Pathophysiology of Arrhythmias Overview

Pathophysiology of Arrhythmias

• Abnormal Impulse Formation: Triggered activity or abnormal automaticity originating from the SA node or other sites.
• Abnormal Impulse Conduction:
  • Re-entry (most common): Impulse travels backward through the conducting pathway.
  • Block: Conducting pathway is blocked, preventing impulse transmission.

Classification of Arrhythmias

• Supraventricular Arrhythmias (Atrial Arrhythmias): Arrhythmias originating above the bundle of His.
  • Sinus bradycardia
  • Sinus tachycardia
  • Atrial flutter
  • Atrial fibrillation (AF)
  • Paroxysmal supraventricular tachycardia
  • Wolff-Parkinson-White (WPW) syndrome
  • Premature atrial contractions (PACS)
• Ventricular Arrhythmias: Arrhythmias originating below the bundle of His.
  • Premature ventricular contractions (PVCs)
  • Ventricular tachycardia (VT)
  • Ventricular fibrillation (VF)

Anti-Arrhythmic Agents

• Adenosine: Rapidly blocks the AV node, used for acute treatment of PSVT (pre-excitation supraventricular tachycardia) causing short-term chest heaviness or flushing.
• CCB (Calcium Channel Blockers): Alternative to adenosine if it's ineffective, administered as an IV bolus or infusion.
• Long-term management: Oral CCBs, beta-blockers, or digoxin may be used as alternatives. Radiofrequency catheter ablation could be used if pharmacological treatment proves insufficient.

Paroxysmal Supraventricular Tachycardia (PSVT)

• Definition: Sudden onset and termination of tachycardia (180-200 beats/min).
• Source: AV nodal re-entry.
• ECG Characteristics: Normal ECG with heart rate of 180-200 bpm.
• Causes: Electrolyte abnormalities, ischemic heart disease (IHD), cardiac surgery, thyrotoxicosis.
• Clinical Presentation: Palpitations, dizziness, presyncope (near-fainting).
• Complications: May degenerate to other serious arrhythmias. PSVT may not increase risk of stroke.
• Treatment: Vagal maneuvers (carotid massage, Valsalva maneuver), followed by drug therapy if those methods fail. Pharmacological treatment for acute episodes.

Wolff-Parkinson-White (WPW) Syndrome

• Definition: Pre-excitation syndrome where an impulse excites the ventricle before the expected regular impulse.
• Source: Accessory bypass tract connecting atria to ventricles.
• ECG Characteristics: Short PR interval, delta wave (fused complex) seen from pre-excitation
• Clinical Presentation: Atrial fibrillation, tachycardia, palpitations, lightheadedness, and fatigue.
• Treatment: Procainamide (FDA-approved for WPW) may be preferable to other anti-arrhythmic drugs; radiofrequency ablation is effective in the long term.

Drugs to Avoid in WPW

• Adenosine
• Beta-blockers
• Diltiazem
• Verapamil
• Digoxin
• Amiodarone

Ventricular Arrhythmias

• Definition: Arrhythmias originating below the bundle of His.
• Source: Irritable ectopic foci within the ventricular myocardium.
• ECG Characteristics: Wide, bizarre-looking QRS complexes.
• Clinical Forms:
  • Premature ventricular contractions (PVCs)
  • Ventricular tachycardia (VT)
  • Ventricular flutter
  • Ventricular fibrillation (VF)
  • Torsades de Pointes (TdP)

Premature Ventricular Contraction (PVC)

• Definition: Extra heart beat arising from irritable ectopic foci of the ventricular myocardium.
• ECG characteristics: Wide and bizarre QRS complex.
• Clinical Presentation: Occasional/asymptomatic, symptomatic as PVCs in high frequency.
• Complication: High risk when it's frequent or in combination with structural heart disease (frequent PVCs, especially with reduced ejection fraction in patients to increase risk of sudden cardiac death).
• Treatment: If frequent, IV beta-blockers or CCBs may be used. Oral beta blockers or amiodarone are considered to prevent recurrence.

Nonsustained Ventricular Tachycardia (NSVT)

• Definition: Three or more consecutive PVCs lasting less than 30 seconds, self-terminating.
• ECG Characteristics: Three or more consecutive premature ventricular complexes(PVCs) lasting < 30 seconds, with or without symptoms.
• Clinical Presentation: Palpitations, lightheadedness.
• Complication: Risk of sudden cardiac death (SCD)
• Treatment: Varies based on the patient's ejection fraction and symptoms, usually no treatment needed if EF >40%
• IV beta blockers may be considered, if EF <40%.

Sustained Ventricular Tachycardia (SuVT)

• Definition: Three or more consecutive PVCs lasting more than 30 seconds.
• Source: Irritable ectopic foci that cause a sustained cardiac rhythm.
• ECG Characteristics: Three or more consecutive PVCs lasting >30 seconds, P-waves are lost in the QRS complex.
• Clinical Presentation: Pale, diaphoretic, lightheadedness, and may not respond to commands.
• Complication: Ventricular fibrillation, sudden cardiac death (SCD).
• Treatment: Hemodynamically stable patients may receive intravenous lidocaine/procainimide infusions; if these fail, other medications such as sotalol, and amiodarone may be used for long-term treatment.

Torsades de Pointes (TdP)

• Definition: Rapid polymorphic ventricular tachycardia that occurs at abnormal intervals with QT interval prolongation.
• ECG characteristics: Rapid, irregular QRS complexes and is identified in the presence of prolonged QT interval
• Clinical Presentation: Dizziness, consciousness if unstable
• Causes & Risk: Proarrhythmic drugs (class IA drugs except amiodarone and ibutilide), macrolide antibiotics.
• Complication: Ventricular fibrillation, sudden cardiac death (SCD)
• Treatment: Treatment if hemodynamically unstable includes electrical cardioversion and if hemodynamically stable magnesium as first-line measure and class IB antiarrhythmic agents as second-line measure.

Cardiac Conduction Blocks

• Supraventricular Blocks:
  • First-degree AV block
  • Second-degree AV block
  • Third-degree AV block
• Ventricular Blocks:
  • Right bundle branch block (RBBB)
  • Left bundle branch block (LBBB)

Bradyarrhythmias

• Treatment (Symptomatic):
  • Atropine injection (0.5-3 mg IV)
  • Alternative treatments if unresponsive to atropine include transcutaneous pacing, dopamine infusion, epinephrine infusion, isoproterenol, transvenous pacing, and implantable pacemaker for refractory cases.

Implantable Cardioverter-Defibrillator (ICD)

• Overview: Implanted device under the skin with wires that detects and treats dangerous arrhythmias.
• Capabilities: Sensing, pacing, and defibrillation.

Cardiopulmonary Arrest

• Causes: Ventricular fibrillation (VF), pulseless ventricular tachycardia (VT), pulseless electrical activity (PEA), asystole.
• Treatment: Cardiopulmonary resuscitation (CPR), drug therapy (epinephrine, amiodarone), defibrillation.