Posts Tagged ‘absolute refractory period’

We know, The Mysterious Alibaba cave opens  with a voice password . . . legend  tell us it had unlimited hidden treasures. It would appear , CTOs mimic the cave in several ways. What is inside ? Should we open it ?  Can we come out safely ? Do we have any magical password in cath lab to get across the complex tissue boulders ?,   every cardiologist would love to have one !

chronic total occlusion alibaba cave corsair fileder xt pronova guideliner micro catheter asahi cart reverese cart cross boss sting ray

Dear CTO,Open Sesame . . . I have come with all the wires you love !  Please let me in !


“CTOs are never an emergency  . . .but please realise  we can very easily create one  while resuscitating a dead snake  ! 

Don’t think hard on evidence , then , you may not do a single case of CTO in your life .Forget all those pessimistic trials like OAT,COAT, etc and the recent ones DECISION-CTO. Ignore all guidelines. Ask your patient, and his insurance company , if they are willing , reserve the cath lab and get ready.

Pre-procedure  planning

Spend at least a hour to analyse the CTO Imagery one day prior and create n action plan.

Keep knowledgeable staff for assisting , but never ask for fellow colleagues help because it hurts our ego !  Cardiac surgeon’s back up is a welcome addition even if it’s on paper.

If possible , try to ask the patient genuinely ,what is his symptom at least once !  before starting the procedure. 

Timing of the procedure.

Don’t post a CTO patient  either on a busy Monday morning  or lazy Friday afternoon.

Hardware Inventory

The wires ,catheters, the balloons form the essential tool box .There is more than a  handful of coronary automobile companies manufacture this .It is all about metallurgy , knowledge of wires, catheters , and tip thickness, (Bullet shaped as in Asahi ) , slipping , hydrophophic or philic,  polymer coating , trackability, pushability , memory etc etc.

Guide wire tip morphology is as Important as the  Lesion characteristics !

Analysis of the lesion (Probably most important)

Unlike conventional PCI we have no initial target.We need to poke first and find the target next ! Distal vessel status  is most important ( Careful review of retrograde filling  through collaterals could give more information than CT angiograms .Calcification, diffuse disease can be a real hurdle)

Lesion morphology

Softness of lesion has to be felt (Requires good wire which has sensor (Paccinian corpuscles and Merckle disc ideal ?) I guess the cortical tactile feel is as vital as the  intervention expertise .I know at least one diabetic colleague of mine who finds it difficult  to cross a CTO  and admits he never found it easy to feel  the lesion through the wires . Autonomic dysfunction ?)

Operator  expertise

(Note: These are like reading  swimming guidelines , you can’t learn in the shores reading books ! you have to plunge !)

Many techniques are proposed .Sequential approach (Ironically experts are licensed to use  specialized wired wires directly .Beginners  are advised to go with non specialized hardware and escalate step by step) Some centers are blessed with new age weapons like cross Boss and sting ray that confront the lesions in multiple frontiers. (Carpet bombing?)

CTO playground. : Its essentially a coronary contact sport with expert septal surfing , tunnelling, knuckling , kneeling , bending . Of course , It  can end up in a gratifying win in few , still most of us tend to play this game without a goal (post !)

They are basically about poking the head of the lesion and trying to cross an occluded vessel  millimeter  by mm towards the presumed distal vessel in an Imaginary trajectory. Proximal cap, central core ,the blind tunnel , distal capsule and exit points each must be successfully conquered.

CTO crossing is  the ultimate capacity of the operator to realise and feel the position of the wires in true lumen and their confidence levels in their conviction!

Multiple wires up to three are used some times to poke the lesion two of them are used to shut the false tracks and the other one is expected to enter the true lumen (Looks too good on theory !) . These are referred to in as many terms like parallel wire see-saw , CART ,Reverse CART etc .Retrograde techniques do help us but has no magic solutions.The lumen contrast , guide wire tip movement and its  side branch entry  would help.

Tacking complication :Always anticipate , it’s not negative mind set to look for it  !

Keep pericardiocentesis kit , covered stents , micro  snares and other retrieval devices ready in cart. Your support staff should be well versed with what is happening around them. Some of  the dye leaks and stains are safe .They imply minor perforations that form  sealed hematomas  (The plane of perforations also matters. myocardial (ab-pericardial ) leaks are well tolerated .Distal perforations are also safe as long as CTO is not opened ) Online echocardiography should be readily available to monitor  pericardial space leak.

When bleed into pericardial space is life threatening , A comical, but life saving option is to close the artery and restore the CTO  its original state and come out of the lab quietly ! 

Newer Imaging guidance : Can be useful , still may not matter much  when considering the interventional acumen .

CTO PCI : Time as therapeutic end point.

CTO is not an endless game with out time frame .In my opinion it shouldn’t cross 45 minutes each as in a  soccer  game with a brief  strategic time out and of course with liberal use of ,yellow and red cards

Future directions

Japanese are the ones who pioneered  CTO Interventions . We expect more Innovations ! Is it the forward looking IVUS ? It is akin to tunneling for underground metro train with GPS guiding .If you can mark the proximal and distal  points , rest will be be taken care by mortised self tunneling catheters from Robotic arms steered by sophisticated algorithms.

Final  message

CTO PCI remains a real Interventional challenge. We are often double blinded  in both directions (antegrade as well as retrograde ). Needs much effort ,time, hardware and most importantly a non fatigued mind and body. The benefits we get may vary  between  gratifying to outright mediocre .Of course , it surely satisfies operator ego and express pride and courage !

Is crossing and stenting  a CTO  synonymous with true success ?

Yes it is , for the cardiologist and  the hospital  . . . I’m not sure about it for the patient !

In this  sense , CTOs  mimic the mysterious Alibaba cave that tempts us with Imaginary treasures but can trap us with a wrong password !


* Who should CTO PCI  ?

I have seen  young , enthusiastic cardiologists with Immature support staff attempting CTO in remote sub- urban settings ! Though patience and expertise are essential ingredients, some amount of organised training and hardwares make CTO PCI safe and effective. Enthusiasm and affordability alone can’t be an Indication for this complex set of coronary lesions.



I still wonder why  this vital paper was never published , it was just presented in the Annual ACC conference March 2017



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Here is  the link  to  one of  the best illustration for cardiac action potential  which I  have stumbled upon !

Spend some time on the following illustration  depicting  the  normal  cardiac  action potential that  explain the ionic movements . Understand why a cardiac muscle has two refractory periods , why there is a sustained dome for  myocardial action potential  and this is missing in SA and AV nodal potential ?

Click below to reach the online book

Textbook in  Medical Physiology And Pathophysiology

Essentials and clinical problems Copenhagen Medical Publisher

Note :

Red curve indicates electrical action potential .Blue depicts the mechanical contraction . Both red and blue curves together form the electromechanical systole. Realise  ,   QT interval  represents electro mechanical systole . It  includes both cardiac depolarisation and repolarisation .

There is a inherent tendency for our brains  to equate depolarisation with systole and repolarisation with diastole .It is totally a wrong perception. Please , be aware of this !

Identify the gap between the  red and blue curves that represent 50%  of ARP  .This is the time the myocytes can not be stimulated whatever be the  power of stimuli because the Na  channels are closed .

Understand ,the above action potential  represents only half of the cardiac cycle as diastole is not fully illustrated here .Recognise  the fact ,  diastole begins at the end of phase 3  and  goes into phase 4 as diastolic depolarisation  by a slow Na current.

After learning   the basics of action potential   read about the antiarrhythmic drugs . You will get to understand it better .

Learn  which drug acts on which receptors or channels and what does it do  to the various intervals  .For example ,  any drug that is prolonging an action potential  duration is fraught with risk of  ventricular arrhythmia as it is synonymous with prolonging QT interval (Eg Class 1 A /1B/Class 3) .

Sicilian gambit is the receptor & channel based classification for anti arrhythmic drugs . (Sicilian gambit 2 )

  • Understand the paradox of  QT interval getting shortens with Class 1 B (ligocaine /Mexilitine ) while 1 A  does the opposite !

Class 1   Drugs blocks sodium channels .The blockage  occurs in  a complex rate dependent fashion . It blunts the slope  the phase 0 and hence prolongs the action potential .

Class 2 . Beta blockers

Class 3 . Blocks K + Channels and hence prolongs the AP

Class 4  .Calcium blockers

Finally  don’t forget to say thanks to Copenhagen medical  publishers  for this excellent illustration .

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