Beta-blocker and calcium channel blocker overdoses can both cause profound cardiovascular collapse.
But the shock is not only electrical or hemodynamic.
It is also metabolic.
Beta-blockers reduce heart rate, contractility, and AV nodal conduction. Some agents also block sodium channels or cross the blood-brain barrier, causing seizures or QRS widening.
Calcium channel blockers reduce calcium entry into cardiac and vascular smooth muscle cells. Non-dihydropyridines such as verapamil and diltiazem can cause bradycardia and myocardial depression. Dihydropyridines may cause profound vasodilation.