Cardioplegia Principles And Problems. In: Sperelakis N, editor. Physiology and Pathophysiology of the Heart. Boston: Springer US; 1989. pp. 655-68. [DOI: 10.1007/978-1-4613-0873-7_32]

Hearts during ischemia with or without HTK-protection analysed by dielectric spectroscopy

OBJECTIVE

We investigated canine hearts during ischemia after aortic cross clamping (UI, n  =  20) and after HTK-cardioplegia (HTK, n  =  24) at 35 °C, 25 °C, 15 °C, and 5 °C with the aim to compare tissue changes caused by the activity of anaerobic metabolism(AAM), cell membrane destruction(CD), and gap junction uncoupling(GJU).

APPROACH

We measured continuously the complex dielectric spectrum(DS), ATP- and lactate content, extracellular pH, and rigor contracture. To identify changes in DS caused by AAM, CD, and GJU we performed additional experiments on the gap junction-free skeletal muscle. We used heart model simulations to calculate the effect of temperature.

MAIN RESULTS

AAM affected the DS at 10 MHz and we found a strong correlation between DS and the proton concentration with a maximum of DS at 10 mmol g^-1 dry weight in ATP-concentration. The time of GJU was detected by a characteristic increase in DS and CD by a characteristic decrease at 13 kHz. In comparison to UI, GJU, AAM and CD were delayed by HTK and by hypothermia, indicating a minimization of energy consumption and an improved preservation of tissue structure.

SIGNIFICANCE

The novel findings were that in UI at 5 °C GJU occurred earlier and AAM remained constant, indicating a less effective preservation in UI by deep hypothermia in contrast to HTK.

Preservation of cardiac myocytes subjected to different preconditions: a comparative morphometric study of beating, fibrillating, and cardioplegically arrested canine hearts

This study compares the ultrastructure of beating canine hearts with that of hearts subjected to different clinically common forms of cardiac arrest. The contraction state per test field was ascertained according to a specially developed classification. The volume density of myofibrils and the surface to volume ratio of mitochondria were used as parameters for cellular and mitochondrial swelling. Contraction bands were not found in any of the differently pretreated hearts. Following immersion fixation, contractions as well as over- and hypercontractions in beating, fibrillating, and St. Thomas-arrested hearts are significantly more pronounced than in HTK-arrested hearts. Cellular and mitochondrial volumes were similar in beating and fibrillating hearts. St. Thomas-perfusion significantly decreased cellular and mitochondrial volume compared to beating hearts, but these values were in the same range as in fibrillating hearts. Only HTK-solution actually led to a strong reduction of these compartments. Compared to immersion, perfusion fixation after coronary perfusion with cardioplegic solutions led to comparable cellular volumes, but significantly elevated the percentage of relaxed sarcomeres and significantly reduced mitochondrial swelling. The best structural preservation of myocytes was found after HTK-perfusion and perfusion fixation. Such ultrastructural quantitative and morphometrical parameters are powerful tools since results confirm that the degree of myocardial preservation depends on the method of cardiac arrest. This forms the basis for the choice of preconditions for subsequent ischemia. Furthermore, significant alterations of myocardial ultrastructure depend on a combination of the functional state of the heart, the method of cardioplegia, and the technique of fixation.

The effect of magnesium added to secondary cardioplegia on postischemic myocardial metabolism and contractile function--a 31P NMR spectroscopy and functional study in the isolated pig heart

This study investigated whether increasing the magnesium concentration during secondary cardioplegia improves postischemic myocardial recovery. Twenty-four isolated pig hearts were divided into four groups. All hearts were initially subjected to control perfusion with modified Krebs-Henseleit solution for 30 min, followed by a single infusion of St. Thomas' solution #2. The hearts were then maintained without perfusion at 12 degrees C for 4 h. Following this hypothermic preservation, the hearts in group I were reperfused with modified Krebs-Henseleit solution for 50 min, while hearts in group II and III were reperfused with a secondary cardioplegic solution containing 16 or 0 mmol/L magnesium, respectively, for 20 min followed by 30 min of perfusion with modified Krebs-Henseleit solution. In group IV, the hearts were initially reperfused with Krebs-Henseleit solution containing 16 mmol/L potassium for 20 min, followed by 30 min of reperfusion with modified Krebs-Henseleit solution. The changes in high-energy phosphates and intracellular pH were monitored throughout the experiments using 31P nuclear magnetic resonance (NMR) spectroscopy. Heart rate, left-ventricular systolic developed pressure, and rates of pressure increase and decrease were measured during control perfusion and reperfusion to calculate the percent contractile functional recovery. Needle biopsies for measurement of energy metabolites with high performance liquid chromatography were performed at the end of preservation and reperfusion to confirm the NMR measurements. All six hearts in group I showed significantly less recovery of contractile function during reperfusion when compared to the hearts in groups II, III, IV (p less than 0.05). There was no difference in either recovery of metabolism or mechanical function among the latter three groups of hearts. None of hearts in groups II, III, and IV showed ventricular fibrillation, which occurred in all six hearts of group I upon reperfusion. The results suggest that a short period of re-arrest perfusion following ischemia ("secondary cardioplegia") improves postischemic contractile functional recovery and prevents reperfusion-induced ventricular fibrillation. Increased magnesium concentration in the secondary cardioplegia did not provide additional benefit to the ischemic myocardium, possibly due to the low permeability of the sarcolemmal membrane to magnesium.

Ultrastructural effects induced by global ischaemia on the AV node compared with the working myocardium. A qualitative and morphometric investigation on the canine heart

The cardiac conduction system is considered to be particularly resistant to ischaemia. Nevertheless, following open heart surgery with short periods of ischaemia disturbances in AV conduction or ventricular arrhythmia have been reported. We compared the ultrastructure of AV node and working myocardium following 30 min global ischaemia at 25 degrees C, during pure ischaemia and with HTK cardioplegia qualitatively and morphometrically. After 30 min of pure ischaemia, interstitial and intracellular oedema together with considerable changes in organelles in AV nodes predominate over mainly cellular oedema in working myocardium. Sometimes irregular overcontractions of sarcomeres occur in the AV node, though very seldom in working myocardium. In pure ischaemia, mitochondrial swelling is comparable in both types of tissue. Following HTK cardioplegia and 30 min ischaemia, cellular oedema and mitochondrial swelling are significantly reduced in AV nodal cells and working myocardium, but remain more extensive in the AV nodes. Irregularities in the contractile state of sarcomeres are not observed. The extent of the ultrastructural alterations corresponds to the degree of metabolic change in the working myocardium. Thus, despite considerable differences during pure ischaemia and HTK cardioplegia, ultrastructurally the AV nodal cells do not display a greater resistance to ischaemia than working myocardium.

The surface to volume ratio of mitochondria, a suitable parameter for evaluating mitochondrial swelling. Correlations during the course of myocardial global ischaemia

Cellular changes occurring in the left ventricular myocardium during ischaemia after different methods of cardiac arrest have been evaluated by morphological and morphometric parameters: volume densities of mitochondria (VVMi), sarcoplasm (VVSp), myofibrils (VVMf), surface densities of mitochondria (SVMi). The surface to volume ratio of mitochondria (SVratioMi) has been used as an independent parameter of mitochondrial swelling. Since ischaemic swelling of myocardial cells increases the volume of the reference space and ischaemic swelling of mitochondria decreases the free sarcoplasm, VVMi and VVSp cannot be considered as reliable indicators of the degree of oedema. SVMi/VVMf remains nearly constant after different forms of cardiac arrest, demonstrating the integrity of mitochondrial outer membranes. The inverse linear ratio between SVratioMi and the mean mitochondrial volume indicates that the increase in mitochondrial volume is achieved by surface smoothing. Loss of matrix structure and fragmentation of cristae occur at an SVratioMi of about 5.8, cristolysis at 5.5 to 5.6 and amorphous matrix densities at an SVratioMi of less than 5.5 micron2/micron3. The SVratioMi is a suitable parameter for evaluating mitochondrial swelling both at the onset and during global myocardial ischaemia, independent of the method of cardiac arrest used. It serves as an indicator of the state of structural preservation of mitochondria during ischaemia.

The cardioplegic solution HTK: effects on membrane potential, intracellular K+ and Na+ activities in sheep cardiac Purkinje fibres

The effects of the cardioplegic solution HTK on membrane potential (EM) and intracellular K and Na activities (aiK, aiNa) were studied in sheep cardiac Purkinje fibres by means of conventional and ion-selective microelectrodes. HTK contains (mM): Na 15, K 10, Ca 0, Mg 4, histidine 180. (1) In control conditions EM was -74.3 +/- 3.3 mV (n = 25), aiK was 116.4 +/- 4.1 mM (n = 7) and aiNa was 8.2 +/- 1.4 mM (n = 15). (2) Exposure to HTK led to a depolarization to -59.7 +/- 3.6 mV (n = 25) which exceeded by about 5-7 mV that induced in a Tyrode solution of 10 mM K and in a modified HTK solution supplemented by 2 mM Ca (n = 6). (3) Addition of 0.5 mM barium eliminated the difference in the steady-state depolarization. (4) HTK superfusion increased aiK to 120.1 +/- 4.4 mM (n = 7) and decreased aiNa to 3.9 +/- 0.9 mM (n = 15). (5) The decrease in aiNa was insensitive to amiloride (1 mM) and to external alkalization but was slightly increased by addition of 2 mM calcium. (6) When the calcium in Tyrode solution was lowered from 2.0 mM to 0.05 mM, aiNa hardly decreased during subsequent exposure to unmodified HTK and it increased in the presence of 0.1 mM dihydroouabain. We propose the hypothesis (1) that the difference in membrane depolarization between HTK and a 10 mM K-Tyrode is caused by a decrease in K conductance by the HTK solution and (2) that the aiNa decline mainly results from a coupled Ca influx via Na-Ca exchange due to a delayed washout of external calcium.