ECG / EKG Dysrhythmia Review

Sinus (SA-Node) Rhythms

Sinus Bradycardia

  • Exact replica of Normal Sinus Rhythm (NSR) except for rate.

    • Rate <60\;\text{bpm} (e.g., strip shown at 50\;\text{bpm}).

  • 5-Step Check

    • Regular rhythm.

    • P : QRS = 1 : 1.

    • PR interval normal (0.12\text{–}0.20\;\text{s}).

    • QRS narrow/normal (<0.12\;\text{s}).

  • Management

    • Usually “treat the cause” (e.g., hypoxia, drugs, vagal tone, electrolyte problems).

    • If unstable → ACLS bradycardia algorithm (atropine, pacing, etc.).

Sinus Tachycardia

  • Same criteria as NSR but fast.

    • Rate >100\;\text{bpm} (classroom example "students across receive an education fast").

  • 5-Step Check identical to bradycardia except for rate.

  • Management

    • Identify & reverse trigger (pain, fever, dehydration, hypovolemia, anxiety, sepsis…).

    • If unstable → follow ACLS tachycardia algorithm.

Atrial Dysrhythmias

  • Pathophysiology: Impulse arises above ventricles but outside the SA node.

  • ECG clue set:

    • P-wave abnormalities (shape, absence, multiplicity).

    • Often irregular rhythm (because ectopic foci fire unpredictably).

    • QRS generally unaffected (ventricles still depolarise through normal His–Purkinje system).

Atrial Fibrillation (AFib)

  • Multiple ectopic atrial sites fire → atria quiver (no unified contraction).

  • ECG

    • Irregularly irregular R–R intervals.

    • No true P-waves; baseline appears wavy/chaotic.

    • QRS narrow/normal.

    • Cannot measure PR interval (no distinct P’s).

  • Rate categories

    • Controlled AF <100\;\text{bpm}.

    • Rapid Ventricular Response (RVR) >100\;\text{bpm} if AV node conducts excessively.

  • Significance

    • ↓ atrial kick → risk of thrombus → stroke.

    • Rate control & anticoagulation foundational.

Atrial Flutter

  • Usually 1–2 ectopic atrial foci firing in circuit → organized but very fast atrial rate 120\text{–}300\;\text{bpm}.

  • AV node blocks many impulses; ventricles often slower.

  • ECG

    • Characteristic “saw-tooth” baseline (multiple F-waves per QRS).

    • Common conduction ratios: 2:1,\;3:1,\;4:1 but can vary beat-to-beat → usually irregular.

    • QRS narrow; PR not measurable (no single P precedes QRS consistently).

  • Can flip into RVR if AV node lets more impulses through.

  • Lead selection tip: If F-waves unclear, switch leads or order 12\text{-lead} ECG.

Supraventricular Tachycardia (SVT)

  • Umbrella term for any rapid rhythm originating above the ventricles.

  • Distinguishing feature vs sinus tachycardia = very high rate plus hidden P-waves.

    • Rate classically \ge 150\;\text{bpm} (can be 130\text{–}140).

    • P-wave buried in preceding T-wave → one merged wave between QRS complexes.

  • 5-Step Summary

    • Rhythm: usually regular (can appear regular even if triggered by AFib when extremely fast).

    • Rate: “extremely fast” (example strip 187\;\text{bpm} using 1500-box method).

    • P : QRS ratio: indiscernible P-waves.

    • QRS narrow <0.12\;\text{s}.

    • PR unmeasurable.

  • Management

    • Vagal manoeuvres → adenosine bolus (chemical cardioversion).

    • Calcium-channel or β-blockers; if unstable → synchronized cardioversion.

  • Physiologic limit: Heart cannot sustain (\approx 180\text{–}200\;\text{bpm}) for long → rapid hemodynamic collapse.

Ventricular Dysrhythmias ("Deadly Rhythms")

  • Origin = ventricles → compromises cardiac output.

  • Focus on QRS complex (wide, bizarre, or absent).

  • Must recognise instantly – no 5-step analysis – and assess pulse.

Ventricular Tachycardia (VTach / Wide-Complex Tachycardia)

  • ECG Hallmarks

    • Wide QRS complexes (>0.12\;\text{s}) repeating rapidly.

    • Rate typically >100\;\text{bpm}.

    • No visible P- or T-waves – uniform or polymorphic morphology.

  • Clinical Pearl: May be "VT with a pulse" or pulseless VT.

    • Immediately check patient.

    • Pulseless → start CPR, defibrillate per ACLS.

    • Pulse present → antiarrhythmic drugs (amiodarone, lidocaine), synchronized cardioversion.

    • Example anecdote: patient maintained VT w/ pulse 4 h before conversion – uncommon, high-risk.

Ventricular Fibrillation (VFib)

  • Ventricles quiver → no forward flow, never a pulse.

  • ECG: Chaotic, erratic baseline; no coordinated QRS, P, or T.

  • Management

    • This is cardiac arrest. Verify rhythm quickly (rule out artifact), shout for help, start CPR, defibrillate ASAP.

    • Follow ACLS VF/VT algorithm (shock → CPR × 2 min → drug → shock…).

Clinical Approach & Interventions

  • Always correlate monitor with patient assessment (pulse, BP, LOC).

  • Unstable criteria: hypotension, altered mentation, chest pain, signs of shock.

  • Key Drugs Mentioned

    • Adenosine (SVT, some VT with pulse): transient AV-node block to “reset” rhythm.

    • Calcium-channel blockers (diltiazem), β-blockers: rate control.

    • Amiodarone / Lidocaine: ventricular arrhythmias.

  • Electrical Therapies

    • Synchronized cardioversion: unstable tachyarrhythmias w/ pulse (SVT, AFib RVR, flutter, VT w/ pulse).

    • Defibrillation: pulseless VT/VF.

  • Supportive care: oxygen, IV access, treat reversible causes (H’s & T’s).

Additional Study Points

  • Premature beats (PACs, PVCs) & heart blocks also appear on exams – detailed lessons available on nrsmg.com EKG course.

  • Master waveform anatomy and rate calculation methods (1500-box, 300-rule, 6-second). Understanding these fundamentals helps distinguish similar rhythms.