ECG Logic

  Adenosine: Mechanism of Action and Its Role in Atrial Flutter – Including Conversion to Atrial Fibrillation with AV Block --- Introduction Adenosine is a naturally occurring purine nucleoside widely used in cardiology for the diagnosis and termination of supraventricular tachycardias (SVTs). While it is highly effective in AV node–dependent tachycardias such as AVNRT and AVRT, its role in atrial flutter is primarily diagnostic rather than therapeutic. Understanding its electrophysiologic effects is crucial, especially because adenosine can occasionally convert atrial flutter into atrial fibrillation with transient AV block — a phenomenon that can alarm clinicians if not anticipated. --- Cellular and Electrophysiologic Mechanism of Adenosine Adenosine acts via specific G-protein–coupled receptors: A1 receptors (cardiac effects – most important clinically) A2A receptors (coronary vasodilation) A2B and A3 (less relevant in arrhythmia management) 1. Action on the AV Node In the heart...

Post Fascicular Ventricular Tachycardia (Belhassen VT) Introduction Post fascicular ventricular tachycardia (PFVT), commonly called fascicular VT or Belhassen VT, is a distinct form of idiopathic left ventricular tachycardia. It typically occurs in young patients without structural heart disease and is characteristically verapamil sensitive. Unlike scar-related VT seen in structural cardiomyopathy, PFVT originates from the specialized conduction system of the left ventricle—most often the posterior fascicle of the left bundle branch. --- Historical Background This arrhythmia was first clearly described and treated successfully with verapamil by Hein J. J. Wellens and later characterized by Menashe Belhassen, hence the term Belhassen tachycardia. --- Epidemiology Typically affects young males (15–40 years) Structurally normal heart Accounts for 10–15% of idiopathic VTs Often misdiagnosed as SVT with aberrancy --- Mechanism PFVT is a re-entry tachycardia involving the Purkinje system. Mo...

PR Interval on ECG – Measurement and Clinical Significance How to Measure PR Interval on ECG? Definition: PR interval is measured from the beginning of the P wave to the beginning of the QRS complex. Step-by-step method: 1. Use Lead II (usually best P wave visibility). 2. Identify: Onset of P wave Onset of QRS complex (first deflection – Q or R) 3. Count small boxes between them. ECG Paper Speed: 25 mm/s 1 small box = 0.04 sec (40 ms) 1 large box = 0.20 sec (200 ms) Normal PR interval: 120–200 ms (3–5 small boxes) Measure in multiple beats and take the average if rhythm is irregular. --- What Does PR Interval Represent? Atrial depolarization AV nodal conduction His bundle conduction It reflects AV nodal delay. --- PR Interval Abnormalities 1. Prolonged PR Interval (>200 ms) Diagnosis: First-degree AV block Causes: Increased vagal tone Drugs (β-blockers, CCBs, digoxin) Ischemia (especially inferior MI) Myocarditis Electrolyte imbalance Clinical significance: Usually benign May progre...