5.2 Tachycardia With a Pulse
Key Takeaways
- Tachycardia is a rate over 100/min, but the algorithm acts when the rate is the cause of instability (hypotension, altered mental status, shock, ischemic chest discomfort, or acute heart failure).
- Unstable tachycardia with a pulse is treated with synchronized cardioversion, not drugs.
- Stable regular narrow-complex SVT: try vagal maneuvers, then adenosine 6 mg rapid push, then 12 mg if needed.
- Stable wide-complex regular tachycardia (likely VT) uses an antiarrhythmic — procainamide, amiodarone, or sotalol — and adenosine only if regular AND monomorphic.
- Irregular wide-complex rhythms (polymorphic VT, AF with WPW) must NOT receive AV-nodal blockers; treat polymorphic VT as a defibrillation problem.
First Question: Stable or Unstable?
Tachycardia is a heart rate above 100/min, but symptomatic, rate-related tachycardia rarely matters below about 150/min in adults. org/en/resuscitation-science/cpr-and-ecc-guidelines/adult-advanced-life-support) opens with the same instability question as bradycardia: is the fast rate producing hypotension, acutely altered mental status, signs of shock, ischemic chest discomfort, or acute heart failure? If yes, the patient is unstable and the answer is synchronized cardioversion — full stop, no diagnostic dawdling. If the patient is stable, you have time to obtain a 12-lead, classify the rhythm, and choose a drug.
The second sorting question is QRS width, and the third is regularity. These three axes — stability, width, regularity — define every branch of the algorithm.
Tachyarrhythmia recognition
| Rhythm | Width / regularity | Typical clue |
|---|---|---|
| Sinus tachycardia | Narrow, regular | Rate usually < 150, P before each QRS; treat the cause (fever, pain, hypovolemia) |
| SVT / AVNRT | Narrow, regular | Rate 150-250, P waves buried; vagal then adenosine |
| Atrial flutter | Narrow, regular (often 2:1) | Sawtooth flutter waves, atrial rate ~300, ventricular ~150 |
| Atrial fibrillation | Narrow, irregularly irregular | No discrete P waves, chaotic baseline |
| Monomorphic VT | Wide, regular | Uniform wide QRS, rate > 100; assume VT until proven otherwise |
| Polymorphic VT / torsades | Wide, irregular | Twisting QRS axis; often long QT — defibrillate if unstable |
A practical bedside rule: sinus tachycardia is a response, not a primary arrhythmia. When the rate is under ~150 and rises and falls gradually with a clear P before every QRS, the patient is compensating for fever, pain, hypovolemia, hypoxia, anxiety, or anemia — you treat the cause, not the rate. Cardioversion and adenosine are wrong for sinus tachycardia. The faster, abrupt, fixed rates (150-250) with no findable cause point toward a re-entrant tachycardia like SVT, where rhythm-specific therapy applies.
Stable Narrow-Complex Tachycardia
For stable, regular, narrow-complex tachycardia (most commonly SVT/AVNRT), work the steps in order:
- Vagal maneuvers — Valsalva (forced exhalation against a closed glottis), the modified/leg-lift Valsalva, or carotid sinus massage (avoid in patients with carotid bruits or prior stroke). Vagal maneuvers transiently slow AV conduction and can break re-entrant SVT.
- Adenosine 6 mg IV rapid push, immediately followed by a 20 mL normal saline flush through a large proximal vein, because adenosine has a half-life under 10 seconds.
- If no conversion, adenosine 12 mg IV rapid push (a second 12 mg dose is acceptable in many protocols).
- If still uncontrolled and the rhythm is SVT, consider a beta-blocker or calcium-channel blocker (diltiazem, verapamil) for rate control, with expert input.
For irregular narrow-complex tachycardia (usually atrial fibrillation or multifocal atrial tachycardia), adenosine is NOT a conversion tool; the strategy is rate control with diltiazem or a beta-blocker and addressing anticoagulation — not pushing adenosine. Atrial flutter (regular, sawtooth) responds poorly to adenosine for conversion but adenosine can unmask the flutter waves diagnostically.
Narrow-complex quick reference
| Pattern | Likely rhythm | Action |
|---|---|---|
| Regular narrow | SVT/AVNRT | Vagal -> adenosine 6 then 12 mg |
| Regular narrow, sawtooth | Atrial flutter | Rate control; adenosine to diagnose |
| Irregularly irregular | Atrial fibrillation | Rate control (diltiazem/beta-blocker); no adenosine |
Adenosine administration technique
Because adenosine's half-life is under 10 seconds, technique determines success. Use the most proximal large vein available (antecubital), push the 6 mg as fast as possible, and immediately follow with a rapid 20 mL saline flush (a two-syringe stopcock technique or a simultaneous push works best). Warn the patient about a few seconds of flushing, chest pressure, and a sense of impending doom — these transient effects are expected and self-limited. If 6 mg fails, the 12 mg dose follows the same fast-push-and-flush method.
Wide-Complex Tachycardia and Unstable Cardioversion
A wide-complex tachycardia (WCT) — QRS at least 0.12 s — should be assumed to be ventricular tachycardia until proven otherwise, especially in patients with structural heart disease. For stable, regular, monomorphic WCT, options include adenosine (only if regular AND monomorphic, as a diagnostic/therapeutic trial) and an antiarrhythmic infusion:
| Drug | Dose | Caution |
|---|---|---|
| Procainamide | 20-50 mg/min until arrhythmia suppressed, hypotension, QRS widens > 50%, or max 17 mg/kg; maint 1-4 mg/min | Avoid in prolonged QT or heart failure |
| Amiodarone | 150 mg IV over 10 min, may repeat; maint 1 mg/min x 6 h then 0.5 mg/min x 18 h | Hypotension with rapid push |
| Sotalol | 100 mg (1.5 mg/kg) IV over 5 min | Avoid in prolonged QT |
Give only one antiarrhythmic; adding a second without expert consultation risks hypotension and proarrhythmia. Irregular wide-complex rhythms (polymorphic VT, or AF conducting down an accessory pathway in WPW) must never receive AV-nodal blockers (adenosine, diltiazem, verapamil, beta-blockers) — these can accelerate conduction and precipitate VF. Polymorphic VT in an unstable patient is treated like VF with unsynchronized defibrillation; if associated with long QT (torsades), give magnesium sulfate.
Unstable: synchronized cardioversion
If the patient is unstable, perform synchronized cardioversion (covered in detail in 5.3). General initial energies (biphasic): narrow regular ~50-100 J, narrow irregular (AF) ~120-200 J, wide regular (VT) 100 J; wide irregular is NOT synchronized — defibrillate. The AHA now advises referring to your device's recommended energy.
Scenario anchor: A patient at 190/min with chest pain, hypotension, and confusion needs synchronized cardioversion now, not adenosine. The common traps are giving adenosine to an unstable patient, forgetting to press SYNC before shocking a perfusing rhythm, and giving a calcium-channel blocker in wide-complex tachycardia.
A stable patient has a regular, narrow-complex tachycardia at 180/min. Vagal maneuvers fail. What is the correct adenosine sequence?
Second-degree AV block Type I (Wenckebach / Mobitz I) is best characterized by which ECG finding?
A patient has atrial fibrillation with a rapid ventricular response that is conducting down an accessory pathway (WPW). Which medication should be avoided?