Rhythm analysis, conduction disease and device reasoning
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 AV-node-dependent reentry and may transiently expose flutter waves by slowing AV conduction; it does not reliably terminate atrial flutter. Pre-excited atrial fibrillation is a separate dangerous setting for AV nodal blockade. 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 rhythm near 150 bpm can represent atrial flutter with 2:1 conduction as well as other supraventricular mechanisms. Examine atrial activity and the clinical context rather than naming AVNRT from the rate alone. In a suitable stable regular narrow-complex tachycardia, vagal maneuvers and appropriately supervised medication may help. Hemodynamic instability attributable to an organized tachyarrhythmia can require synchronized cardioversion; pulseless rhythms and polymorphic ventricular tachycardia require the appropriate unsynchronized resuscitation pathway.
Mechanism and risk are different questions
An ECG diagnosis, a decision about acute stability and an estimate of future embolic or sudden-death risk are related but separate tasks. A patient whose ventricular rate is controlled can still need stroke prevention. Conversely, a high stroke-risk score does not establish the mechanism of a wide-complex tachycardia. Name the actual risk tool when performing arithmetic: traditional CHA2DS2-VASc includes sex category, while the 2024 ESC approach uses CHA2DS2-VA without that component. Do not silently mix their totals or thresholds. Bleeding assessment should identify modifiable risks and inform shared decisions rather than automatically canceling anticoagulation whenever any bleeding-risk factor exists.
Device reasoning must also separate symptom relief, prevention of bradycardic events, ventricular synchrony and prevention of sudden arrhythmic death. A pacemaker does not perform every function of an implantable defibrillator. An ICD does not remove the need to treat ischemia, electrolyte disturbances or heart failure. A reduced ejection fraction alone is not a complete implantation decision without timing, adequate therapy, expected survival, reversibility and the specific disease context. In inherited arrhythmia and cardiomyopathy cases, a suggestive pattern supports further evaluation but does not prove a particular genetic variant. Explain the mechanism supported by the data instead of inferring an unmeasured genotype from a memorable clinical association.