Tachycardias – Study Notes

Tachycardias – Study Notes

General Framework

• Two main mechanisms:

  1. Altered impulse formation

     • Enhanced automaticity (ectopic pacemaker firing too fast).

     • Triggered activity (ion imbalances: Ca²⁺, K⁺, Mg²⁺, drugs, stimulants).

  2. Altered impulse conduction

     • Accessory pathway (short-circuits AV node).

     • Reentry circuits (electrical “looping” → tachycardia).

• Assessment of tachycardia:

  1. Stable vs. unstable patient (BP, mentation, perfusion).

  2. Rate.

  3. QRS width (narrow vs. wide).

  4. Rhythm (regular vs. irregular).

  5. Site of origin (sinus node, atria, AV node, ventricle).

  6. Never hesitate to repeat EKG or use double speed to clarify flutter waves.

Narrow Complex Tachycardias (SVTs)

Regular

• Sinus tachycardia – normal P before each QRS; physiologic causes.

• SVT (AVNRT/AVRT) – no clear P-waves; sudden onset/offset.

• Atrial flutter (with fixed conduction) – sawtooth waves, usually ~150 bpm.

Irregular

• Multifocal atrial tachycardia (MAT) – ≥3 different P-wave morphologies, irregular rhythm; often COPD, theophylline, PE.

• Atrial fibrillation – no organized P-waves, irregularly irregular, rate variable.

Wide Complex Tachycardias

Regular

• Monomorphic VT – wide QRS, AV dissociation, capture/fusion beats.

• SVT with aberrancy – consider if history of BBB or rate-dependent aberrancy.

Irregular

• Polymorphic VT / Torsades de pointes – wide, chaotic, irregular.

• V-fib – disorganized, no identifiable QRS.

Clinical Pearls

• When a patient says “don’t let me die” → take it seriously.

• Stable vs. unstable determines treatment.

  • Stable: vagal maneuvers, adenosine (for SVT), meds.

  • Unstable: immediate synchronized cardioversion.

• Adenosine – very short half-life; warn patients about transient symptoms.

• Carotid massage – only one side at a time.

• Flutter not lead-specific – must appear in multiple leads.

• Afib – rate can be controlled (60–80) or dangerously rapid (>200).

• MAT in younger patient → consider pulmonary embolism.

• Capture beats + fusion beats → diagnostic of VT.

• Tools: calipers or simple paper marks to check regularity.

Simplified Classification Table

Narrow QRS

• Regular → Sinus tach, SVT, Atrial flutter.

• Irregular → Afib, MAT.

Wide QRS

• Regular → VT, SVT with aberrancy.

• Irregular → Polymorphic VT, Vfib.