Arrhythmias & Conduction Blocks

• Any unstable tachyarrhythmia needs synchronized cardioversion immediately (sedate when time allows).
• AF rate control via β-blocker/diltiazem (avoid in HFrEF — amiodarone/digoxin); regular narrow-complex: vagal first, then adenosine 6→12→12 mg.
• Treat wide-complex rhythms as VT until proven otherwise (Brugada); stable monomorphic gets amiodarone or procainamide, torsades gets magnesium 2 g and overdrive pacing.
• Symptomatic bradycardia: atropine 1 mg, transcutaneous pacing, dopamine or adrenaline infusion, then pacing wire.

Advanced Cardiac Life Support Tachycardia Treatment Pathway

• Tachycardia + pulses
• Assess and support the ABCs · give oxygen · monitor ECG (identify rhythm), BP, oximetry · hunt down and treat reversible causes
• Symptoms persist — is the patient stable? (unstable signs: hypotension or other shock signs, altered mental status, ongoing chest pain; rate-related symptoms are uncommon under heart rate <150/min)
• Obtain IV access · 12-lead ECG (when available) or rhythm strip
• QRS narrow (<0.12 seconds)?
• NARROW QRS — regular rhythm?
• Try vagal maneuvers · adenosine 6 mg rapid IV push; no conversion → 12 mg rapid IV push; may repeat 12 mg once
• Rhythm converted?
• Probable reentry SVT: observe for recurrence; if it recurs use adenosine or longer-acting AV nodal blockers (e.g., diltiazem, beta blockers)
• Possible atrial flutter, ectopic atrial tachycardia, or junctional tachycardia: treat the underlying cause · control rate with diltiazem or beta blockers (caution in pulmonary disease or CHF) · consider expert consultation
• Irregular narrow-complex tachycardia — probable atrial fibrillation, possible atrial flutter or MAT (multifocal atrial tachycardia) · consider expert consultation · control rate (diltiazem, beta blockers — beta-blocker caution in pulmonary disease or CHF)
• WIDE QRS (≥0.12 seconds) — regular rhythm? (expert consultation advised)
• Ventricular tachycardia or uncertain rhythm: give amiodarone 150 mg IV over 10 min, repeated as needed up to max 2.2 g/24 hours · ready elective synchronized cardioversion. For SVT with aberrancy: adenosine (regular narrow-complex pathway)
• Atrial fibrillation with aberrancy — manage as irregular narrow-complex tachycardia
• Pre-excited atrial fibrillation (AF + WPW): AVOID AV nodal blockers (adenosine, digoxin, diltiazem, verapamil) · expert consultation advised · antiarrhythmics an option (e.g., amiodarone 150 mg IV over 10 minutes)
• Polymorphic VT that recurs → get expert help; torsades de pointes → magnesium (load 1–2 g over 5–60 minutes, then infusion)
• Immediate synchronized cardioversion · establish IV access and sedate if conscious — never delay cardioversion · consider expert consultation · pulseless arrest → Pathway 18.3
• Instability at any point → immediate synchronized cardioversion. During evaluation: secure and verify airway and vascular access when possible · consider expert consultation · prepare for cardioversion
• Contributing factors to treat: hypoxia · hypovolemia · hydrogen ion (acidosis) · hypothermia · hypo/hyperkalemia · toxins · tension pneumothorax · cardiac tamponade · thrombosis (coronary or pulmonary)

Advanced Cardiac Life Support Bradycardia Treatment Pathway

• Bradycardia: heart rate <60 bpm, inadequate for the clinical condition
• Airway patent; assist breathing as needed · give oxygen if hypoxemic · ECG (identify rhythm), BP, and oximetry monitoring · establish IV access
• Poor perfusion from the bradycardia? (acute altered mental status, ongoing chest pain, hypotension or other shock signs)
• Get ready for transcutaneous pacing — do not delay with high-degree block (type II second-degree block or third-degree AV block)
• Atropine 1 mg IV is reasonable while awaiting the pacer — repeatable every 3–5 min to 3 mg total; begin pacing if ineffective
• While awaiting the pacer, or if pacing fails, infuse epinephrine (2–10 µg/min) or dopamine (5–20 µg/kg/min)
• Ready transvenous pacing · treat contributing causes · consider expert consultation
• Perfusion adequate → observe/monitor
• Pulseless arrest → Pathway 18.3. Search and treat contributing factors: hypovolemia · hypoxia · hydrogen ion (acidosis) · hypo/hyperkalemia · hypothermia · toxins · cardiac tamponade · tension pneumothorax · thrombosis (coronary or pulmonary)

Advanced Cardiac Life Support Pulseless Arrest Pathway

• PULSELESS ARREST — BLS: shout for help, begin CPR; oxygen when available; monitor/defibrillator attached when available
• Check rhythm: shockable?
• VF/VT — deliver one shock: manual biphasic typically 120–200 J (unknown → use 200 J; AED device-specific; monophasic 360 J); immediately resume CPR
• Five cycles of CPR (2 min), then recheck rhythm
• Shockable: CPR continues while the defibrillator charges; one shock; immediately resume CPR; give epinephrine 1 mg IV every 3–5 min once initial defibrillation attempts fail (IV preferred over IO; vasopressin no longer recommended — epinephrine alone)
• Recheck after five cycles; if shockable, shock again plus an antiarrhythmic — amiodarone 300 mg IV/IO once, then 150 mg once (alternatively lidocaine 1–1.5 mg/kg, then 0.5–0.75 mg/kg ×3); magnesium 1–2 g IV/IO for torsades de pointes
• Asystole/PEA — immediately resume CPR for five cycles (2 min)
• Epinephrine 1 mg IV every 3–5 min as early as feasible (IV preferred over IO; vasopressin no longer recommended — epinephrine alone); atropine has been dropped from arrest care
• After five cycles of CPR, recheck the rhythm: asystole → resume at box 1; electrical activity → check for a pulse — pulse present → begin post-resuscitation care; no pulse → resume CPR
• During CPR: push hard and fast (100–120/min) · allow full chest recoil · minimize interruptions · avoid hyperventilation · rotate compressors every 2 min · secure airway · search reversible causes — hypoxia, hypovolemia, hydrogen ion (acidosis), hypothermia, hypo/hyperkalemia, toxins, tension pneumothorax, tamponade (cardiac), thrombosis (coronary or pulmonary)

Differentiating Narrow QRS Complex Tachycardias

• Rate irregular?
• P waves present?
• "Sawtooth" P waves → atrial flutter, variable conduction
• ≥3 P-wave morphologies → MAT (multifocal atrial tachycardia)
• Normal P preceding each QRS → sinus tachycardia with frequent premature atrial contractions
• Atrial fibrillation
• Rate about 150 beats/min?
• Think of atrial flutter with 2:1 conduction
• P waves absent?
• AVNRT (atrioventricular nodal reentrant tachycardia) — P waves, when present, are generally narrow, inverted waves at the end of the QRS
• P wave follows the QRS?
• Orthodromic reciprocating tachycardia (ORT) — P usually right after QRS, before the T wave
• Atrial tachycardia, ectopic

Differentiating Wide QRS Complex Tachycardias

• Rate regular?
• VT vs SVT with RBBB, LBBB, aberrant conduction, or ART. VT if any: 1) AV dissociation (P waves not associated with QRS) · 2) R onset to S nadir (lowest point) >0.1 seconds (100 ms) · 3) no RS complex in leads V1 through V6
• If still uncertain, examine QRS morphologies — RBBB supported by: V1 mono- or biphasic QRS, V6-QS or RS complex · LBBB supported by: V1- or V2-notched downslope of S, V1/V2-onset QRS to nadir S >0.07 seconds, V1/V2-broad R >0.04 seconds, V6-Q wave. Examine old ECGs for prior bundle branch block
• VT supported?
• Monomorphic VT: DC cardioversion · procainamide an option if stable
• → Pathway 18.1 and the SVT section
• Does the QRS vary in size and shape?
• QT interval prolonged?
• Torsades de pointes: magnesium sulfate 2 g IV · stop QT-prolonging agents
• Polymorphic VT: if unstable, DC cardioversion · class I or III antiarrhythmics · seek and treat underlying ischemia
• RBBB/LBBB plus: atrial fibrillation · atrial flutter · MAT · sinus with PACs
• Treat wide complex tachycardias (except clear sinus tachycardia with aberrancy) as ventricular tachycardia (VT) initially; urgency depends on patient condition and hemodynamics

Treating Atrial Fibrillation and Atrial Flutter (See Chapter 91 Common Drug Dosages and Side Effects)

• Atrial fibrillation/flutter with serious hemodynamic instability needing immediate treatment?
• DC cardioversion, synchronized
• Atrial fibrillation/flutter with WPW?
• With WPW, AV nodal blockers are forbidden — they may worsen tachycardia: 1) DC cardioversion or 2) procainamide (preferred) or ibutilide
• Duration of atrial fibrillation/flutter?
• 48 HOURS OR LESS — Step 1, rate control: impaired ventricular function (EF <40%) → digoxin or amiodarone (AVOID diltiazem/verapamil in HFrEF) · preserved ventricular function → diltiazem or verapamil or metoprolol (or another beta blocker), and consider one of procainamide, amiodarone, digoxin
• Step 2, rhythm conversion with DC cardioversion and/or antiarrhythmics — impaired ventricular function (EF <40%): amiodarone · preserved ventricular function: amiodarone, procainamide, ibutilide, flecainide, propafenone
• 48 HOURS OR MORE OR UNKNOWN DURATION — Step 1, rate control: preserved ventricular function → diltiazem or verapamil or metoprolol (or another beta blocker) — AVOID antiarrhythmics for rate control (may convert rhythm and cause embolization) · impaired ventricular function (EF <40%) → digoxin or amiodarone (AVOID diltiazem/verapamil in HFrEF)
• Step 2, rhythm conversion — DC cardioversion. Urgent cardioversion: 1) start IV heparin · 2) TEE to exclude atrial clot · 3) no clot → cardioversion within 24 hours · 4) if rhythm converts, anticoagulate four more weeks. Delayed cardioversion: 1) anticoagulate to INR 2–3 for at least 3 weeks · 2) cardioversion · 3) if rhythm converts, anticoagulate four more weeks
• Premedicate when possible with sedative (diazepam, midazolam, ketamine, etomidate) and analgesic (fentanyl, morphine). Synchronized cardioversion for AF/AFL starts at 200 J biphasic, escalating as needed. Asynchronous cardioversion if synchronization delays with worsening clinical status