February 2002, Volume 52, Issue 2

Original Article

Abnormalities of Conduction after total correction of Fallot’s Tetralogy: a Prospective Study

A. Hussain  ( Department of Cardiac Surgery, National Institute of Cardiovascular Diseases, Karachi. )
A. Malik  ( Department of Cardiac Surgery, National Institute of Cardiovascular Diseases, Karachi. )
A. Jalal  ( Department of Cardiac Surgery, National Institute of Cardiovascular Diseases, Karachi. )
M. Rehman  ( Department of Cardiac Surgery, National Institute of Cardiovascular Diseases, Karachi. )

Abstract

Objective:To determine the frequency of post-operative conduction abnormalities in Pakistani patients undergoing total correction for Fallot’s Tetralogy.
Patients and Methods:One hundred and fifteen patients of Fallot’s Tetralogy underwent definitive repair between January,1999 and April, 2000. Their mean age was 12.89 years ( range 3-30 years). One hundred nine patients (94.78%) had severe cyanosis and 6 patients (5.21%) were moderately cyanotic due to mild right ventricular outflow tract (RVOT) obstruction. Thirty percent patients required frequent hospital admissions within 6 months before the time of operation due to -hyper-cyanotic spells. The mean haematocrit was 50.83 (range 28-71). The majority of patients were in NYHA class-Ill (57%) and 45% had previous palliative shunt procedures done. Surgical access was through the RVOT in 90% cases and trans-atrial in 10%. RVOT patch was used in 55.9%, Pulmonary artery patch in 13.5% and trans-annular patch in 17.1% of cases.
Results:The mean bypass time was 79.15 min and the mean cross clamp time 51.23 min. Average stay in the intensive care unit was 4.48 days. Twenty-three patients required re-exploration for bleeding. Sixty-nine patients required Inotropic support. Fifteen patients had transient heart blocks and two had complete heart block requiring permanent pace-maker. Nineteen patients had various transient arrhythmias which were managed medically. Univariate analysis showed that higher age at operation, low preoperative heart rate, prolonged bypass time, prolonged cross clamp time and presenceof patch on pulmonary artery were more àommon in patients who developed various heart blocks. However, none of these factors had statistical significance or definitive cause-effect relationship with heart blocks.
Conclusion:With careful surgical technique, total correction of Fallot’s tetralogy can be conducted in children and young adults, with a very low risk of conduction abnormalities (JPMA 52:77:2002).

Introduction

Surgical correction of the Fallots’ Tetralogy (TOF) is one of the commonest operations in paediatric cardiac surgery. However, there are still controversies regarding the surgical approach and the optimal age for operation. Most of the surgeons in the developed world prefer to operate earlier as a one stage procedure. The definitive repair in infancy have been reported to carry low mortality and morbidity1-4. However, in developing countries like Pakistan, staged repair is still practised due to various limitations, Total correction in older children and young adults is very challenging. The repair through right atrium alone becomes technically difficult and right ventriculotomy is required quite frequently5. Since very few adult cases of Fallot’s Tetrology are seen in the developed world, there is very little information about the results and post-operative problems of surgery in this age group. The largest series of over 800 such cases was reported by John et al.6 which showed 0.4% incidence of complete heart block, This study however, does not provide any information about the risk factors for conduction defects. This study was done to determine frequency of the post- operative incidence of conduction abnormalities and to identify any possible incremental risk factors.

Patients and Methods

Patient Characteristic
From January 1999 to April 2000, 115 cases of TOF underwent total correction at National Institute of Cardiovascular Diseases, Karachi.
Standard cardiopulmonary bypass with hypothermia to 28° C and cold crystalloid cardioplegia was used in all patients. In patients with perimembranous VSD, right ventriculotomy was used to access the VSD. Incision was made either transverse or vertical depending upon anatomy of coronary arteries. However in VSDs extending more towards inflow tract, trans-atrial approach was used. The resection of RVOT was done by excising parietal band. The dissection was then carried upwards, dividing all obstructing muscle bands and excising the fibrous tissue. The main pulmonary artery was opened longitudinally only if it was small i.e. size two standard deviation or more below the normal mean size for the patients. Pulmonary valvotomy was performed by incising through the existing commissures. The adequacy of the right ventricular outflow tract was assessed either visually or in doubtful cases by passing a Hegar’s dilator of adequate size for age and body weight and body surface area. The pulmonary valve annulus was saved wherever possible, A patch of Dacron was used to repair VSD. Double ended 5/0 prolene (Ethicon) on 16 mm round body needle was used for stitching. Majority (90%) of patients had perimembranous VSDs. In small VSDs with entirely membranous poster9inferior rim we used pledgetted interrupted mattress sutures, stitched upto the middle of the superior rim of crista supra ventricularis then leading onwards by continuous over and over stitching for the rest of the VSD. In VSDs with muscular postero inferior rim, we used continuous over and over stitching all around. Any gross leak was checked by injecting saline through the LV vent passed via right superior pulmonary vein at the beginning of the operation. Since, in the region ofposterio-inferior rim of V SD the conduction tissue lies in the left ventricular side, we used superficial bites. The RVOT and the pulmonary artery were closed with autologous pericardial patch whenever required. All patients were electively ventilated and stayed in the intensive care unit for customary 24-48 hours for invasive monitoring.
Follow-up was conducted by the surgical team at six weeks, three months, six months and one year. The clinical evaluation was supplemented with ECO and echocardiography. Six months follow-up was complete in 100% cases and the median follow up was 12 months. Data was collected by filling the individual forms and electronic data sheet (Excel 97).
Statistical Analysis
Data was analysed using .SPSS software. Descriptive statistics i.e. frequencies, mean, medians, standard deviations and 95% confidence intervals were calculated for all preoperative and post-operative variables. Univariate analysis was done using student’s t test for continuous variables and chi-square (x2) test for categoric variable and Fisher’s exact test was used where ever necessary (Tables 4 and 5). The correlation between heart block and categoric variables was assessed by using Phi-statistics (0). The level of significance for all these test results was set at P value of <0.05.

Results

There were 77 males (66.95%) and 38 females (33.04%). The mean age at the time of the operation was 12.89 years with a standard deviation of 5.02 years (range 3-30 years). The frequency distribution of ages is shown in the histogram (Figure).


The associated cardiac anomalies were found in 54 patients (46.95%) included patent foramen ovale (PFO), atrial septal defect (ASD), patent ductus arteriosus (PDA) and multiple small ventricular septal defects (VSD). Anomalies of coronary arteries were detected in 12 patients (10.43%). Severe cyanosis was found in 109 patients (94.78%) and 6 patients (5.21%) had moderate cyanosis as their RVOT obstruction was not very severe. Thirty percent patients had repeated cyanotic spells requiring emergency hospital admissions within 6 months before the time of operation. The mean haematocrit was 50.83% (range 28-71%). Majority of the patients were in NYHA class-Ill (57%). Fourtyfive percent patients had previous shunt procedures. The pre-operative patient characteristics are summarised in Table 1.


The operative procedure in all cases was uncomplicated. The average bypass time was79.70 minutes (range: 50-240 minutes) , the cross clamp time was 51.91 minutes (range: 26-100 minutes). The bypass and the cross-clamp times were similar in both groups i.e. with or without rhythm/conduction abnormalities (Table 2).


Out of 115 total patients, 85 patients (69.1%) remained in normal sinus rhythm. Whereas 28 (22.8%) developed temporary conduction abnormalities but remained haemodynamically stable and were treated with temporary pacing for a period between 1-7 days. Only 2 patients developed complete heart block and required permanent pacemaker insertion after being on temporary pacemaker for 3 weeks. Various types of heart blocks were observed in other patients. The mean ICU and hospital stays were 4.27 days (range 1-13) and 9 days (range 7-18 days) respectively. These were longer in patients who developed conduction abnormalities. However the difference did not reach statistical significance (Table 3).


Other postoperative complications include re­exploration for bleeding, renal impairment, hypoxia, pneumothorax and pleural effusion. All these had uniform distribution in both groups i.e., with or without conduction abnormalities. No patient in this study developed any neurological complication (Table 3).
Fourteen patients (12.17%) died in the early postoperative period. None of these deaths were associated with any of the conduction abnormalities but due to biventricular failure in majority of the patients. The causes of death are given in Table 3.
Surgical correction of Fallot’s Tetrology can be carried out as early as the first year of life7,8 with low mortality and morbidity9,10. However in a developing country hkc Pakistan, two-stage repair involving initial shunt procedure at infancy followed by delayed surgical repair is still practiced, due to limitation in the intensive care management of infants. In the developed countries two-stage repair is only indicated in cases with pulmonary atresia, an associated very small right or left pulmonary artery, or an anomalous coronary artery. The initial shunt procedure provides some time for the pulmonary vasculature to develop to normal size. Interventricular septum and specially the margins of the ventricular septal defect becomes thicker and technically it becomes easier to take superficial bites at the posteroinferior rim of the VSD by avoiding injury to the conduction system which lies on the left ventricular side of the rim of the VSD. The low incidence (2 patients, 1.7%) of the permanent postoperative heart block can be attributed to the relatively older age (mean 12.9 years) of patients in this study.
Although grown up children can cope well with complicated intra-cardiac repair procedure, total correction in older children and young adults is a very challenging job. The massive right ventricular hypertrophy completely obscures the morphology of defects hence making the exposure of VSD technically difficult. In majority of these patients, satisfactory repair through right atrium alone is technically difficult and right ventriculotomy is required quite frequently.
There is evidence that transventricular approach increases the risk of ventricular arrhythmias and bundle branch blocks11-13, Nevertheless, transventricular approach has been used for many years and is still in use with good results by some surgeons,14. Marco et al15 have recommended the use of right ventriculotomy in patients with hypoplastic right ventricular outflow tract. The right ventriculotomy rate in their series was 31.8%. However, avoiding a ventriculotomy is very appealing and many authors have proposed a transatrial or transatrial-plus­transpulmonary approach as the preferred route of access in all cases16-18.
The incidence of arrhythmias quoted in literature is highly variable. The commonest form of arrhythmia after total correction is multiple ventricular ectopics which can give rise to runs of ventricular tachycardia or even ventricular fibrillations19,20. The commonest conduction defect following repair is the right bundle branch block (RRBB). Its incidence alone or in combination with left anterior hemi block has been reported between 40-100% and 8-22% respectively21. We noticed RBBB in 8.1% and RBBB with left anterior hemi block in 2.4% of our cases. An injury to right bundle branch (RBB) can occur at three levels22. The first level of injury is at the septal portion of the right bundle branch (i.e.proximal RBBB). This usually occurs during repair of VSD in its posteroinferior portion. The 2nd level of injury i.e.. distal RBBB, is at the moderator band. This can occur during resection of the muscle below the level of the VSL) (the trabecula septomarginalis). The 3rd level of injury i.e. terminal RBBB is due to the transection of all major branching systems of right bundle branch at the junction of the moderator and parietal band. This occurs during extensive ventriculotomy or infundibulectomy through transatrial approach.
The site of injury can be determined non-invasively by echocardiography by measuring the time taken by the cardiac impulse to travel from the AV node to the apex of the right ventricle i.e. V-RVA interval. This is ‘longer than 35msec in proximal right bundle branch block but normal in terminal RBBB23. The RBB13 alone has very limited clinical significance and does not require any treatment. The other types include different degrees of AV blocks and the combination of RBBB and LAH which is frequently associated with symptoms like syncopal attacks and requires insertion’ of permanent pacemaker. Very little is known about the risk factors that can predict the development of heart block after the operation. We studied large number of preoperative and operative variables to find out any possible incremental risk factors. A complete list of these variables is given in Tables land 2.
In the univariate analysis, we noticed that patients who developed heart blocks, had higher preoperative RVOT gradient and longer bypass as well as cross-clamp time than those who did not develop heart blocks. However the P­values of differences between these groups remained above 0.05  making them statistically insignificant. More over the prolonged bypass and cross clamp time resulted in temporary conduction defects which recovered without requiring pacemaker insertion. This study also shows that patients who developed conduction problems after operation had mean preoperative heart rate of 80/mm whereas those who remained in sinus rhythm without any block and mean heart rate of 97/rn in. This is an interesting observation, however, the study does not provide any evidence that what heart rate is low enough to definitely produce a heart block after the operation.
This study does not show very strong association between any pro or peroperative variable with the development of heart block (Table 4).

A closer look at the data reveals that findings like higher preoperative RVOT gradient and longer bypass and cross clamp times in heart block group indirectly indicate complexity and difficulty of procedure. In other words the main factor in the development of conduction disorders is difficult morphology of disease (Table 5).

If such is the case, the only way to prevent rhythm complications and heart blocks is to use an extreme degree of surgical care utilizing the thorough knowledge of anatomy of conduction tissue and the pathological morphology of this disease.
We conclude that children and young adults with Fallot’s tetralogy can undergo total correction with very low rate of postoperative rhythm problems. The heart block can be avoided by taking care of the anatomy of the conduction system and by using interrupted stitches in the region of the conduction bundle.

References

1.Waish E.P., Rockenmnher S., Keane iF., etal. Latç results in patients with tetralogy of Eallot repaired during infancy. Circulation, 1988;77:1062-7.
2.Martin R., Khaghani A., Radley-Smith R, et al. Patient status 10 ormoreyears after primary total correction of tetralogy of Fallot under the age of two years. Br. I lean .1,, 1985;53:666-7.
3.Castaneda AR, Freed MD, Williams RU, et at. Repair of tetralogy of Fallot in infancy: early and late results. J. Thorac. Cnrdiovasc. Surg., 1977:71:372-81.
4.Gustafson R.A, Murray OF, Warden HE, et aL Early primaty repair of tetratogy of ‘allot Ann. Thorac Surg., 1988:45:235-41.
5.Horowitz LN, Vetter VL, Harken AU, et at, Electrophysiologic characteristics of sustained ventricular tachycardia occurring after repair of tetratogy of Fallot. Am. J. Cardiot. 1980;46:446-52.
6.John S, John C, Bashi VY, stat. Tetralogy of Fallot: intracardiac repair in 840 subjects. Cardiovase, Surg., 1993;1:285-90.
7.Caspi J, Zaistein E,. Zucker N, et at. Surgical management of tetralogy of Fallot in the first year of life. Ann. Thorae, Surg., 1999;68: 1344-49.
8.Hennien I IA, Mosca RS, Vrecelay 0, et al. Intermediate results after complete repair of TOF in neonates. J. Throac. Cardiovasc. Surg., 1995;109:332-44.
9.Touati GD., Voube P.R., Amodco A., et al. Primaty repair of tetralogy of Fallot in infancy. J, Thorac, Cardiovasc. Surg., 1990;99:396-403.
10.Hornereffer PJ, Zahka KG, Rowe SA, et al. Long term results of total repair oftetratogy of Fallot in childhood. Ann. Thorac, Surg., 1990;50:179-85.
11.Dictl CA, Cazzaniga ME, Dubner Si. at at, Life threatening arrhythmias and RV dusfunction after surgical repair of TOF: comparison between transvcntricular and transatrial approaches. Circulation, 1 994;90:11 .7-11.12.
12.Miura T, Nakano S, Shimazaki Y, et at. Evaluation of Rt. Ventricular function in patients after correction of TOF: comparison of transventricular and non transventricular repair. J. Thorac. Cardiovasc. Surg., 1992:104:917-23.
13.Chandar JS, WoIffGS, Garson A, et al. Ventricular arrhythmias in postoperative TOF, Am. J. Cardiol., 1990;65:655-61.
14.Harrison DA, Harris L, Siu SC, et at, Sustained ventricular tachycardia in adults after repair of TOF. 3. Am. Coil. Cardiol., 1997;30:1368.73.
15.Marco P, Dipesh BT, Denis K, et al. Tctratogy of Fatlot: What operation, at what age?. Eur. i. Cardiottiorac. Surg., 2000, 17:631-36.
16.Miura T, Nakone S, Shimazaki Y, et al. Evaluation of Right ventricular function Liter correction of TOF, comparison of transventricular and non­ transventricular approach. 3, Thorac. Cardiovasc. Surg., 1992,104:917.23.
17.Guy V. Fourner A, Davignon A, et al. Frequency and prognosis of arrhythmias after operative correction of TOF, Am. 3. Cardiot., 1990,66:346-9.
18.Norgard G, Gatzoulis MA. Morales F, etal. Relation between type of outflow tract repair and post right ventricular function in TOF. Circulation, 1996,94:3276-80.
19.Gatzoulis MA, Till JA, Somervilli J, at al. Electromechanical interaction of TOF: QRS prolongation retates to RV size and predicts malalignment ventricular arrhythmias and sudden death. Circulation, 1995,92:231-7.
20.Deanfield JE, Ho S, Andersen HA, at al. Late sudden deaths after repair of terralogy of Fallot. Circulation, 1993.67:626-31.
21.Oechslin EN, Harrison DA, Harris L, et at. Re-operation in adults with repair of TOP. 3. Thorac. Cardiovasc. Surg., 1999;1 18:245-51.
22.Houyel L, Vaksmann G, Formier A, et al. Neutricular arrhythmias after correction ofVSl): importance of surgical approach. 3. Am. Coil. Cardiot., 1990, 16:1224-28.
23.Starnes VA, Luciani RB, Latter DA, at at. Current surgical management of tetralogy ofFallot, Ann. Thorac, Surg., 1994:58:211.15.

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