Bradley S. Allen

Superiority of magnesium cardioplegia in neonatal myocardial protection

BACKGROUND We have shown that magnesium can offset the detrimental effects of normocalcemic cardioplegia in hypoxic neonatal hearts. It is not known, however, whether magnesium offers any additional benefit when used in conjunction with hypocalcemic cardioplegia. METHODS Twenty neonatal piglets underwent 60 minutes of ventilator hypoxia (FiO2 8% to 10%) followed by 20 minutes of normothermic ischemia on cardiopulmonary bypass (hypoxic-ischemic stress). They then underwent 70 minutes of multidose blood cardioplegic arrest. Five (Group 1), received a hypocalcemic (Ca+2 0.2 to 0.4 mM/L) cardiologic solution without magnesium, whereas in 10, magnesium was added at either a low dose (5 to 6 mEq/L, Group 2) or high dose (10 to 12 mEq/L, Group 3). In the last 5 (Group 4), magnesium (10 to 12 mEq/L) was added to a normocalcemic cardioplegic solution. Function was assessed using pressure volume loops and expressed as percentage of control. RESULTS Compared to hypocalcemia cardioplegic solution without magnesium (Group 1), both high- and low-dose magnesium enrichment (Groups 2 and 3) improved myocardial protection resulting in complete return of systolic (40% vs 101% vs 102%) (p < 0.001 vs Groups 2 and 3) and global myocardial function (39% vs 102% vs 101%) (p < 0.001 vs Groups 2 and 3), and reduced diastolic stiffness (267% vs 158% vs 154%) (p < 0.001 vs Groups 2 and 3). Conversely, even high-dose magnesium supplementation could not offset the detrimental effects of normocalcemic cardioplegia resulting in depressed systolic (End Systolic Elastance [EES] 41%+/-1%) (p < 0.001 vs Groups 2 and 3) and global myocardial function (40%+/-1%) (p < 0.001 vs Groups 2 and 3), and a marked rise in diastolic stiffness (258%+/-5%) (p < 0.001 vs Groups 2 and 3). Hypocalcemic magnesium cardioplegia has now been used successfully in 247 adult and pediatric patients. CONCLUSIONS Magnesium enrichment of hypocalcemic cardioplegic solutions improves myocardial protection resulting in complete functional preservation. However, magnesium cannot prevent the detrimental effects of normocalcemic cardioplegia when the heart is severely stressed. This study, therefore, strongly supports using both a hypocalcemic cardioplegic solution and magnesium supplementation as their benefits are additive.

Experience with an alternative technique for the management of anomalous left coronary artery from the pulmonary artery

BACKGROUND Several operative approaches are utilized for the management of anomalous origin of the left coronary artery from the pulmonary artery, each with some limitation. The long-term results of a technique that facilitates direct and tension-free implantation of the anomalous artery to the aorta in all patients are described. METHODS From January 1, 1992 through August 30, 2000, 10 consecutive patients with anomalous left coronary artery underwent operation using this technique. It consists of isolating an anterior and posterior transverse segment of pulmonary artery in continuity with the origin of the anomalous coronary artery. The two segments are folded with the orifice of the coronary as its fulcrum, and the edges sutured together to form an extension tube of pulmonary artery tissue. This lengthens the coronary artery and allows direct aortic implantation (posterior to the pulmonary artery) without tension. The pulmonary artery is reconstructed with autologous pericardium. RESULTS Patient age ranged from 3 weeks to 3 years old (median 8 weeks), with 80% of patients less than 11 weeks old. Median weight was 4.6 kg (3.7 to 23 kg). The left ventricle was dilated with an end-diastolic diameter z-value of +1 to +3, and the shortening fraction was markedly reduced to 16% +/- 6% (7% to 28%), with 8 of 10 patients having a shortening fraction less than 20%. Mitral regurgitation was severe in 5 patients, moderate in 2 patients, and all patients were in congestive heart failure. After repair there were no hospital deaths. Inotropic support was needed in all patients, but none required mechanical assistance. At a follow-up of 4.3 +/- 2.5 years (0.5 to 8.5 years), 9 patients are asymptomatic and 1 patient has intermittent chest pain. All patients (10/10) have echocardiographic documented patency of the reimplanted coronary artery, as well as marked improvement in the left ventricular shortening fraction (37% +/- 5%; p > 0.05 versus preoperative) and decrease in the end-diastolic diameter z-value (-1 to +1; p > 0.05 versus preoperative). Mitral regurgitation was absent in 4 patients, mild in 4 patients, and moderate in 2 patients. severe in 1 patient. Four patients have evidence of mild supravalvar pulmonary stenosis (15 to 32 mm Hg), 1992. CONCLUSIONS This technique allows a tension-free direct aortic connection in all cases, has a low rate of coronary artery occlusion, and avoids significant pulmonary artery distortion or stenosis, making it an excellent alternative for the surgical management of anomalous origin of the coronary artery.

Conditioned blood reperfusion markedly enhances neurologic recovery after prolonged cerebral ischemia

OBJECTIVES To determine whether controlled reperfusion using conditioned leukodepleted blood can substantially limit cerebral reperfusion injury following prolonged ischemia. METHODS Eighteen pigs (25-35 kg) underwent 90 minutes of hypothermic circulatory arrest (19 degrees C) to produce brain ischemia. At the start of rewarming, 10 pigs received uncontrolled reperfusion with unmodified (normal) blood. The other 8 pigs underwent 10 minutes of controlled reperfusion by selectively perfusing both common carotid arteries with blood passed through a CoBRA filter. This filter conditions the blood by removing white blood cells, platelets, and attenuating complement. Two other pigs underwent cooling and rewarming only (controls) without ischemia. Neurologic assessment was done using neurologic deficit scoring (0 = normal, 500 = brain death), and jugular venous samples were obtained for biochemical analysis postreperfusion. RESULTS There were no statistical differences in hemodynamics between groups. At 6 hours postanesthesia, all animals receiving normal blood were substantially neurologically impaired. At 24 hours, they all had abnormal positioning and all but 1 were unable to sit or stand (neurologic score 124 +/- 19). In contrast, nonischemic controls and pigs receiving conditioned blood reperfusion showed only minor neurologic deficits at 6 hours, and at 24 hours all were considered normal (neurologic scores 0 and 6 +/- 5; P <.005 vs uncontrolled reperfusion). Compared with pigs receiving normal blood reperfusion, oxygen free radical formation (conjugated dienes 1.70 +/- 0.03 vs 1.60 +/- 0.02 Abs 240 nm; P <.05 vs uncontrolled reperfusion), and endothelin-1 release (2.12 +/- 0.09 vs 1.84 +/- 0.06 pg/mL; P <.05 vs uncontrolled reperfusion) were also significantly lower in animals receiving conditioned blood. CONCLUSIONS Following prolonged cerebral ischemia, reperfusion injury is avoided by delivering conditioned blood, which is devoid of white cells, platelets, and membrane attack complex. These results suggest that this modality is clinically useful in situations where the brain is subjected to prolonged ischemia.

L-arginine, prostaglandin, and white cell filtration equally improve myocardial protection in stressed neonatal hearts.

OBJECTIVES L-Arginine may improve cardioplegic protection by increasing nitric oxide production. However, L-arginine may also be detrimental because it generates the free radical peroxynitrite. It would, therefore, be advantageous if the benefits of L-arginine could be achieved by another means. METHODS Twenty neonatal piglets underwent 60 minutes of ventilator hypoxia (inspired oxygen fraction 8%-10%) followed by 20 minutes of ischemia on cardiopulmonary bypass (stress) and were then protected for 70 minutes with multiple doses of blood cardioplegic solution. In 5 piglets (group 1), the cardioplegic solution was not modified; in 5 (group 2), low-dose L-arginine (4 mmol/L) was added; in 5 (group 3), prostaglandin E(1) (alprostadil, 4 microgram/L) was added; and in 5 (group 4), the cardioplegic solution was passed through a leukodepleting filter. Myocardial function was assessed by pressure volume loops and expressed as percentage of control, and coronary vascular resistance was measured with each cardioplegic infusion. RESULTS Unmodified blood cardioplegic solution (group 1) was unable to protect the severely stressed myocardium, resulting in depressed systolic function (39% +/- 1%) and preload recruitable stroke work (40% +/- 1%), increased diastolic stiffness (239% +/- 3%), and high conjugated diene production, myeloperoxidase activity, and coronary vascular resistance. In contrast, cardioplegic solutions modified with L-arginine, prostaglandin E(1), or leukodepletion, resuscitated the stressed myocardium, resulting in complete return of systolic function (100% vs 101% vs 101%; P <.001 vs group 1) and preload recruitable stroke work (100% vs 101% vs 101%; P <.001 vs group 1), minimal increase in diastolic stiffness (160% vs 162% vs 160%; P <. 001 vs group 1), and lowered conjugated diene production, myeloperoxidase activity, and coronary vascular resistance (P <.001 vs group 1 for each). CONCLUSIONS (1) Unmodified blood cardioplegic solution is unable to protect the severely stressed myocardium. (2) L-Arginine, prostaglandin E(1), and leukocyte filtration all improve myocardial protection equally and appear to work by limiting a white blood cell-mediated injury. This reduces oxygen-derived free radical formation, maintains vascular function, and restores functional recovery. Since L-arginine may be detrimental, surgeons should consider using prostaglandin E(1) and/or a leukocyte filter instead.

The clinical significance of the reoxygenation injury in pediatric heart surgery

Significant advances have been made in the technical performance of operations for infants and neonates with congenital heart disease. However, postoperative organ dysfunction is a frequent problem, particularly in hypoxic (cyanotic) infants. We review both our experimental and subsequent clinical experience with the injury caused by abrupt reoxygenation of the hypoxic patient and examine the modalities of gradual reoxygenation and leukodepletion in limiting this injury, thereby improving operative outcomes for cyanotic lesions. As a result of our experimental and clinical experience we conclude that: (1). reoxygenation injury is a real source of postoperative cardiac and pulmonary dysfunction; (2). white blood cells play an integral role in the production of oxygen-free radicals that are responsible for the damage; and (3). this injury can be modified and possibly ameliorated by changes in the intraoperative management of cardiopulmonary bypass.