Cardiac Dysrhythmias

Foundational Role of Dysrhythmia Interpretation in Emergency Nursing

Cardiac dysrhythmias (arrhythmias) are disorders of the heart’s electrical conduction system that result in abnormal heart rate or rhythm. Recognizing and managing dysrhythmias is a core competency for the Certified Emergency Nurse (CEN) because unstable dysrhythmias can quickly lead to hemodynamic compromise, cardiac arrest, and death.^[1] High-yield exam concepts include identifying key rhythms on a monitor strip, linking dysrhythmias to patient symptoms, and prioritizing interventions based on stability.

Essential Electrophysiology Terminology for Dysrhythmia Analysis

• Depolarization: Electrical activation of cardiac cells leading to contraction. On ECG, the P wave (atria) and QRS complex (ventricles) represent depolarization.
• Repolarization: Electrical recovery of cardiac cells. The T wave represents ventricular repolarization.
• Automaticity: The ability of cardiac cells to spontaneously generate an electrical impulse. Normally the sinoatrial (SA) node is the dominant pacemaker.
• Escape rhythm: A backup rhythm that emerges when a higher pacemaker fails (e.g., junctional escape, ventricular escape).
• Irregular rhythm: Any rhythm that lacks consistent R-R intervals. Atrial fibrillation is the most common irregular rhythm in the ED.^[2]

Methodical Approach to ECG Rhythm Strip Interpretation

Normal Conduction Pathway

1. SA node → atria (P wave)
2. Atrioventricular (AV) node (delay – PR interval)
3. Bundle of His → right and left bundle branches
4. Purkinje fibers → ventricles (QRS complex)

Systematic Rhythm Strip Analysis

1. Rate: Count large boxes (300 ÷ number of large boxes between R waves) or small boxes (1500 ÷ small boxes).
2. Rhythm: Are R-R intervals regular? P-P intervals regular?
3. P wave morphology: Present? Uniform? One P before each QRS?
4. PR interval: Normal 0.12–0.20 sec (3–5 small boxes).
5. QRS width: Normal <0.12 sec (narrow, <3 small boxes).
6. Interpretation: Name the rhythm, then assess clinical context (stable vs. unstable).

Dysrhythmia Profiles: ECG Findings and Patient Symptoms

Sinus Tachycardia

• Rate >100 bpm, regular, normal P-QRS-T.
• Often a response to pain, fever, fear, hypovolemia, or pulmonary embolism.
• Treatment: address underlying cause. Avoid β-blockers unless the patient has ongoing myocardial ischemia.^[3]

Atrial Fibrillation (AF)

• Chaotic atrial activity → no clear P waves, “irregularly irregular” R-R intervals.
• Ventricular rate may be slow (controlled) or rapid (uncontrolled >100 bpm).
• Risk of thromboembolic stroke: CHA₂DS₂-VASc score guides anticoagulation.^[4]
• Rate control (β-blockers, calcium channel blockers) or rhythm control (cardioversion).

Ventricular Tachycardia (VT)

• Wide QRS (>0.12 sec), rate usually 120–250 bpm, regular or slightly irregular.
• Patient may be unstable (hypotension, chest pain, altered mental status) or stable.
• Treat unstable VT with synchronized cardioversion (100 J, then escalate).^[5]
• Stable VT: amiodarone 150 mg IV over 10 min.

Ventricular Fibrillation (VF)

• Chaotic, unorganized electrical activity – no QRS, no pulse.
• Immediate defibrillation (biphasic 120–200 J) is the only definitive treatment.
• CPR, epinephrine per ACLS protocol.^[5]

Heart Blocks

Systematic Patient Evaluation in Dysrhythmia Management

• Primary assessment (ACLS approach): Check responsiveness, airway, breathing, circulation. If pulseless, start CPR, defibrillate VF/pVT, give epinephrine.
• HbA1C and electrolytes: Hypokalemia, hypomagnesemia, hyperkalemia can provoke dysrhythmias. Check potassium (aim >4.0 mEq/L) and magnesium (aim >2.0 mg/dL) in at-risk patients.^[7]
• Echocardiogram: Bedside echo can evaluate wall motion, ejection fraction, and pericardial effusion.
• Continuous cardiac monitoring: Use leads II and V1 for best P- and QRS visualization.

Pharmacologic and Electrical Interventions for Dysrhythmias

• Stable vs. Unstable: Always ask: Is the patient hypotensive, confused, having chest pain, or showing signs of shock? Unstable = electrical intervention (cardioversion or defibrillation).
• Pharmacologic management by rhythm:
  • AF/Rapid SVT: Adenosine (SVT), diltiazem (rate control), amiodarone (rhythm).
  • Stable Wide Complex Tachycardia: Amiodarone 150 mg IV over 10 min, or procainamide.
  • Bradycardia with symptoms: Atropine 0.5 mg IV every 3–5 min (max 3 mg); if ineffective, transcutaneous pacing.^[5]
• Synchronized cardioversion: For unstable atrial or ventricular tachyarrhythmias (except VF). Deliver shock synchronized to R wave.

Safety Measures and Adverse Event Prevention in Dysrhythmia Care

• Always confirm pulselessness before defibrillating – do not shock a rhythm with a pulse.
• When using defibrillation, avoid injury: “Clear!” – no one touches the bed or patient.
• Anticoagulation in AF: Assess bleeding risk (HAS-BLED score). For cardioversion, either >3 weeks of therapeutic anticoagulation or rule out atrial thrombus with TEE.^[4]
• Wide QRS tachycardia – assume ventricular tachycardia until proven otherwise (especially with known structural heart disease).^[6]
• Proarrhythmia: Antiarrhythmic drugs (especially class III: sotalol, ibutilide) can prolong QT interval and cause torsades de pointes. Monitor ECG after administration.

Testable Concepts and Distractors for Dysrhythmia Questions

• Memorize normal intervals: PR 0.12–0.20 (3–5 small boxes), QRS <0.12 (less than 3 small boxes), QT < half the R-R interval at normal rates.
• Use the “300 rule” for rate: 300, 150, 100, 75, 60, 50 (number of large boxes between R waves).
• Know the difference between VF and VT on exam questions: VF is “coarse” or “fine” wavy baseline with no QRS; VT has consistent wide QRS complexes.
• Unstable rhythm → immediate electricity: Shock for VF/pVT, cardioversion for unstable SVT, AF, flutter, VT with a pulse. Pacing for unstable bradycardia.
• For heart blocks: Mobitz I is usually benign; Mobitz II and third-degree require a pacemaker.
• Common CEN distractors: “Asystole requires defibrillation” (false – give epinephrine and CPR; no shock). “Atropine for bradycardia works even in a heart transplant” (false – it may not work due to denervation; use pacing).

References & Sources

1. American Heart Association. ACLS Provider Manual. 2020. Available at: https://doi.org/10.1161/CIR.0000000000000912.
2. Lewis SL, Dirksen SR, Heitkemper MM, Bucher L, Barry M. Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 10th ed. Elsevier; 2017. ISBN 978-0-323-32585-5.
3. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison's Principles of Internal Medicine. 20th ed. McGraw-Hill; 2018. https://doi.org/10.1002/9781118643628.
4. January CT, Wann LS, Calkins H, et al. 2019 AHA/ACC/HRS Focused Update of the 2014 Guideline for the Management of Patients With Atrial Fibrillation. Circulation. 2019;140:e125–e151. https://doi.org/10.1161/CIR.0000000000000665.
5. Panchal AR, Bartos JA, Cabañas JG, et al. Part 3: Adult Basic and Advanced Life Support: 2020 American Heart Association Guidelines for CPR and ECC. Circulation. 2020;142(16_suppl_2):S366–S468. https://doi.org/10.1161/CIR.0000000000000916.
6. Urden LD, Stacy KM, Lough ME. Critical Care Nursing: Diagnosis and Management. 9th ed. Elsevier; 2021. https://doi.org/10.1016/B978-0-323-64875-7.00001-5.
7. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death. Circulation. 2018;138:e272–e391. https://doi.org/10.1161/CIR.0000000000000549.