Exercise Tolerance in Extracardiac Total Cavopulmonary Connection
Zongtao Yin, PhD,
Cengwei Wang, MD,
Hongyu Zhu, MD,
Renfu Zhang, MD,
Huishan Wang, PhD,
Xinmin Li, MD
Department of Cardiovascular Surgery, Shenyang Northern Hospital, Shenyang, China
Zongtao Yin, PhD, Tel: +86 24 2305 1214, Email: yzt1210{at}hotmail.com, Department of Cardiovascular Surgery, Shenyang Northern Hospital, 83 Wenhua Road, Shenhe District, Shenyang 110016, China.
ABSTRACT
Cardiopulmonary adaptation during exercise was compared in patients with an extracardiac total cavopulmonary connection and controls with biventricular repair of Fallot’s tetralogy. Heart rate, blood pressure, respiratory frequency, and transcutaneous oxygen saturation increased with treadmill exercise intensity below grade 3 in patients who had undergone extracardiac total cavopulmonary connection. When exercise intensity exceeded grade 4, blood pressure and oxygen saturation decreased continuously, respiratory rate kept increasing, and heart rate showed no significant change. In cases of fenestrated cavopulmonary connection, heart rate peaked at grade 5 exercise intensity, and blood pressure at grade 4; but both peaked at grade 3 in non-fenestrated patients. During all exercise testing, fenestrated patients had a higher respiratory rate but lower oxygen saturation than those without fenestration. Exercise tolerance was below normal after a cavopulmonary connection, but patients still adapted to exercise below grade 3 with appropriate increases in heart rate and respiratory rate. Due to insufficient right heart systems, patients with a cavopulmonary connection showed obvious exercise limitation at exercise intensity grade 3 or more. Total exclusion of the right heart system may also have adverse effects on the sinoatrial node, leading to impaired heart rate regulation.
Key Words: Exercise Tolerance • Heart Bypass • Right • Heart Defects • Congenital
INTRODUCTION
Extracardiac total cavopulmonary connection (TCPC), a surgical connection to route blood flow from the vena cava to the pulmonary artery, has become the final palliative choice for patients with a functional single ventricle but normal pulmonary resistance.1,2 Due to total exclusion of the right heart in TCPC, the driving force for systemic venous blood to move into the pulmonary circulation is completely dependent on vena caval pressure. The long-term surgical outcome of TCPC, especially the effect of circulation reconstruction on exercise tolerance, is rarely reported.3 We evaluated exercise tolerance in 36 patients with TCPC to provide some data and recommendations on this issue.
PATIENTS AND METHODS
Forty-one patients (22 males and 19 females) with functional single ventricle, who underwent extracardiac TCPC at Shenyang Northern Hospital from March 1990 to December 2005, were enrolled in this study. A control group comprised 36 patients undergoing radical repair of tetralogy of Fallot, who were similar to the TCPC group in age, sex, and height. The characteristics of the study population are summarized in Table 1
. One patient who received a modified Fontan operation for single-ventricle heart (AIII) 1 year earlier was re-treated with the TCPC procedure because of postoperative supraventricular tachycardia. TCPC was also performed in a patient with single-ventricle heart (AII) and in 4 who had received bidirectional Glenn shunts due to tricuspid atresia (Ib). Sixteen operations were performed under cardiopulmonary bypass with moderate hypothermia and intermittent cold crystalloid cardioplegia. Concomitant procedures included atrial septal defect enlargement in 4 cases, and mitral valve plasty in 2. The other 25 patients were operated on under hypothermic cardiopulmonary bypass with a beating heart. The inferior vena cava was anastomosed to the right pulmonary artery in 23 cases. End-to-side anastomosis of a vascular graft conduit to the pulmonary artery trunk was performed in 18 cases. The extracardiac conduits had a mean internal diameter of 18.9 ± 2.7 mm. The pulmonary valve orifice was sutured closed. In 18 operations, a 5-mm fenestration was made between the conduit and the right atrium because vena caval pressure exceeded 20 mm Hg. There was no significant pressure gradient across the superior and inferior venae cavae, extracardiac conduit, and pulmonary artery. Mean pulmonary arterial pressure was 16 ± 3 mm Hg. Early postoperative mortality was 9% (4/41) due to low cardiac output syndrome in 2 patients, cardiac arrest in 1, and failure to wean from the respirator in 1. Another one died 6 months after the operation form refractory pleural effusion combined with hypoproteinemia. The 36 survivors performed a progressive exercise test on a programable treadmill (GE Marquette Series 2000). Exercise intensity was classified into 7 grades, and the procedure was divided into 9 stages. A summary of the exercise protocol is given in Table 2. Heart rate (HR), blood pressure (BP), oxygen saturation via pulse oximetry (SpO2), and respiratory frequency (Rf) were measured every 2 min during each stage.
All data are expressed as mean ± standard deviation. Analyses were performed with SPSS version 10.0 statistical software (SPSS, Inc., Chicago, IL, USA).
RESULTS
At the start of the exercise test, all patients maintained sinus rhythm. Of the 36 patients in the TCPC group, 34 completed the test; 1 stopped due to intolerable discomfort at grade 5 exercise intensity, and another due to bigeminal ventricular premature beats at grade 5. All 36 patients in the control group completed exercise testing to grade 7. HR, BP, SpO2, and Rf in the TCPC group increased with exercise intensity below grade 3. However, above grade 4, BP and SpO2 decreased continuously (minimum at grade 7), Rf kept increasing (maximum at grade 6), and HR showed no significant changes. After the 5-min rest, HR and Rf were still higher than before exercise. Under resting conditions, HR and Rf of the TCPC group were higher than the control group (t = 2.14, p < 0.05; t = 2.32, p < 0.05), but SpO2 was lower (t = 2.47, p < 0.05). When exercise intensity exceeded grade 3, HR, BP, and SpO2 decreased more significantly, but Rf increased continuously and recovered more slowly in the resting stage (Figures 1–4). In the 18 patients with fenestrated TCPC, HR peaked when exercise intensity reached grade 5, and BP peaked at grade 4; whereas in 18 non-fenestrated patients, HR and BP were maximal at grade 3. During the whole process of exercise testing, fenestrated patients showed a higher Rf but lower SpO2 than those without fenestration (Figures 5–8).
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Figure 1. Heart rate changes with exercise intensity in 36 patients who underwent extracardiac total cavopulmonary connection (TCPC) and 36 controls. *p < 0.05. **p < 0.01.
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Figure 2. Systolic pressure changes with exercise intensity in 36 patients who underwent extracardiac total cavopulmonary connection (TCPC) and 36 controls. *p < 0.05. **p < 0.01.
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Figure 3. Respiratory rate changes with exercise intensity in 36 patients who underwent extracardiac total cavopulmonary connection (TCPC) and 36 controls. *p < 0.05. **p < 0.01.
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Figure 4. Oxygen saturation changes with exercise intensity in 36 patients who underwent extracardiac total cavopulmonary connection (TCPC) and 36 controls. *p < 0.05. **p < 0.01.
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Figure 5. Heart rate changes with exercise intensity in patients who underwent extracardiac total cavopulmonary connection with (n = 18) or without (n = 18) fenestration. *p < 0.05.
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Figure 6. Systolic pressure changes with exercise intensity in patients who underwent extracardiac total cavopulmonary connection with (n = 18) or without (n = 18) fenestration. *p < 0.05. **p < 0.01.
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Figure 7. Respiratory rate changes with exercise intensity in patients who underwent extracardiac total cavopulmonary connection with (n = 18) or without (n = 18) fenestration. *p < 0.05.
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Figure 8. Oxygen saturation changes with exercise intensity in patients who underwent extracardiac total cavopulmonary connection with (n = 18) or without (n = 18) fenestration. *p < 0.05. **p < 0.01.
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DISCUSSION
During the last 20 years, the Fontan operation has undergone several modifications of the detailed connections between the vena cava and pulmonary artery. Associated with a simplified operative procedure, expanded indications, and fewer complications, the extracardiac TCPC procedure (a modified Fontan operation to directly connect the superior/inferior vena cava to the pulmonary artery) has become the final palliative choice for patients with functional single ventricle but normal pulmonary resistance.1,2,4 It is currently accepted that a rational surgical option, modified operative procedure, well-developed pulmonary vascular bed, and normal ventricular function are the determinants of good exercise tolerance in post-Fontan patients. However, some patients who were confirmed to have a well-developed pulmonary vascular bed and normal pulmonary resistance by preoperative catheterization and angiography, experienced failure of the Fontan-type circulation due to increased pulmonary resistance.5 Thus a study of the effect of circulation reconstruction on exercise tolerance is of great significance in predicting the long-term outcome.
As a palliative operation, TCPC shows the biggest difference from biventricular repair in the hemodynamic changes under exercise conditions, which is due to the fact that the right ventricle is totally excluded in TCPC, and lung perfusion is fully dependent on vena caval pressure. Thus patients with tetralogy of Fallot with cyanosis were chosen as a control cohort to study the changes in single-ventricular physiology. According to previous reports, intrapleural negative pressure during the process of respiratory movement can affect lung perfusion significantly by promoting venous blood return to the right heart and enhancing lung blood flow. Post-Fontan patients usually have considerable increases in HR and respiration to compensate for the right ventricular deficiency. Post-TCPC patients in our study showed moderate increases in HR and Rf, consistent with a study by Redington and colleagues.6 It has been reported that the Fontan procedure leads to lower postoperative exercise tolerance than biventricular repair, and that increasing exercise intensity worsens exercise intolerance, which is manifested by tachycardia and decreased cardiac output and oxygen saturation. The HR, BP, Rf, and SpO2 of the TCPC group increased with exercise intensity < grade 3, but>grade 3 led to no further increase in HR and BP, accompanied by increased Rf and a continuous decrease in SpO2. These finding are not completely consistent with the report of Durongpisitkul and colleagues.7
The important differences between TCPC and the traditional Fontan operation are complete right heart exclusion and proximity to the sinoatrial (SA) node with TCPC. Thus we postulate that TCPC might be associated with SA node dysfunction during physical activity. As far as is known, normal cardiac pacemaker activity of the SA node depends not only on the tissue tension around the SA region, caused by venous return to the right atrium, but also on the blood temperature in this area. With increasing exercise, stronger muscle contraction enhances venous return and right atrial pressure, while muscle heat production increases blood temperature. These 2 factors lead to increased HR and cardiac output by enhancing SA node excitability, which coordinates well with the sympathetic-related increase in Rf and gas exchange. All these changes are responsible for the body’s adaptability to increasing oxygen demand during physical activity. TCPC, a procedure causing total right heart exclusion, makes it impossible for the stimuli of venous pressure and blood temperature to travel to the SA node during physical activity. As a result of impaired HR control, the heart will not beat faster with an increase in exercise intensity, and it finally leads to BP dysregulation (failure of BP to rise during exercise), systemic hypoperfusion, and activity intolerance, which are manifested by a decrease in SpO2. Thus an increase in Rf becomes the last choice for the body to increase blood oxygen content, and additional work of breathing is necessary to compensate for right heart exclusion.
Among the TCPC patients, we further compared non-fenestrated TCPC patients with the fenestrated group who showed better adaptability of HR and BP control but a more obvious drop in SpO2. These differences result from the increased shunt through the fenestration, which is related to high vena caval pressure caused by failure of the Fontan circulation to drive the venous return into the left heart. On one hand, increased venous return to the left atrium increases HR and BP via SA node stimulation, but on the other hand, the increased right-to-left shunt causes a decrease in oxygen saturation and worsening cyanosis and activity intolerance. This further indicates that loss of sinus rhythm in the TCPC procedure has great significance on HR regulation during exercise. The fenestrated TCPC operation aims to prevent vena caval hypertension, but an increased right-to-left shunt on exercise will still worsen cyanosis and activity intolerance. Perhaps with exercise, the normal rise in pulmonary pressure leads to a more significant right-to-left shunt; although increased cyanosis is a direct consequence, perhaps cardiac output is better maintained, so we should be cautious about closure of the fenestration. In addition, pleural space integrity should be preserved in the Fontan operation, because negative pressure in the pleural cavity is the major driving force that facilitates pulmonary perfusion.
Our study also showed that TCPC patients tolerated physical activity below grade 3 intensity with appropriate increases in HR and Rf; however, due to an insufficient right heart system, they exhibited obvious exercise limitation at grade 3 or more. The traditional atriopulmonary Fontan and lateral tunnel cavopulmonary connections, characterized by partial right atrial exclusion and SA node preservation on the right heart side, show good exercise tolerance due to SA node regulation of HR and cardiac output on mild or moderate exercise, although both techniques have been criticized for the long-term postoperative complication of atrial arrhythmia due to right atrial hypertension. Both intercaval tunnel and extracardiac TCPC, featuring exclusion of the right heart and SA node on the left atrial side, cause poor exercise tolerance due to loss of HR control by the SA node. However, the extracardiac and lateral tunnel TCPC procedures with autologous pedicled pericardium, a recent procedure with less suturing of the right atrium and exclusion of most of the atrial wall, can decrease long-term atrial arrhythmias. Meanwhile, the extracardiac and lateral tunnel TCPC permit SA node preservation on the right heart side, which may enhance post-TCPC exercise tolerance. Moreover, autologous pedicled pericardium can grow with the child, which avoids reoperation for tube graft replacement and reduces postoperative complications including embolization. Although extracardiac and lateral tunnel TCPC are believed to be free of many disadvantages, further studies are necessary to confirm the therapeutic effects.
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Asian Cardiovasc Thorac Ann 2009;
17:39-44
© 2009 by SAGE Publications
DOI: 10.1177/0218492309102531
