Feeds:
Posts
Comments

Posts Tagged ‘ventricualr tachycardia’

Though heart is  primarily  known  as a  mechanical  organ , in reality   it is a vital  electrical organ as well . The entire mesh of electrical  pathway  from SA node to  Purkinje  fiber  would easily cross  a mile or two .Maintaining and protecting  such a  delicately  woven network  needs lots of  electrical sense  .  It is not surprising to note  , VT or VF  can be induced  virtually  in  every human heart  if stimulated rapidly. Electrocution  induced  by VF is  the typical example.Cardiac surgeons  do it regularly  before  surgery .

So , inducible  VT  in the EP  lab need to be  defined in a strict manner .

  •       VT must be triggered  by a  single stimuli  (or  two )
  •       Multiple sites should not be stimulated(ideally  single site , at most two )
  •       It should be sustained.
  •       Only mono-morphic VT has  significance
  •       Induced  p0lymorphic VT  has no clinical value.
  •       Pharmacological  stimulus  such as isoprenaline   can be used but reduces specificity.

*If a VT  rapidly degenerate  into VF  it  usually  means a polymorphic VT  while   unstable irregular  polymorphic VT   could be  same as   VF )

How do you make sure  what we induce in  EP lab is same as the clinical VT ?

This is the most difficult task for electro -physiologists. In real life setting VT is  often induced by ischemia hypoxia , local  acidosis and electrolytic imbalance. However  rarely mind this issue . In EP lab we induce  it  with  artificial electrodes  . Does it make sense to compare  these two totally different  set of triggers  in real life and a virtual EP life . Ideally  to confirm ischemic  VT  one has to induce ischemia  in EP lab and look for  VT . (Adenosine  stress ? )  Further ,  only re -entrant VTs  can be induced in EP lab by programmed stimulation . Automatic VTs can not be induced by stimulation .

The chances of inducing a VT in EP lab is  directily proportional to the aggression of the electro physiologists and patience  of  the  patient ! One can afford to use  more aggressive  protocols only   if a clinical VT was  recently the   documented .

 Electrical stress testing of heart

It may be tempting  to refer    induction of VT  in EP lab  as  electrical stress testing  for the heart. But fundamentally there is a difference  between this and  the conventional EST . Unlike exercise stress  test the  inducibility of VT highly unpredictable . It has far too many variables . (The surface area of contact , number , Intensity ,  site of stimuli , scar location , irritability of viable myocardium  ,  inertness of scarred myocardium ,  and finally the cellular milieu etc  )

Thoughts to ponder over Is it not  “a fundamentally a wrong concept”  to give importance  to inducible VT  ?

Why should we  treat a clinically non relevant inducible VT ? We do not know yet whether inducible VT in other wise normal LV function  has any long-term significance . Currently it makes   no sense   to intervene in VT  if the LV function is good and the episodes  are not clinical but only inducible.

Note: If there is severe LV dysfunction (EF < 30 % ) one can implant an  ICD without   an  EP study . ( Of course   to state more dramatically   without even single documented VT  !) MADIT 2

Final message .

A VT which is inducible in EP lab has no meaning ,  if the LV function is normal , while  even a  non-existent  (potential  )VT  in the setting of severe LV dysfunction is vitally important !

Though  we  differentiate cardiac function  into mechanical and electrical for academic purposes , it is astonishing to note   how the heart is able to function  as a  single unit  . We know today , the ultimate  outcome of   VT  is  not  dictated  by  electrical status of the heart rather , the mechanical ability  to  with -stand  sudden dis-organized  ventricular  contractions ( A ventricle with good contractile function has inherent  capacity  to extinguish most episodes  of VT .(Myocytes with inbuilt biological ICDs ?)

It is a million dolor question why some VT remain as non- sustained while others rapidly degenerate into  fast VT and VF thereafter

Reference

The two contrasting studies

The MUSTT (1999) trial exposed the limitation of   clinical utility of inducible VT . Multicenter Unsustained Tachycardia Trial (MUSTT) Investigators

While   MADIT 2  (2002)which recommends an ICD in every patients with  severe LV dysfunction following MI without even a EP study .

Read Full Post »

Ventricular tachycardia as a group , constitute a major  group of cardiac arrhythmias. Most of the VTs are managed  by cardioversion  followed by medical management.  Few require , implantable defibrillator when there is severe LV dysfucntion .(ICD) Localising the origin of  VT and subsequent , ablation is the treatment of choice in some of the  patients  with VT.

Traditionally VT was thought to arise fro the endocardial aspects of myocardium. Now  we realise many times VT originate from the epicardial aspects of  ventricle.

Epicardial VT : Defintion

Epicardial ventricular tachycardia (VT) is defined as VT in which the critical sites of the reentrant circuit (or the ‘sites of origin’) are located exclusively in the subepicardial tissue, as shown by entrainment manoeuvres or VT that is terminated within 10 s with standard radiofrequency (RF) pulses, or both.  E. SOSA,M. SCANAVACCA et  all  http://www.springerlink.com/content/w608142674154tp5/ 

 

 How to recognise epicardial origin of VT by surface ECG ?

  • Terminal S wave in V2 and q in lead 1 strongly suggest VT of sub epicardial origin.
  • Pseudodelta wave 
  • Intrinsicoid deflection time of  85 ms
  • RS complex duration of  >120msec

Suggest   epicardial origin of the VTs.

Important Links

http://www.circ.ahajournals.org/cgi/content/full/113/13/1659 

Berruezo      criteria ,http://circ.ahajournals.org/cgi/content/full/109/15/1842  ( Must  read)

http://cogprints.org/4222/2/tada.pdf

 

What is the clincal significance of epicardial VT ?

Endo cardial ablation  not likely to be successful

Trans pericardial approach may be needed.

Read Full Post »

Ventricular  tachycardia (VT)  is one  of  the   dangerous form of  cardiac arrhythmias.

When it occurs , it may present  in  many ways

  • Cardiac arrest with immediate degeneration into ventricular fibrillation. 
  • Pulseless VT in a  conscious patient but in  in shock.
  • With pulse, relatively stable , not much fall in blood pressure.
  • Incidentally detected.*(Rare)

This , gives us  an idea  that VT  as an electrical abnormality has wide clinical presentations , life threatening  at one end and,  patient walking into the hospital with minimal palpitation on the other hand !

The management issues

  • In patients with hemodynamic instability , decision making is easy as there is only option of DC shock.
  • In patients with stable VT, it is natural for the physicians to get tentative or even confused.This is because , dangers of shocking a stable patient has to be weighed against the currently available excellent antiarrhytmic drugs( Amiodarone, Ibutilide etc) .

 

The major issue here is  in  ruling out underlying structural heart disease.

Never shock a stable VT, without knowing the myocardial and valvular function.There has been many occasions underlying  severe LV dysfunction is missed   and they may go for asystole.

VT in the setting of cardiomyopathy, Post MI(Scar mediated) are often refractory even to DC shocks.It is the drugs that will  ultimately control the arrhythmia.DC shock is just used to terminate the VT.

VT  structurally normal heart , especially arising the outflow tracts of LV or RV  behave very differently (Fortunately they are more benign)

  • Have less hemodynamic  impact as it involves the outflow tract and  not over the  the pumping  zone of LV as in conventional ischemic myocardial VT .
  • They  respond to calcium blockers  verapamil to be precise (As they share properties of SVTs)
  • Sensitivity to verapamil by no way convey a meaning of Amiodarone resistance.Out flow tract VTs will also respond to Amiodarone many times.
  • Degeneration into VF is rare.

 

Also  read  Therapeutic issues in stable ventricular tachycardia

Presented and published in Indian heart journal

vtvt-therapeutic-issues1

Click  on link download PPT ventricular tachycardia

 

Related topics

Why some ventricular tachycardias are resistant , even to multiple DC shocks ?

Read Full Post »

Lignocaine , probably has saved more lifes  world over  than any other cardiac drug .

It was the only choice for ventricular tachycardia  till 1990s, both in pre and post  thrombolytic era.Every coornary care unit has reverted tens of thousands of  unstable VTs with this simple and cheap intravenous drug.the utility value of lignocaine is not limited to ischemic VT alone it is effective in in almost all forms of VT.It was classically administered in two or more boluses followed by an infusion.

What happened to this wonder drug  with great performance record ?

The  power of   statistics , and inappropriate interpretation by the scientific community  has left a serious blow to this wonder drug .Now the drug has been made redundant, and mainstream cardiac literature has made everyone feel  guilty , if  anybody  uses this drug for VT .

Why did lignocaine lose the battle ?  The reason is three fold

  1. The advent of  much fancied Amiodarone
  2. One negative study  for antiarrhythmic drugs in post MI period (CAST) 
  3. And two so called  positive studies  for Amiodarone (ALIVE & ARREST) has sounded the death bell for this drug  which has resuscitated millions of life !

CAST study http://content.nejm.org/cgi/content/abstract/321/6/406 

All , CAST  said was routine suppression of  asymptomatic ventricular arrhythmias  in the post MI period is unwarranted. But you know , how this  world interpreted it  “Lignocaine  has no role in ventricular arrhythmias in post MI setting ”  The most funny thing  was  lignocine was never used in CAST study .

The  studies involving one to one comparison  of Lignocaine and Amiodarone (ALIVE and ARREST study) was also not interpreted  properly.These studied only shock resistant VTs. What about the role of lignocaine where defibrillator was not available ?

Link to ALIVE and ARREST  read and make your own conclusion.

http://content.nejm.org/cgi/content/abstract/346/12/884

http://content.nejm.org/cgi/content/full/341/12/871?ijkey=8fa241f3cebb86a177632ec6ccadfb5a3ded7bc2

 Final message

  • Lignocaine is not  only a topical anesthetic  , it is powerful and gentle myocardial anesthetic when administered in post MI period.
  • With this property it  successfully cardioverts and prevents dangerous ventricular arrhythmias.
  • Time tested and worthiness proven.
  • While , we are made to believe  the success rate of  Amiodarone in VT is far superior than ligncaine .It is a falsehood.
  • Any experienced cardiologists will recognise ,  many times even  Amiodarone resistant VTs often respond to Lignocaine .
  • The fact of the matter is , without a good quality  one to one study  , lignocaine was ditched. One reason for this could be  Lignocaine ,  is a generic drug and has no market value.

Let us take home , the message (scientific or unscientific ! ) Lignocaine still has a great role to play in the management of dangerous ventricular arrhythmias .The only caution is ,  it should not be used routinely and indiscriminately in all asymptomatic patients with  VPDs or nonsustained VT . (Acknowledging CAST conclusion.)

Read Full Post »

The cell of origin of ventricular tachycardia is rarely discussed at bedside. It is still in research labs !

                                    Ventricles are not made up off entirely myocytes. Apart from myocytes it contains specialised  purkinje cells , fibrocytes, interstitial cells and  some times primitive mesenchymal cells. Ventricular tachycardia can arise either in purkinje cells, the myocytes  or even the fibrocytes. The myocyte  VT  classically occur during ACS or post infarct VTs.They are  more often hemodynamically unstable and quickly degenerate into ventricular fibrillation. Myocardial VT is likely to be pulseless and require DC cardiversion frequently. Purkinje VTs are relatively less unstable. If VT arise proximally in the septum near the distal his, or in bundle branches (BBR) the VT is more stable.They  are likely to respond to be medical management.

What is the therapeutic implication of knowing  myocardial VT ?

                               In fact  ,simply knowing the cell of origin of VT is not suffice .The ionic currents inside the cell that trigger and sustain the VT is more important. There are few ionic circuits responsible for VT. Sodium , Intra cellular calcium, potassium , beta receptor mediated calcium current.If we know the individual ionic culpirit we can block that specifically  . Now we have multi purpose ion blockers  like amiodarone which acts like a broad spectrum antibiotic and terminates a VT.

                              So as of now there is no real purpose of breaking our head  in locating the cell  of origin  and the ions responsible for VT  at  the bed side ,( Researchers will do that for us !).  We have only few  antiarrhythmic drugs available in our crash cart  .Our job is to choose the optimal  drug  which will fit in for our patient. In electro physiology labs, radio frequency ablation is done .This is  nothing but shooting down the abnormal electrical  focus (Cluster of cells or a samll segment of myocardium).  In future,  a single abnormal  cell could be selectively neutralised with cell based therapy assisted by  nanopore robots !

Read Full Post »

Follow

Get every new post delivered to your Inbox.

Join 315 other followers