Cardiac Dysrhythmia Interpretation

 Cardiac Dysrhythmia Interpretation – Notes

1. General Approach to EKGs

• EKGs can feel intimidating but are manageable with practice.

• Use a systematic approach (e.g., mnemonic: A Rare PQRST).

• Intervals listed at the top (PR, QRS, QT) are reliable → check them first.

• Don’t rely solely on automated interpretations; always use your eyes.

• Practice: pick up discarded EKGs in the ED and review them.

2. Basics

• Small box = 0.04 sec (horizontal, time), vertical = amplitude.

• P wave → atrial depolarization.

• QRS → ventricular depolarization.

• T wave → ventricular repolarization.

3. AV Blocks

• 1st Degree AV Block: PR > 200 ms (> 5 small boxes). Usually benign (young athletes or aging).

• 2nd Degree AV Block Type I (Wenckebach): PR prolongs progressively until a QRS is dropped. Usually benign, often medication-related.

• 2nd Degree AV Block Type II (Mobitz II): Constant PR, sudden dropped QRS. More concerning → may need pacing.

• 3rd Degree AV Block: Complete dissociation between P waves and QRS. Ventricular escape rhythm (usually slower). Emergent → cardiology consult, pacing.

4. Atrial Dysrhythmias

• PACs: Premature atrial contractions. Usually benign; patients may feel palpitations.

• SVT (Paroxysmal Narrow Complex Tachycardia):

  • Regular, narrow, usually 150–220 bpm.

  • Stable → vagal maneuvers (Valsalva, modified Revert technique, ice in peds).

  • If unsuccessful: adenosine (warn patient about transient asystole feeling).

  • Unstable → synchronized cardioversion (100 J).

• Wide Complex Tachycardia: Could be VT or SVT with aberrancy.

  • If unstable → cardiovert.

  • If stable → take time, assume VT until proven otherwise.

• Atrial Flutter:

  • Atrial rate ~300 bpm, ventricular rate divisor of 300 (150, 100, 75).

  • Sawtooth baseline.

  • Often self-limited; unstable → cardiovert.

• Atrial Fibrillation:

  • Irregularly irregular rhythm.

  • Acute triggers: alcohol (“holiday heart”), hyperthyroidism, PE, ACS, etc.

  • Chronic Afib with RVR = equivalent to sinus tach → search for trigger (bleeding, infection, pain).

  • Avoid reflexively slowing rate if underlying cause is shock/bleeding.

  • Rate control (if needed): beta-blockers, calcium channel blockers, amiodarone.

  • Avoid cardioversion if >48h without anticoagulation (unless unstable).

• Multifocal Atrial Tachycardia (MAT):

  • ≥3 different P-wave morphologies, irregular rhythm.

  • Associated with COPD.

  • Treat underlying cause (e.g., hypoxia).

5. Wolf-Parkinson-White (WPW)

• EKG clues: short PR, delta wave, wide QRS.

• Narrow, regular rhythm → treat like SVT.

• Wide, irregular rhythm (Afib with WPW): dangerous! Can degenerate to VF.

  • Avoid AV nodal blockers (adenosine, beta-blockers, CCBs).

  • Treat with procainamide or cardioversion if unstable.

• If unsure with wide complex tachycardia → procainamide is safe.

6. Ventricular Dysrhythmias

• PVCs: Common, usually benign. No treatment needed unless very frequent, multifocal, or associated with ischemia/electrolyte imbalance.

• VT (Ventricular Tachycardia):

  • ≥3 PVCs in a row.

  • Sustained (>30 sec) vs. nonsustained.

  • Older/sicker patients = more likely true VT.

  • Stable → consider procainamide, amiodarone, or lidocaine.

  • Unstable → synchronized cardioversion.

• VF (Ventricular Fibrillation): chaotic, pulseless. Immediate defibrillation + ACLS.

7. Pearls

• Always assess stability first (unstable = shock, stable = think/medicate).

• Wide complex tachycardia → safer to assume VT.

• Afib with RVR in chronic afib → look for cause before slowing rate.

• WPW + Afib with irregular wide complex → procainamide (never AV nodal blockers).

• Practice EKG reading daily to reduce anxiety and increase recognition skills.