Tetralogy of fallot

Posted by e-Medical PPT Saturday, December 14, 2013
Tetralogy of fallot
First anatomic description…Danish anatomist Niels Stensen, in 1672...
Described in detail by fallot in 1888…’la maladie bleue’

Tetralogy of fallot with pulmonary atresia…10%
Rarer variants include tetralogy of fallot with absent (or dysplastic) pulmonary valve and tetralogy of fallot with common atrioventricular canal[<5%]
Prevalence … 0.26 to 0.48 per 1,000 live births

In about 70% of tetralogy of Fallot patients, a putative genetic etiology remains to be determined.

Genes identified : NKX2.5, [4%];  JAG1 in Alagille syndrome.; TBX5 in Holt-Oram syndrome.

Sibling recurrence rate …2.5% to 3% if only one sibling is affected…likely to increase substantially if more than one sibling is affected.
Environmental factors
maternal diabetes [threefold increased risk], retinoic acids, maternal phenylketonuria (PKU), and trimethadione

Genetic cause : heterogeneous
Syndromes and associations…..
DiGeorge/Velocardiofacial syndrome, Down syndrome, Alagille syndrome, cat's-eye syndrome, recombinant chromosome (or San Luis Valley) and Kabuki syndromes, and CHARGE and VATER/VACTERL associations

Pathophysiology and Hemodynamics
Severe cyanosis in profound RL shunting,
Some pts have a net LRshunt.

Hemodynamic features…RV hypertension because of the large VSD, with normal or low PAP.The low distal PAP is maintained as a result of the various levels of pulmonic obstruction. The PVR in the distal pulmonary arterial bed is usually normal.

The extent and direction of shunting ….determined by the cumulative amount of obstruction to PBF(Subpulmonic obstruction in all; obstruction @ valvular, supravalvular, and branch arteries are also common).

HYPERCYANOTIC SPELLS OR TETRALOGY SPELLS :
best described in TOF;can occur with other forms of structural heart disease…. mediated, in part, by dynamic changes (acute increase)in subpulmonic obstruction….. changes in contractility  due to ‘endogenous catecholamines or exacerbated by hypovolemia’
other mechanisms[pulmonary atresia and VSD] …. decrease in systemic vascular resistance.
Child may assume squatting posture (instinctive) during spells …
Pathogenetic mechanisms : Vulnerable respiratory control centres ;Increase in HR ; Increase in CO & VR ;Increase in R L shunt; Infundibular contraction may reinforce,but does not initiate
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