How should I manage a patient with a heart rate of 170 beats per minute?

Management of Heart Rate 170 bpm

Immediately assess hemodynamic stability—if the patient shows signs of shock, altered mental status, chest pain, acute heart failure, or hypotension attributable to the tachycardia, proceed directly to synchronized cardioversion without delay. 1, 2

Initial Stabilization and Assessment

• Provide supplementary oxygen if the patient shows signs of increased work of breathing (tachypnea, retractions) or inadequate oxyhemoglobin saturation, as hypoxemia is a common cause of tachycardia. 1, 2

• Attach cardiac monitor, establish IV access, and measure blood pressure while simultaneously evaluating the patient's clinical status. 1, 2

• Obtain a 12-lead ECG to define the rhythm and determine QRS duration (narrow <120 ms vs. wide ≥120 ms), but do not delay cardioversion if the patient is unstable. 1, 2

• Identify reversible causes including fever, anemia, hypotension, dehydration, hypoxia, electrolyte disturbances, hyperthyroidism, or medications (stimulants, bronchodilators, illicit drugs). 1, 2

Critical Decision Point: Stable vs. Unstable

If UNSTABLE (hypotension, altered mental status, chest pain, acute heart failure, shock):

• Perform immediate synchronized cardioversion without waiting for further workup. 1, 2
• Sedate the conscious patient if time permits, but do not delay if extremely unstable. 1
• Use appropriate energy: 100-200 J for atrial fibrillation, 50 J for atrial flutter, 100 J for monomorphic VT. 2

If STABLE, proceed with rhythm-specific management:

Management Based on Heart Rate and Rhythm

Heart Rate 170 with Narrow QRS Complex (<120 ms):

At 170 bpm, symptoms of instability are likely caused primarily by the tachycardia itself, making urgent treatment necessary. 1

Regular Narrow Complex (likely SVT):

• Try vagal maneuvers first (Valsalva maneuver or unilateral carotid massage if no carotid bruit). 1, 2
• Adenosine 6 mg rapid IV push followed by saline flush; if no response after 1-2 minutes, give 12 mg, then repeat 12 mg if needed. 1, 2
• Alternative agents if adenosine fails: IV metoprolol 2.5-5 mg every 2-5 minutes or IV diltiazem 20 mg (0.25 mg/kg) over 2 minutes. 2

Irregular Narrow Complex (likely atrial fibrillation/flutter):

• Beta-blockers (metoprolol) or non-dihydropyridine calcium channel blockers (diltiazem) are first-line for rate control in hemodynamically stable patients. 1, 2
• Target resting heart rate <100 bpm for adequate control. 1, 2
• IV digoxin is reserved principally for patients with severe LV dysfunction and heart failure. 1, 2

Sinus Tachycardia at 170 bpm:

• Do NOT treat the heart rate directly—this represents a physiologic response to an underlying condition. 1, 2
• The upper limit of sinus tachycardia is approximately 220 minus the patient's age; at 170 bpm, this is within physiologic range for younger patients. 1
• Aggressively identify and treat the underlying cause (fever, sepsis, hypovolemia, anemia, hypoxia, pain, anxiety, hyperthyroidism). 1, 2
• Critical warning: When cardiac function is poor, cardiac output depends on rapid heart rate—"normalizing" the rate can be detrimental and cause hemodynamic collapse. 1, 2

Heart Rate 170 with Wide QRS Complex (≥120 ms):

Assume ventricular tachycardia until proven otherwise, even in young healthy patients. 2

If Stable:

• Amiodarone 150 mg IV over 10 minutes is first-line treatment, followed by maintenance infusion of 1 mg/min for first 6 hours, then 0.5 mg/min. 1, 2
• Alternative agents: Lidocaine (1 mg/kg IV bolus, may repeat 0.5 mg/kg every 8-10 minutes to maximum 4 mg/kg) or procainamide. 1, 2
• Adenosine may be considered for stable, regular, monomorphic wide-complex tachycardia if the etiology cannot be determined, but should NOT be given for irregular or polymorphic wide-complex tachycardia. 1

If Unstable:

• Immediate synchronized cardioversion for monomorphic VT (100 J initially). 2
• Immediate unsynchronized cardioversion (defibrillation) for polymorphic VT (200 J). 2

Critical Pitfalls to Avoid

• NEVER use AV nodal blocking agents (beta-blockers, calcium channel blockers, digoxin, adenosine) in patients with Wolff-Parkinson-White syndrome and wide-complex tachycardia—they can accelerate ventricular rate and precipitate ventricular fibrillation. 1, 2

• Do NOT aggressively treat compensatory tachycardia in patients with poor cardiac function, shock, or hypovolemia—stroke volume is limited and cardiac output depends on the elevated heart rate. 1, 2

• Do NOT assume narrow complex means benign—SVT at 170 bpm can cause significant hemodynamic compromise and requires urgent treatment. 1, 2

• Avoid combining AV nodal blocking agents with longer half-lives (e.g., giving a beta-blocker after a calcium channel blocker)—profound bradycardia can develop. 1

• Do NOT use verapamil if the patient has taken beta-blockers, as this risks profound bradycardia and hypotension. 1

Monitoring and Disposition

• Continuous cardiac monitoring with frequent blood pressure checks (every 5-15 minutes initially) is mandatory. 3

• Refer patients with recurrent SVT to a cardiac arrhythmia specialist for consideration of catheter ablation, especially if episodes are recurrent or the patient desires freedom from medications. 1, 4

• For wide-complex tachycardia of unknown etiology, refer to an arrhythmia specialist after successful termination. 1