Rapid Review·Cardiovascular
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HY Approach
T1Must knowApproach to Tachyarrhythmias
Focus on
Two questions sort every fast rhythm: is the QRS narrow or wide, and is it regular or irregular? Then one more: is the patient stable? Unstable → synchronized cardioversion, whatever the rhythm. Stable narrow regular → vagal maneuvers and adenosine; irregular → AF/flutter/MAT pathways; wide → VT until proven otherwise.
Key takeaways
Approach to palpitations
Resting electrocardiogram (ECG)
often normal between episodes.Continuous monitoring
to catch a transient arrhythmia.Where to monitor
by risk.- Outpatient ambulatory monitoring (Holter, insertable monitor) suits a young patient (under 40) without structural heart disease.
- Admit for monitoring and expedited evaluation when the patient is older, has structural disease (prior infarct), or has an abnormal ECG.
Rate and instability
hemodynamic instability from a tachyarrhythmia usually needs a rate over 150.Sorting a tachycardia
Question 1, the QRS
narrow (under 120 ms) is supraventricular; wide (120 ms or more) is ventricular or pre-excited.Question 2, the rhythm
regular or irregular; manage by the box below.Unstable patient (any rhythm)
synchronized cardioversion.| Regular | Irregular | |
|---|---|---|
| Narrow | Sinus tachycardia (normal P before each QRS); AVNRT or orthodromic AVRT (no visible P or retrograde P); atrial flutter with fixed block (saw-tooth) | Atrial fibrillation (no P waves); multifocal atrial tachycardia (3 or more P shapes); flutter with variable block |
| Wide | Monomorphic ventricular tachycardia; antidromic AVRT; supraventricular tachycardia (SVT) with aberrancy (treat as VT until proven otherwise) | Polymorphic VT and torsades; atrial fibrillation with pre-excitation (WPW) |
Treating the stable patient
Stable narrow regular
vagal maneuvers, then adenosine; beta blockers or calcium-channel blockers as alternatives (AV Nodal Reentrant Tachycardia).Stable narrow irregular
rate control with a beta blocker or non-dihydropyridine calcium-channel blocker; treat the cause in multifocal atrial tachycardia (Atrial Fibrillation, Multifocal Atrial Tachycardia).Stable wide
by the rhythm.- Monomorphic VT: amiodarone (lidocaine, procainamide, sotalol).
- Torsades: magnesium.
- Pre-excited atrial fibrillation or antidromic atrioventricular re-entrant tachycardia (AVRT): procainamide; never an atrioventricular (AV) nodal blocker (Wolff-Parkinson-White Syndrome).
The atrial arrhythmias at a glance
| Rhythm | Associations | ECG | Management |
|---|---|---|---|
| Sinus tachycardia | Pain, infection, exercise, hypovolemia, fear, hypoxia, anemia, pulmonary embolus | Regular, P before every QRS | Treat the cause |
| Atrial fibrillation | Hypertension, coronary disease, rheumatic disease, catecholamines, hyperthyroidism, atrial enlargement | Irregularly irregular, no P waves, erratic baseline, narrow QRS | Rate control plus anticoagulation; rhythm control or ablation |
| Atrial flutter | Right atrial re-entry at about 300 | Regular saw-tooth F waves, ventricular rate 150, 100 or 75 | As for fibrillation; ablation is first-line rhythm control |
| Multifocal atrial tachycardia | Severe lung disease (COPD), catecholamine excess | Irregular, 3 or more P morphologies, variable PR and R-R, 100 to 200 | Treat the lung disease |
| AV nodal re-entrant tachycardia (AVNRT) | Fast and slow pathways in the AV node | Regular narrow at 150 to 220, P buried or retrograde | Vagal maneuvers or adenosine |
| AVRT | AV node plus an accessory pathway | Regular at 150 to 250; orthodromic narrow with P after QRS, antidromic wide with short PR | Vagal maneuvers or adenosine (orthodromic) |
| Wolff-Parkinson-White (WPW) | Accessory pathway, familial, may bring atrial fibrillation | Short PR, delta wave, wide QRS in sinus rhythm | Procainamide; avoid AV nodal blockers |
A stable patient has an irregular wide-complex tachycardia at 240 with varying QRS shapes and a known delta wave in sinus rhythm. What is the rhythm, the drug, and the drug class to avoid?
Pre-excited atrial fibrillation (WPW): give procainamide (synchronized cardioversion if unstable). Never AV nodal blockers (adenosine, beta blockers, calcium-channel blockers, digoxin).
How it's tested
Regular narrow tachycardia at 180 that started abruptly in a healthy 25-year-old, BP 118/76: vagal maneuvers, then adenosine — AVNRT.
Same rhythm with BP 70/40 and confusion: synchronized cardioversion, no drugs first.
Irregular wide-complex tachycardia at 220 with varying QRS in a young man with a known delta wave: pre-excited AF — procainamide or cardioversion; adenosine or diltiazem could cause VF.
Regular wide-complex tachycardia in a man with a prior MI, stable: VT — amiodarone or procainamide; do not assume SVT with aberrancy.
Palpitations in a 68-year-old with a prior MI and a normal ECG: admit for monitoring — structural heart disease makes VT the concern.
Go deeper
Guidelines: 2025 AHA Adult Advanced Life Support Guidance · 2015 ACC/AHA/HRS Supraventricular Tachycardia Guideline
Related Step 2 pages: ECG Basics, AV Nodal Reentrant Tachycardia, Atrial Fibrillation, Atrial Flutter, Wolff-Parkinson-White Syndrome, Ventricular Tachycardia, Cardiac Arrest & ACLS
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