Am medical professional, if you receive a substantial electrical shock you should seek medical attention ASAP. There is the potential for a lethal arrhythmia to evolve even if you feel relatively fine immediately afterward.
Quite. And the time period for changes to evolve is comparatively long -- up to 12 hours -- if the heart muscle is damaged and a scar forms later on, leading to the potential for life-threatening arrhythmias. Bradycardia is also sometimes reported long after the event. On top of that, there are reported "cTNI +ve without pain" events indicating significant cardiac injury detected only via ECG or blood tests (for cardiac troponin).
> Exposure to high voltage can cause asystole directly
Yep. This is what defibrillation is. When you use a defibrillator, you're shocking the heart into asystole in the hopes that it will restart itself. Shocking an already "flatlined" heart will not restart it, contrary to what many movies would have you believe.
> The SA nodes are particularly vulnerable; patients may effectively give themselves an SA node ablation
A very good summary article is here: https://www.bmj.com/content/357/bmj.j1418 .
Take home points:
-- Arrhythmias (superventricular and ventricular) are common
-- Exposure to high voltage can cause asystole directly
-- Delayed [life threatening!] ventricular arrhythmias have been reported for up to 12 hours post incident, both with high and low voltage shocks
-- Delayed, serious bradycardia can result months or years after the accident
-- The SA nodes are particularly vulnerable; patients may effectively give themselves an SA node ablation
-- Direct myocardial injury may occur without chest pain (due to nerve damage)
-- MI may also occur via coronary spasm or thrombus.
That neglects the rest of the body -- where the effects can also be significant.
Electricity in large amounts is bad for you – c.f. the electric chair!