Tachyarrhythmias
Atrial fibrillation
Irregularly irregular narrow complexes with no P waves and a wandering baseline.
What you see
- Irregularly irregular ventricular response — the defining feature.
- Absent P waves, replaced by a fibrillatory baseline best seen in V1.
- Narrow QRS unless there is pre-existing or rate-related bundle branch block.
- Rate anywhere from slow (if the AV node is diseased or blocked) to over 150.
Why it looks like that
Multiple re-entrant wavelets in atrial tissue depolarise it chaotically at 400–600 per minute. The AV node's refractory period filters those impulses irregularly, and the ventricular response inherits that irregularity.
What to do
- Rate control with a beta-blocker or rate-limiting calcium channel blocker; digoxin only for the sedentary or in heart failure.
- Anticoagulate on CHA₂DS₂-VASc, using HAS-BLED to address modifiable bleeding risk rather than to withhold treatment.
- Immediate DC cardioversion if there is shock, syncope, myocardial ischaemia or pulmonary oedema.
- Cardiovert without three weeks of anticoagulation only if onset is clearly under 48 hours or a TOE excludes thrombus.
The trap
AF with a broad, very fast, irregular complex tachycardia is pre-excited AF, not AF with bundle branch block. AV nodal blockers — adenosine, verapamil, digoxin — can accelerate conduction down the accessory pathway into VF. That patient needs electricity, or procainamide.
More in tachyarrhythmias
Atrial flutter
Sawtooth flutter waves at about 300 per minute, usually conducted 2:1 to give a ventricular rate near 150.
AV nodal re-entrant tachycardia
Regular narrow complex tachycardia around 180 with P waves hidden inside or just after the QRS.
Monomorphic ventricular tachycardia
Broad, regular, identical complexes — assume VT in any broad complex tachycardia until you have proved otherwise.
Torsades de pointes
Polymorphic VT twisting around the baseline, on a background of a long QT.