Why is alternating current (AC) at standard household frequencies (50–60 Hz) significantly more dangerous to the human heart than direct current (DC) of equivalent voltage?
Answer and explanation
Correct answer: A. AC currents bypass capacitive skin impedance and match cardiac repolarization, causing fibrillation
Human skin acts as an electrical resistor in parallel with a capacitor. The 50–60 Hz alternating frequency significantly lowers capacitive skin impedance, allowing greater current to penetrate deep tissues. 50–60 Hz cycles coincide with the vulnerable phase of cardiac ventricular repolarization (the T wave on an ECG), repeatedly exciting cardiac myocytes during relative refractory periods and precipitating disorganized ventricular fibrillation at currents as low as 50–100 mA.
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