Posted in Uncategorized, tagged classification of pvt polymorphic vt, polymorphic vt on October 16, 2015| Leave a Comment »
A classification of Polymorphic VT .
It can be classified according the etiology, morphology or hemodynamic stability . However , for some reason classifying PVT with reference to the preceding QT interval and the manner in which tachycardia twists its axis along the qrs axis has been the most popular theme . ( Obviously ,the classification process should evolve further , and management strategies should be linked with it )
Read a related article :Different Avatars of polymorphic VT
Posted in Uncategorized, tagged epicardial brekthrough, how to recognise multiple focus in a VT, monomorphic vt, multifocal ventricular tachycardia, multiform vs multifocal vt, polyfocal vt, polymorphic vt, torsades de pointes, unifocal ventricualr on September 23, 2011| Leave a Comment »
Ventricular tachycardia can be classified in a variety of ways. Monomorphic VT and polymorphic VT is one such classification based on VT morphology.Polymorphic VT generally conveys a meaning of origin from multiple focus .But in reality bulk of the polymorphic VT originate from a single focus . 
How does a single focus have a multiple QRS morphologies ?
This is possible because , even though VT arises from a single focus , the route it takes to exit from the myocardium is different and hence they inscribe different QRS morphology for each beat. It is also possible , as the conduction time varies with each exit route the VT becomes irregular. This phenomenon is called polymorphic VT.
It is assumed the VT focus is often located in the sub endocardium and breakthrough occur in the epicardial side as we record the activity in the surface ECG. Electrophysiology of VT is not that simple , focus of VT can be anywhere , the focus can be single or multiple and exit pathways can also be multiple it and it may even exit into endocardial cavity . Please note , even a single electrically abnormal cell shall act as a focus . To confuse us further , some of VTs may not exit at all , extinguishes before reaching the surface.
It is a difficult job to fix a given polymorphic VT to arise from a single focus or from multiple focus . Multifocal VT can be diagnosed with confidence only after a through electro physiological study.Clinically few clues are there. Electrolytic disorders and ischemia are usually multifocal, while scars VT gives single focus .Other famous example of polymorphic VT are Torsedes de pointes .
Polymorphic VTs are usually hemodynamically unstable but it is not a rule. Surprisingly ,some of the polymorphic VTs are well tolerated . This is especially common in multi focal polymorphic VTs which are hemodynamically and electrically better off . Ironically , presence of multiple focus may be a blessing as they compete with each other , in the process pulling down the other focus from triggering a VF . It is possible one focus acts like a natural anti tachycardia pacing for a VT from another focus.
Ventricular fibrillation can be termed as an extreme form of irregular polymorphic VT as the wavefront breaks into innumerable fragments each exiting the myocardium at will in a random fashion bringing ventricles to a standstill.
Final message
The term multifocal polymorphic VT is generally been abandoned at the bedside as distinguishing it from single focal polymorphic VT is a difficult task*.Still the concept of multifocal VT is alive and kicking in the EP labs , giving sleepless nights to our Electro-cardiologists!
*Please note , multi focal VPDs can be recognised with ease by different coupling intervals, but it is difficult to identify during a run of VT .
Posted in Cardiology-Arrhythmias, Uncategorized, tagged amiodarone, anti tacyhcardia pacing, atp, brady tachy syndrome, burst pacing, cardiac arrhythmias, coupled pacing, digoxin induced tachycardia, electrical storm, over drive pacing, pace maker, paired pacing, polymorphic vt, ramp pacing, refractory vt on November 7, 2009| Leave a Comment »
It is one of the greatest innovation in medicine . . . that is . . . electric current being used as a drug to treat disorders of heart . Of course , it is not a surprising finding when we know heart is an electro mechanical organ , and electricity can be used to treat various disorders of heart by delivering it in an optimal dosage and site.
Devices that help administer electric current in cardiac disease.
What is the difference between cardioversion and pacing ?
Cardioversion is reverting a tachycardia with a electric shock that is delivered diffusely throughout the heart This electrical wavelets traverse the focus of tachycardia and the adjoining myocardium which is called critical electrical mass (Usually reentrant) .This depolarises the cells responsible for tachycardia and extinguishes the abnormal electrical activity.
Defibrillation is same as cardiversion except that it is a high energy shock and delivered without synchrony with qrs complex . In VF, we defibrillate in all others we cardiovert .
What are the disadvantages of cardioversion ?
Eventhough it is a very successful modality for treating cardiac arrhythmias it also has some issues.
What is difference between cardioversion applied externally on the chest wall and intracardiac cardiversion as in Implantable cardiovertor defibrillator(ICDS) ?
The underlying principle is same except that the energy required is a fraction of that applied in the chest wall . The average energy required is up to 20 joules . while it requires up to 300 joules
What is anti tachycardia pacing ? Why this concept came into vogue ?
When it became clear , cardioversion may not work in all forms of tachycardia and risks of multiple shocks on the myocardium not be taken lightly , experts in those times (1970s) thought a pace maker lead in a optimal site can do the job of cardiovertor. .
Pacing rapidly in the tachycardia zone provide us an opportunity to enter the tachycardia circuit , interfering , interrupting and blocking the reentrant circuit (We call it entrainment) . If it is an automatic tachycardia pacing in close vicinity of the tachycardia focus result in a electrical line of barrier which acts as an exit block ( Like the lakshman reka ! in Ramayana )
The term ATP is used as a general term as anti tachycardia pacing .Over drive pacing can be used synonymously.
What is the main advantage of ATP ?
How to perform overdrive pacing ?
Can we use the external transcutaneous pacemaker paddles for overdrive pacing ?
Yes we can, it may be termed a non invasive external overdrive pacing .This mode is not popular among cardiologists not because it is ineffective , rather we have not fully realised it’s potential .
Different types of overdrive pacing
What is coupled pacing ?
It is a type of overdrive pacing where patient’s own spontaneous rhythm is used trigger a pacemaker stimulus and hence only alternate beats or pacing beats which is coupled with the pateint,s own rhythm it is called coupled pacing . This is different from from paired pacing in that only single pacemaker stimulus per cycle .
What is paired pacing ?
Two pacing stimulus are given.The first impulse is maintained constant and the second impulse is done with varying coupling interval to scan the entire cardiac cycle .It is expected at some point of paired pacing the second impulse would block the reentrant circuit.
What is random paired pacing ?
The atrium is delivered a pair of random stimulus ( . . Like a bite of snake !) is delivered into the atria .This can revert many of the reentrant atrial and ventricular re entrant tachycardia.
What is the unique value of sinus paired pacing ?
In patients with persistent sinus tachycardia, especially in patients with high MVo2 situations or dysfunctional ventricle we have no option to control the heart rate without depressing myocardial contraictility . Most of the negative chronotropic drugs have negative inotropic action also. In these situations pairing a pacemaker stimulus with a sinus impulse can produce a compenstatry pause and result in reduction in net heart rate as well as increased contractility due to post extrasystolic potentiation.
How does a catheter whip inside the atria terminate many of the procedure related tachycardias in cath lab ?
It is a common maneuver in cath lab , to forcibly whip the catheter for terminating many of the transient procedure related SVTs and outflow tract VTs . The arrhythmias get terminated either due to catheter hit induced mechano electrical cardioversion (5 joules ?) or the atrial subendocardial stretch due to the whip lash .
What are the tachycardias that may respond to overdrive pacing ?
It is logical to expect any of the reentrant tachycardia might respond to ATP. The exact success rate can not be established since this modality is not applied in vast majority of patients . Only if a patient is not responding to drugs or multiple DC shocks ATP is thought off . Of course ATP can not considered a first option unless othe patient is on a temporary pacer.
What is the caution for using ATP ? Why atrial overdrive pacing is preferred over ventricular overdrive pacing ?
Pacing a ventricle rapidly carries a risk of inducing ventricular fibrillation . So whenever possible ATP should be administered through an atrial lead. This may not be possible always as in the presence of AV block a VT can not be captured by atrial pacing .
It is also a fact many times when the ventricular overdrive pacing fails to revert a VT , an atrial overdrive pacing has been successful . This is due to the more uniform depolarization wave fronts , that reach the ventricle and reset the VT .
Currently ATP is useful in
In some of the modern pacemakers and in all ICDs ATP is a an important programmable parameter .In fact, using this mode liberally would conserve battery life .Many times a simple hemodynamically stable VTs are shocked by ICDs instead an ATP will do the job . It is a well recognised fact that ATP is underutilsed in ICDs .This issue needs to be addressed.
Final message
Pacemakers are not only meant to treat bradycardias but also tachycardia. Even though it is a well-known fact for over 3 decades, for some reason this simple and effective concept is not getting the attention of the current generation cardiologists which it definitely deserves!
Reference
Over-drive pacing : A practical approach
Dr.S.Venkatesan MD 