Ventricular tachycardia can be a killer arrhythmia that can arrest the heart within seconds or behave like your pet, gently cuddling the heart and terminating spontaneously. The latter phenomenon we call it casually as benign non-sustained VT. Such VTs are more common in the out flows, fascicles or in HCMs. Most of us do not have time, to wonder why some of these blessed arrhythmias are not able to sustain.
Of course, the definition of non sustained VT can be challenging and keep changing with time. We have examples for both extremes , ie hemodynamically stable sustained VTs as well as unstable , but still, not sustained one.
Coming back to the mechanism behind these VT ,Let me provoke an answer from the readers.
Why some VTs are non sustained ?
A. The forward head of VT energy front is weak.
B. Source-Sink mismatch and tissue fatigue .
C.Disconnect between upper & lower loop of VT
D.Rate induced functional Exit or Entry block in the circuit
E. All of the above
F. None of the above , it is largely decided by the fate of the patient
While most EP specialists are busy taming the sustained one, very few are actively doing research about the mechanisms underlying the non-sustainability of VT. Here is interesting paper that discusses possible mechanism of termination of re-entrant VT.
The clinical importance of this question is, if we can convert sustained VT to non-sustained ones with drugs, it is indeed a therapeutic success. Drugs can slow down or terminate the arrhytmia circuit by acting in any of the four phases of action potential. The research in the field of anti-arrhythmic drugs has almost stopped in the last four decades for some unexplained reason. I think, we (Pharma companies?) decided to close the doors of anti-arrhythmic drugs after Dronedarone or Ibutilide . Renewed interest in Mexiletine, Norpace and Sotolol is a welcome move though. My suggestion is, oral forms of cardio specific lignocaine analogues could be a game changer in the filed of cardiac arrhythmias. Phenytoin sodium is old warrior drug, could make a comeback.
If only we had tried more, we might have produced more powerful drugs ( One obvious reason being cardiologists have decided to take on cardiac arrhythmias with electrical and mechanical weaponry in the hope of avoiding drugs. But, that aim has not really been accomplished except in AVNRT/AVRT. We still need the assistance of drugs in many classes of VT, even after ablation as well as an ICD.
Final message
As far as the answer to the MCQ, is concerned, response E is correct. If we look at the question again, quixotically, we may need to agree response F, (ie none of the above) is also right. Destiny decides the presence or absence of factors A to D in a given patient.
Reference
- The Renal Warrior Project. Join Now
- Source: https://drsvenkatesan.com/2024/12/12/why-do-some-vts-are-non-sustained/