Conducting tissues in univentricular heart of right ventricular type with double or common inlet.

Four specimens of univentricular hearts of the right ventricular type, three with two atrioventricular valves and one with a common valve, have been examined histologically to identify the atrioventricular conduction system. Three of the specimens were initially thought to have only one chamber within the ventricular mass, a chamber which had a right ventricular trabecular pattern. On detailed examination and with removal of blocks of tissue for histologic study, a second, rudimentary chamber was found in the posterior ventricular wall. This chamber had a trabecular zone of the left ventricular type and was connected with the main chamber only via a small defect in the septum which separated the two chambers. In all four cases the connecting atrioventricular node was dound in normal relationship to atrial markers and the penetrating bundle descended onto the posterior wall of the main chamber. In three cases it ran along the crest of the septum between the main chamber and rudimentary chamber, in relation to the septal defect. In two cases left bundle branch tissue was identified running into the rudimentary chamber. This pattern of conducting system is different from that previously identified in other varieties of univentricular heart and again underlines the importance of intraoperative mapping of the conduction system during surgery of the univentricular heart.     

Right ventricular dynamic cardiomyoplasty for the univentricular heart with pulmonary hypertension

OBJECTIVES: We conducted an acute experimental study to test the feasibility of dynamic cardiomyoplasty in a setting of modified Fontan procedure for univentricular heart with pulmonary hypertension to obtain a possible proxy for high-risk Fontan candidates. METHODS: After electrical preconditioning of the left latissimuss dorsi for 6 weeks in 8 dogs, the right ventricular cavity was totally obliterated with concomittent closure of the tricuspid valve and right pulmonary artery. Modified Fontan circulation was established with the aortic homograft anastomosed between the right atrium and pulmonary trunk, incorporated with a pericardial pouch as a compression chamber (neoright ventricle) fixed onto the epicardial surface of the ventricle. After cardiopulmonary bypass termination, a latissimus dorsi was applied to wrap the pericardial pouch and ventricle clockwise and stimulated with a trained-pulse (25 Hz) at 1:1 synchronization ratio with cardiac beats. RESULTS: Profound right heart failure was noted during Fontan circulation in increased pulmonary vascular resistance (11 +/- 3.2 Wood units), whereas graft pacing showed significant augmentation of systolic pulmonary pressure by 54 +/- 12%, the mean pulmonary flow by 68 +/- 23%, and aortic pressure by 23 +/- 5% at a physiological range of central venous pressure (13.2 +/- 0.7 mmHg). Right heart function curve analysis confirmed marked augmentation of right heart performance, restoring almost normal pulmonary circulation. These functional benefits were sustained up to 4 hours in 4 animals until experiments were terminated. CONCLUSIONS: Dynamic cardiomyoplasty in a modified Fontan procedure is a viable surgical option for univentricular heart, not a Fontan candidate.     

Atrioventricular conduction in dogs during anesthesia with isoflurane.

The effects of 1.25, 2.0, and 2.5 MAC isoflurane on atrioventricular conduction were studied by His-bindle electrocardiography during atrial pacing in ten dogs. No effect upon atrioventricular conduction as evidenced by changes in A--H interval (the time of conduction from low right atrium to His-bundle, representing primary AV nodal conduction) was found at these concentrations. Atrial pacing to 200 beats/min did not influence the A--H interval at the three anesthetic concentrations. The stability of cardiac rhythm observed clinically with isoflurane may be related to this lack of effect upon the AV node.     

Production and reversibility of right ventricular hypertrophy and right heart failure in dogs.

Combined heart-lung transplantation has been used for end-stage primary pulmonary hypertension. Experience with single-lung transplantation for other conditions suggested that associated severe right ventricular dysfunction resulting from increased afterload would recover after placement of a satisfactory lung allograft. Early experience with the application of single-lung transplantation for pulmonary hypertension supports this contention. We devised a reversible canine model of chronic progressive pressure-overloaded right heart failure by pulmonary artery banding to study the echocardiographic, hemodynamic, and pathological reversibility of the failing right heart. Clinical right heart failure was defined as the development of ascites and pleural effusions. Right heart failure developed in 23 dogs 67 to 348 days after banding, and they were divided into two groups to determine its early and long-term effects. Group 1 dogs (n = 11) were either sacrificed immediately after the onset of right heart failure (n = 5) or unbanded (n = 6); group 2 dogs (n = 12) were maintained in right heart failure for 3 months and then either sacrificed (n = 6) or unbanded. Unbanded dogs in both groups were observed for 4 additional months before sacrifice. A control group of 6 normal dogs was sacrificed for pathological comparisons. After unbanding, the right ventricular systolic pressure fell from 97 +/- 17 mm Hg (group 1) and 88 +/- 31 mm Hg (group 2) to 44 +/- 11 mm Hg and 47 +/- 13 mm Hg, respectively. Despite this persistent gradient across the pulmonary artery, echocardiographic and hemodynamic measures of right ventricular function returned to normal, albeit more slowly in the group 2 dogs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Septation of the univentricular heart. Transatrial approach.

The technique of septation of the univentricular heart via a transatrial approach is described in detail. Clinical details of four patients having Type A-III univentricular heart document the feasibility of working through the right-sided atrioventricular valve to place a cloth prosthesis into the ventricle to divide it into approximately equal chambers. Improved hemodynamics were observed in the postoperative period, which probably were related to retaining the integrity of the ventricular wall. This approach seems best suited to the ventricular chamber estimated to be large by echocardiography without severe pulmonary outflow tract obstruction. Techniques for enlargement of the pulmonary outflow tract are also described.     

Norwood operation for univentricular heart with subaortic stenosis in the neonate.

In the setting of a single ventricle, subaortic stenosis may be enhanced by pulmonary artery banding and may later contraindicate a Fontan operation. The Norwood operation may prove a preferable alternative in some infants as a preparatory procedure. We have successfully used this procedure as the initial operation to palliate a newborn with tricuspid atresia, transposition of the great arteries, coarctation, and severe arch hypoplasia secondary to a restrictive bulboventricular foramen.     

Management of univentricular heart with systemic ventricular outflow obstruction by pulmonary artery banding and Damus-Kaye-Stansel operation

BACKGROUND: Some patients with univentricular hearts who are candidates for Fontan operation may develop ventricular outflow tract obstruction after pulmonary artery banding (PAB) or Fontan. However, the indication for Damus-Kaye-Stansel (DKS) operation for these patients has not been clear. To clarify the indication, the changes in the diameter of ventricular outflow tract and the feasibility of DKS operation before or with Fontan were investigated. METHODS: Among the patients with univentricular heart who underwent PAB, 21 patients had probable ventricular outflow obstruction with an aorta arising from the morphologic right ventricle. Diameter of ventricular outflow tract was measured before and after PAB, Glenn, and Fontan operations with or without DKS, and indexed by normal value (%VOT). RESULTS: Six patients died after PAB. In the surviving 15 patients, %VOT decreased significantly from 103% (median, range 75%-153%) to 75% (range 52%-153%) after PAB. Four with very small %VOT (52% to 63%) after PAB needed DKS with bidirectional Glenn or central shunt operation, and 5 with moderately small %VOT (67% to 109%) after PAB needed DKS concomitantly with Fontan. A patient with %VOT of 117% before Fontan required DKS after Fontan. A patient with %VOT of 153% underwent Fontan without DKS and obstruction did not develop after Fontan. The remaining 4 patients were under consideration for Glenn or Fontan operation. CONCLUSIONS: The diameter of the ventricular outflow tract decreased after PAB and Fontan operations. DKS operations might be indicated before Fontan if the indexed diameter of ventricular outflow tract after PAB was below 70% and concomitantly with Fontan if it was below 120%.     

Results of the Fontan procedure for patients with univentricular heart.

One hundred twenty-four consecutive patients with univentricular heart undergoing the Fontan operation were reviewed. Patients with tricuspid atresia or biventricular heart with hypoplasia of one ventricle were excluded. Eighty-four patients had left ventricular morphology. Atrioventricular connection was double-inlet (n = 76), common (n = 29), absent left atrioventricular connection (n = 14), and absent right atrioventricular connection (n = 5). Actuarial survival was 77% (70% confidence limits, 73% to 81%) at 1 year, 66% (70% confidence limits, 60% to 72%) at 5 years, and 49% (70% confidence limits, 36% to 61%) at 10 years, indicating a continuing risk for premature death. Multivariate analysis identified preoperative ventricular function and hypertrophy as risk factors for survival. High postrepair right atrial pressure (greater than 15 mm Hg) emerged as a strong intraoperative predictor of survival. Logistic regression analysis of these factors predicts high probability of death for certain subgroups of patients after the Fontan operation. Forty-four percent (n = 53) of these original 124 patients are alive and in New York Heart Association class I at follow-up. Thirty-eight percent (n = 33) of survivors have worse ventricular function than preoperative. Long-term survival is disappointing. Certain identifiable subgroups of patients with univentricular heart have unacceptable risks for the Fontan operation and should have alternate management. High postrepair right atrial pressure is an ominous sign, and if it persists the Fontan should be fenestrated or taken down.     

Surgical management of univentricular heart with subaortic obstruction

In children with a univentricular heart and a rudimentary subaortic chamber, surgical relief of subaortic obstruction caused by a restrictive bulboventricular foramen is associated with high morbidity and mortality. A 6-year-old child with a univentricular heart of the left ventricular type, a rudimentary subaortic chamber, and atresia of the left-sided atrioventricular valve had pulmonary artery banding in infancy. Severe subaortic obstruction subsequently developed. At operation, the pulmonary artery was transected and the stump was anastomosed directly to the posterior aspect of the ascending aorta, diverting left ventricular blood into the aorta through the pulmonary valve. The distal pulmonary artery was anastomosed side-to-side to the ascending aorta to provide pulmonary blood flow. Cardiac catheterization fifteen months after the operation demonstrated an excellent hemodynamic result. When the pulmonary artery is adequate in size, a bypass operation by way of an anastomosis between the ascending aorta and the pulmonary artery is a relatively safe and effective means of relieving the ventricular outflow obstruction caused by a restrictive bulboventricular foramen.     

Dynamic right ventricular dimension. Relation to chamber volume during the cardiac cycle

Whereas the left ventricle has been analyzed extensively, the apparent complexity of right ventricular geometry and contraction has hindered analysis of right ventricular performance by an assessment of instantaneous ventricular dimensions and volume during the cardiac cycle. To address this issue, we examined the temporal and quantitative relation between dynamic right ventricular free wall dimension, rate of pressure development (dP/dt), and pulmonary artery flow in the open-chest dog. Right ventricular free wall chord dimension was recorded by sonomicrometry, right ventricular pressure by micromanometer-tipped catheter, and pulmonary flow by electromagnetic probe. The point of peak positive right ventricular dP/dt closely correlated with the end of isovolumic contraction and initiation of ejection, occurring within 10 +/- 25 msec of initiation of pulmonary flow. Right ventricular dimension at peak positive dP/dt differed from dimension at initiation of chord shortening by less than 3%. Peak negative dP/dt correlated with end ejection, occurring within 10 +/- 25 msec of cessation of pulmonary flow. Right ventricular dimension at peak negative dP/dt differed from minimal dimension by less than 1%. In all dogs, volume ejected from the right ventricular chamber during each cardiac cycle was directly related to the change in right ventricular dimension during the same period (mean r = 0.969). This relationship between right ventricular stroke volume and dimensional change remained linear and was not changed (p = NS) by increases in right or left ventricular afterload induced by constricting the pulmonary artery or descending aorta. Right ventricular stroke work, calculated as the integral of instantaneous right ventricular pressure and dimension, correlated well (mean r = 0.980) with directly measured global right ventricular stroke work over a wide range; it was also not changed (p = NS) by changes in afterload. Accurate assessments of beat-to-beat right ventricular chamber volume and stroke work can be obtained by analysis of dynamic right ventricular chord dimension.     

Atrioventricular pacing in congenital heart disease.

We have attempted to optimize cardiac performance in patients with congenital heart disease requiring artificial pacing by using pacemakers capable of both sensing and pacing both the atrium and the ventricle (DDD). We reviewed our results with 88 patients receiving DDD devices to determine the safety and dependability of these devices in children. Age ranged from 1 hour to 25 years. Endocardial leads were used in 68 patients, whereas epicardial leads were used in 20 patients. Previous cardiac procedures had been done in 30 patients. There were nine deaths but none due to pacemaker malfunction. Endocardial leads functioned better than epicardial leads. Ninety-eight percent of patients with endocardial leads and 62% of patients with epicardial leads were maintained in the DDD mode. Complications were infrequent and all were corrected without long-term sequelae. The DDD mode may offer considerable benefits to children who require artificial pacing. Our data allow us to conclude that most children can be paced safely and dependably in the DDD mode.     

Atrioventricular conduction during adenosine-induced hypotension in dogs anaesthetized with sevoflurane

We have studied the effects of adenosine-induced hypotension on A-H interval (atrioventricular (AV) nodal conduction time during sinus rhythm), St-H interval (intra-atrial plus AV nodal conduction time during atrial pacing), H-V interval (His-Purkinje conduction time) and H-S interval (total ventricular conduction time) by His-bundle electrocardiography in addition to surface electrocardiogram during both sinus rhythm and atrial pacing in nine dogs anaesthetized with 1 MAC of sevoflurane. Stepwise increases in infusion rates of adenosine to 0.1, 0.3, 0.5 and 1.0 mg kg-1 min-1 produced a dose-related decrease in mean arterial pressure from 91 (6) to 38 (2) mm Hg. Adenosine significantly increased the A-H interval at infusion rates of 0.5 mg kg- 1 min-1 and above, and the St-H interval at 1.0 mg kg-1 min-1. The H-V and H-S intervals remained unchanged. Heart rate decreased significantly only at 1.0 mg kg-1 min-1 with a significant increase in the PR interval. Adenosine-induced hypotension did not have deleterious effects on AV conduction times and the surface electrocardiogram in dogs anaesthetized with 1 MAC of sevoflurane. This may indicate that the effects of adenosine on AV conduction were small and therefore are unlikely to be a contraindication to the use of adenosine for inducing hypotension in patients with initially normal conduction during sevoflurane anaesthesia.      

The enabler right ventricular circulatory support system for beating heart coronary artery bypass graft surgery.

BACKGROUND: Beating heart coronary artery bypass graft surgery of the left anterior descending, diagonal, and right coronary artery can be performed safely with the Octopus Stabilization System. However, tilting of the heart, which is necessary to reach the obtuse marginal and distal right coronary arteries, causes hemodynamic instability. This study was performed to investigate the possible role of the Enabler right ventricular circulatory support system in counteracting this instability. METHODS: In 8 sheep, the Enabler cannula was introduced via the jugular vein and positioned with the inlet valve in the right atrium and outlet valve in the pulmonary artery. The Octopus was used to expose the inferior wall and the posterior wall of the left ventricle. The hemodynamic effects of this tilting with and without Enabler right ventricular support were recorded, including Pressure Volume (PV) loops measured by conductance catheters in both ventricles. RESULTS: Tilting caused a reduction in stroke volume (inferior 31%, posterior 17%) and Enabler activation increased stroke volume (inferior 13%, posterior 31%). CONCLUSIONS: Tilting the heart has severe hemodynamic consequences that can be partially counteracted by the use of the Enabler for right ventricle support.     

Severe pulmonary vascular change in patients dying with right ventricular failure after heart transplantation.

Two patients died following heart transplantation from failure of the donor right ventricle. Histological examination of the lungs showed occlusion of pulmonary veins. A more reliable method is required to predict the outcome for potential heart transplant recipients with a "borderline" pulmonary vascular resistance.     

Effects of left heart bypass on right ventricular performance. Evaluation of the right ventricular end-systolic and end-diastolic pressure-volume relation in the in situ normal canine heart

Although left heart bypass has gained popularity as a powerful technique to assist the severely failed left heart, apparent right heart failure has often developed during the bypass procedure. We investigated whether the coexisting right heart failure is attributable to the left heart bypass in 16 open-chest dogs. We evaluated the effects of left heart bypass on the right ventricular systolic properties by the slope of the end-systolic pressure-volume relation and its effects on the diastolic properties by chamber compliance. Overall right ventricular performance was assessed by the end-diastolic pressure versus cardiac output relationship. The left heart bypass decreased the slope slightly when the assisted flow ratio exceeded 75% (-14% +/- 8% at the assisted flow ratio of 100%, p less than 0.02) and thus had a deleterious influence on right ventricular performance. The left heart bypass, on the other hand, had a counteracting beneficial influence on right ventricular performance through the increase in chamber compliance (38% +/- 5%, p less than 0.01) and the decrease in pulmonary arterial input resistance (-15% +/- 12%, p less than 0.01). The net effect of the left heart bypass was the increase in cardiac output (20% +/- 2%, p less than 0.05) for any given right ventricular end-diastolic pressure. We conclude that in normal hearts the left heart bypass augments right ventricular performance. We ascribe these beneficial effects to diastolic ventricular interdependence and afterload unloading.