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Archive for November, 2015

What are the determinants of  dissecting  path   in Aortic dissection ?

 

Aortic dissection stanford002

Aortic dissection is  taught to us as a dramatic cardiac emergency where the blood  enters one of the planes of aortic wall and travels  in a random way . The wrong way blood instead of flowing within the lumen invades the vessel wall .(Vascular Tsunami ?) It may (or may not) leave the aorta at a distance resulting in various combinations of true and false lumen. Much like a tsumani  its also triggered by an energy releasing  blood pressure spikes hitting on the weakened  aortic wall rupturing the Intima. While acute dissection are often dramatic chronic dissection can be more subtle clinically.

Apart from the site of entry , blood pressure , condition of aortic vessel wall , there seems to be an invisible force that direct the dissecting tract.How it spares or compromises the arch vessels in selected few , as it travels down remain a mystery . If we can predict and track the plane of dissection by any means with computational  hemodynamic models , that will help us plan strategies. Beta blockers are used to reduce the shearing pressure , and emergency surgery is required in many type A dissections.

 

aortic dissection animation stanford a b classification 002

Do we see a “mini” Interventional opportunity here  ? To arrest or direct the dissecting tracts  into less benign zone. Shall we deploy an emergency  metal ring barrier  just proximal to aortic arch in Type A or  just above renal arteries in type B to prevent vital organ compromise ? This procedure can  be done fast , instead  planning a  elaborate endovascular intervention which is logistically difficult in  arch vessel dissection .This could also act as a bridge to definitive surgery. (Can we compare this with  bush fire fighting which are tamed by c0ntroled artificial fire lines and thus  avoiding spread to residential areas ! )

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Preamble * This article is meant  specifically  for cardiac professionals only .There has been so many queries to me about this device Megavac from patients  and public. It is  just another tool for assisting angioplasty in very special situations . Successful angioplasty can be performed without the need for such devices 9 out of 10 times.  I request the non medical readers to skip this article and follow your cardiologist’s advice  and don’t get unduly  anxious.

Dr Venkatesan .Chennai.India

If thrombus is the chief culprit in any vascular emergency  there can be  no second thoughts as it needs immediate  arrest without warrant! (STEMI,Acute pulmonary embolism , DVT, Acute limb ischemia etc) Since pharmacological lysis of thrombus is easy and  be done immediately  it will continue to play a major role still , in many clinical situations that critically compromise organ function .

However , large  thrombus burden  (or in which medical therapy fails to do a good job )  we must  intervene mechanically  to change the course of event.Though vascular surgery is a definitive option its always better we try out catheter based thrombectomy.

Many hardwares are being developed in the recent times. Aspiration catheters, baskets etc * .This  one from vascular capture (Minnesota USA)  appear promising as its a universal capture device that can be  used anywhere coronary , pulmonary or even in deep veins .

Clinical case examples using megavac : Video

*Few  examples of Thrombectomy devices.

1.They can be mechanical rotational devices like Amplatz Thrombectomy Device (ATD) Microvena,  Straub Rotarex (Straub Medical, Wangs, Switzerland) and the Tretorotola Device ( Arrow International, USA) employ a high-velocity rotating helix or nitinol cage that macerates the  thrombus.Disadvantage is endothelial contact with moving mechanical parts.

2.The Angiojet device (Angiojet; Possis, Minneapolis, USA) uses a rheolytic mechanism with possible   less endothelial injury as there is no true contact with endothelium.

3.Ultrasound mediated lyis ( EKOS Endowave (EKOS Corporation, USA) and Omniwave (Omnisonics Medical Technologies,  USA)  fragment with high frequency ultrasonic waves.

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Effect of PCI on Long-Term Survival in Patients with Stable Ischemic Heart Disease are just out in NEJM.

The results are as expected !

“Let us get more Courage , to say no when we want to say no !”

Reference

http://www.nejm.org/doi/full/10.1056/NEJMoa1505532?query=TOC

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These are the common ECG terminologies with which clinical cardiology is being practiced over the years .In this era of instant interventions the exact meaning for these terms  may not matter much for many of us.Still , Ischemia could denote a more benign connotation , while injury suggests an emergency (like an accident) .Of course , this is a dangerous way of defining them. Still, there may not be an entity called  “chronic injury”. while chronic ischemia is all too common.

Logistically , both could  mean the same (except the perception) and related to the intensity of the index reduction in blood supply to the varying thickness of myocardium.While injury is diagnosed by ST segment elevation , ischemia is diagnosed by ST depression  or T inversion.

No, its wrong , come again please ,

Shall we say . . . most injures are ST elevating  while most ischemia are ST depressing , but  still injuries can be ST depressing  as well.  We know Ischemia can be sub-endocardial , transmural or  rarely sub-epicardial ,while injury can either be sub-endocardial or subepicardial (Rarely transmural ?)

Can you refine it ?

Only  subepicardial ischemia(Injury)  elevates  ST  segment while sub endocardial ischemia depress it.The leads facing the affected subendocardial and epicardial surface will determine whether its going to be ST elevation or depression .

Go further,

Does the opposing sub-endocardial and sub-epicardial forces negate or  cancel out  ? If so what is the status  of reciprocal ST depression in STEMI if remote ischemia occurs in sub-endocardial  or  sub-epicardial zones ?  Can there be reciprocal ST elevation for primary ST depressive forces ?

If ischemia and Injury are to be defined only with reference to ST segment , which area of myocardium is linked to  critical T wave ischemia (Both Tall T and dynamic Wellens type T )

Still more , If Injury is  represented by ST elevation,  then what represents  infarct ?

ST elevation in acute MI-STEMI is actually due to  transmural* injury while infarct is represented by Q waves in strict sense.In that case not all acute STEMIs are not true Infarcts.Thats why many STEMI can get totally aborted with zero LV dysfunction and negligible enzyme release.  (Should we call these as Non Infarct STEMIs ?)

*Though STEMI results in  transmural ischemia , it is the sub-epicardial zone of injury that elevates the ST segment. This  implies any degree of subepicardial injury is suffice to elevate ST segment (eg pericarditis) and transmurality of ischemia is not mandatory.

What is reversible vs irreversible Injury ?

If irreversible injury is equivalent to infarct , reversible injury is same as ischemia ? (Whats the histopathological  correlates , Cell swelling, mitochondrial / nuclear death .(We know , enzyme release are  linked to cell death even in  chronic stable angina )

Where is the epicardium  for the IVS ?

Most ACS involve interventricular septum .In this case does septum has  any defined sub-epicardium or endocardium? How does septal STEMI forces behave with reference to partial or full thickness septal  infarct ?

Final message

Acute Ischemia and injury can mean “one and the same thing” or  “totally different” entities  depending upon  the totality of obstruction within the coronaries and  sparing of  sub epicardial zones of  myocardium. In my view , any acute ischemia can be labeled as injury.Bifurcating ACS into STEMI and NSTEMI has largely removed the embarrassment of these entities .

Be grounded

Forget the basic science , electro-physiological concepts can wait.Lets live in a realistic world. Get to know the underlying lesion . What can be done for it ? Go ahead , wheel your patient to cath lab . Alert the staff .Be pragmatic ,make sure your patient has sufficient insurance coverage to open up  all his blocks ! That’s it !

Postamble

The intention is not to confuse the readers.Only to make us realise ,the gap in  basic science is “huge and wide” which I hope is  filled up by the generation next !

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There is something to understand in the movement of dissection flaps with reference to incoming coronary blood flow.Why some dissections dangerously escalate and totally occlude within moments while some others seal spontaneously ? Though uncommon ,  retrograde dissections has some unique hemo–anatomical property .

dissection flaps antegrade vs retrograde

 

 

 

benign dissection no flow limiting self sealing

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