John L. Myers

Ventricular-Assist Pumping in Patients with Cardiogenic Shock after Cardiac Operations

A ventricular-assist pump was used to support the circulation in eight patients who could not be separated from cardiopulmonary bypass after open-heart operations. In five patients with left ventricular failure, the systemic circulation was maintained with pumping from the left atrium to the aorta for 7.0 +/- 1.8 days (mean +/- S.E.M.); three of these patients were well four to 17 months after surgery. In two patients with biventricular failure, right and left ventricular bypass supported the circulation, but neither patient survived. One other patient had isolated right ventricular failure; pumping from the right atrium to the pulmonary artery maintained the pulmonary circulation for 2.2 days. This patient lived for 18 months. Use of the ventricular-assist pump in our patients provided complete support of the systemic or pulmonary circulation or both. Profoundly depressed ventricular function is potentially reversible if technical problems in employing the pump can be avoided.

Outcome After Open-Heart Surgery in Infants and Children

We have studied the neurodevelopmental outcome of 104 consecutive unselected children who underwent open-heart surgery from 1987 through 1989. Survivors had formal neurologic and psychometric examinations after 2 years of age. Mean IQ was 90, and 78% had scores above 70. Cerebral palsy occurred in 22%. Deep hypothermia for longer than 45 minutes was associated with IQ less than 85 (P < .001) and later cerebral palsy (P = .02). Those less than 1 month old at operation had a median IQ of 96, and 25% had cerebral palsy. Median IQ for survivors of hypoplastic left heart syndrome was 66, only one had an IQ above 70, and 57% had cerebral palsy. Median IQ for transposition of great arteries was 109, only one was less than 85, and all had normal neurologic examinations. Those between 1 and 6 months of age at operation had a median IQ of 93, with 64% above 85, and 5% had cerebral palsy. Those older than 6 months had a median IQ of 99, with 70% above 85, and 13% had cerebral palsy. For infants less than 1 month old at operation, a strong association existed between outcome, type of lesion, and duration of deep hypothermia (P < .01), although not in all cases. In those older than 1 month at operation, no association existed between outcome and any study variable. Although the majority of children have an uneventful outcome after open-heart surgery, a significant morbidity exists. This is related to several factors, including type of lesion and duration of hypothermia, particularly in neonates; preoperative congenital and acquired lesions; and possible perioperative cerebrovascular events. (J Child Neurol 1996;11:49-53).

Long-term MRI changes in brain after pediatric open heart surgery.

We performed magnetic resonance imaging (MRI) on the brain and neurologic examinations on 23 children after open heart surgery for congenital heart disease. Twenty children also had psychometric assessments. Examinations were performed at a mean age of 66 months (range, 26 to 180 months). Age at operation was less than 1 month in 43% and more than 6 months in 45%. Abnormal scans were found in 17 (74%) and showed diffuse findings consistent with hypoxic-ischemic encephalopathy, with or without areas of cortical infarction; focal cortical infarction alone; and (in one patient) callosal agenesis and abnormal neuronal migration. Normal IQ and neurologic examinations were found in all six of those who had a normal MRI, and five of six children with changes consistent with focal cortical infarction without diffuse change had a normal neurologic examination. Cerebral palsy and mental retardation was common in the group with diffuse abnormality (in eight of nine children), and this was more likely to occur in those who underwent prolonged (> 45 minutes) hypothermic circulatory arrest and operation during early infancy (P = .004). Focal cortical findings without diffuse changes were more likely in those who underwent open heart surgery without hypothermic circulatory arrest and were older than 6 months at operation, and these children were less likely to have frank neurodevelopmental sequelae. Thus, in our population, focal cortical lesions were common after open heart surgery, and, in addition, diffuse brain abnormality on MRI plus neurologic sequelae were common after prolonged hypothermic circulatory arrest. (J Child Neurol 1994;9:390-397).

Major factors in the controversy of pulsatile versus nonpulsatile flow during acute and chronic cardiac support.

During the past 50 years, the controversy over the benefits of pulsatile versus nonpulsatile flow in cardiac surgery has not been solved.1 A detailed investigation in all published literature reveals that in a majority of publications, the investigators could not show any differences between perfusion modes during acute or chronic cardiac support. However, in more than 20 articles, it appears clear that pulsatile flow causes significantly less vital organ injury and systemic inflammation during cardiopulmonary bypass (CPB) procedures and chronic cardiac circulatory support.1–23 To the best of our knowledge, there is not a single publication that clearly shows the benefits of nonpulsatile perfusion over pulsatile perfusion in acute or chronic clinical or animal settings. The pro-nonpulsatile flow investigators can only claim that there is no difference between perfusion modes, whereas the pro-pulsatile investigators have documented clear benefits.1–23 The objective of this editorial is to examine the major causes for this continuing controversy and suggest potential solutions to end it. Following are the two major causes for the controversy, and both are valid for acute or chronic settings.

The Norwood operation and subsequent Fontan operation in infants with complex congenital heart disease

From April 1987 to September 1993, 60 infants underwent a Norwood operation for complex congenital heart disease including hypoplastic left heart syndrome (n = 41), ventricular septal defect and subaortic stenosis with aortic arch interruption/severe coarctation (n = 7), complex single right ventricle with subaortic stenosis (n = 8), critical aortic stenosis with endocardial fibroelastosis (n = 2), and malaligned primum atrial septal defect with coarctation (n = 2). Age at operation ranged from 1 day to 3.9 months (mean 9 days, median 3.5 days). The operative mortality (< 30 days) was 33% (20 patients). Late mortality was 17% (10 patients). Nine of the 20 (45%) operative deaths occurred during the first 2 days after the operation as a result of sudden hemodynamic instability. All four infants with premature closure of the foramen ovale had pulmonary lymphangiectasia and died of pulmonary failure. Seven operative deaths have occurred in 36 patients since 1990 (19%); in the past 2 years, no operative deaths have occurred in 22 patients. Overall, there are 30 long-term survivors (50%). Twenty-one of these 30 infants have undergone a two-stage repair with a modified Fontan operation at 7.3 to 27.6 months of age (mean 18.1 months) with no mortality. Six patients have entered a three-stage repair strategy by undergoing a hemi-Fontan procedure at 6.8 to 23.0 months (mean 8.8 months) with no mortality, and two of these patients have now had their modified Fontan operation at 23.0 to 46.7 months of age with no mortality (four are still awaiting surgery). Two patients have undergone a two-ventricle repair with a Rastelli procedure, with no mortality at 7.4 and 14.1 months of age. Early in our experience, infants undergoing the Norwood operation had a high early mortality most often related to sudden hemodynamic instability. After we instituted a protocol that adds carbon dioxide to the inspired gas during postoperative mechanical ventilation, the postoperative course became more stable and there have been no operative deaths. In summary, the operative mortality for the Norwood operation continues to improve. A subsequent Fontan operation can be performed with excellent clinical results.

The role of vascular laboratory criteria in the selection of patients for lower extremity amputation.

We evaluated clinical and vascular laboratory data on 126 patients with below-knee or forefoot amputation. Vascular laboratory examination included Doppler systolic blood pressure and arterial wave form analysis using the segmental plethysmograph. Fifty-four patients had below-knee amputation. A calf systolic pressure greater than 70 torr was associated with 97% (33/34) success (p less than 0.005), an ankle systolic pressure greater than 30 torr yielded 91% (39/43) success (p less than 0.025), and an ankle systolic pressure greater than zero yielded an 87% success (p less than 0.005). In the absence of each of the above criteria, the predictive value of a negative test was only 32%, 40%, and 52%, respectively. The presence of a popliteal pulse was associated with 97% success (p less than 0.025); however, 88% of those with an absent popliteal pulse also achieved successful healing of below-the-knee amputations. Prior vascular reconstructive surgery was detrimental to healing of below-knee amputations. with 33% failure rate (p less than 0.025). For the 72 forefoot amputations, an ankle systolic pressure greater than 70 torr yielded a 65% success (p less than 0.025). The sensitivity of an ankle systolic pressure greater than 70 torr was 80% (32/40) and an ankle systolic greater than 35 yielded a sensitivity of 95% (38/40). The specificity was low for both of these reference values. Clinical and vascular laboratory criteria can identify patients who will have a successful below-knee amputation; however, because of the high false negative rate, patients should not be denied below-knee amputation solely on the basis of Doppler systolic pressure. Vascular laboratory criteria for predicting healing of forefoot amputations are also limited by the high rate of false positive and false negative results.

Vascular Anastomoses in Growing Vessels: The Use of Absorbable Sutures

Primary end-to-end infrarenal aortic anastomoses were performed in 36 piglets using two synthetic absorbable suture materials: polydioxanone and coated polyglactin. Animals were killed at 1, 4, and 11 weeks and 6 months following operation. Each aorta was removed, burst-tested to 300 mm Hg, radiographed, and examined histologically. All anastomoses were patent, and no burst-test failures occurred. Stenosis occurred in 14 of 17 animals at 1 and 4 weeks, respectively. One of 5 animals exhibited stenosis at 11 weeks, and none of the 14 animals had stenosis 6 months postoperatively. Histological examination revealed fibrosis replacing areas of disrupted elastica at 6 months in both suture groups. This study suggests that absorbable suture material, in particular polydioxanone, because of its excellent handling characteristics and prolonged tensile strength retention, will be useful for the repair of vascular and cardiac anomalies where growth of the suture line is required.

Quantification of perfusion modes in terms of surplus hemodynamic energy levels in a simulated pediatric CPB model.

The objective of this investigation was to compare pulsatile versus nonpulsatile perfusion modes in terms of surplus hemodynamic energy (SHE) levels during cardiopulmonary bypass (CPB) in a simulated neonatal model. The extracorporeal circuit consisted of a Jostra HL-20 heart-lung machine (for both pulsatile and nonpulsatile modes of perfusion), a Capiox Baby RX hollow-fiber membrane oxygenator, a Capiox pediatric arterial filter, 5 feet of arterial tubing and 6 feet of venous tubing with a quarter-inch diameter. The circuit was primed with a lactated Ringers solution. The systemic resistance of a pseudo-patient (mean weight, 3 kg) was simulated by placing a clamp at the end of the arterial line. The pseudo-patient was subjected to five pump flow rates in the 400 to 800 ml/min range. During pulsatile perfusion, the pump rate was kept constant at 120 bpm. Pressure waveforms were recorded at the preoxygenator, postoxygenator, and preaortic cannula sites. SHE was calculated by use of the following formula {SHE (ergs/cm3) = 1,332 [((∫ fpdt) / (∫ fdt)) – Mean Arterial Pressure]} (f = pump flow and p = pressure). A total of 60 experiments were performed (n = 6 for nonpulsatile and n = 6 for pulsatile) at each of the five flow rates. A linear mixed-effects model, which accounts for the correlation among repeated measurements, was fit to the data to assess differences in SHE between flows, pumps, and sites. The Tukey multiple comparison procedure was used to adjust p values for post hoc pairwise comparisons. With a pump flow rate of 400 ml/min, pulsatile flow generated significantly higher surplus hemodynamic energy levels at the preoxygenator site (23,421 ± 2,068 ergs/cm3 vs. 4,154 ± 331 ergs/cm3, p < 0.0001), the postoxygenator site (18,784 ± 1,557 ergs/cm3 vs. 3,383 ± 317 ergs/cm3, p < 0.0001), and the precannula site (6,324 ± 772 ergs/cm3 vs. 1,320 ± 91 ergs/cm3, p < 0.0001), compared with the nonpulsatile group. Pulsatile flow produced higher SHE levels at all other pump flow rates. The Jostra HL-20 roller pump generated significantly higher SHE levels in the pulsatile mode when compared with the nonpulsatile mode at all five pump flow rates.

Current status of cardiac surgery: A 40 year review

Cardiac surgery has undergone dramatic advancements during the past 3 decades. The introduction of cardiopulmonary bypass and cardioplegic arrest ushered in the true era of open heart surgery. Bioprostheses and mechanical valves as well as techniques for valve reconstruction permit routine repair or replacement of stenotic and regurgitant native valves. Progress in the disciplines of mechanical and electrical engineering has led to the development of pocket watch-sized, physiologically responsive pacemakers as well as a variety of circulatory assist devices that include the intraaortic balloon pump, ventricular assist device and total artificial heart. The synthesis of cardiotonic and vasoactive drugs and advancements in anesthetic management, postoperative monitoring and nursing care greatly facilitate perioperative patient management. This summary of state of the art cardiac surgery begins with a brief historical background followed by a review of recent advances in six main categories: coronary artery disease, acquired valvular heart disease, congenital cardiac disease, cardiac transplantation, myocardial preservation and mechanical circulatory assistance. In conducting the review of recent literature, particular attention was directed to large clinical series that document the results of contemporary surgical procedures, novel therapeutic approaches to current clinical problems and unresolved controversies in the field of cardiac surgery. The abundance of surgical literature and constraints on the length of this article do not permit an exhaustive review. Apologies are extended to clinicians and laboratory investigators whose important contributions to the understanding and treatment of cardiac disease are not included herein.

Detection and classification of gaseous microemboli during pulsatile and nonpulsatile perfusion in a simulated neonatal CPB model.

We compared the effects of perfusion modes (pulsatile vs. nonpulsatile) on gaseous microemboli delivery using the Emboli Detection and Classification (EDAC™) Quantifier at postpump, postoxygenator, and postarterial filter sites in a simulated pediatric cardiopulmonary bypass (CPB) model. The mock loop was subjected to five different pump flow rates of equal 100 ml/min intervals, ranging from 400 to 800 ml/min. When the target pump flow rate was achieved, 5 cc air was introduced into the venous line. The EDAC™ system recorded gaseous microemboli counts simultaneously at three locations in 5-minute intervals. Regardless of the type of perfusion mode, when the pump flow rate was increased, more gaseous microemboli were generated at postpump site. Compared with nonpulsatile flow, pulsatile flow did deliver significantly more gaseous microemboli at postpump site, but there was no difference between two groups at postoxygenator and postarterial filter sites. Capiox Baby-RX hollow-fiber membrane oxygenator significantly reduced the gaseous microemboli counts in both groups at all five pump flow rates with either pulsatile flow or nonpulsatile flow in this model. Our results suggest that using this novel EDAC™ system, we could detect the size of gaseous microemboli, as small as 10 &mgr;m, and the percentage of detected gaseous microemboli, <40 &mgr;m, was about 90% in total gaseous microemboli counts at any flow rate with pulsatile or nonpulsatile flow.