Tetrology Of Fallot

Question 1

What are the features of Tetrology of Fallot?

Answer 1

1. RVOTO (stenosis or atresia of the pulmonary artery)
2. Interventricular communication (VSD)
3. Deviation of the aorta to the right (over-riding aorta)
4. RV hypertrophy

Question 2

Where does the pulmonary blood flow come from in TOF with PA?

Answer 2

PDA or MAPCA’s

Question 3

The primary determinant of pre-operative physiology is the degree of RVOTO and amount of pulmonary blood flow. Explain the difference between a pink and a blue tet in relation to the degree of RVOTO.

Answer 3

Pink tet: mild RVOTO, get left to right shunt across the VSD, and signs of pulmonary over-circulation. Oxygen sats will be normal, but may develop congestive heart failure with the decrease in the pulmonary artery pressure over the first few weeks of life

Blue tet: severe RVOTO, shunt right to left at the VSD, sats of 70

Question 4

What happens in a tet spell?

Answer 4

Drop in SVR or an increase in PVR, leads to right to left shunting and marked desaturation
Desaturation and acidosis further increase PVR and worsen left to right shunt.

Question 5

What are two different ways a tet could present?

Answer 5

1. Signs and symptoms of congestive heart failure (tachypnea, FTT, hepatomegaly) - this would be a in a neonate with mild RVOTO, who develops pulmonary overcirculation from left to right shunting as the PAP drops in the first few weeks of life
2. Cyanosis - if RVOTO is severe, will result in right to left shunting
   - > can develop worsening cyanosis as the PDA closes. Presence of MAPCAs alleviates cyanosis to a variable degree, however as the infant grows, the PBF will become inadequate and cyanosis will develop. Also, MAPCAs can stenose

*if pulmonary blood flow is adequate, but not excessive, the infant may go undiagnosed

Question 6

Describe the physical exam findings for a TOF.

Answer 6

May have signs and symptoms of CHF, if increased PBF
Thrill
Harsh systolic murmur along the left upper sternal border (flow across the stenotic outflow tract)
Absence of a systolic murmur should raise concern for PA
Continuous murmur also represent PDA or large MAPCA
During a tet spell, the murmur should disappear.

Question 7

Describe what you might see on CXR in TOF

Answer 7

Boot shaped heart (cavity in the region of the main PA, prominent upturned cardiac apex)
Great vessel shadow is diminished in the superior mediastinum because of the decreased caliber of the PA
Right sided aortic arch in 25% of TOF
Decreased, normal or increased pulmonary vascular markings

Question 8

What are the findings on ECG for TOF?

Answer 8

RV hypertrophy
Right axis deviation
Upright and peaked t waves in the right precordial leads
Reversal of R/S ratio

Question 9

Lost some common post-operative complications after TOF correction

Answer 9

RV dysfunction/failure -> watch for hepatomegaly and peripheral edema -> some surgeons will leave the foramen open as a pop off valve, to allow right to left shunt, offloading of the RV. Similar to the fenestration in a Fontan
Low CO (post CPB, and likely related to RV dysfunction)
Dysrhythmias - complete heart block, RBBB (in almost all patients with a ventriculotomy), JET

Question 10

What is JET?

Answer 10

Dysrhythmia characterized by:
Warm-up phase with gradual increase in tachycardia (typically occurring on the first post-operative night)
AV dissociation
Typically rates of 200-230

Question 11

What are the options for surgical repair of a TOF?

Answer 11

1. Early palliation for hypercyanotic spells or severe cyanosis with a modified BT shunt (from right subclavian or innominate artery to the right PA)
2. Total repair (requires CPB, cross clamp)
   - relieve RVOTO by resection of obstructive muscle
   - closure of VSD
   - pulmonary arterioplasty or pulmonary valvotomy, may require a transannular patch across the pulmonary valve annulus to fully relieve the right ventricular outflow tract obstruction