Laws of fluid dynamics dictate there is a pressure drop across a point of narrowing and recovery thereafter . At recovery point if the vessel wall is weak it tends to balloon out .This is called post- stenotic dilatation .This is the anatomical equivalent of Bernoulli or venturi effect. This theoretically occur only distal to obstruction .
How do you explain the common observation of pre- stenotic dilatation?
- Intimal weakening due to disease process is the prime suspect.
- Pre stenotic increment in mean pressure also play a role .
- Mechanical distention due to stagnated blood proximal to critical obstruction is a logical explanation.
- Finally and most importantly ,contagious , sub – angiographic atherosclerosis.
How is dilatation different from ectasia ?
May be they are all related phenomenon. The definitions of ectasia , dilatation, aneurysm are more to do with semantics than with academics.
Clinical and hemodynamic implication in cath lab
- Sluggish flow prone for thrombus
- Stent selection errors likely
- Stent dislodgment and migration
Long term effects
- In stent re-stenosis is more common if adjacent segment show dilatation.
Enlargement of vessel wall in both pre and post stenotic segments are possible . In small vessels pre- stenotic dilatation is more common , while in large vessels post stenotic dilatation is more prevalent .(Aorta, Pulmonary artery) The mechanisms are slightly different. Apart from the lesion tightness , hemodynamic and genetic factors are also responsible These dilatations are often labeled as ectasia in coronary artery and most cardiologists tend to ignore this finding especially if the margins are smooth.
But , newer imaging modalities like IVUS, OCT have given better insight about these dilatations.These are actually an expression of the contagious atherosclerosis . Pre- stenotic segments are prone for extensive disease than even the diseased segment due to more hemodynamic turbulence. There is some evidence atherosclerosis progresses proximally more than distally.Smooth margins within the pre -stenotic dilatation does not guarantee disease free status.
During PCI there could be an argument for covering the dilated pre- and post stenotic segments as well* . (We vouch for endovascular stenting when aorta is dilated why do we hesitate in coronary ?) .Careful selection of coronary stent size is recommended and allowance should be given for these two (Pre and post coronary dilatation ) patho -anatomic phenomenon.
* Stent missing a lesion is stylishly called geographical miss ! This should logically include dilated segments also.