Arrhythmias and Conduction Disorders
Core concepts
Arrhythmia questions test rate, regularity, QRS width, P-wave relationship, hemodynamic stability, and reversible triggers. Distinguish sinus tachycardia, AVNRT, AVRT, atrial flutter, atrial fibrillation, atrial tachycardia, junctional rhythms, and ventricular tachycardia. AV block is classified by PR prolongation, dropped beats, and QRS width; symptomatic high-grade block needs pacing. AF management addresses anticoagulation, rate control, rhythm control, and trigger modification. Sudden cardiac arrest risk depends on EF, syncope, family history, and genetic disease.
Question traps
A wide-complex tachycardia is VT until proven otherwise, especially with prior MI or structural disease; do not give verapamil. Avoid AV nodal blockers in pre-excited AF. Adenosine can terminate AVNRT but may worsen flutter or reveal a broad-complex rhythm. Check QT and electrolytes before antiarrhythmics. Syncope in a patient with structural heart disease or an abnormal ECG is not benign.
Worked example / rule of thumb
A regular narrow-complex tachycardia at 150 bpm without visible P waves is treated as AVNRT; vagal maneuvers, then adenosine, are reasonable if stable. If the patient is unstable, synchronized cardioversion is the answer. Rule: stable? diagnose and treat. Unstable? electricity first.