Atrial Fibrillation
Irregularly irregular rhythm with absent P waves; rate control (beta-blocker/Diltiazem) vs rhythm control; stroke risk stratification via CHA2DS2-VASc.
Atrial Flutter
Sawtooth baseline flutter waves in inferior leads (II, III, aVF) at ~300 bpm atrial rate with 2:1 or 4:1 AV block; definitive cure with cavotricuspid isthmus ablation.
Ventricular Tachycardia
Wide-complex tachycardia (> 120 ms) with AV dissociation; unstable mandates synchronized cardioversion; pulseless mandates unsynchronized defibrillation.
Third-Degree AV Block
Complete AV dissociation (P waves and QRS complexes beat completely independently); escape junctional or ventricular rhythm; mandates emergent temporary or permanent pacemaker.
Narrow vs. Wide Complex Tachyarrhythmias
| Arrhythmia | ECG Characteristics | Hemodynamically Stable Therapy | Unstable Emergency Protocol |
|---|---|---|---|
| Atrial Fibrillation (AFib) | No distinct P waves; fibrillatory baseline; irregularly irregular RR intervals | Rate control (Metoprolol, Diltiazem); anticoagulation based on CHA2DS2-VASc (≥ 2 in men, ≥ 3 in women -> DOAC) | Immediate synchronized electrical cardioversion (100–200 J biphasic) |
| Supraventricular Tachycardia (AVNRT) | Regular narrow-complex tachycardia (150–220 bpm); retrograde P waves buried within or immediately after QRS | Vagal maneuvers (Valsalva, modified ice immersion) -> IV Adenosine 6 mg rapid push (follow with 12 mg if unsuccessful) | Synchronized electrical cardioversion (50–100 J) |
| Ventricular Tachycardia (Monomorphic VT) | Wide QRS complexes (> 120 ms), regular rhythm, rate 140–250 bpm; AV dissociation, capture beats, fusion beats | IV Amiodarone 150 mg infusion over 10 min, or IV Procainamide | Pulse present: Synchronized cardioversion (100 J); Pulseless: CPR + unsynchronized defibrillation (200 J) |
| Torsades de Pointes | Polymorphic VT twisting around the isoelectric line; preceded by prolonged QT interval (> 450 ms men, > 470 ms women) | IV Magnesium sulfate (2 g IV push); discontinue all QT-prolonging drugs; temporary pacing if bradycardia-dependent | Immediate defibrillation; emergent overdrive transvenous pacing |
Atrioventricular (AV) Blocks Master Algorithm
| AV Block Type | PR Interval Behavior | QRS & Drop Pattern | Anatomical Level & Clinical Disposition |
|---|---|---|---|
| First-Degree AV Block | Fixed prolonged PR interval (> 200 ms or 5 small boxes) | Every P wave followed by QRS; no dropped beats | AV node delay; benign; observation, review AV nodal blocking drugs |
| Mobitz Type I (Wenckebach) | Progressive PR lengthening with each beat until dropped QRS | Regularly irregular; grouped beating | AV node; typically benign, inferior MI / high vagal tone; atropine if symptomatic |
| Mobitz Type II | Constant, fixed PR interval prior to sudden, unpredictable dropped QRS | Intermittent dropped QRS without PR warning; high risk of progression to 3rd degree | His-Purkinje system (infranodal); anterior septal MI; permanent pacemaker indicated |
| Third-Degree (Complete) AV Block | PR intervals completely variable and inconsistent | P waves and QRS complexes beat completely independently; slow escape rhythm (30–45 bpm) | Complete failure of AV conduction; transcutaneous/transvenous pacing -> permanent pacemaker |
OMM Board Correlate: Cardiac Conduction System & Vagus
- Right vs. Left Autonomic Distribution: Right sympathetic chain (T1–T2) and Right Vagus nerve (CN X) project primarily to the SA node; hyperactivity predisposes to sinus tachycardia or sinus bradycardia. Left sympathetic chain and Left Vagus project to the AV node; imbalance predisposes to AV block or ventricular arrhythmias.
- Suboccipital Decompression: Gentle suboccipital traction at the OA articulation normalizes vagal outflow passing through the jugular foramen (bordered by occipital and temporal bones), soothing hyperactive cardiac autonomic reflexes.
Board Traps & Common Distractors
- In patients with Wolff-Parkinson-White (WPW) syndrome presenting with AFib, NEVER administer AV-nodal blocking drugs (ABCD: Adenosine, Beta-blockers, CCBs, Digoxin); blocking the AV node shunts conduction down the accessory pathway (Bundle of Kent), precipitating ventricular fibrillation and cardiac arrest. Use IV Procainamide or synchronized cardioversion.
- Mobitz Type II second-degree AV block is an unstable infranodal disease that will rapidly degenerate into third-degree complete heart block; transcutaneous pacing pads must be placed immediately.
- Always correct hypokalemia and hypomagnesemia in patients taking Digoxin or antiarrhythmics to prevent refractory ventricular arrhythmias and Torsades de Pointes.