Tetralogy of Fallot (TOF)

Tetralogy of Fallot (TOF)

1. Tetralogy of Fallot (TOF) Dr. Sayeedur Rahman Khan Rumi [email protected] MD Final Part Student NHFH&RI

2. Introduction It is the most common form of cyanotic heart disease . It occurs in approximately 1 in 3000 live births and accounts for 10% of CHD. It is also the most common CHD requiring surgical correction in the first year of life without which only 10% of patient survive beyond the age of 20 yrs.

3. French physician Étienne-Louis-Arthur Fallot , who first described TOF in the late 19th century . Arthur Fallot

4. Development of TOF During the fifth week, pairs of opposing ridges appear in the truncus ( right superior truncus swelling & left inferior truncus swelling ) . Hence , while growing toward the aortic sac, the swellings twist around each other, foreshadowing the spiral course of the future septum. After complete fusion, the ridges form the aorticopulmonary septum, dividing the truncus into an aortic and a pulmonary channel .

5. Development of TOF TOF, is due to an unequal division of the conus resulting from anterior displacement of the conotruncal septum.

6. Pathology The original description of TOF included the following four abnormalities: A large VSD RVOT obstruction RVH , and O verriding of the aorta.

7. Pathology In actuality, only two abnormalities are required, a VSD large enough to equalize pressures in both ventricles and an RVOT obstruction. The RVH is secondary to the RVOT obstruction, and the overriding of the aorta varies. The VSD in TOF is a large perimembranous defect with extension into the subpulmonary region. The RVOT obstruction is most frequently in the form of infundibular stenosis (45%). The obstruction is rarely at the pulmonary valve level (10%). A combination of the two may also occur (30%). The pulmonary valve is atretic in the most severe form of the anomaly (15%)

8. Abnormal Physiology Because the VSD is large, with an area about as great as that of the aortic valve, both ventricles and the aorta have essentially the same systolic pressures. The most important hemodynamic factor is the ratio between the resistance to flow into the aorta and the resistance to flow across the right ventricular infundibulum . If the stenosis is not severe and resistance to right ventricular outflow is not large, the pulmonary flow may be more than twice the systemic flow, and the arterial oxygen saturation may be normal ( acyanotic tetralogy of Fallot ). However, the resistance to the pulmonary flow may be increased markedly, causing right-to-left shunting, arterial desaturation, and subsequent polycythemia .

9. The drugs, heart rate, or maneuvers that increase myocardial contractility or decrease right ventricular volume increase infundibular obstruction, often partially dynamic. In addition, the infundibular hypertrophy may increase gradually over time. As the systolic pressure in the right ventricle cannot exceed that in the left ventricle because of the large VSD, the right ventricle is “protected” from excessive pressure and work, and so heart failure is uncommon .

10. Associated defects Right aortic arch ( 30 %) Anomalous origin of LAD from RCA (10%) ASD secundum (15%) : pentalogy of Fallot Persistent left SVC (10%)

11. Natural History Infants with acyanotic TOF gradually become cyanotic. Patients who are already cyanotic become more cyanotic as the infundibular stenosis worsens and polycythemia develops . Polycythemia develops secondary to cyanosis . D evelopment of relative iron-deficiency states (i.e ., hypochromia ). Hypoxic spells may develop in infants. Growth retardation may be present if cyanosis is severe . Brain abscess and cerebrovascular accident rarely occur. Subacute bacterial endocarditis (SBE) is occasionally a complication . Some patients, particularly those with severe TOF, develop aortic regurgitation (AR). Coagulopathy is a late complication of a long-standing cyanosis .

12. Clinical Manifestations

13. History Most patients are symptomatic with cyanosis at birth or shortly thereafter. Dyspnea on exertion , squatting, or hypoxic spells develop later even in mildly cyanotic infants. Occasional infants with acyanotic TOF may be asymptomatic or may show signs of CHF from a large left-to-right ventricular shunt.

14. Physical Examination Growth is usually normal unless cyanosis is extreme. Clubbing of the fingers and toes occurs after 3 months of age and is proportional to the level of cyanosis . Varying degrees of cyanosis, tachypnea, and clubbing (in older infants and children) are present.

15. Increased right ventricular activity is observed. A systolic thrill may be palpable at the left midsternal border, with a harsh midsystolic murmur in that location. The shorter the murmur, the more severe the infundibular pulmonary stenosis. The first heart sound (S1) is usually normal Second heart sound is characteristically single, because the pulmonary component is too soft to be heard. A continuous murmur is heard if a PDA or large collateral vessels are present. An early systolic ejection sound at the left sternal border and apex is uncommon; its presence suggests primarily valvular pulmonary stenosis.

16. Cardiac findings in cyanotic tetralogy of Fallot . A long ejection systolic murmur at the upper and mid left sternal border and a loud, single S2 are characteristic auscultatory findings of TOF.

17. Investigation

18. Hematologic and Other Laboratory Studies Hemoglobin and hematocrit Platelet counts and clotting studies Serum uric acid levels To evaluate - Iron deficiency anemia, Polycythemia & Hyperuricemia

19. Electrocardiography RAD There is right ventricular hypertrophy, with a tall R wave in the right precordial leads and a deep S wave in the left leads. A QRS duration of >180 ms is a predictor of sustained VT and sudden cardiac death. Some of these patients have right atrial hypertrophy.

20. Chest X-ray The total heart size is usually normal on chest xray , but right ventricular enlargement is present in the lateral view. The pulmonary segment is concave and the apex is elevated, giving the coeur en sabot (boot-shaped) contour . The aorta arches to the right in many cases. Pulmonary flow is diminished.

21. Echocardiography Two-dimensional echocardiography and Doppler studies usually make the diagnosis and quantitate the severity of TOF. A large , perimembranous infundibular VSD and overriding of the aorta are readily imaged in the parasternal long-axis view. Anatomy of the RVOT, the pulmonary valve, the pulmonary annulus, and the main PA and its branches is imaged in the parasternal short-axis and subcostal short-axis views.

22. Doppler studies estimate the pressure gradient across the RVOT obstruction. Anomalous coronary artery distribution can be imaged accurately by echocardiographic studies. The major concern is to rule out any branch of the coronary artery crossing the RVOT. Associated anomalies such as ASD and persistence of the left superior vena cava (LSVC) can be imaged.

23. PLAX view showing the overriding aorta and a large subaortic VSD (star). RVH is also present

24. Color flow imageing showing VSD jet

25. PLAX view of repaired TOF showing RV is dilated and the echogenic region at the superior portion of the IVS represents synthetic patch (arrow)

26. Cardiac Catheterization To assess the anatomy of RVOT and main PA branches, RV and LV function, site and size of VSD and competence of aortic valve. Arterial O2 saturation is <85% Identical systolic pressure in RV and LV and low systolic pressure in PA (diagnostic of TOF)

27. RV graphy Percentage of overriding aorta Size of the VSD RVOT obstruction To differentiate TOF from DORV

28. LV graphy

29. Root & Arch aortography

30. Hypoxic Spell

31. Hypoxic Spell A lso called cyanotic spells, hypercyanotic spells, “ tet ” spells Hypoxic spells are characterized by: P aroxysm of hyperpnea (i.e., rapid and deep respiration ), I rritability and prolonged crying, I ncreasing cyanosis, and Decreasing intensity of the heart murmur. Hypoxic spells occur in infants, with a peak incidence between 2 and 4 months of age. These spells usually occur in the morning after crying, feeding , or defecation. A severe spell may lead to limpness, convulsion, cerebrovascular accident , or even death.

32. Mechanism of hypoxic spell Hypercyanotic episodes (spells) in patients with tetralogy are of uncertain origin. It is likely that some episodes are caused by unusual hyperactivity of muscular fibers in the right ventricular outflow tract that produce or exaggerate the infundibular stenosis, increasing pulmonary resistance and thus increasing the right-to-left shunting. Some spells may be caused by a decrease in peripheral resistance and systemic arterial pressure, which also may cause the right-to-left shunt to increase and pulmonary blood flow to decrease.

33. A vicious circle of hypoxic spell. A decrease in the arterial PO2 stimulates the respiratory center, and hyperventilation results. Hyperpnea increases systemic venous return. In the presence of a fixed right ventricular outflow tract (RVOT), the increased systemic venous return results in increased right-to-left (R-L) shunt, worsening cyanosis .

34. Treatment of Hypoxic spell Treatment of hypoxic spells is aimed at breaking this circle by using one or more of the following maneuvers: The infant should be picked up and held in a knee–chest position . Oxygen: high flow high conc. Morphine sulfate, 0.2 mg/kg administered subcutaneously or intramuscularly, suppresses the respiratory center and abolishes hyperpnea (and thus breaks the vicious cycle ). Acidosis should be treated with sodium bicarbonate (NaHCO3), 1 mEq /kg administered IV. NaHCO3 reduces the respiratory center–stimulating effect of acidosis.

35. Propranolol, 0.01 to 0.25 mg/kg (average, 0.05 mg/kg) administered by slow IV push, reduces the heart rate and may reverse the spell. If the hypoxic spells do not fully respond to these measures, the following medications can be tried: Ketamine , 1 to 3 mg/kg (average, 2 mg/kg) administered IV over 60 seconds. It increases the systemic vascular resistance (SVR) and sedates the infant . Vasoconstrictors like Phenalepherine 0.02mg/kg I/V. General Anesthesia (rarely required)

36. Management

37. Medical H ypoxic spells should be recognized and treated promptly. It is important to educate parents to recognize the spells and know what to do . Oral propranolol therapy , 0.5 to 1.5 mg/kg every 6 hours, is occasionally used to prevent hypoxic spells while waiting for an optimal time for corrective. Relative iron-deficiency states should be detected and treated. Iron-deficient children are more susceptible to cerebrovascular complications.

38. Surgical

39. Palliative Shunt Procedures Shunt procedures are performed to increase Pulmonary Blood Flow. Indication : Neonates with TOF and pulmonary atresia Infants with hypoplastic pulmonary annulus Children with hypoplastic PAs Unfavorable coronary artery anatomy Infants younger than 3 to 4 months old who have medically unmanageable hypoxic spells Infants weighing less than 2.5 kg

40. Palliative Shunt Procedures Classic BT shunt , anastomosed between the subclavian artery and the ipsilateral PA, is usually performed for infants older than 3 months because the shunt is often thrombosed in young infants. With a modified BT shunt , a Gore-Tex interposition shunt is placed between the subclavian artery and the ipsilateral PA. This is the most popular procedure for any age, especially for infants younger than 3 months of age. The surgical mortality rate is 1% or less.

41. Classic Blalock Taussig Shunt Modified Blalock Taussig Shunt

42. The Waterston shunt , anastomosed between the ascending aorta and the right PA, is no longer performed because of a high incidence of surgical complications. The Potts operation , anastomosed between the descending aorta and the left PA, is no longer performed either. It may result in heart failure or pulmonary hypertension, as in the Waterston operation.

43. Complete Repair Surgery Total repair of the defect is carried out under cardiopulmonary bypass, circulatory arrest, and hypothermia. The procedure includes patch closure of the VSD, widening of the RVOT by division or resection of the infundibular tissue ; and pulmonary valvotomy . Mortality: For patients with uncomplicated TOF, the mortality rate is 2% to 3% during the first 2 years . Patients at risk are those younger than 3 months and older than 4 years, as well as those with severe hypoplasia of the pulmonary annulus and trunk.

44. Diagrammatic representation of surgical repair of tetralogy of Fallot . Patch closure of a VSD Right ventricular outflow/main pulmonary artery outflow patch ( transannular patch)

45. Complications Bleeding problems may occur during the postoperative period, especially in older polycythemic patients. Pulmonary valve regurgitation may occur, but mild regurgitation is well tolerated. Right bundle branch block (RBBB) on the ECG caused by right ventriculotomy , which occurs in more than 90% of patients, is well tolerated. Complete heart block (i.e., <1%) and ventricular arrhythmia are both rare

46. Thank you