What are the differential diagnoses for tachycardia in a 45-year-old female?

Differential Diagnoses for Tachycardia in a 45-Year-Old Female

The differential diagnosis for tachycardia in a 45-year-old woman must first distinguish between narrow-complex (<120 ms) and wide-complex (≥120 ms) tachycardias on 12-lead ECG, as this fundamentally determines the diagnostic approach and potential life-threatening conditions. 1

Initial Assessment Framework

Before considering specific arrhythmias, evaluate for physiologic causes of sinus tachycardia (heart rate >100 bpm), which is the most common etiology 1:

• Hypoxemia - assess oxygen saturation and work of breathing (tachypnea, intercostal retractions, suprasternal retractions) 1
• Fever - infectious or inflammatory processes 1
• Anemia - reduced oxygen-carrying capacity 1
• Hypotension/shock - compensatory mechanism to maintain cardiac output 1
• Hypovolemia - dehydration or blood loss 1
• Pain or anxiety - though anxiety is often misdiagnosed when true arrhythmia exists 2

Critical caveat: In sinus tachycardia with poor cardiac function, the rapid rate may be compensatory; "normalizing" the heart rate can be detrimental as cardiac output depends on rate when stroke volume is limited 1.

Narrow-Complex Tachycardia Differentials (QRS <120 ms)

When QRS duration is narrow, the tachycardia is almost always supraventricular 1:

Regular Narrow-Complex Tachycardias

• Atrioventricular Nodal Reentrant Tachycardia (AVNRT) - most common mechanism when no P waves are visible and RR interval is regular 1. Look for pseudo-r' wave in V1 and pseudo-S waves in inferior leads (II, III, aVF), which are pathognomonic 1, 3

• Atrioventricular Reentrant Tachycardia (AVRT) - suspect when P wave is present in ST segment separated from QRS by >70 ms 1

• Atypical AVNRT or Permanent Junctional Reciprocating Tachycardia (PJRT) - when RP interval is longer than PR interval 1

• Atrial Tachycardia (AT) - focal or multifocal, may have RP longer than PR 1

• Atrial Flutter with 1:1 or 2:1 conduction - atrial rate exceeds ventricular rate 1

Irregular Narrow-Complex Tachycardias

• Atrial Fibrillation - irregularly irregular rhythm; when associated with rapid ventricular response, irregularity may be less easily detected and can be misdiagnosed as regular SVT 1

• Multifocal Atrial Tachycardia (MAT) - irregular ventricular rate with multiple P wave morphologies 1

• Atrial Flutter with Variable AV Conduction - irregular ventricular response 1

Wide-Complex Tachycardia Differentials (QRS ≥120 ms)

Critical principle: If SVT cannot be proven easily, treat as ventricular tachycardia (VT) to avoid potentially fatal mismanagement 1, 3. Intravenous verapamil or diltiazem given for presumed SVT may precipitate hemodynamic collapse in VT 1.

Three Main Categories 1:

1. Ventricular Tachycardia - most important to identify due to worst prognosis 4

Key ECG features suggesting VT 1, 5:

• AV dissociation with ventricular rate faster than atrial rate (diagnostic when present) 1
• Fusion complexes (diagnostic when present) 1
• QRS duration >140 ms in right bundle branch block (RBBB) pattern or >160 ms in left bundle branch block (LBBB) pattern 5
• Precordial concordance (all QRS complexes positive or negative) 1
• "Northwest" QRS axis 5
• Absence of RS complex in V1-V6 or RS interval >100 ms 5
• History of myocardial infarction or structural heart disease 6

2. Supraventricular Tachycardia with Bundle Branch Block

• Pre-existing BBB visible on baseline ECG 1
• Rate-related (functional) BBB occurring during tachycardia when bundle branch is refractory 1
• QRS morphology during tachycardia identical to sinus rhythm suggests SVT 1
• ECG findings typical of BBB: for LBBB = rS or QS in V1-V2 with R wave in V6; for RBBB = rSR' in V1 with RS in V6 4

3. SVT with Pre-excitation via Accessory Pathway

• Antidromic AVRT - anterograde conduction over accessory pathway, retrograde over AV node 1
• Atrial fibrillation with WPW syndrome - irregular wide-complex tachycardia, can degenerate to ventricular fibrillation 1
• May occur during AT, atrial flutter, AF, or AVNRT with accessory pathway conduction 1

Age and Gender-Specific Considerations

For a 45-year-old woman specifically:

• Upper limit of sinus tachycardia is approximately 175 bpm (220 minus age) 1
• Women experience more symptoms during SVT episodes, including higher rates of fatigue, near-syncope, and syncope 1
• Perimenopause-related factors may include thyroid dysfunction, anemia, or autonomic changes (general medical knowledge)
• Structural heart disease is unusual in SVT patients 2

Diagnostic Approach Summary

Step 1: Obtain 12-lead ECG during tachycardia and in sinus rhythm 1, 3

Step 2: Classify as narrow (<120 ms) or wide (≥120 ms) complex 1

Step 3: Assess regularity of ventricular response 1

Step 4: For narrow-complex, look for P wave relationship to QRS 1

Step 5: For wide-complex, apply VT criteria; if uncertain, default to VT diagnosis 1, 4

Step 6: Consider adenosine or carotid massage with 12-lead ECG recording to aid diagnosis in narrow-complex regular tachycardias 1, 3

Common pitfall: Automatic ECG interpretation systems are unreliable and commonly suggest incorrect diagnoses - always perform manual interpretation 3.