcium channel blocker) or potassium chloride. The last ones reduce concentration of intracellular calcium, cellular metabolism, energy consumption and myocardial excitability [6, 7]. Crystalloid component is mixed with autologous oxygenated blood (4:1). O’Blenes S. et al. [8] showed that Del Nido cardioplegia prevents spontaneous myocardial contractions during asystole caused by calcium ions, reduces troponin release and provides excellent myocardial protection in experiment. These benefits can contribute to myocardial protection in adults. Del Nido cardioplegia was originally developed for pediatric practice due to the differences between immature and mature myocardium. Numerous observational studies have shown that Del Nido solution is safe and effective in adults [9—11].

Importantly, the vast majority of studies, including those devoted to isolated aortic valve replacement, have no specific indications of severity of myocardial hypertrophy. This issue is extremely important for cardioplegia and can affect perioperative period. There are few literature data on morphological and ultrastructural assessment of myocardium in different periods of surgery. Visualization of destruction and reversibility of ischemic processes depending on the type of cardioplegia can be useful for development of a personalized algorithm for myocardial protection.

The purpose of the study was to compare two methods of myocardial protection in patients with severe myocardial hypertrophy caused by aortic stenosis or hypertrophic cardiomyopathy.

Material and methods

Prospective randomized single-center study included 17 patients between January, 2022 and December, 2022. Inclusion criteria: myocardial hypertrophy due to aortic stenosis or hypertrophic cardiomyopathy (HCM), elective cardiac surgery (aortic valve replacement (AVR) or septal myectomy (SME)), informed consent. Exclusion criteria: redo cardiac surgery, combined surgery, left ventricular ejection fraction (LV EF) < 30%, LV end-diastolic volume (LV EDV) ≥ 250 ml, previous allergic reaction to one or more components of cardioplegia solution, refusal of the patient to participate in the study. Patients were randomized depending on technique of cardioplegia: group A (Del Nido, n=9) and group B (Custodiol, n=8).

We analyzed perioperative clinical characteristics, laboratory and intraoperative histological data. The primary endpoints were rhythm recovery and number of defibrillations after aortic clamp release, troponin I at several time points (induction of anesthesia, 2 hours after cardiopulmonary bypass, 12 and 24 hours after admission to intensive care unit), perioperative myocardial infarction (considering objective data and underlying disease) and the need for inotropic and vasopressor support. Secondary endpoints: CPB and aortic cross-clamping time, transesophageal echocardiography data, ventilation time, length of ICU- and hospital-stay. Intraoperative biopsy was performed before cardioplegia, 20 min later, before suturing of aorta and 20 min after reperfusion. Myocardial specimens were stained using HBFP method (hematoxylin-basic fuchsin-picric acid) to identify acute ischemic and metabolic damage.

After aortic cross-clamping, antegrade selective or non-selective cool cardioplegia was administered depending on severity of aortic regurgitation. Body temperature during CPB was maintained within 33-34°C.

Custodiol was administered at a rate of 1 ml per 1 g of estimated heart weight. Baseline perfusion pressure in aortic root was 100-110 mm Hg, after cardiac arrest — 40-50 mm Hg. Perfusion time was at least 6-8 min to achieve concentration and temperature equilibrium in the myocardium.

Del Nido cardioplegia solution included Ionoplasm 1000 ml (similar to original Plasma-Lit solution in ionic composition), mannitol 20% 16.3 ml, magnesium sulfate 50% 4 ml, sodium bicarbonate 8.4% 13 ml, potassium chloride 15% 13 ml, lidocaine 1% 13 ml, oxygenated blood and crystalloid solution 1:4 [7]. Solution was prepared immediately before surgery. Next, solution was placed in a refrigerator and cooled to 5°C. Blood was added to crystalloid solution immediately before coronary perfusion. Primary dose of Del Nido cardioplegia was 20 ml/kg (but not more than 1 liter) with perfusion throughout 2-3 min.

There were no demographic and anthropometric between-group differences (Table 1). There were 6 (66.7%) women and 3 (33.3%) men in group A, 4 (50%) women and 4 (50%) men in group B.

Table 1. Demographic and anthropometric characteristics of patients

Analysis of echocardiography data revealed no differences. All patients had severe myocardial hypertrophy without decompensation of the underlying disease and LV dilatation (Table 2). To objectify LV wall hypertrophy, we used the index of LV wall thickness, i.e. the ratio of sum of IVST and PWT to transverse LV size. This indicator was slightly higher in patients with HCM compared to patients with aortic stenosis (0.84±0.21 vs. 0.63±0.14, p<0.05). However, there were no differences between the groups of cardioplegia.

Table 2. Preoperative echocardiography data

SME and AVR were performed in 8 (88.9%) and 1 (11.1%) patient in the first group, respectively. In the second group, these procedures were carried out in 4 (505) and 4 (50%) patients, respectively.

Statistical analysis

Statistical analysis was performed using the IBM SPSS Statistics version 23.0. Quantitative data are presented as means with standard deviations or median with interquartile range. Categorical data are presented as absolute values and percentages (%). Distribution normality was analyzed using the Shapiro-Wilk and Kolmogorov-Smirnov tests. Considering small sample size and significant heterogeneity of parameters in each group, we used Mann-Whitney and Fisher’s exact tests. Differences were significant at p-value < 0.05.

Results

There were no significant between-group differences regarding CPB and aortic cross-clamping time (Table 3).

Table 3. Intraoperative characteristics

CPB time was higher in group B that may be due to the absence of spontaneous rhythm recovery in 25% of cases and repeated defibrillations. In the second group, there were 10 (max) defibrillation discharges in one patient. Group A showed significantly higher percentage of spontaneous rhythm recovery (66.7 vs. 25%, p=0.047).

Intraoperative echocardiography data were similar (Table 4).

Table 4. Intraoperative echocardiography data

None patient required inotropic or mechanical circulatory support. In Del Nido group, 2 patients developed vascular insufficiency in post-perfusion period that required norepinephrine infusion (p=0.57). In Custodiol group, a similar situation was noted in 1 patient (p=0.28). Vascular insufficiency was defined as need for norepinephrine > 100 ng/kg/min. All patients with vascular failure were transferred to the ward on the first postoperative day. The maximum duration of norepinephrine infusion was 18 hours in one patient. There were no significant between-group differences in overall intraoperative hydrobalance (p=0.27).

Intraoperative pacing was not necessary in group A. In group B, two patients required pacing in post-perfusion period due to sinus or nodal bradycardia (p>0.05). In group A, two patients had postoperative cardiac arrhythmias (left bundle branch block) without troponin I elevation. These data may be associated with a large percentage of septal myectomy in this group (88.9%).

Baseline troponin I was normal in both groups (0 vs. 0.1 ng/mL, p=0.181). Troponin I in 2 (p=0.689), 12 (p=0.328) and 24 hours after CPB (p=0.607) was similar in both groups and tended to decrease one day after surgery (Fig. 1).

Fig. 1. Troponin I at different stages.

There were no surgical complications in both groups. ICU-stay differed due to delirium in one patient of the second group. Length of hospital-stay was similar (Table 5).

Table 5. Length of ICU-stay and hospital-stay

Histological analysis of myocardial tissue before cardioplegia revealed signs of cardiomyocyte hypertrophy, dystrophic lesions and stromal sclerosis in both groups. Patients with HCM had more severe dystrophic lesions, thicker vascular walls, metabolic signs of chronic hypoxia of cardiomyocytes, disordered arrangement of myofibrils and perinuclear halo. The most severe morphological changes were observed in 20 min after reperfusion. Both groups were characterized by interstitial edema (66.7% vs. 75%, p>0.05) and mild decrease in glycogen concentration (44.4% versus 50%, p>0.05). Before suturing the aorta and after restoration of cardiac contractility, stromal edema was observed in 77.8% and 75% of cases, respectively (p>0.05). Signs of necrobiosis were absent (Fig. 2, 3).

Fig. 2. Myocardium before cardioplegia.

a — patient with aortic stenosis; b — patient with hypertrophic cardiomyopathy (HCM). In the HCM group, there were cardiomyocytes with large, bizarrely shaped hyperchromic nuclei. Hypertrophy and dystophytic changes in cardiomyocytes and cardiac sclerosis in both groups (van Gieson staining, ×400).

Fig. 3. Myocardium in 20 min after blood flow release.

a — Custodiol cardioplegia; b — Del Nido cardioplegia. Interstitial and intracellular edema, ischemic damage to cardiomyocytes (contracture damage, fragmentation of myofibrils, changes in tinctorial properties of cytoplasm) (staining with hematoxylin and eosin, ×200).

Discussion

In this pilot study, we compared Del Nido cardioplegia and Custodiol for myocardial protection in patients with severe myocardial hypertrophy. In our opinion, no significant between-group differences in several parameters is a favorable sign. Certain equivalence of clinical, biochemical and histological parameters, no perioperative myocardial infarctions and the need for inotropic support in both groups suggest that Del Nido cardioplegia may be an alternative to Custodiol in patients with severe myocardial hypertrophy.

There are few available studies comparing Del Nido cardioplegia and Custodiol. Talwar S. et al. [12] compared Del Nido cardioplegia and Custodiol in pediatric patients with tetralogy of Fallot in a prospective randomized controlled trial (N=100). Del Nido cardioplegia was characterized by more stable cardiac index, shorter duration of mechanical ventilation, shorter ICU- and hospital-stay, less need for inotropic support and lower troponin I. Electron microscopy revealed less myocardial edema, better preservation of myofibrillar architecture and glycogen stores in Del Nido group.

Del Nido cardioplegia has several advantages. In particular, this method provides myocardial protection for a long time (> 90 min) after a single injection [11]. Del Nido cardioplegia prolongs the intervals between infusions and provides adequate myocardial protection. In fact, a single infusion of Del Nido solution should suffice for most cardiac surgeries [8].

Stable cardioplegia is an important part of myocardial protection strategy. Del Nido cardioplegia includes lidocaine (class 1b antiarrhythmic agent). The last one blocks sodium channels, prolongs refractory period and reduces negative consequences of myocardial arrest via decrease of intracellular concentration of sodium and calcium. Crystalloid solution does not contain calcium, and magnesium sulfate reduces intracellular concentration of calcium via competitive blockade of calcium passage of through the membrane.

In a systematic review, Chan J. et al. [13] evaluated the efficacy and safety of crystalloid (Del Nido and Custodiol) and blood cardioplegia in minimally invasive cardiac surgery. The authors established this objective in context of almost complete absence of the need for repeated cardioplegia in the group of crystalloid solutions and potential reduction of CPB time. The primary endpoint was in-hospital or 30-day mortality. The study included 9 articles. Del Nido cardioplegia was associated with less volume of solution compared to blood cardioplegia (1105.6 ± 123.47 vs. 14.8 (Del Nido) vs. 138.1 ± 21.3 (Custodiol) vs. 119.4 ± 26.9 min (blood cardioplegia, p<0.001) and aortic cross-clamping (75.0 ± 18.6 vs. 82.0 ± 17.3 vs. 93.7 ± 8.9 min, respectively, p < 0.001). In-hospital/30-day mortality and incidence of atrial fibrillation and stroke were similar. Finally, no difference was found between blood and crystalloid cardioplegia in adult minimally invasive cardiac surgery. The authors concluded that the choice of cardioplegia in minimally invasive cardiac surgery is determined by surgical preferences.

There are few national literature data on Del Nido cardioplegia. Krichevsky L.A. et al. [14] compared perioperative data in patients undergoing Del Nido, warm Calafiore blood and crystalloid cardioplegia with Custodiol and Consol. Parameters of post-perfusion central hemodynamics, postoperative left ventricular function and serum lactate at the end of surgery were similar. Del Nido cardioplegia was followed by less need for epinephrine (p<0.05), and inotropic/vasopressor support was short-term (p<0.1). However, these findings did not lead to any between-group differences in duration of mechanical ventilation, ICU-stay and in-hospital mortality. There were lower levels of total creatine phosphokinase and MB fraction after Del Nido cardioplegia. Their postoperative increment was also less significant in the same group (p<0.05). The authors concluded that Del Nido cardioplegia was accompanied by lower degree of myocardial damage, less active inotropic and vasopressor therapy. Nevertheless, overall results of cardiac surgery were similar.

Analyzing these data, we can emphasize several aspects. Several studies have found benefits of Del Nido cardioplegia regarding certain intraoperative and early postoperative parameters, including cardiac markers. However, there are usually no differences in clinical outcomes, including morbidity and mortality, with other cardioplegia techniques. We can conclude that Del Nido cardioplegia provides adequate myocardial protection with less intraoperative tissue damage. The latter may also be important for clinical outcomes in certain high-risk patients.

A comprehensive analysis of myocardial contractility after reperfusion (echocardiography and, in particular, speckle tracking) may be interesting. Global strain is a very sensitive marker of subendocardial contractility.

Importantly, there are no specific indications on severity of myocardial hypertrophy regarding intraoperative protection in majority of studies including those devoted to isolated aortic valve replacement. This aspect is also the cornerstone when choosing a cardioplegia technique. Moreover, there are few data on morphological assessment of myocardium in different periods of surgery. Visualization of cardiomyocyte destruction and analysis of reversibility of ischemic processes can be useful to develop the concept of a personalized choice of cardioplegia.

The positive side of our study is myocardial biopsy at several stages in each patient. Histological examination confirmed severe myocardial hypertrophy in all patients and absence of irreversible ischemic lesion after cardiac arrest and in 20 min after reperfusion. Interstitial edema was found in many specimens. Edema regressed in early postoperative period and did not affect cardiomyocyte function.

Further large-scale analysis of myocardial hypertrophy regarding appropriate cardioplegia will reveal the advantages and disadvantages of a particular cardioplegia technique. This will expand the indications, reduce economic costs and improve outcomes after cardiac surgery.

The authors declare no conflicts of interest.