• In longstanding unrepaired TOF, right ventricular hypertension induces fibrosis leading to RV systolic and diastolic dysfunctions and ventricular arrhythmias.
• Neonate with TOF should be carefully assessed by echo to see if the PS is so severe that ductal patency is needed. If this is the case, give PGE1 infusion and do early surgery.
• Cyanotic spells can occur in acyanotic TOF also.
• Treatment of cyanotic spells includes oxygen, volume expansion, sedation with morphine or ketamine and vasopressors like phenylephrine.
• Patients with relative anemia are at more risk of cerebrovascular accidents and hypercyanotic spells.

Interventional catheterization procedures

• Preoperative-

Palliation of cyanosis by RVOT stent placement or balloon valvuloplasty. This avoids need for BT shunt which may cause pulmonary artery distortion.
Coil embolization of aortopulmonary collaterals.

• Postoperative- For residual pulmonary artery obstruction- ballooning and stenting.

Primary repair

• This is done via median sternotomy.
• Approaches-
  • Atrial route- This is the preferred route. The VSD is closed by a Dacron patch. RVOT obstruction is resected. Atrial route was earlier done only for patients with coronaries crossing the RVOT. Now it is done for other patients also as it avoids the need for ventriculotomy.
  • Right ventriculotomy- A vertical incision is made over the infundibulum. RVOT obstruction is relieved. VSD is closed by a Dacron patch. RVOT is patched with pericardium. If the pulmonary annulus is hypoplastic (Z score preoperatively and visual impression of the surgeon intraoperatively), the initial incision is extended onto the pulmonary artery. A transannular patch is placed. A monocusp pericardial valve may be placed to avoid pulmonary regurgitation.
  • Combined atrial and transpulmonary approach- avoids need for ventriculotomy.
• AP collaterals- These are coiled prior to surgery to avoid steal phenomenon during cardiopulmonary bypass which causes neurologic sequelae. If it constitutes the sole blood supply to the lung, it should be incorporated into the final repair.

Palliative procedures

• Initial palliative BT shunt is not preferred due to PA distortion, ventricular volume loading and the surgical risks of an additional thoracotomy. Primary repair is directly done. But palliation may need to be done in severe PA hypoplasia and aberrant LAD form RCA.
• Blalock Thomas Taussig shunt and central shunt are used now. Waterston shunt and Potts shunt are not used now. Modified BTT shunt is the most commonly used one. It is done opposite to the side of the aortic arch. Shunt size in newborn is usually 3.5 to 4 mm.

Surgical results-

• Early primary repair is not associated with higher incidence of early complications or late reintervention compared to late repair. Also, primary repair is not associated with more reintervention for residual obstruction  compared to staged repair. Hence, early primary repair is preferred though repair in first 3 months of life increases intensive care morbidity.
• Hospital survival for repair is 100% even for early surgery. 20 year survival after primary repair is 98% for TOF with PS and slightly lower for TOF with primary atresia.
• In TOF with PS, after primary repair, at 2 years 25% needed reoperation usually for residual obstruction in RV or PA. The indication for reoperation in older patients is different and is residual VSD.

Long-term follow-up

• Early repair may be associated with less long term incidence of arrhythmias, ventricular dysfunction and cognitive dysfunction.

Sudden death and arrhythmias

• Incidence of sudden death is 1.2% at 10 years, 2.2% at 20 years, 4% at 25 years and 6% at 30 years.
• Sudden death is not more in patients who underwent surgery before 80s.
• Ventricular arrhythmias are more in patients who undergo surgery at older age. These patients are predisposed to ventricular arrhythmias before surgery itself due to their older age and surgery does not decrease the chance of ventricular arrhythmias.
• Ventricular arrhythmias are more in patients with PR and in those with RV dilation.
• EP studies are not clearly shown to predict sudden death in patients with ventricular arrhythmias.
• Other predictors of sudden death are significant PR, sustained ventricular arrhythmias, QRS duration more than 180 msec and LV dysfunction.
• Other arrhythmias noted in the long term are sinus dysfunction, atrial flutter , atrial fibrillation and supraventricular tachycardia. The incidence of supraventricular tachycardia is 10% at 12 years after repair.

Residual defects and hemodynamic abnormalities

• Branch PA stenosis
  • After shunt procedures.
  • After RVOT patch, due to compression by the redundant patch.
  • Treated by ballooning or stenting- the complications include aneurysms, stent migration and stent thrombosis.
  • Redundant RVOT patch should be surgically revised.
• Membranous subaortic stenosis- uncommon late complication.
• Coronary to RV fistula
• Pulmonary regurgitation
  • All patients have PR by echo.
  • Some have audible PR.
  • Pan-diastolic PR with end-diastolic velocity of 1 m/s indicates mild PR and good pulmonary valve anatomy.
  • PR signal ending before the end of diastole indicates that pulmonary valve function is poor and that the RV is stiff. This occurs due to equalization of PA diastolic pressure and RV diastolic pressure in diastole itself.
  • PR may occur due to increased pulmonary arterial impedance which is due to either stenosis of main or branch pulmonary arteries or elevated LA pressure due to causes like LV dysfunction. If branch PA stenosis is the cause of PR, it may be treated by interventional catheterization. If LV dysfunction is the cause of PR, it may decrease with treatment of the LV dysfunction.
  • For significant PR, pulmonary valve replacement (homograft) will be needed.
• Tricuspid regurgitation
  • Present in many.
  • Not audible unless RV pressure is elevated.
  • May need repair.
• Aortic dilation
  • Aorta is dilated in TOF patients after repair. This dilation may progress.
  • Avoid isometric exercise and high blood pressure.
  • Serial monitoring for enlargement and development of AR is needed.

Exercise testing

• Reduced exercise capacity is present in patients with PA stenosis, PR or RV dysfunction.

Bacterial endocarditis

• Prophylaxis is needed in unoperated patients, palliated patients, in repaired patients for 6 months and in repaired patients with prosthetic valves.

http://www.heartpearls.com/2009/06/tetralogy-of-fallot-an-article-part-1.html

http://www.heartpearls.com/2009/06/tetralogy-of-fallot-an-article-part-2.html

http://www.heartpearls.com/2009/08/tetralogy-of-fallot-an-article-part-3.html

The hallmark of tetralogy of Fallot is anterior and cephalad deviation of the conotruncal septum.

Pulmonic stenosis – is always significant and hence pulmonary artery pressure is normal or low, never high as in pure VSD. The obstruction is subpulmonic. If this is severe, distal obstructions are more commonly present. Usually pulmonary arteries are of adequate size to permit surgical repair. In pulmonary atresia, pulmonary artery size may be too less for repair.

Subpulmonic obstruction is due to both antero-cephalad deviation of the conotruncal septum and muscular hypertrophy of the deviated septum and the right ventricular free wall. In addition, there may be intracavitary obstruction due to hypertrophied muscle bundles.

The pulmonary valve is commonly small and stenotic and is usually unicuspid or bicuspid. Supravalvular discrete stenosis may occur. Branch ostial stenosis may occur, especially on the left. In pulmonary atresia, the pulmonary arteries are very small and are feeded by aortopulmonary collaterals.

Ventricular septal defect- This has fibrous continuity between tricuspid and aortic valve and hence is a true perimembranous defect, even though it lies in a subarterial location. It is non-restrictive by definition, though some defects may be restrictive due to tricuspid valve tissue.

Aortic override- This may vary from 15% to 95%. Override of more than 50% does not mean double outlet right ventricle- this needs presence of both subaortic conus (absent aorto-mitral continuity) and subpulmonary conus. Aortic override is not only due to the malalignment. It is also due to aortic dilation due to malseptation of the conotruncus and due to rotation of the aorta so that the right aortic sinus becomes more anterior (and left).

Coronary arteries-

1. 15% have a large conal branch or accessory left anterior descending artery.
2. 5% have origin of left anterior descending artery from right coronary artery. This then crosses the right ventricular outflow tract- this is important surgically as the surgeon cannot approach through this area for repair.
3. 4% have single origin of coronaries.

Coronary artery origin has to be found by echocardiography, angiography or MRI before surgery.

Aortic arch anomalies – These are more common if there is Catch 22. Right aortic arch is present in 25%. Aberrant origin of ipsilateral subclavian artery and origin of left subclavian artery from pulmonary artery are sometimes seen.

Aortopulmonary collaterals- Rabinovich type 1 (bronchial artery collaterals) collaterals are uncommonly present in Tetralogy of Fallot with pulmonic stenosis. Collaterals are much more common in Tetralogy of Fallot with pulmonary atresia.

Other anomalies- ASD is present in 83%. Left superior vena cava is found in 11%. Atrioventricular septal defect may be associated, especially in Down’s syndrome. Left sided anomalies are rare.

http://www.heartpearls.com/2009/06/tetralogy-of-fallot-an-article-part-1.html

http://www.heartpearls.com/2009/08/tetralogy-of-fallot-an-article-part-3.html

http://www.heartpearls.com/2009/08/tetralogy-of-fallot-an-article-part-4.html

First described by Niels Stensen in 1672.

First correlation between pathology and clinical features by Fallot in 1888.

First aortopulmonary shunt by Blalock, Taussig and Thomas in 1945.

First intracardiac repair by Lillihei.

Prevalence

Tetralogy of Fallot is one of the most common cyanotic congenital heart diseases, by some series it is the commonest eg the BWIS study.

The prevalence of tetralogy of Fallot is 0.33 per 1000 live births.

Some studies have shown slight male preponderance in TOF eg BWIS study.

Recurrence

The sibling recurrence rate is 3%.

The chance of getting tetralogy of Fallot if a parent has tetralogy of Fallot is higher and is in the range of 1 to 8%. The chance may be higher if the affected parent is the mother.

Environmental factors

These include maternal diabetes, maternal phenylketonuria and maternal intake of retinoic acid, trimethadione or paramethadione.

Chromosomal anomalies

Some form of extracardiac anomaly is present in one-third of tetralogy of Fallot.

The most important syndromes associated with tetralogy of Fallot are Catch 22 and Alagille syndrome.

Catch 22 syndrome is characterized also by truncus arteriosus and interrupted aortic arch type B. The extracardiac anomalies are distinct facies, palatal anomalies, speech defects, learning defects, psychiatric defects, hypocalcemia and immunodeficiency. Earlier terms used for the syndrome were DiGeorge syndrome and velocardiofacial or Shprintzen syndrome. It is due to 22q11 deletion.

Alagille syndrome is characterized also by peripheral pulmonic stenoses. The extracardiac features are typical facies, ocular defects, skeletal defects and bile duct paucity. The defective gene is Jagged 1. The defect is inherited as autosomal dominant.

Development

The conotruncus refers to the bulbus cordis and the truncus arteriosus together. It gives rise to the ventricular outflow tracts and the great arteries. It is divided into two by ingrowth of the truncal-bulbar ridges. It also undergoes a rotation. The conotruncal septum joins with the trabecular ventricular septum. There is a defect between these two that is closed by the membranous septum.

Tetralogy of Fallot is caused by malrotation of the truncal-bulbar ridges. This causes malalignment between the conotrunal septum and the trabecular septum.

http://www.heartpearls.com/2009/06/tetralogy-of-fallot-an-article-part-2.html

http://www.heartpearls.com/2009/08/tetralogy-of-fallot-an-article-part-3.html

http://www.heartpearls.com/2009/08/tetralogy-of-fallot-an-article-part-4.html

1. Diabetes in mother- This increases the chance of tetralogy of Fallot (TOF) three times.

2. Retinoic acids- If taken during the first trimester, there is increased chance of tetralogy of Fallot (TOF) along with nervous system and facial anomalies.

3. Phenylketonuria in the mother- tetralogy of Fallot (TOF) is especially likely to occur if the mother did not control intake of phenylalanine during pregnancy.

4. Trimethadione or paramethadione treatment during pregnancy.

Pathology

The four components are a large VSD, RVOT obstruction, RVH and overriding of the aorta. Actually, only the first two are needed.

The VSD is perimembranous, with subpulmonary extension.

The RVOT obstruction is most commonly infundibular only (45%). 30% cases have infundibular + valve stenosis. 10% have valve stenosis alone.

Pulmonary atresia is seen in 15%.

Right aortic arch occurs in 25%.

Pulmonary arteries are small. Branch PA ostial stenosis can occur, especially on the left.

5% have abnormal coronaries- commonest being LAD originating from RCA and passing in front of the RVOT, disallowing an incision here.

AVSD occurs in 2%, especially in Downs.

Clinical features

Cyanosis at birth. Murmur at birth.

Cyanotic spells in infancy.

Dyspnoea on exertion and squatting later in life.

Left parasternal tap.

Pulmonary ejection systolic murmur, usually with a thrill. If RVOT obstruction is very severe, the murmur will be soft.

Single S2 because P2 is soft.

Aortic ejection click.

ECG

Right axis deviation.

RVH without strain. No strain because RV pressure is not suprasystemic.

CXR

Decresed pulmonary vasculature.

Concave pulmonary bay.

Upturned apex with no cardiomegaly- called boot-shaped heart or coeur en sabot. Coeur en sabot means wooden shoe in French.

Natural history

Cyanosis worsens with age due to increasing RVOT obstruction and polycythemia.

Hypoxic spell

The incidence peaks between 2 and 4 months of age. It usually occurs in the morning. It is characterised by crying, hyperpnea and cyanosis. Murmur becomes less intense during the spell. There is no relation with the degree of cyanosis at rest.

Hold the child in knee-chest position. Give morphine 0.2 mg/kg SC or IM. This works by suppressing the respiratory center.  Oxygen is usually given. Soda bicarbonate is useful if there is acidosis.

In refractory cases, phenylephrine, ketamine or propranolol are useful. Phenylephrine is a systemic vasoconstrictor. Ketamine is a sedative and a systemic vasoconstrictor.

For prevention, propranolol 1 mg/kg qid orally is given if there is a delay to surgery.

Palliative procedures

Indications are low weight babies (<2.5kg), very young babies (<3M), unfavourable coronary anatomy, pulmonary atresia in neonate, hypoplastic pulmonary annulus in infant and hypoplastic pulmonary arteries in children.

Classic Blalock-Taussig shunt is an end to side anastomosis of the right subclavian artery to the right pulmonary artery (left for right aortic arch). This can be done only if age is more than 3 months.

Modified Blalock-Taussig shunt – a Gore-Tex interposition shunt is placed between the left subclavian artery and the left pulmonary artery (right for right aortic arch). This can be done even if age is less than 3 months.

Waterston shunt, between ascending aorta and right pulmonary artery, and Potts shunt, between descending aorta and left pulmonary artery, are not done now due to many complications like a very large shunt.

Repair

Indications for repair are hypoxic spell and oxygen saturation less than 80%.

Elective repair is done at 1 to 2 years. Earlier repair is done if symptoms are present.

The repair is preferably done via atrial and pulmonary artery approaches rather than via a right ventriculotomy. The VSD is closed with a patch, the infundibular stenosis is resected and the valvular stenosis is relieved by a pulmonary valvotomy. Placement of a fabric patch in the RVOT is avoided if possible.

If LAD courses in front of the RVOT, primary repair may not be adequate, in which case, a conduit is also placed between the RV and the PA so that there are two outlets now for the RV.

This is a parasternal view (PLAX view) of tetralogy of Fallot. Note the large VSD. Note that the aorta is overriding the VSD. There is more than 50% aortic override. The same situation occurs in DORV also. To make the distinction, look for aortic-mitral continuity. In this case, there is aortic-mitral continuity. Thus, the diagnosis is TOF. If the aortic valve were more than 5mm away from the mitral valve, it would have meant that aortic-mitral continuity was absent and then the diagnosis would have been DORV.