Ventricular arrhythmias

Question 1

Triggers and modulators of ventricular arrhythmias

Answer 1

o Autonomic nervous system: ↑∑ activity reported in sustained ventricular arrhythmias
 Stimulation of Na+/K+ pump → hyperpol → ↑ availability of Na+ channels → ↑ conduction velocity
 ↓ repol duration + effective refractory period → dispersion of refractoriness
 ↑ slope pf phase 4 + ↑slow inward current
 Promote DADs by stimulating Ca2+ currents → ↑ intra [Ca2+]
 α adrenergic agonist: block Ik and Ito → prolong AP duration
o Neurogenic adrenergic stimulation: NE form ∑ nerve
 Sudden, for a short period of time
o Humoral adrenergic stimulation: epi from adrenal glands
 Gradually, for a longer period
o Changes in ∑ balance with CHF
o Modify effectiveness of antiarrhythmic drugs

Question 1

Therapy goals

Answer 1

o ↓ risk of death/c/s → Vfib, asystole, pulseless idioventricular rhythm
o ↓ frequency of dangerous arrhythmias
 Vfib: multiple re-entrant circuits from dispersion of refractoriness
* Dispersion of refractoriness required for re-entry loop in ventricles > atria
o Rare for normal heart to develop Vfib spontaneously
 HR = most determinant of hemodynamic compromise
 Electrical instability + below features require tx
* Polymorphic VPCs
* Short coupling interval → R on T phenomenon
* Short cycle length
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Question 2

Drug effect on ECG

Answer 2

• Prolongation of QT interval
• Large T waves
• U waves
  o Heterogeneous repol
  o M cells