Read with caution . This may either injure or cure your patient !
How does verapamil terminate a VT ?
Physicians often debate vigorously before labeling a cardiac arrhythmia as ventricular , atrial junctional , abberant or not etc etc . But for an arrhythmia it matters little from what chamber it is going to to originate . After all , any cell in the heart if excited can generate an arrhythmia . The ion channel abnormality and the influx and efflux of ions that determines how a drug is going to terminate an arrhythmia.
In fact , way back in 1989 the Sicilian Gambit stressed this concept when classifying anti-arrhythmic drugs .This classification taught us , even though there is a huge list of clinical cardiac arrhythmias , from the therapeutic point of view there are only a handful of receptors (scattered all around ) to target !
When we look at this angle , we realise , many of ventricular action potentials have important slow calcium currents similarly junctional action potentials do have some sodium currents. Calcium current is present in every myocardial cell more so in the vicinity of AV junction. Further , at times of ischemic or hemodyanmic stress these ion channels may take a different avatar altogether.Slow sodium channels and fast calcium channels etc ! (A wild imagination or is it a fact ?) Other important targets are potassium channels
Heart is a complex structure both macro and microscopically . In the three dimensional histopathologic interface between atrium and ventricle (Especially in the basal areas , outflow tracts , around the AV grooves ) there are lot of sharing and overlap of different morphology of cells . A high septal VT can behave exactly like an SVT which includes the tendency to get terminated by calcium channel blockers.
Amiodarone is a most popular drug for VT termination ? Are we clear about the mechanism of it’s action in terminating VT ?
It is more of a perception and belief that class 3 action may be responsible for termination of VT by Amiodarone . In reality it is very difficult to prove this point. As Amiodarone has all the 4 classes action that includes beta and calcium blocking properties.. In fact , now there is evidence to suggest beta or calcium blocking action may be more important in terminating VT when it is administered IV . (While the class 3 action predominates in long term oral therapy )
A verapamil sensitive VT may successfully be terminated by Amiodarone not by its unique action instead it may simply represent its calcium blocking property.
Many of the VTs terminated by Amiodarone could also be verapamil sensitive . Since verapamil is never tried first we will never ever know the incidence of such phenomenon that gives pseudo credit to Amiodarone
It may not be big crime to try injection verapamil in some of the stable ventricular tachycardias( As my fellow did ) especially when we we know there is an entity called verapamil sensitive VT !
Q for the readers :
How many deaths are reported in cardiology literature regarding fatality following verapamil in VT ?
I am trying to find the answer the data is very hard to come by !
Critical comments welcome.