Cardiology

Background 

Arrhythmia, also known as dysrhythmia, refers to any abnormality in the heart’s rhythm—be it irregular, too fast, or too slow. It can originate from the atria, AV node, or ventricles, and may result in a wide spectrum of clinical manifestations ranging from asymptomatic to life-threatening. While some arrhythmias are benign and transient, others can result in hemodynamic compromise, embolic events, or sudden cardiac death. 

Arrhythmia is caused by disruptions in the generation or conduction of electrical impulses in the heart. It may involve: 

• Rate disturbances: bradyarrhythmias (<60 bpm) or tachyarrhythmias (>100 bpm). 

• Rhythm disturbances: irregular (e.g., atrial fibrillation) or ectopic rhythms (e.g., PVCs). 

• Conduction abnormalities: heart blocks, reentry circuits, or accessory pathways. 

Classification/Types

I) By Rate: 

• Bradyarrhythmias: Sinus bradycardia, AV blocks, junctional  rhythms. 

• Tachyarrhythmias: Atrial fibrillation, atrial flutter, SVT, VT, VF. 

II) By Origin: 

• Supraventricular: Atrial fibrillation/flutter, SVT, WPW syndrome. 

• Ventricular: PVCs, VT, VF. 

• Junctional: Junctional escape or tachycardia. 

III) By Clinical Impact: 

• Benign/Physiologic: Sinus arrhythmia, isolated PVCs. 

• Pathologic: Sustained VT, AF with RVR, complete heart block. 

Pathophysiology 

Arrhythmias arise from abnormalities in: 

• Impulse formation: Enhanced automaticity, triggered activity (e.g., afterdepolarizations). 

• Impulse conduction: Reentry circuits, conduction delays or blocks. 

• The effect of arrhythmias on cardiac output depends on rate, rhythm regularity, and underlying cardiac function. They may cause hypotension, ischemia, thromboembolism, or syncope. 

Epidemiology 

• Atrial fibrillation is the most common arrhythmia worldwide, affecting over 3 million people in the U.S. 

• Bradyarrhythmias are more common in the elderly due to conduction system degeneration. 

• Supraventricular tachycardias are more frequent in younger individuals. 

• Ventricular arrhythmias are often associated with structural heart disease and post-MI patients. 

Etiology 

I. Causes 

• Electrolyte abnormalities (e.g., hypokalemia, hyperkalemia, hypomagnesemia). 

• Ischemic heart disease (especially post-MI). 

• Heart failure, cardiomyopathy, valvular disease. 

• Medications: Digoxin, antiarrhythmics, beta-blockers, QT-prolonging drugs. 

• Structural heart defects: Congenital or acquired. 

• Infiltrative diseases: Amyloidosis, sarcoidosis. 

• Infections: Myocarditis, endocarditis. 

• Endocrine/metabolic: Hyperthyroidism (AF), hypothyroidism (bradycardia), hypoxia. 

• Substance use: Alcohol (“holiday heart”), cocaine, caffeine. 

II. Risk Factors 

• Age >60 

• Hypertension, diabetes, CAD 

• Heart failure or LV dysfunction 

• Obstructive sleep apnea 

• Valvular heart disease 

• Family history of arrhythmias or sudden death