Who said this non-sensible statement? ( I guess ,this would be the first response from many cardiologists !) If you feel the same, then this post might not be for you.
Relationship between Ischemia and arrhythmia
While the relationship between Ischemia and VT is really complex, the term “Ischemic VT” itself adds more twists. Its all about timing, intensity of Ischemia , associated factors and finally the baseline arrhythmic risk that includes the mystery defects in myocyte gap junctions and ion channels.
Following are some of the observations.
Primary VT
This is the true Ischemic VT. Even here, it is the associated factors, like hypoxia or acidosis are the triggers which of course are resultant of Ischemia. There are further problems . Even critical Ischemia, as in high grade unstable angina, rarely Initiate a VT, while STEMI seems to have the exclusive rights to trigger it , by its ability to produce acute transmural ischemia . (Note: Whether primary VT occurs before or after myocardial necrosis is not clear) There is evidence to prove, susceptibility to VT at times of Ischemia is in the genetic make-up of ion channels, as pointed out by famous French electrophysiologist Haïssaguerre. (NEJM 2008)
Post Infarct VT : (24 hrs to 2 weeks ,an empirical criteria we use)
This can be called as Ischemic, still we ‘wouldn’t know whether the arrhythmia is originating from dead or live tissue. It can even be combined Ischemic-Scar VT
Late Ischemic VT
These are the typical scar – substrate -mediated ,micro/macro reentry VT .The strip of tissue on the border zones of conflict (between viability and non viability is always restless (Gaza strip of VT?) This is rarely amenable to revascularization, unless some one is able make that area 0% Ischemic , which is a highly improbable scenario. The alternate option is diagonally opposite .EP guys are empowered with a deadly solution, and authorized to shoot down focus (or isolate) instead of the futility of revascularisation. (Please note, this doesn’t work and should not be attempted in early ischemic VT, though few case reports of RF ablations during VT storm li- Juan Qu et al AMJS 2924 )
Final message
The relationship between Ischemia and VT is poorly understood, (rather than to say complex.) It is true ,acute Ischemic VTs has more closer relation with Ischemia, often settles down with prompt revascularization.
In chronic VT , shooting down the ischemic focus by ablation is more likely to extinguish the arrhythmia ,rather than revascularization. This is because partial revascularization irritates the viable myocardium and keep the ischemic focus active. ( Class C evidence) ICD though a revolutionary technology to prevent a SCD in these circumstance it makes a poor choice to reduce the arrhythmic burden .At best , it is just a back up device to tackle the escaped VTs in spite of RF ablation and drugs.
Reference
Dr.S.Venkatesan MD 