Pathophysiology of Arrhythmias Overview

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.

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)

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.

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.

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.

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)

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.

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%.

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.

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.

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)

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.

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

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