ECG Electrophysiology Basics 3

Question 1

Which electrolyte abnormality classically produces peaked T waves and widened QRS on ECG?

Accepted Answer

Hyperkalemia

Answer

Hyperkalemia reduces the resting membrane potential, slows conduction (widened QRS), and causes tall peaked T waves due to accelerated repolarization.

Question 2

What does the term 'overdrive suppression' refer to in cardiac electrophysiology?

Accepted Answer

A faster pacemaker suppressing the automaticity of slower ones

Answer

Overdrive suppression occurs when a faster pacemaker drives slower subsidiary pacemakers, accumulating intracellular Na+ and hyperpolarizing the slower cells via Na+/K+ ATPase.

Question 3

Re-entry arrhythmias require which of the following conditions?

Accepted Answer

Two pathways with different conduction velocities and refractoriness

Answer

Re-entry requires a circuit with unidirectional block in one pathway and slow conduction in the other, allowing the impulse to re-excite previously depolarized tissue.

Question 4

Which phase of the cardiac action potential corresponds to the plateau and is maintained primarily by L-type calcium channels?

Accepted Answer

Phase 2

Answer

Phase 2 (the plateau) is maintained by a balance of slow inward Ca2+ current through L-type channels and outward K+ current.

Question 5

What is the approximate conduction velocity through the AV node?

Accepted Answer

0.05 m/s

Answer

The AV node conducts very slowly at approximately 0.05 m/s, creating the necessary delay between atrial and ventricular contraction.

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ECG Electrophysiology Basics 3