Which of the following decreases defibrillation threshold:-
**Core Concept**
The defibrillation threshold (DFT) is the minimum energy required to successfully terminate a ventricular fibrillation (VF) or ventricular tachycardia (VT) with a biphasic defibrillator. Reducing the DFT is crucial for improving the efficacy of defibrillation.
**Why the Correct Answer is Right**
Catecholamines, such as epinephrine, decrease the DFT by increasing the excitability of the myocardium. This is achieved through the stimulation of beta-1 adrenergic receptors, which increases the slope of phase 0 of the action potential, allowing for more effective electrical conduction and defibrillation. Additionally, epinephrine promotes a more uniform distribution of electrical activity across the myocardium, making it easier to achieve successful defibrillation.
**Why Each Wrong Option is Incorrect**
**Option A:** Isoproterenol, another beta-agonist, has a similar effect to epinephrine in increasing the DFT. It is not the correct answer in this case.
**Option B:** Calcium channel blockers, such as verapamil, actually increase the DFT by reducing the excitability of the myocardium and slowing conduction velocity.
**Option C:** Lidocaine, a class Ib antiarrhythmic, increases the DFT by blocking sodium channels and reducing the slope of phase 0 of the action potential.
**Clinical Pearl / High-Yield Fact**
Remember that catecholamines, such as epinephrine, can be used to decrease the defibrillation threshold in cases of refractory VF or VT, but their use should be carefully considered due to potential adverse effects.
**Correct Answer:** D. Epinephrine decreases the defibrillation threshold.