According to Harrison's, what are the initial assessment steps and pharmacologic management for cardiac arrhythmias, including supraventricular, ventricular, and bradyarrhythmias?

Initial Assessment and Management of Cardiac Arrhythmias

Immediate Hemodynamic Assessment

If the patient is hemodynamically unstable (hypotension, altered mental status, chest pain, acute heart failure), proceed immediately to synchronized cardioversion without delay for pharmacologic therapy or additional diagnostic workup. 1, 2

• Obtain at minimum a monitor strip before cardioversion, even in cardiac arrest, but do not delay treatment 3, 1
• Use synchronized cardioversion for organized rhythms; use unsynchronized defibrillation for ventricular fibrillation or pulseless ventricular tachycardia 1

Diagnostic Approach for Stable Patients

Obtain a 12-lead ECG during tachycardia whenever possible, as this is essential for determining the mechanism and guiding therapy. 3, 1, 2

Classification by QRS Width

The critical first step is determining QRS duration, which separates supraventricular from ventricular mechanisms 3, 2:

Narrow QRS (<120 ms): Almost always supraventricular in origin 3

• If no visible P waves and regular RR interval: AVNRT most likely 3
• If P wave present in ST segment separated from QRS by >70 ms: AVRT likely 3
• If RP interval longer than PR interval: atypical AVNRT, PJRT, or atrial tachycardia 3

Wide QRS (>120 ms): Presume ventricular tachycardia until proven otherwise 2

• This assumption is critical for patient safety, as treating VT as SVT can be fatal 2

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Management of Supraventricular Tachycardias (Stable Patients)

First-Line Intervention: Vagal Maneuvers

Begin with vagal maneuvers in the supine position as the initial intervention for all stable narrow QRS tachycardias. 3, 1, 2

• Valsalva maneuver or carotid sinus massage (if no carotid bruits) 3
• Record a 12-lead ECG during adenosine or vagal maneuvers to aid diagnosis 3

Pharmacologic Management

If vagal maneuvers fail, adenosine is the first-line pharmacological therapy. 3, 1, 2

• Adenosine 6 mg rapid IV push, followed by 12 mg if ineffective, then another 12 mg if needed 3
• Adenosine terminates AVNRT and AVRT by blocking AV nodal conduction 3

For rate control or rhythm conversion when adenosine fails or is contraindicated: 3

• Beta-blockers (metoprolol 2.5-5 mg IV over 2 minutes, up to 3 doses) or calcium channel blockers (diltiazem 0.25 mg/kg IV over 2 minutes, then 0.35 mg/kg if needed) 3
• Critical caveat: Never use AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers, digoxin) in pre-excited atrial fibrillation (WPW with AF), as this can accelerate ventricular response and cause ventricular fibrillation 3, 2

Long-Term Pharmacologic Options

For recurrent SVT requiring chronic suppression 3:

• Beta-blockers: First-line for most patients without contraindications 3
• Calcium channel blockers (diltiazem or verapamil): Avoid in patients with LV dysfunction or hypotension 3
• Class IC agents (flecainide 50 mg every 12 hours or propafenone 150 mg every 8 hours): Only in patients WITHOUT structural heart disease, ischemic heart disease, or conduction disease 3
• Class III agents (amiodarone, sotalol, dofetilide): Reserved for refractory cases or when other agents contraindicated 3

Important precaution: Do not initiate class I or class III antiarrhythmic drugs without documented arrhythmia due to proarrhythmia risk 3

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Management of Ventricular Arrhythmias

Stable Monomorphic Ventricular Tachycardia

For stable monomorphic VT in patients without severe heart failure or acute MI, IV procainamide is the preferred first-line agent. 1

• Procainamide: Load with 10-17 mg/kg IV at 20-50 mg/min 3
• Alternative: Sotalol (if no structural heart disease) 2

If there is any concern for impaired left ventricular function, severe heart failure, or acute MI, amiodarone 150 mg IV over 10 minutes is the preferred agent. 3, 1, 2

• Amiodarone has superior hemodynamic tolerability in patients with structural heart disease 3
• Can repeat 150 mg IV every 10 minutes as needed, then maintenance infusion of 1 mg/min for 6 hours, then 0.5 mg/min 3

Unstable Ventricular Tachycardia

Immediate synchronized cardioversion is mandatory for any VT causing hemodynamic instability. 1, 2

• Start with 100-200 J biphasic 3
• For pulseless VT or ventricular fibrillation, use unsynchronized defibrillation at maximum output 1

Polymorphic Ventricular Tachycardia

Check QT interval immediately: 3

• Normal QT (polymorphic VT): Treat as acute coronary syndrome; consider beta-blockers and urgent revascularization 3
• Prolonged QT (torsades de pointes): Magnesium sulfate 2 g IV push, correct electrolytes, discontinue QT-prolonging drugs, consider temporary pacing 3

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Management of Bradyarrhythmias

Symptomatic Bradycardia

For symptomatic bradycardia (hypotension, altered mental status, chest pain, heart failure): 3

• Atropine 0.5-1 mg IV (can repeat every 3-5 minutes, maximum 3 mg) 4
• If atropine ineffective: Transcutaneous pacing or dopamine/epinephrine infusion 3, 4

Evaluation for Reversible Causes

Before permanent pacing, evaluate for: 3, 5

• Medications (beta-blockers, calcium channel blockers, digoxin, amiodarone) 3
• Electrolyte abnormalities (hyperkalemia, hypercalcemia) 5
• Hypothyroidism, hypothermia, increased vagal tone 3, 5
• Myocardial ischemia or infarction 3

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Essential Electrolyte Management

Check and correct potassium, magnesium, and calcium immediately in all patients with tachyarrhythmias, as electrolyte disorders commonly precipitate arrhythmias. 1, 5

• Target potassium >4.0 mEq/L (>4.5 mEq/L for VT) 5
• Target magnesium >2.0 mg/dL 5
• Hypomagnesemia and hypokalemia frequently coexist and both must be corrected 5

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Post-Stabilization Management and Referral

All patients with documented wide complex tachycardia require ICU/CCU admission and immediate cardiology/electrophysiology consultation. 1, 2

Mandatory referral to arrhythmia specialist for: 1, 2

• Any wide complex tachycardia of unknown origin 1, 2
• Wolff-Parkinson-White syndrome 1
• Narrow complex tachycardias with drug resistance or intolerance 1
• Severe symptoms during palpitations 1
• Recurrent SVT (consider catheter ablation, which has >95% success rate for AVNRT and AVRT) 3

Long-Term Ventricular Arrhythmia Management

For patients with heart failure and reduced ejection fraction: 3

• ICD therapy is indicated for secondary prevention in survivors of cardiac arrest or sustained VT 3
• ICD therapy is indicated for primary prevention in patients with LVEF ≤35%, NYHA class II-III, on optimal medical therapy, with reasonable expectation of survival >1 year 3
• Amiodarone, sotalol, or beta-blockers may be considered as alternatives when ICD not feasible, but are inferior to ICD for mortality reduction 3

Asymptomatic nonsustained VT in heart failure patients should not be treated with antiarrhythmic drugs, as suppression does not improve prognosis. 3