USMLE Guide: Cardiology of Arrhythmias

Introduction

This guide aims to provide an overview of the important concepts and principles related to cardiology of arrhythmias. It will cover the classification, diagnosis, and management of arrhythmias, focusing on the key information required for the United States Medical Licensing Examination (USMLE) Step 1 and Step 2.

Table of Contents

1. Arrhythmia Classification
2. Diagnosis of Arrhythmias
3. Management of Arrhythmias
4. Specific Arrhythmias
   • Atrial Fibrillation
   • Ventricular Tachycardia
   • Supraventricular Tachycardia
   • Atrioventricular Block
5. Conclusion

Arrhythmia Classification

Arrhythmias can be classified into two main categories:

1. Tachyarrhythmias: Abnormally fast heart rhythms, typically characterized by a heart rate greater than 100 beats per minute.
2. Bradycardias: Abnormally slow heart rhythms, typically characterized by a heart rate less than 60 beats per minute.

Diagnosis of Arrhythmias

To diagnose arrhythmias, the following steps are often involved:

1. Patient History: Gathering information about the patient's symptoms, medical history, and medications.
2. Physical Examination: Assessing vital signs, heart sounds, and peripheral pulses.
3. Electrocardiogram (ECG): The primary tool for diagnosing arrhythmias, which records the electrical activity of the heart.
4. Holter Monitoring: Ambulatory ECG monitoring over 24-48 hours to capture intermittent arrhythmias.
5. Event Recorder: A portable device that captures ECG tracings during specific symptoms or events.
6. Electrophysiological Studies (EPS): Invasive tests to evaluate the electrical properties of the heart and induce arrhythmias for diagnosis and treatment planning.

Management of Arrhythmias

The management of arrhythmias involves the following approaches:

1. Pharmacological Therapy: Medications such as beta-blockers, calcium channel blockers, antiarrhythmics, and anticoagulants may be prescribed based on the underlying arrhythmia and patient characteristics.
2. Electrical Cardioversion: The delivery of a synchronized electrical shock to the heart to restore normal rhythm in certain arrhythmias.
3. Catheter Ablation: A minimally invasive procedure in which abnormal electrical pathways in the heart are destroyed using radiofrequency or cryotherapy.
4. Implantable Devices: Devices such as pacemakers, implantable cardioverter-defibrillators (ICDs), and cardiac resynchronization therapy (CRT) devices may be used for long-term management of specific arrhythmias.
5. Lifestyle Modification: Encouraging healthy habits such as regular exercise, smoking cessation, limiting alcohol and caffeine intake, and stress reduction.

Specific Arrhythmias

Atrial Fibrillation

• Most common sustained cardiac arrhythmia characterized by rapid, irregular atrial electrical activity.
• Risk factors include age, hypertension, heart failure, valvular heart disease, and hyperthyroidism.
• Symptoms may include palpitations, dyspnea, fatigue, and dizziness.
• Diagnosis confirmed by ECG showing absence of P waves and irregularly irregular ventricular response.
• Management involves rate control, anticoagulation therapy, and rhythm control if necessary.

Ventricular Tachycardia

• Defined as three or more consecutive ventricular beats at a rate exceeding 100 beats per minute.
• Can occur in structurally normal hearts (idiopathic) or in the presence of underlying heart disease.
• Symptoms range from palpitations to hemodynamic instability or sudden cardiac arrest.
• Diagnosis confirmed by ECG showing wide QRS complexes with a consistent morphology.
• Treatment may involve antiarrhythmic drugs, catheter ablation, or implantable cardioverter-defibrillator (ICD) placement.

Supraventricular Tachycardia

• Broad term encompassing various tachycardias originating above the ventricles (e.g., atrioventricular node, atria).
• Symptoms often include palpitations, anxiety, and lightheadedness.
• Diagnosis confirmed by ECG showing narrow QRS complexes with a regular rhythm.
• Vagal maneuvers and adenosine are often used for acute termination.
• Catheter ablation may be considered