Cardiac Dysrhythmias & Syncope
Evidence-based emergency management of cardiac rhythm disturbances: vagal maneuvers, adenosine protocols, rate vs rhythm control in AFib with RVR, stable vs unstable monomorphic VT, transcutaneous pacing in bradycardia, and San Francisco / Canadian Syncope decision rules.
Resuscitation Quick Ribbon (First 2 Minutes)
Bottom-Line Clinical Pearl
In any tachy- or brady-dysrhythmia, evaluate hemodynamic stability first: 'Is the patient unstable?' (Hypotension, ischemic chest pain, altered mental status, acute pulmonary edema, shock). Unstable tachydysrhythmias require immediate SYNCHRONIZED CARDIOVERSION; unstable bradycardias require immediate ATROPINE (1 mg) and TRANSCUTANEOUS PACING. In stable regular SVT, the Modified REVERT Vagal Maneuver achieves 43% cardioversion success compared to 17% with standard Valsalva.
Before analyzing complex rhythm strips or selecting medications, immediately answer the primary question: Is the patient hemodynamically stable or unstable? Signs of instability include: 1) Hypotension (SBP < 90 mmHg, MAP < 65 mmHg); 2) Ischemic chest pain; 3) Altered mental status / confusion; 4) Acute heart failure (pulmonary rales, pulmonary edema); 5) Clinical signs of shock. Unstable patients with a pulse mandate immediate electrical therapy.
| Rhythm Morphology | ECG Characteristics | Synchronized Shock Energy | Procedural Caveat |
|---|---|---|---|
| Narrow Complex, Regular (SVT, Atrial Flutter) | QRS < 120 ms, regular R-R intervals | 50–100 Joules (biphasic) | Engage 'SYNC' button; verify sync markers appear on R-wave peaks. |
| Narrow Complex, Irregular (Atrial Fibrillation) | QRS < 120 ms, irregularly irregular R-R | 120–200 Joules (biphasic) or 200J monophasic | Higher initial energy needed to overcome atrial mass; re-arm SYNC after each discharge. |
| Wide Complex, Regular (Monomorphic VT) | QRS >= 120 ms, uniform ventricular morphology | 100 Joules (biphasic) | If patient becomes pulseless or rhythm degrades to VF: DISENGAGE sync and deliver 200J unsynchronized defibrillation. |
| Wide Complex, Irregular (Polymorphic VT / Torsades) | QRS >= 120 ms, twisting QRS peaks around isoelectric line | 200 Joules UNSYNCHRONIZED Defibrillation | Cannot synchronize to twisting peaks; synchronized discharge will fail or discharge on T-wave. |
For hemodynamically stable patients, differentiate regular from irregular rhythms:
| Clinical Entity | First-Line Intervention | Second-Line / Maintenance Regimen | Critical Safety Traps |
|---|---|---|---|
| Supraventricular Tachycardia (AVNRT / AVRT) | Modified REVERT Vagal Maneuver: Semi-recumbent strain into 10 mL syringe (40 mmHg) for 15 sec, then lay supine with legs elevated 45 degrees for 15 sec (43% cardioversion rate). | Adenosine 6 mg rapid IV push in large antecubital vein with 20 mL saline flush. If no conversion in 1–2 min, give Adenosine 12 mg rapid IV push. | Adenosine causes brief asystole (warn the patient). Contraindicated in severe asthma and Wolff-Parkinson-White with irregular wide complex. |
| Atrial Fibrillation with RVR (Rate Control) | Diltiazem 0.25 mg/kg IV over 2 min (typical dose 15–20 mg). If needed, give 0.35 mg/kg IV (20–25 mg) in 15 min; follow with infusion 5–15 mg/h. | Metoprolol 5 mg IV push q5min x 3 doses (total 15 mg). If Heart Failure with reduced EF: Use Digoxin 0.25–0.5 mg IV or Amiodarone 150 mg IV. | AVOID diltiazem/beta-blockers in pre-excited AFib (WPW with AFib); blocking the AV node causes preferential conduction down accessory pathway into VF arrest. |
| Wolff-Parkinson-White with AFib (Pre-Excited AFib) | Procainamide 20–50 mg/min IV infusion until arrhythmia suppressed, hypotension, or QRS widens > 50% (max 17 mg/kg). | Synchronized Cardioversion 100–200J if unstable. | AVOID ALL AV-NODAL BLOCKING DRUGS: 'ABCD' (Adenosine, Beta-blockers, Calcium channel blockers, Digoxin). |
Treat every wide-complex tachycardia (QRS >= 120 ms) as Ventricular Tachycardia until proven otherwise (80% of all WCT is VT; in patients with prior MI or structural heart disease, > 95% is VT). Misdiagnosing VT as 'SVT with aberrancy' and administering verapamil or diltiazem precipitates catastrophic cardiovascular collapse.
- Stable Monomorphic VT: First-line pharmacotherapy is Amiodarone 150 mg IV in 100 mL D5W infused over 10 minutes (repeat 150 mg if VT recurs; follow with 1 mg/min infusion for 6h, then 0.5 mg/min for 18h). Alternatively, Procainamide (10–17 mg/kg IV at 20–50 mg/min) has proven superior conversion rates to amiodarone in the PROCAMIO randomized trial.
- Polymorphic VT / Torsades de Pointes: Administer Magnesium Sulfate 2g IV push over 1–2 minutes, followed by 1–2g/hr infusion. Correct hypokalemia (target K 4.5–5.0 mEq/L). If refractory, initiate overdrive pacing (isoproterenol or transcutaneous pacing at HR 100–120 bpm) to shorten the baseline QT interval.
| Phase | Clinical Action | Drug / Pacing Parameter | Clinical Goals & Precautions |
|---|---|---|---|
| Step 1: First-Line Vagolytic | Atropine Administration | Atropine 1.0 mg IV push q3–5min (maximum total dose 3.0 mg) | Effective in sinus bradycardia and AV-nodal blocks (Mobitz I). Ineffective in Mobitz II and 3rd-degree block with wide QRS (infranodal). |
| Step 2: Electrical Pacing | Transcutaneous Pacing (TCP) | Apply pads (anterior-posterior). Set rate to 60–80 bpm. Increase current (mA) until electrical capture (wide QRS + broad T after each pacer spike). | VERIFY MECHANICAL CAPTURE: Palpate the right femoral pulse (do NOT check carotid—carotid jerking is caused by pectoral muscle twitching). |
| Step 3: Chronotropic Infusion | Epinephrine or Dopamine Infusion | Epinephrine 2–10 mcg/min IV infusion OR Dopamine 5–20 mcg/kg/min | Alternative bridge while preparing transvenous pacer wire in cardiac cath lab. |
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