Cardiac Dysrhythmias – Study Notes

General Principles

• EKGs are daunting but manageable with a systematic approach.

• Avoid relying solely on machine interpretations → check with your eyes.

• Use a consistent system (mnemonics like “RAPID PQRST” or Dubin’s method).

• Get comfortable by looking at EKGs often (“pink paper rounds” in the ED).

Basics of EKG

• Small box = 0.04 sec (horizontal) / amplitude = 0.1 mV (vertical).

• Normal sequence: P → QRS → T.

• Intervals: PR, QRS, QT (machine is reliable for these).

• Don’t just read the words on top (the “Ortho interpretation”).

Heart Blocks (AV blocks)

1. First-degree AV block

   • PR > 200 ms (longer than 5 small boxes).

   • Benign; common in young athletes or aging adults.

   • No treatment, just note it.

2. Second-degree AV block

   • Mobitz I (Wenckebach): PR gets progressively longer → dropped beat.

     • Often benign; may be medication-related.

   • Mobitz II: Constant PR intervals → sudden dropped beat.

     • More concerning; risk of progression to complete block.

3. Third-degree (complete) block

   • P waves march independently of QRS.

   • Ventricular escape rhythm slower (~40–60 bpm).

   • Always pathologic in acute settings → needs pacing/cardiology consult.

Premature Atrial Contractions (PACs)

• Extra atrial beat comes early with pause after.

• Usually benign; common after caffeine, alcohol, stress, poor sleep.

Supraventricular Tachycardia (SVT)

• Narrow complex, regular, rapid (often 170–220 bpm).

• Common in young, healthy patients with palpitations.

Management:

• Unstable: Synchronized cardioversion (100 J).

• Stable:

  • Vagal maneuvers (Valsalva, REVERT method, carotid massage in kids, ice on face in infants).

  • Adenosine 6 mg IV push (warn about transient asystole, chest pressure, dyspnea).

  • Calcium channel blockers (verapamil/diltiazem) or beta-blockers if needed.

Key: If wide and regular → could be VT or SVT with aberrancy. Treat as VT if unsure.

Atrial Flutter

• Atrial rate ~300 bpm; “sawtooth” baseline.

• Ventricular response is divisor of 300 (150 bpm with 2:1 block, 100 with 3:1, etc.).

• Often seen with “holiday heart” (alcohol, bingeing).

• Usually self-limited.

• If unstable: cardioversion.

• If stable: usually no acute treatment.

Atrial Fibrillation (AFib)

• Irregularly irregular rhythm (key finding).

• Two key scenarios:

  • New onset: may need workup, cardioversion, anticoagulation.

  • Chronic AFib with RVR (>100 bpm): treat like sinus tach → find the trigger (infection, bleed, PE, hypovolemia).

• Don’t reflexively slow rate if tachycardia is compensatory (e.g., bleeding).

• Rate control (beta-blocker, calcium channel blocker, amiodarone) only if indicated.

• If AFib >48h → avoid cardioversion in ED unless unstable (risk of stroke).

Multifocal Atrial Tachycardia (MAT)

• Multiple ectopic atrial foci → ≥3 different P-wave morphologies.

• Irregular, narrow tachycardia.

• Classically seen in COPD patients.

• Treat underlying condition (O₂, bronchodilators), not the rhythm itself.

Wolff-Parkinson-White (WPW) Syndrome

• Accessory conduction pathway → risk of rapid ventricular rates.

• EKG clues:

  • Short PR interval.

  • Delta wave (slurred upstroke).

  • Wide QRS.

Management:

• Narrow, regular SVT → treat like typical SVT.

• Wide, irregular AFib with WPW → very dangerous.

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

  • Use procainamide (safe for all wide-complex tachycardias if unsure).

Wide Complex Tachycardia (WCT)

• Assume ventricular tachycardia (VT) until proven otherwise.

• Unstable: cardioversion.

• Stable:

  • If uncertain → treat as VT.

  • Procainamide is drug of choice for stable WCT.

Key Clinical Pearls

• Always assess stability first.

• If unstable → shock (synchronized if organized rhythm).

• For wide tachycardia: safer to assume VT.

• Adenosine is diagnostic and therapeutic for narrow SVT but never give in AFib with WPW.

• Chronic AFib with RVR is often physiologic tachycardia—look for the cause before treating the rate.