Left ventricular morphology influences mortality after the Norwood operation

BACKGROUND

Within the spectrum of congenital heart disease referred to as hypoplastic left heart syndrome (HLHS), there is variation in the morphology and function of the left ventricle which could influence outcomes after stage I Norwood palliation.

OBJECTIVE

To determine if left ventricular (LV) morphology is associated with outcome after stage I Norwood palliation for HLHS.

METHODS

Echocardiograms were reviewed from 108 patients who had undergone Norwood palliation at our institution over the past 11 years. Total cardiac diameter, thickness of the interventricular septum (IVS), LV area and LV myocardial area were calculated. Competing risk analysis was performed for survival to a stage II operation and to determine potential predictors.

RESULTS

From the Norwood operation up to stage II operation, mortality was predicted by IVS thickness, while the absence of right ventricular (RV) dysfunction was predictive of survival to stage II operation. For the complete pathway, from Norwood to the Fontan operation, mortality was predicted by IVS, a lower RV fractional area change and the presence of significant tricuspid regurgitation. Cardiac transplantation during this period was predicted by a lower RV fractional area change (p = 0.02) and a larger LV area in diastole.

CONCLUSIONS

These results indicate that LV hypertrophy and decreased RV function adversely effect survival after the Norwood operation. They suggest that LV morphology, especially septal hypertrophy, can influence outcomes in HLHS and should be considered when evaluating treatment options.

Assessment of the relationship between cerebral and splanchnic oxygen saturations measured by near-infrared spectroscopy and direct measurements of systemic haemodynamic variables and oxygen transport after the Norwood procedure

OBJECTIVES

To evaluate the clinical utility of near-infrared spectroscopic (NIRS) monitoring of cerebral (ScO2) and splanchnic (SsO2) oxygen saturations for estimation of systemic oxygen transport after the Norwood procedure.

METHODS

ScO2 and SsO2 were measured with NIRS cerebral and thoracolumbar probes (in humans). Respiratory mass spectrometry was used to measure systemic oxygen consumption (O2). Arterial (SaO2), superior vena caval (SvO2) and pulmonary venous oxygen saturations were measured at 2 to 4 h intervals to derive pulmonary (Qp) and systemic blood flow (Qs), systemic oxygen delivery (DO2) and oxygen extraction ratio (ERO2). Mixed linear regression was used to test correlations. A study of 7 pigs after cardiopulmonary bypass (study 1) was followed by a study of 11 children after the Norwood procedure (study 2).

RESULTS

Study 1. ScO2 moderately correlated with SvO2, mean arterial pressure, Qs, DO2 and ERO2 (slope 0.30, 0.64. 2.30, 0.017 and -32.5, p < 0.0001) but not with SaO2, arterial oxygen pressure (PaO2), haemoglobin and O2. Study 2. ScO2 correlated well with SvO2, SaO2, PaO2 and mean arterial pressure (slope 0.43, 0.61, 0.99 and 0.52, p < 0.0001) but not with haemoglobin (slope 0.24, p > 0.05). ScO2 correlated weakly with O2 (slope -0.07, p = 0.05) and moderately with Qs, DO2 and ERO2 (slope 3.2, 0.03, -33.2, p < 0.0001). SsO2 showed similar but weaker correlations.

CONCLUSIONS

ScO2 and SsO2 may reflect the influence of haemodynamic variables and oxygen transport after the Norwood procedure. However, the interpretation of NIRS data, in terms of both absolute values and trends, is difficult to rely on clinically.

Long-term survival after mitral valve replacement in children aged <5 years: a multi-institutional study

BACKGROUND

Short- and long-term outcomes after prosthetic mitral valve replacement (MVR) in children aged <5 years are ill-defined and generally perceived as poor. The experience of the Pediatric Cardiac Care Consortium (45 centers, 1982 to 1999) was reviewed.

METHODS AND RESULTS

MVR was performed 176 times on 139 patients. Median follow-up was 6.2 years (range 0 to 20 years, 96% complete). Age at initial MVR was 1.9+/-1.4 years. Complications after initial MVR included heart block requiring pacemaker (16%), endocarditis (6%), thrombosis (3%), and stroke (2%). Patient survival was as follows: 1 year, 79%; 5 years, 75%; and 10 years, 74%. The majority of deaths occurred early after initial MVR, with little late attrition despite repeat MVR and chronic anticoagulation. Among survivors, the 5-year freedom from reoperation was 81%. Age-adjusted multivariable predictors of death include the presence of complete atrioventricular canal (hazard ratio 4.76, 95% CI 1.59 to 14.30), Shone's syndrome (hazard ratio 3.68, 95% CI 1.14 to 11.89), and increased ratio of prosthetic valve size to patient weight (relative risk 1.77 per mm/kg increment, 95% CI 1.06 to 2.97). Age- and diagnosis-adjusted prosthetic size/weight ratios predicted a 1-year survival of 91% for size/weight ratio 2, 79% for size/weight ratio 3, 61% for size/weight ratio 4, and 37% for size/weight ratio 5.

CONCLUSIONS

Early mortality after MVR can be predicted on the basis of diagnosis and the size/weight ratio. Late mortality is low. These data can assist in choosing between MVR and alternative palliative strategies.

Independent factors associated with longevity of prosthetic pulmonary valves and valved conduits

OBJECTIVE

To evaluate the age dependence of variables predictive of pulmonary valve prosthesis replacement, we conducted the following analysis.

METHODS

Retrospective analysis of 945 operations in 726 patients undergoing placement of pulmonary valve prostheses was performed. Age was identified as a strong independent predictor of valve failure. The database was stratified into age-based subsets and predictors of valve replacement were identified within each subset.

RESULTS

For the entire cohort, freedom from valve replacement at 5 years was 81%. Younger age was strongly associated with decreased time to valve replacement by multivariable analysis (hazard ratio: 0.71/log-year, P <.001). Other independent factors included diagnosis, type of prosthesis, and time-dependent requirement for pulmonary valve stent placement. Important predictors of valve failure varied among age groups and are as follows: for Age Less Than 3 Months: valve type; for Age 3 Months To Less Than 2 Years: smaller normalized valve prosthesis size; for Age 2 Years To Less Than 13 Years: sex, smaller normalized valve prosthesis size, placement of endovascular stents, and valve type; for Age 13 Years To 65 Years: smaller normalized valve prosthesis size, placement of endovascular stents, and increased number of previous valve placements.

CONCLUSION

Age is a dominant risk factor predictive of pulmonary valve prosthesis failure. A significant interaction exists between age and the effects of diagnosis, valve type, and size on prosthetic pulmonary valve longevity.

Interventions associated with minimal fontan mortality

BACKGROUND

The operative mortality rate for the first 400 Fontan procedures at this institution was 15% but declined to 4% for the next 100 procedures.

METHODS

The cases of 100 consecutive patients receiving the Fontan procedure and associated with this change in mortality rate were reviewed to determine associations.

RESULTS

The mortality rate in the first and second 50 patients was 16% and 0%, respectively. There were no differences in age, number of risk factors, diagnosis, or operating surgeon between the two groups. Patients in the lower-mortality era were significantly more likely to have had a cavopulmonary anastomosis before a Fontan procedure (90% versus 70%) and to have an extracardiac Fontan procedure (38% versus 8%), shorter cross-clamp (45+/-24 minutes versus 58+/-22 minutes) and cardiopulmonary bypass times (121+/-42 minutes versus 141+/-45 minutes), magnesium-rich cardioplegia (100% versus 39%), hemoconcentration after bypass (67% versus 4%), and institution of pharmacologic support in the operating room.

CONCLUSIONS

Patient characteristics and risk factors were similar in the two groups. However, several interventions that were increasingly utilized in the lower-mortality era, including the extracardiac Fontan procedure and modified ultrafiltration after bypass, are associated with lower mortality. Each one had the potential to improve postoperative myocardial function.

Balloon aortic valvuloplasty in a 1,600-gram infant

We present a 1,600 g infant who underwent successful balloon aortic valvuloplasty from the right carotid artery approach. A simple technique to facilitate access to the left ventricle and expedite the procedure is described. Issues unique to performing balloon aortic valvuloplasty on such a small child are discussed.

Endovascular stent implantation for the management of postoperative right ventricular outflow tract obstruction: clinical efficacy

OBJECTIVE

Extracardiac conduits between the right ventricle and pulmonary arteries commit patients to multiple reoperations. We reviewed our experience with stent implantation in obstructed conduits.

METHODS

Between 1990 and 1997, stents were implanted across 43 conduits. The median age at procedure was 6 years (0.5-17 years), and the median interval between conduit insertion and stent implantation was 2.4 years (0.3-14 years).

RESULTS

Mean systolic right ventricular pressures and gradients, respectively, decreased from 71 +/- 18 mm Hg and 48 +/- 19 mm Hg before to 48 +/- 15 mm Hg and 19 +/- 13 mm Hg after stent placement. Mean percentage of predicted valve area for body surface area increased from 26% +/- 12% to 48% +/- 17% after stent placement. Fifteen patients underwent a second transcatheter intervention (dilation or additional stent), and 2 patients, a third, allowing further postponement of surgery in 8 patients. One sudden death occurred 2.8 years after stent placement. Surgical conduit replacement has occurred in 20 patients. Body growth was maintained during follow-up. Freedom from surgical reintervention was 86% at 1 year, 72% at 2 years, and 47% at 4 years. Higher right ventricular pressure and gradient before and after stent placement and lower percentage of predicted valve area for body surface area after stent placement were associated with shorter palliation.

CONCLUSION

Endovascular stent placement across obstructed conduits is a safe and effective palliation that allows for normal body growth.

Relentless pulmonary vein stenosis after repair of total anomalous pulmonary venous drainage

BACKGROUND

Progressive stenosis of the pulmonary veins after repair of total anomalous pulmonary venous drainage is frequently refractory to surgical therapy.

METHODS

Retrospective review of 170 consecutive patients treated for total anomalous pulmonary venous drainage identified 13 patients with postrepair pulmonary vein stenosis. Preoperative and operative data were analyzed to define the patterns of progression and efficacy of surgical techniques.

RESULTS

Seventeen reoperations were performed in 13 patients. Postrepair pulmonary vein stenosis was most common in the infracardiac and mixed subtypes (p < 0.02). All 4 patients with unilateral stenosis, 2 of whom had progression of stenosis resulting in nearly complete unilateral pulmonary vein occlusion, survived. Six of 9 patients with bilateral disease died (p < 0.05 versus unilateral); 2 of the 3 survivors were repaired with a novel technique creating a sutureless neoatrium without evidence of restenosis at 1.8 years' follow-up. Stenting was uniformly unsuccessful.

CONCLUSIONS

In unilateral stenosis, progression of disease may be survivable with loss of single-lung perfusion. Although bilateral disease is lethal in most cases, creation of a sutureless neoatrium has demonstrated short-term freedom from disease progression.

Surgical management of total anomalous pulmonary venous drainage: impact of coexisting cardiac anomalies

BACKGROUND

Recent reports have cited improving results for surgical management of isolated total anomalous pulmonary venous drainage. Complex cases (with other cardiac anomalies) are less frequently reported and are associated with higher mortality.

METHODS

Retrospective review identified 170 consecutive patients treated for total anomalous pulmonary venous drainage from 1982 to 1996: 44 cases were "complex" (with significant associated cardiac lesions) and 126 cases were "simple."

RESULTS

Operative mortality for simple cases decreased from 26% to 8%, and mortality for complex cases remained constant at 52%. Age, size, and the presence of atrial isomerism were univariate predictors of mortality. Multivariable analysis identified only univentricular hearts and associated cardiac lesions as predictors of operative mortality. Pulmonary artery (n = 16) and arteriopulmonary (n = 7) shunting strategies for complex cases resulted in less than 30% long-term survival.

CONCLUSIONS

Despite improvement in survival for simple cases, management of total anomalous pulmonary venous drainage with single-ventricle hearts or other associated cardiac lesions remains problematic.

Does cardiopulmonary bypass alone elicit myoprotective preconditioning?

BACKGROUND

Brief episodes of ischemia can precondition myocardium. Ischemic preconditioning (PC) has been proposed as an adjuvant method of improving myocardial protection during cardiac surgery. It is unknown whether CPB without an episode of ischemia generates the PC response.

METHODS AND RESULTS

To prove that PC occurs in sheep, groups 1 (non-CPB control) and 2 (non-CPB ischemic PC, three 5-minute episodes of normothermic regional ischemia) were studied. Groups 3 (CPB alone), 4 (CPB-alpha receptor blockade, phentolamine 5 mg/kg), and 5 (CPB-adenosine receptor blockade, 8-sulfophenyltheophylline 5 mg/kg) were placed on CPB for 30 minutes and subsequently weaned. All groups underwent 60 minutes of normothermic regional ischemia and 150 minutes of reperfusion. The area at risk (AR) was delineated by Monastryl blue pigment, whereas the infarct size (IS) was determine by tetrazolium staining. Body mass, left ventricular mass, and AR were not different between groups. Ischemic PC was demonstrated in this ovine model by a 54% reduction of IS relative to AR (group 1 versus group 2, P < .01). CPB alone produced a similar percentage IS reduction without ischemia (group 3 versus group 1, P < .01) that was prevented by either alpha-adrenergic receptor (group 4 versus group 3, P < .01) or adenosine receptor (group 5 versus group 3, P < .01) blockade.

CONCLUSIONS

CPB alone appears sufficient to elicit the PC response important for myocardial protection during cardiac surgery. These data suggest that myocardial alpha-adrenergic receptor and adenosine receptor stimulation are involve in initiating CPB-induced PC.

Limitations of R-average as an index of left ventricular isovolumic relaxation

Freeman et al. (1993) have recently introduced a new index measuring isovolumic relaxation in the in situ left ventricle. This index, called the R-average, shows less variability than the traditionally used monoexponential time constant (tau), and could therefore represent an alternative measure of isovolumic relaxation during different physiological or pathophysiological interventions. However, the R-average represents the average pressure fall during isovolumic relaxation (isovolumic pressure fall divided by the isovolumic time period), and is therefore highly influenced by the end-systolic pressure level. The present study was done in order to assess whether small increments in loading conditions would alter the R-average without changes in the isovolumic relaxation period or the monoexponential pressure decay tau. We used a right heart bypass porcine model, and end-systolic pressure was altered between 92 and 140 mmHg by pre-loading (servo-pump) or after-loading (phenylephrine) in spontaneously beating and paced hearts. During loading, we found a significant increase in the R-average and a close correlation (r = 0.72 - 0.99) between R-average and en-systolic pressure. However, no alterations were found in the duration of the isovolumic relaxation time period or monoexponential pressure decay (tau) during these loading conditions. In our view, the R-average indicates the systolic loading level for the ventricle, but does not necessarily reflect alterations in the process of active relaxation.

Blood cardioplegia in the senescent heart

As an increasingly aged population undergoes cardiac surgery, myocardial protective strategies must address the fundamental differences between adult and senescent myocardium. In a test of the hypothesis that senescent myocardium is less tolerant of cardioplegic arrest, adult (0.5 to 1.0 years) and senescent (6 to 9 years) sheep underwent 55 minutes of hypothermic blood cardioplegic arrest. A 5-minute dose of terminal warm blood cardioplegic solution was administered followed by 30 minutes of vented reperfusion. Left ventricular volume was monitored by means of sonomicrometric crystals in three orthogonal planes. Myocardial function was assessed with the preload recruitable stroke work relationship. Diastolic function was assessed with two techniques: the "stiffness" coefficient (beta), derived from the exponential end-diastolic pressure-volume relationship, and the time constant of isovolumic left ventricular pressure decay (tau). Data were acquired before arrest and after the reperfusion period. Contractility in the adult hearts was well preserved (preload recruitable stroke work: 63.7 +/- 6.1 versus 56.8 +/- 4.1 mJ/beat per milliliter per 100 gm, prearrest versus postarrest, p = not significant). In contrast, senescent heart contractility was poorly preserved (56.8 +/- 4.1 versus 35.4 +/- 4.2 mJ/beat per milliliter per 100 gm, p < 0.025). Early diastolic relaxation (tau) was prolonged in the adult hearts (42.5 +/- 3.3 versus 48.8 +/- 3.5 msec prearrest versus postarrest, p < 0.05), whereas the senescent hearts were essentially unchanged (49.3 +/- 3.1 versus 52.3 +/- 4.5 msec. p = 0.35). Myocardial stiffness (beta) was unchanged in both groups. When compared with adult hearts, contractility in senescent hearts is poorly preserved after cold blood cardioplegic arrest. Active diastolic relaxation, however, is more prolonged in adult hearts. Passive diastolic properties are unchanged in both groups. Because there are specific age-related differences in tolerance to cardioplegic arrest, extrapolation of myocardial protective strategies from studies in adult hearts to elderly patients may not be appropriate.

Ischemia-dependent efficacy of phosphodiesterase inhibition

To evaluate the inotropic efficacy of phosphodiesterase inhibition in hearts with and without ischemic injury, 27 sheep were evaluated sonomicrometrically during incremental volume loading on right heart bypass. Contractility was assessed with the preload recruitable stroke work relationship. Active relaxation rate was estimated using the time constant of isovolumic pressure decay (tau). For nonischemic assessment, groups 1 and 2 (n = 6 each) underwent 45 minutes of vented perfusion after which milrinone was administered to group 1; group 2 served as nonischemic controls. There was no detectable increase in preload recruitable stroke work or decrement in tau after milrinone administration. Groups 3 and 4 underwent 15 minutes of 37 degrees C ischemia (aortic cross-clamping) followed by 30 minutes of vented reperfusion. Milrinone was then administered to group 3 (n = 7); group 4 (n = 8) served as ischemically injured controls. Inotropic and lusitropic effects were present (group 3 preload recruitable stroke work: 35.4 +/- 5.8 mJ.beat-1.100 g-1.mL-1 before milrinone to 49.5 +/- 4.4 mJ.beat-1.100 g-1.mL-1 after milrinone [p < 0.05]; group 3 tau: 51.8 +/- 5.5 ms before milrinone to 32.2 +/- 2.5 ms after milrinone [p < 0.02]). Although milrinone restored contractility and increased the rate of active relaxation in the postischemic hearts, there was no detectable inotropic effect in nonischemic hearts. In this model, milrinone augments contractility and relaxation in postischemic myocardium but offers little inotropic benefit in non-ischemically injured hearts.

Perfusion deficits with retrograde warm blood cardioplegia

Prior studies of cold retrograde cardioplegia have demonstrated the existence of regional deficits in perfusate delivery. To address the hypothesis that these deficits persist with the use of warm perfusate, cardioplegic arrest was induced in 7 swine hearts with retrograde warm blood cardioplegia. Regional perfusion was assessed with the simultaneous infusion of colored 10-microns microspheres. The percentage microsphere recovery (regional microsphere count/total number of microspheres counted x 100) was greatest in the anterior (43% +/- 4%) and lateral (35% +/- 6%) left ventricle. The microsphere recoveries in the posterior left ventricle (7% +/- 1%) and anterior septum (14% +/- 4%) were intermediate, and were statistically lower than those in the anterior left ventricle (p < 0.01). The lateral right ventricle (0.6% +/- 0.2%) and the posterior septum (1.4% +/- 0.9%) exhibited minimal perfusion versus that in the anterior left ventricle (p < 0.01). Less than 1% of the infused microspheres were recovered in the aortic root; 67% were recovered in the right ventricle and are presumed to have bypassed the microcirculation as nonnutritive flow. These data demonstrate that cold retrograde perfusion patterns persist during retrograde warm blood cardioplegia. Limited perfusion of the right ventricle and the posterior septum as well as a large nonnutritive flow were also noted. These perfusion deficits in metabolically active arrested hearts may limit myopreservation at low cardioplegia flow rates.