What is the initial approach to managing a patient with acute tachycardia?

Differential Diagnosis for Acute Tachycardia

Primary Classification by QRS Width

The initial approach to acute tachycardia requires immediate assessment of hemodynamic stability, followed by systematic ECG analysis to differentiate narrow-complex from wide-complex tachycardia, as this distinction fundamentally determines both the differential diagnosis and management strategy. 1, 2

Narrow-Complex Tachycardia (QRS <120 ms)

Sinus Tachycardia

• Heart rate >100 bpm but typically <150 bpm, with upper limit approximately 220 minus patient's age 1
• Most common cause in acute settings—represents physiologic response to underlying stressors 1
• Look for: fever, dehydration, anemia, hypotension/shock, hypoxemia, pain, anxiety, sepsis 1, 3
• Critical pitfall: This is a compensatory mechanism, not a primary arrhythmia—"normalizing" the heart rate in patients with poor cardiac function can be detrimental as cardiac output depends on rapid rate 1

Supraventricular Tachycardia (SVT)

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT): Most common pathologic SVT, typically presents with sudden onset palpitations, neck pulsations, shortness of breath, rarely syncope 1, 4
• Atrioventricular Reentrant Tachycardia (AVRT): Involves accessory pathway (Wolff-Parkinson-White syndrome) 1, 5
• Atrial Tachycardia: Less common, may be multifocal (especially in critically ill patients with precipitating factors) 3
• Atrial Flutter: Typically presents with regular rhythm, often 2:1 conduction producing ventricular rate ~150 bpm 3
• Atrial Fibrillation: Irregularly irregular rhythm, variable ventricular response 3, 4

Wide-Complex Tachycardia (QRS ≥120 ms)

Ventricular Tachycardia (VT)

• Presume VT until proven otherwise—this is the most important principle when encountering wide-complex tachycardia 6, 7
• Monomorphic VT: Uniform QRS morphology, suggests scar-related reentry (post-MI most common) 7
• Polymorphic VT: Varying QRS morphology, suggests acute ischemia or electrolyte abnormalities 7
• Torsades de Pointes: Specific polymorphic VT with QT prolongation, requires different management 3

SVT with Aberrant Conduction

• Pre-existing bundle branch block 8
• Rate-related aberrancy 8
• Antidromic AVRT (pre-excited tachycardia via accessory pathway) 1

Accelerated Idioventricular Rhythm

• Ventricular rate <120 bpm, usually benign reperfusion rhythm requiring no treatment 6

Critical Initial Assessment Algorithm

Step 1: Assess Hemodynamic Stability (Takes Priority Over Everything)

Unstable patients (any of the following):

• Hypotension or signs of shock 1, 2
• Acute altered mental status 1, 2
• Ischemic chest discomfort 1
• Acute heart failure 1
• Syncope 2

→ Proceed immediately to synchronized cardioversion without delay 1, 2, 7

• Do NOT delay for 12-lead ECG 2
• Sedate if conscious but do not delay if extremely unstable 2, 7
• Use 100 J synchronized for monomorphic VT, 200 J unsynchronized for polymorphic VT resembling VF 7

Step 2: For Stable Patients—Determine Rate Threshold

Heart rate <150 bpm: Unlikely that tachycardia is primary cause of symptoms unless ventricular dysfunction present—search aggressively for underlying causes 1

Heart rate ≥150 bpm: More likely primary arrhythmia requiring specific treatment 1

Step 3: Identify and Address Reversible Causes

Always evaluate for:

• Hypoxemia (check pulse oximetry, work of breathing) 1
• Electrolyte abnormalities (hypokalemia, hypomagnesemia) 6, 3
• Acute myocardial ischemia 6, 7
• Acid-base disturbances 6
• Drug toxicity or proarrhythmia 3
• Hyperthyroidism 3

Step 4: ECG Criteria for Wide-Complex Tachycardia Differentiation

Favor VT if any present:

• QRS >140 ms with RBBB pattern or >160 ms with LBBB pattern 7
• AV dissociation (gold standard but only present in ~25% of VT) 7
• Fusion or capture beats 7
• RS interval >100 ms in any precordial lead 7
• Negative concordance in precordial leads 7
• QR complexes (indicates myocardial scar, present in ~40% post-MI VT) 7

Common Diagnostic Pitfalls

Never assume wide-complex tachycardia is supraventricular—when uncertain, always treat as VT to avoid potentially lethal consequences 6, 7, 8

Avoid calcium channel blockers (diltiazem/verapamil) in wide-complex tachycardia unless absolutely certain of fascicular VT diagnosis, as they may precipitate hemodynamic collapse in structural VT 6, 7

Do not use adenosine in hypotensive patients—it can worsen hypotension and is inappropriate when immediate cardioversion is needed 2

Recognize that anxiety/panic disorder is commonly misdiagnosed when the actual problem is paroxysmal SVT 5

In pediatric patients, SVT typically exceeds 220 bpm in infants and 180 bpm in children—different thresholds than adults 9