Is there a safe limit to coronary sinus pressure during retrograde cardioplegia?

Although retrograde cardioplegia (RC) delivered via the coronary sinus (CS) is now used routinely, the pressure at which RC can be safely delivered is thought to be 50 to 60 mm Hg. Such practice is based on experiments performed on working, beating hearts with CS ligation and arterial inflow into both the coronary arteries and veins (Beck procedure). However, no data exist on arrested, vented hearts, as occurs clinically during RC. We studied the acute effect of 10 cc/kg of blood RC delivered into the CSs of 16 adult vented pig hearts, which were randomly assigned to four groups of four hearts each according to the CS pressure maintained during perfusion: 40, 80, 100, and 120 mm Hg. After RC, hearts were excised, cut in bread-loaf sections, examined grossly, and then fixed and stained. Sections of right ventricle, septum, and left ventricle were then examined by two blinded cardiac pathologists and two blinded surgeons and scored for the presence of extravascular hemorrhage. None of the 16 hearts tested showed any evidence of gross or microscopic hemorrhage; all hearts showed normal myocardial preservations and structure, including all hearts at 100 and 120 mm Hg CS perfusion pressure. We conclude that CS pressures up to 120 mm Hg cause no extravasation of blood into the myocardium in the vented, arrested heart. These results contradict studies on the working, beating heart, and suggest that high pressures in the CS are well tolerated during RC.

Neurologic sequelae of deep hypothermic circulatory arrest in cardiac transplant infants.

BACKGROUND: Considerable controversy exists experimentally and clinically regarding adverse neurologic effects that may follow deep hypothermic circulatory arrest. Moreover, the techniques of DHCA have never been standardized. METHODS: We prospectively studies the neurodevelopmental outcome in 38 infants undergoing cardiac transplantation using DHCA before the age of 4 months (mean age, 37.0 days). Neurodevelopmental outcome in the 22 boys and 16 girls was tested up to 2.5 years after transplantation using Bayley scale of infant development. Bayley scores were compared with the rate of core cooling and the length of DHCA in all patients. Deep hypothermic circulatory arrest was accomplished using an asanguineous prime resulting in hematocrits of 5% +/- 5% and ionized Ca2+, 0.4 +/- 0.1 mmol/L. No surface precooling was used, but the head was packed in ice. Mean cooling time was 14.0 +/- 3.5 minutes, resulting in rectal temperatures of 18 degrees +/- 2.5 degrees C. Duration of DHCA ranged from 42 to 70 minutes (mean duration, 56.0 +/- 6.6 minutes). RESULTS: Postoperatively, the mean Bayley psychomotor development index was 91 (range, 50 to 130) and mental development index was 88 (range, 50 to 130). No relationship was found between either the rate of cooling or the duration of DHCA and Bayley scores (r = 0.227 and r = 0.322, respectively). CONCLUSIONS: These data suggest that neither the rate of cooling nor DHCA times between 42 and 70 minutes using profoundly low hematocrits and low ionized calcium levels has any measurable effect on neurologic outcome up to 2.5 years postoperatively. It is possible that adverse neurologic outcomes from DHCA reflect particular methods of achieving DHCA.

A prospective evaluation of transcutaneous oxygen measurements in the management of diabetic foot problems.

PURPOSE: To test the hypothesis that lower extremity transcutaneous oxygen (TcPO2) measurements can accurately predict severity of foot ischemia and can be used to select appropriate treatment (conservative versus operative) for patients with diabetes and tissue necrosis or ischemic rest pain. METHODS: Fifty-five patients with 66 limbs were prospectively treated from June 1993 to July 1994. Noninvasive hemodynamic arterial assessment and TcPO2 mapping of the involved limb were obtained before treatment was selected. If the transmetatarsal TcPO2 level was 30 mm Hg or greater, the patient's foot problem was managed conservatively with local wound care, debridement, or a minor foot amputation. If the transmetatarsal TcPO2 level was less than 30 mm Hg, arteriography was performed with the anticipated need for vascular reconstruction. The endpoints for determining treatment success or failure were complete wound healing or relief of ischemic rest pain. RESULTS: Thirty-one of 36 (86%) limbs with an initial transmetatarsal TcPO2 level of 30 mm Hg or greater were treated successfully with conservative care, including 73% (11 of 15 feet) of limbs without a palpable pedal pulse. After either bypass or angioplasty, 20 of 24 (83%) limbs achieved a transmetatarsal TcPO2 level greater than 30 mm Hg and had complete resolution of their presenting foot problem. An initial or postintervention transmetatarsal TcPO2 level of 30 mm Hg or greater was more accurate (90%, p = 0.001) than a palpable pedal pulse (65%, p = 0.009), in predicting ultimate wound healing or resolution of rest pain. CONCLUSIONS: TcPO2 mapping is a useful noninvasive modality that can prospectively determine severity of foot ischemia, aid in selecting appropriate treatment for patients with diabetes and foot salvage problems, and decrease the total cost of such care.

Successful survival of primates receiving transplantation with "dead," nonbeating donor hearts.

A paucity of donor organs is the principal limitation in human heart transplantation. Prompted by our short-term studies of reanimating "dead" donor hearts in sheep, we applied the same reperfusion modifications in juvenile baboons to determine human applications in an anoxic arrest model (as occurs when non-brain-dead patients are extubated and allowed to die). Ten juvenile baboons (mean weight 3.6 kg) were studied. Five baboons were used as donors. After being anesthetized, donors were pretreated with methylprednisolone (Solu-Medrol), 50% dextrose, nifedipine, and prostaglandin E1 and then paralyzed and extubated. Donors became pulseless at 7 +/- 1 minutes and had electric arrest 9 to 18 minutes after paralysis. The five donors were left undisturbed and warm for 15, 22, 30, 30, and 31 minutes, respectively, after asystole. They were then given 250 ml of 4 degrees C Roe's crystalloid cardioplegic solution via the aortic root and the hearts were explanted into iced Euro-Collins solution. Five baboons served as recipients. After donor harvest, recipients were placed on cardiopulmonary bypass, given prostaglandin E1, and cooled to 18 degrees C; circulatory arrest was instituted and the recipient's heart excised. The donor heart was transplanted in an orthotopic position. Before reinstitution of bypass, 250 ml of terminal leukocyte-depleted blood cardioplegic solution was given, then bypass was restarted and the hearts were reperfused for 60 minutes. All animals were weaned from bypass without the use of inotropic agents. All animals were extubated within 2 to 4 hours after bypass and received standard immunosuppression. Peak creatine kinase MB/total creatine kinase ratio was 0.2% +/- 0.2%. Postoperative ejection fractions by echocardiography were 75% to 80% (mean 76%). Animals survived 1, 9, 13, 16, and 34 days, with three deaths caused by acute rejection and one each by stroke and diarrhea/dehydration. Pathologic findings showed no areas of fibrosis or ischemic damage. We conclude that successful reanimation and engraftment can be achieved with the use of the asystolic primate heart; this work suggests that human application is realistic and could greatly expand the donor pool.