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Ann Thorac Surg 2003;75:153-157
© 2003 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH, USA
b Department of Pediatric Cardiology, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, USA
Accepted for publication July 8, 2002.
* Address reprint requests to Dr Pearl, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA.
e-mail: pearj0{at}chmcc.org
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Abstract |
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METHODS: From June 1996 to June 2001, 40 patients underwent a modified Fontan operation. Four patients developed acute pancreatitis postoperatively. The preoperative, intraoperative, and postoperative hemodynamics and ventricular function parameters were retrospectively analyzed and compared to 10 randomly selected Fontan patients who did not have pancreatitis. Preoperative echocardiographic and angiographic data, including digitized ventricular pressure tracings, were reviewed to obtain ventricular relaxation time constant (tau), pulmonary vascular resistance (PVR), ventricular end diastolic pressure (VEDP), positive dp/dt and negative dp/dt values.
RESULTS: Patients developing acute pancreatitis had very high mortality (50%) compared to no mortality in the control group. The mean preoperative tau was significantly prolonged (41 ms vs 26 ms in control group, p < 0.001), and pre operative systemic output (Qs) lower in the pancreatitis group (mean 2.75 L/min/m2) compared with controls (Qs of 5.09 L/min/m2, p < 0.03).
CONCLUSIONS: Impaired ventricular relaxation and decreased preoperative cardiac output are predictive of increased risk of postoperative pancreatitis in Fontan patients. Evaluation of preoperative diastolic function in these patients may provide additional insights in to clinical outcome following the Fontan procedure.
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Introduction |
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Importance of diastolic function on the outcome of Fontan operation was recognized by Mair and colleagues [9], who devised an index for patient selection based on the preoperative pulmonary vascular resistance and ventricular diastolic pressure. Impedance to ventricular filling may translate into elevated right-sided Fontan pressures as well as to decreased systemic cardiac output despite good systolic function. Even in two-ventricle hearts, abnormal diastolic function is incriminated in a significant percentage of adult heart failure patients with normal ventricular ejection fraction [10]. In the postoperative Fontan patients, the combination of elevated central venous pressure, and low cardiac output have been related to impaired visceral perfusion, evidenced by renal insufficiency or failure [8]. The addition of vasoactive agents to support systemic blood pressure further compromises visceral end-organ perfusion. Pancreatic perfusion is particularly susceptible to decreased perfusion pressure resulting in ischemia and pancreatitis.
Echocardiographic indices have been devised to provide noninvasive diastolic function assessment [11, 12]. Determination of the time constant of isovolumic ventricular relaxation, tau, from digitized ventriculogram tracings, has been shown to be a reproducible and accurate method of determining diastolic relaxation [13]. In an effort to identify specific perioperative factors predictive of postoperative pancreatitis in Fontan patients, we retrospectively reviewed our Fontan experience.
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
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A randomly selected comparison group of 10 Fontan patients operated on during the same period, who did not have any clinical signs of pancreatitis in the post operative period was analyzed for comparison.
Patient demographics were similar between the two groups (Table 1). Diagnoses included tricuspid atresia, double inlet left ventricle, hypoplastic left heart syndrome, and pulmonary atresia with intact septum. All patients had undergone at least one prior palliative procedure. More than 80% were staged with a previous bi-directional Glenn or a hemi-Fontan procedure. No patients had previous history of gastrointestinal problems or pancreatitis. Preoperative hemodynamic evaluation, including a transthoracic echocardiogram and cardiac catheterization, was performed in all patients. The ventricular pressure tracings obtained from the pre-Fontan cardiac catheterization were digitized using a curve analysis program (Digisonics, Houston, TX). The pressure data were sampled at 5 ms intervals. Ventricular end diastolic pressure (VEDP) and peak negative dp/dt were measured. Tau was calculated according to the method described by Weiss and coworkers [13], using a semilogarithmic model (zero asymptote) with the true exponential decay starting at peak negative dp/dt and ending at 5 mm Hg above the VEDP. All measurements were expressed as the average of 5 cardiac cycles.
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where Qpi = pulmonary blood flow indexed to body surface area; Qsi = systemic blood flow indexed to body surface area; and Qp and Qs were calculated using Fick’s principal.
Transpulmonary gradients were measured in all the patients at the end of the operation (direct manometric pressure measurement) by subtracting left atrial pressures from the superior vena cava pressures.
Statistical analysis
Student’s t-test was used to compare the mean values of the two groups and to determine the p values. A p value of < 0.05 was considered significant. SAS software was used for statistical analysis (release 8.02; SAS, Cary, NC). Stepwise logistic regression analysis to determine independent predictors for the outcome of pancreatitis was carried out. Preoperative variables analyzed included the following: age at Fontan, body surface area at the time of surgery, ventricular end diastolic pressures (VEDP), positive dp/dt, negative dp/dt, mean pulmonary artery (PA) pressures, pulmonary capillary wedge pressures (PCWP)/left (LA) atrial (or common atrial) pressures, pulmonary vascular resistance (RP), indexed pulmonary flow (Qp), indexed systemic blood flow (Qs), relaxation time constant (tau), and Mairs index. Statistical analysis was also carried out on operative transpulmonary gradients (TPG), cardiopulmonary bypass time (CPB time), cross clamp time (XC time), length of intensive care unit (ICU) stay, and hospital length of stay (LOS).
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Results |
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Primary congenital cardiac defect, ventricular morphology, age, previous operation, and type of Fontan had no bearing on the early postoperative gastrointestinal complications (Table 1). There was no significant difference in preoperative systolic function between groups. Preoperative echocardiography demonstrated qualitatively normal systolic ventricular function and no significant atrioventricular valve regurgitation in both groups (Table 2).
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Patients with pancreatitis had significantly higher tau values (p < 0.007) and lower systemic output Qs (p < 0.03) preoperatively. There was no significant difference in any of the other measured indices between groups. Mairs index, positive dp/dt, negative dp/dt, VEDP, pulmonary vascular resistance (Rp), pulmonary capillary wedge pressure, and mean pulmonary artery pressures were comparable in both the groups. Cross clamp time and transpulmonary gradients measured during the operation did not show any statistically appreciable difference between the two groups (Table 2). Bypass time neared statistical significance between groups, being longer in the pancreatitis group (p < 0.05).
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Comment |
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Long bypass runs, the use of intraveneous calcium, and poor cardiac output, often in conjunction with vasoactive agents, have been implicated in the etiology of pancreatitis following cardiac surgery [14, 18]. There was a trend towards longer bypass times in the pancreatitis group, which may reflect more complex anatomy. The combination of more extensive reconstruction and longer bypass time may increase the risk of end-organ dysfunction including pancreatitis.
In this study, the four patients who developed post-Fontan pancreatitis had evidence of significant ventricular relaxation abnormalities preoperatively as measured by tau and decreased Qs. Low preoperative systemic output (Qs) may be attributed to diastolic dysfunction in the face of normal ventricular systolic function. These patients demonstrated significant differences in these values, despite acceptable classic diagnostic criteria such as VEDP and ejection fraction. Transpulmonary gradients were measured in all the patients twice, once at preoperative angiography and then intraoperatively. No correlation between TPG and postoperative pancreatitis was found.
Tau is a measure of the time constant of the exponential pressure decline during isovolumic relaxation of the ventricle. It is a logarithmic value of exponential fall in ventricular pressure. The smaller the value of tau, the faster is the rate of ventricular relaxation [19]. Increase in heart rate and sympathetic stimulation (inotropic drugs) shorten the tau value, while it is increased by ischemia, ventricular hypertrophy, increase in arterial pressure and increased end diastolic volume [20]. Ventricular hypertrophy was a risk factor for early and late death in a series of 102 Fontan patients operated between 1975 to1985 [21]. In 1990 Caspi and colleague from Toronto [22], found advanced myocardial hypertrophy (potentiated by pulmonary artery banding and subaortic stenosis) as the major morphologic finding in 37 patients who died within 2 months after a Fontan procedure. A previous coarctation repair was the "sole risk factor" for long-term failure of lateral tunnel Fontan in a report from the Children’s Hospital (Boston, MA), published in 2001 [23]. It is only fair to say, that in all of the above mentioned studies with a combined analysis of more than 550 Fontan patients ventricular hypertrophy is incriminated as a major cause of death or Fontan failure. Ventricular hypertrophy may result in poor ventricular diastolic relaxation even with relatively normal VEDP.
Flow in the systemic venous pathway of Fontan circulation is 70% cardiac dependent, while the rest is contributed by the negative intrathoracic pressure during inspiration. Highest flows occur during early diastole with minimum flow in diastasis. Quantitative contribution of early diastolic flow may be much greater as the heart rate is four to five times higher than respiratory rates [24]. Diastolic relaxation dysfunction may lead to higher systemic venous pressures, which in turn reduces the transhepatic venous pressure gradient (difference between "wedged hepatic vein" pressure and the "free" hepatic vein pressures). This inverse correlation is more pronounced in the patients with poor functional class after a Fontan operation [25]. The result is worsening of portal venous flow with portal hypertension and congestion of portal venous pathways. We presume that this is a mechanism of pancreatic congestion exacerbating pancreatic inflammation in the patients with abnormal ventricular diastolic relaxation.
The small number of patients with pancreatitis in this study makes it difficult to implicate diastolic ventricular dysfunction as the sole cause based on statistical analysis. However, abnormalities of diastolic relaxation warrant further investigation as a preoperative predictor of poor postoperative outcome in Fontan patients.
Conclusion
These findings suggest that diastolic dysfunction is a significant contributor to post-Fontan morbidity, specifically with regard to risk of postoperative pancreatitis. Preoperative tau and Qs may be predictive of poor post-Fontan hemodynamics. Post-Fontan pancreatitis is associated with prolonged morbidity and poor outcome. The development of diastolic dysfunction in single ventricle patients may partially be related to hypertrophy and prolonged cyanosis. Theoretically, earlier relief of volume overload, staged palliation, early Fontan, and use of after-load reduction may all reduce the occurrence of diastolic dysfunction.
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Acknowledgments |
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  E. A. Hessel II Abdominal Organ Injury After Cardiac Surgery Seminars in Cardiothoracic and Vascular Anesthesia, September 1, 2004; 8(3): 243 - 263. [Abstract] [PDF]
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 W. L. Border, A. U. Syed, E. C. Michelfelder, P. Khoury, K. C. Uzark, P. B. Manning, and J. M. Pearl Impaired systemic ventricular relaxation affects postoperative short-term outcome in Fontan patients J. Thorac. Cardiovasc. Surg., January 1, 2004; 126(6): 1760 - 1764. [Abstract] [Full Text] [PDF]
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