Diltiazem as an adjunct to cold blood potassium cardioplegia: a clinical assessment of dose and prospective randomization

Effects on Reperfusion Injury of Adding Diltiazem to Tepid Blood Cardioplegia

BACKGROUND

Although the present techniques of myocardial preservation for limiting ischemia/reperfusion injury in open heart operations yield excellent results for most patients, certain subgroups of patients with advanced coronary artery disease present a challenge in terms of intraoperative safety.

METHODS

In a prospective, randomized, controlled study, we assessed the myocardial protective effects of a total dose of 150 +/- 150 = 300 microg/kg diltiazem added to induction and terminal (reperfusion) doses of tepid blood cardioplegia. We determined the myocardial morphological (ultrastructural) and enzymatic (serum assays for the cardiospecific isoenzyme of creatine kinase [CK-MB]) changes and functional recovery (atrioventricular [AV]-node recovery time and postoperative need for inotropic support) in patients undergoing elective coronary artery bypass operations. The determinations were made with respect to values for control patients, who received the same cardioplegia but without the addition of diltiazem.

RESULTS

The mean isoenzyme CK-MB levels and semiquantitative ultrastructural score values of the diltiazem group were significantly less than those of the control group. Although AV-node recovery time was significantly prolonged (P < .05), this factor did not have major clinical impact.

CONCLUSIONS

We concluded that the addition of 150 +/- 150 microg/kg diltiazem to the induction and terminal doses of tepid cardioplegia enhanced myocardial protection in elective aortocoronary bypass surgery in high-risk patients and presented no significant additional operative risk.

St Thomas Hospital Cardioplegia #2 fails to suppress slow reaction pacemaker cell electrical activity

BACKGROUND

Inadequate right atrial myocardial preservation during cardioplegic arrest may promote postoperative supraventricular arrhythmias (SVA). We determined (1). if oxygenated St. Thomas Hospital Cardioplegia #2 (STH2) alone causes slow reaction pacemaker cell (SR) quiescence; and (2). if hypothermia, higher [K(+)], lower [Ca(2+)], and verapamil in STH2 suppresses SR electrical activity.

MATERIALS AND METHODS

A glass microelectrode recorded SA node SR membrane action potentials (AP) in rabbits (n = 23, 1.93 +/- 0.45 kg) randomized to normothermic STH2 (33 degrees C, n = 6), hypothermia (20 degrees C, n = 4), hypothermic STH2 (22 degrees C, n = 3), lower calcium STH2 (n = 3), higher potassium STH2 (n = 4), and STH2 plus Verapamil (n = 3).

RESULTS

Normothermic STH2 depressed SR action potential amplitude and action potential duration (APD), but did not completely suppress action potential generation. Hypothermia alone prolonged APD and sinus cycle length and suppressed SR AP. STH2 with hypothermia (to 20 degrees C) completely suppressed propagating AP and STH2 plus 0.04 Ca(2+) mEq/L inhibited SR AP generation. STH2 plus 30 mEq K(+) and STH2 plus 2.5 mmol/L verapamil failed to generate SR AP.

CONCLUSION

STH2 cannot prevent SA node SR myocardial cells from low-amplitude AP autogeneration above 21 degrees C. STH2 with 30 mEq/L K(+), STH2 with 0.02 mEq/L Ca(2+), and STH2 plus 2.5 mmol/L verapamil can arrest AP generation in SR and potentially prevent postoperative SVA.

Protective effect of JTV519, a new 1,4-benzothiazepine derivative, on prolonged myocardial preservation

BACKGROUND

JTV519 is know to protect cardiomyocytes from calcium overloading-induced damage. The aim of this study was to investigate the potential protective effect of JTV519 on myocardium subjected to prolonged ischemia and the underlying mechanism of such protection. The effect of JTV519 was also compared with that of diltiazem, a 1,5-benzothiazepine derivative.

METHODS

Isolated rat hearts were randomly divided into three groups. Control hearts were arrested with histidine-tryptophan-ketoglutarat (HTK) cardioplegic solution alone. In the JTV519 group of hearts, cardiac arrest was achieved with JTV519 (10(-3) mmol/L) in the HTK solution. Hearts in the diltiazem group were arrested with diltiazem (0.5 mmol/L) in the HTK solution. All the hearts were then subjected to 6-hour storage in HTK solution at 4 degrees C.

RESULTS

After a 30-minute reperfusion, the left ventricular developed pressure in the JTV519 and diltiazem groups were improved significantly compared with the control group. There was a significantly lower left ventricular end-diastolic pressure level and higher recovery of coronary flow in the JTV519 group than in the control group. The postischemic intracellular calcium concentration was attenuated by adding JTV519 or diltiazem to HTK cardioplegia.

CONCLUSION

As an adjunct to cardioplegia, JTV519 showed a significant protective effect on myocardium undergoing 6 hours of ischemia. The beneficial protective effects of JTV519 are correlated with its ability to inhibit the postischemic rise in intracellular calcium.

Blood cardioplegia: a review and comparison with crystalloid cardioplegia

The Oxford International Symposium on myocardial preservation provided an appropriate milestone and impetus to survey one aspect of operative myocardial preservation, namely blood cardioplegia, and to contrast it with the more popular crystalloid cardioplegia. This review is by no means complete or exhaustive but represents my best effort to summarize important information that has accumulated in the literature as blood cardioplegia, and our understanding of it, has evolved. It is appropriate to compare blood and crystalloid cardioplegia with respect to biochemical and physiological differences. Clinical comparison has been limited, for the most part, to randomized studies, and a number of differences and details of clinical management of the two techniques have been omitted, either because they seemed unimportant or there was no good information that would allow an objective comparison of their significance. Hopefully, the reader will recognize the intent to focus on meaningful differences and similarities between the two techniques and to present them fairly.

Pretreatment with nicardipine preserves ventricular function after hypothermic ischemic arrest

Calcium antagonists have a protective effect on postischemic myocardial function when included in normothermic cardioplegia solutions. This effect varies with the calcium antagonist, but is generally lost under hypothermic conditions. The hypothesis tested was that a calcium antagonist would increase postischemic myocardial performance if given before the onset of hypothermic arrest. Isolated working rat hearts were used with an oxygenated modified Krebs-Henseleit buffer solution as a perfusion media. Rats were pretreated with 1 of 9 doses of a nicardipine solution (0 to 100 micrograms/kg, intraperitoneally) 20 minutes before excision of the heart. Nicardipine is a light-stable, water-soluble calcium antagonist with minimal myocardial depressant effects. The hearts were arrested for 25 minutes at 37 degrees C or 93 minutes at 24 degrees C with 20 mL of cardioplegia solution containing 0.05 mmol/L CaCl2. Postischemic performance and adenosine triphosphate content were used as determinants of efficacy. Eighty-three percent of 101 treated hearts recovered in contrast to a mortality of 50% in the 24 nontreated hearts. Pretreatment with 25 micrograms/kg significantly increased (p less than 0.05) the percent recovery (compared with the nontreated group) of the following variables of cardiac function: systolic pressure, 74% to 96% (37 degrees C), 76% to 90% (24 degrees C); cardiac output, 61% to 90% (37 degrees C), 62% to 84% (24 degrees C); stroke work, 49% to 95% (37 degrees C), 50% to 92% (24 degrees C); and adenosine triphosphate, 76% to 87% (37 degrees C), 58% to 68% (24 degrees C). Progressive increases in postischemic function at 37 degrees and 24 degrees C were seen as the dose of nicardipine was increased from 0 to 25 micrograms/kg and decreased function was seen with a pretreatment dose greater than 25 micrograms/kg of nicardipine. Pretreatment with nicardipine significantly improved postischemic myocardial performance under hypothermic conditions and should be administered or at least not discontinued before cardiac operations.

Myocardial protection: what the surgeon does

With changing patient demographics resulting in greater risk of myocardial ischemia, avoidance of low-output states must begin with patient selection. From that point, a variety of well-established surgical techniques can be used to provide myocardial protection. Hypothermia and cardioplegia are fundamental among these; however, it should be recognized that alternate approaches must be considered. The well-documented deleterious effects of overdistension and hypoperfusion must be borne in mind. To this is added the complex formulation of contemporary cardioplegic solutions based on thorough understanding of the pathophysiology of ischemic injury. Specific deleterious consequences of ischemia and/or hypothermia are abnormalities of tissue volume regulation, lack of high-energy substrate availability, reduced capacity for postischemic oxidative metabolism, depressed availability of high-energy phosphate precursors, and the potential damage done by oxygen-induced free-radical-mediated oxidant injury.