Dr.S.Venkatesan MD

Murmur of Tetrology of  Fallot is generated at the level of

1. VSD
2. RVOT
3. Aortic root
4. Any of the above

Answer :   RVOT.

RVOT is the classical site of TOF  murmur , but  there is  a  rider . The murmur of TOF is  inversely proportional to the degree of RVOT obstruction. (Contrary to VPS with intact IVS) .In severe TOF especially during spells the murmur attenuate dramatically and may disappear altogether. Hence a silent and quiet heart do not necessarily  indicate  a mild form of TOF .

Other possibilities also  exist.

• The VSD in TOF is  large and do not restrict  blood flow on either direction . Rarely  restrictive VSD can generate a murmur across VSD.
• Aortic flow is increased in all severe cases of TOF ( Highest in pulmonary atresia and VSD)   Hence there is always a possibility of a soft systolic flow murmur across Aortic valve .
• Other rare  cause for systolic murmur is due to  prolapse of   tricuspid  valve  that occludes the VSD  potentially causing  TR  and in the  process may  convert the  VSD  into restrictive type.
• One more cause for  systolic murmur is sub Infundibular anomalous  muscle bundles criss crossing the RV body .
• Peripheral pulmoanry arterial stenosis is recognised cause for distant faint systolic murmur.
• Diastolic murmurs can also occur in TOF . Absent pulmonary valve and aortic regurgitation can result  in diastolic murmurs .

Question for analysis

What happens to TOF murmur during squatting  ?