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Magnesium ion is beneficial in hypothermic crystalloid cardioplegia
LITERATURE REVIEW Frederick W. Campbell, MD, Editor
SCIENTIFIC ARTICLES
Mowseri M, Meir G, Lotan C, et al: Coronary pathology predicts conduction disturbances after coronary artery bypass grafting. Ann Thorac Surg 51:248252,199l The authors related preoperative coronary angiograms and postoperative cardiac conduction in 55 consecutive patients undergoing coronary artery surgery. Thirty-five patients with either no lesion or a discreet left anterior descending coronary artery (LAD) lesion proximal to and not involving the septal perforator had no major conduction disturbances after surgery. Eleven of 20 patients with an LAD lesion at the origin of the first septal branch or lesions distal to the branch had major conduction disturbances: right bundle branch block (1 patient), right bundle branch block-left anterior hemiblock (2), left bundle branch block (5), and complete heart block requiring pacemaker implantation (3). In the 20 patients with lesions at or distal to the origin of the first septal perforator, appearance of conduction disturbances correlated well with the absence of retrograde flow to the septal branches from the right coronary artery and distal LAD graft. The authors conclude that lesions in the LAD that compromise flow in the first perforator and do not provide adequate circulation following grafting produce conduction disturbances after surgery. This is predictable from preoperative angiography.
Brown PS, Holland FW, Parenteau GL, Clark RE: Magnesium ion is beneficial in hypothermic crystalloid cardioplegia. Ann Thorac Surg 51:359-367, 1991 The importance of the magnesium/calcium relationship in oxygenated crystalloid cardioplegia to hemodynamic recovery was examined in an isolated rat heart model. Hearts were arrested for 20 minutes at 37°C or for 90 minutes at 24°C and received one dose of 9 possible cardioplegic solutions containing varying amounts of magnesium and/or calcium. Ninety-six percent of the magnesiumtreated hearts recovered regardless of the calcium concentration, in contrast to a 52% recovery rate in the hearts not receiving magnesium. Addition of magnesium to a calcium-containing cardioplegic solution significantly increased recovery of cardiac function including blood pressure, cardiac output, stroke work, and adenine triphosphate level. The authors conclude that significant augmentation of ventricular recovery and decreased mortality is produced at 37°C and 24°C with cardioplegia containing high levels of magnesium and low levels of calcium.
Reinhart RA, Marx JJ, Broste SK, Haas RG: Myocardial magnesium: Relation to laboratory and clinical variables in patients undergoing cardiac surgery. J Am Co11Cardiol17:651-656,199l Magnesium concentration in right atria1 appendage tissue sampled during venous cannulation was measured in 100 patients
Journalof Cardiothoracic and Vascular
Anesthesia,Vol5,
undergoing cardiac surgery and associated with clinical variables. Tissue magnesium concentration was lower in patients who developed postoperative cardiac dysrhythmias than in those without dysrhythmias. Atria1 magnesium concentration correlated inversely with age and was lower in diabetic than in nondiabetic patients. The level was insignificantly lower in patients taking potassium/magnesium-depleting diuretics but was not altered by the presence of congestive heart failure or other cardiovascular drug therapy. Atria1 appendage magnesium concentration correlated positively with serum creatinine concentration, negatively with serum calcium concentration, and did not correlate with serum magnesium concentration.
Jolly SR, Keaton N, Movahed A, et al: Effect of hyperkalemia on experimental myocardial depression by verapamil. Am Heart J 121:517-523,199l After observing hypotension and bradycardia in hyperkalemic patients receiving verapamil, this controlled animal study was undertaken. During saline infusion (controls), verapamil (1,195 kg/kg, IV) reduced mean arterial pressure (MAP) (113 to 74 mm Hg) and heart rate (HR) (147 to 86 beatsimin). After infusion of potassium (blood potassium concentration, 6.2 mEq/L), a significantly lower dose of verapamil(428 ug/kg, IV) reduced MAP (102 to 36 mm Hg) and HR (150 to 104 beats/min). Right ventricular isometric contractile force and left ventricular segment length changes were depressed in both groups. The negative inotropic and blood pressure effects were reversed by calcium administration. Authors conclude the negative hemodynamic effects of verapamil may be exaggerated by concomitant hyperkalemia.
Schoen MD, Parker RB, Hoon TJ, et al: Evaluation of the pharmacokinetics and electrocardiographic effects of intravenous verapamil with intravenous calcium chloride pretreatment in normal subjects. Am J Cardiol67:300-304,199l The effects of calcium pretreatment on the disposition and electrocardiographic effects of verapamil were studied in 8 healthy volunteers receiving verapamil (10 mg, IV), calcium chloride (1 g, IV), and calcium chloride-verapamil in a randomized double-blind, crossover manner. Blood verapamil concentrations, blood pressure, heart rate, and PR intervals were measured. Calcium pretreatment of verapamil did not alter the disposition of the drug. Blood pressure was not significantly altered in any treatment phase, although calcium tended to increase mean arterial pressure and verapamil abolished this effect. Calcium had no significant effect on verapamil-induced PR prolongation but prevented the reflex heart rate increase noted after verapamil alone. The authors conclude that in clinical doses calcium and verapamil produce opposing effects on sinus rate and arterial blood pressure but not on atrioventricular conduction. The antiarrhythmic effects of verapamil are preserved despite calcium pretreatment.
No 5 (October), 1991:
pp 525-526
525
SCIENTIFIC ARTICLES
Mowseri M, Meir G, Lotan C, et al: Coronary pathology predicts conduction disturbances after coronary artery bypass grafting. Ann Thorac Surg 51:248252,199l The authors related preoperative coronary angiograms and postoperative cardiac conduction in 55 consecutive patients undergoing coronary artery surgery. Thirty-five patients with either no lesion or a discreet left anterior descending coronary artery (LAD) lesion proximal to and not involving the septal perforator had no major conduction disturbances after surgery. Eleven of 20 patients with an LAD lesion at the origin of the first septal branch or lesions distal to the branch had major conduction disturbances: right bundle branch block (1 patient), right bundle branch block-left anterior hemiblock (2), left bundle branch block (5), and complete heart block requiring pacemaker implantation (3). In the 20 patients with lesions at or distal to the origin of the first septal perforator, appearance of conduction disturbances correlated well with the absence of retrograde flow to the septal branches from the right coronary artery and distal LAD graft. The authors conclude that lesions in the LAD that compromise flow in the first perforator and do not provide adequate circulation following grafting produce conduction disturbances after surgery. This is predictable from preoperative angiography.
Brown PS, Holland FW, Parenteau GL, Clark RE: Magnesium ion is beneficial in hypothermic crystalloid cardioplegia. Ann Thorac Surg 51:359-367, 1991 The importance of the magnesium/calcium relationship in oxygenated crystalloid cardioplegia to hemodynamic recovery was examined in an isolated rat heart model. Hearts were arrested for 20 minutes at 37°C or for 90 minutes at 24°C and received one dose of 9 possible cardioplegic solutions containing varying amounts of magnesium and/or calcium. Ninety-six percent of the magnesiumtreated hearts recovered regardless of the calcium concentration, in contrast to a 52% recovery rate in the hearts not receiving magnesium. Addition of magnesium to a calcium-containing cardioplegic solution significantly increased recovery of cardiac function including blood pressure, cardiac output, stroke work, and adenine triphosphate level. The authors conclude that significant augmentation of ventricular recovery and decreased mortality is produced at 37°C and 24°C with cardioplegia containing high levels of magnesium and low levels of calcium.
Reinhart RA, Marx JJ, Broste SK, Haas RG: Myocardial magnesium: Relation to laboratory and clinical variables in patients undergoing cardiac surgery. J Am Co11Cardiol17:651-656,199l Magnesium concentration in right atria1 appendage tissue sampled during venous cannulation was measured in 100 patients
Journalof Cardiothoracic and Vascular
Anesthesia,Vol5,
undergoing cardiac surgery and associated with clinical variables. Tissue magnesium concentration was lower in patients who developed postoperative cardiac dysrhythmias than in those without dysrhythmias. Atria1 magnesium concentration correlated inversely with age and was lower in diabetic than in nondiabetic patients. The level was insignificantly lower in patients taking potassium/magnesium-depleting diuretics but was not altered by the presence of congestive heart failure or other cardiovascular drug therapy. Atria1 appendage magnesium concentration correlated positively with serum creatinine concentration, negatively with serum calcium concentration, and did not correlate with serum magnesium concentration.
Jolly SR, Keaton N, Movahed A, et al: Effect of hyperkalemia on experimental myocardial depression by verapamil. Am Heart J 121:517-523,199l After observing hypotension and bradycardia in hyperkalemic patients receiving verapamil, this controlled animal study was undertaken. During saline infusion (controls), verapamil (1,195 kg/kg, IV) reduced mean arterial pressure (MAP) (113 to 74 mm Hg) and heart rate (HR) (147 to 86 beatsimin). After infusion of potassium (blood potassium concentration, 6.2 mEq/L), a significantly lower dose of verapamil(428 ug/kg, IV) reduced MAP (102 to 36 mm Hg) and HR (150 to 104 beats/min). Right ventricular isometric contractile force and left ventricular segment length changes were depressed in both groups. The negative inotropic and blood pressure effects were reversed by calcium administration. Authors conclude the negative hemodynamic effects of verapamil may be exaggerated by concomitant hyperkalemia.
Schoen MD, Parker RB, Hoon TJ, et al: Evaluation of the pharmacokinetics and electrocardiographic effects of intravenous verapamil with intravenous calcium chloride pretreatment in normal subjects. Am J Cardiol67:300-304,199l The effects of calcium pretreatment on the disposition and electrocardiographic effects of verapamil were studied in 8 healthy volunteers receiving verapamil (10 mg, IV), calcium chloride (1 g, IV), and calcium chloride-verapamil in a randomized double-blind, crossover manner. Blood verapamil concentrations, blood pressure, heart rate, and PR intervals were measured. Calcium pretreatment of verapamil did not alter the disposition of the drug. Blood pressure was not significantly altered in any treatment phase, although calcium tended to increase mean arterial pressure and verapamil abolished this effect. Calcium had no significant effect on verapamil-induced PR prolongation but prevented the reflex heart rate increase noted after verapamil alone. The authors conclude that in clinical doses calcium and verapamil produce opposing effects on sinus rate and arterial blood pressure but not on atrioventricular conduction. The antiarrhythmic effects of verapamil are preserved despite calcium pretreatment.
No 5 (October), 1991:
pp 525-526
525