Cardiac Conduction Disturbances

Conduction Disturbances

• Heart Anatomy: The heart contains the right coronary artery, the left coronary artery, and the anterior interventricular artery
• Conduction System: The SA node initiates the heartbeat (60-100 bpm), followed by the AV node (40-60 bpm), then the bundle of His, left bundle branch, right bundle branch, and finally the Purkinje fibers (20-40 bpm).

Cardiac Conduction Intervals

• PR Interval: 0.12-0.20 seconds. Measures time from atrial activation to ventricular activation
• QRS Interval: 0.06-0.12 seconds. Measures time from ventricular activation to ventricular depolarization
• QT Interval: Calculated interval, prolonged if >0.47 seconds. Measurement from the start of the QRS complex to the end of the T wave.

Analyzing Cardiac Rhythm

• Rate: Normal range is 60-100 bpm. Bradycardia is <60 and Tachycardia is over 100 bpm.
• Rhythm: Regular or irregular.
• P Waves: One P wave for each QRS. Assess for more or less P waves than QRS waves. P absence indicates no atrial activation.
• **PR Interval:**Normal is 0.12-0.20 seconds. Prolonged is >0.20 seconds. Represents the delay at the AV node.
• QRS Complex: Normal is 0.06-0.12 seconds. Prolonged is greater than 0.12 seconds. Measures ventricular depolarization time.
• QTc: Normal. Lengthened if over 0.47 seconds. Adjusted QT interval that takes into account heart rate.

Dysrhythmias

• Classification by origin: Sinus node, atrial, AV node, and ventricular dysrhythmias are classified by their origin in the heart. AV node blocks are a specific type of AV nodal disturbance.
• Atrial Dysrhythmias: Supraventricular tachycardia (SVT), atrial flutter, and atrial fibrillation (controlled vs uncontrolled).
• Supraventricular Tachycardia (SVT): Characterized by a rapid heart rate (over 150 bpm), regular rhythm, shortened PR interval, and sometimes shortened QRS. Causes can include anxiety, stimulants, and hyperthyroidism. Valsalva maneuver and adenosine can often treat SVT.
• Atrial Flutter: Characterized by a regular rhythm, absent P waves, and instead replaced by F waves, normal ventricular rate. Often related to heart and lung issues.
• Atrial Fibrillation (AF): Characterized by an irregular rhythm, absent P waves, irregular ventricular rate, normal PR interval, and sometimes normal QRS interval. AF can be controlled or uncontrolled, impacting the ventricles varying degrees.
• Ventricular Dysrhythmias: Ventricular tachycardia, Torsades de Pointes, and ventricular fibrillation.
• Ventricular Tachycardia: Characterized by a wide, bizarre QRS complexes, a fast heart rate, and a regular rhythm. Causes include electrolyte imbalance, drug toxicity, and ischemia. Treatment approach depends on whether the patient has a pulse.
• Torsades de Pointes: A type of polymorphic ventricular tachycardia. It's often associated with a prolonged QT interval. Treatment includes intravenous magnesium.
• Ventricular Fibrillation: Characterized by an irregular rhythm and absent P waves and ventricular contraction. Treatment includes CPR, defibrillation, and medications such as epinephrine and amiodarone.

AV Blocks

• First-degree AV block: Prolonged PR interval (> 0.20 seconds) with a regular rhythm. Causes include aging, CAD, and medications. No treatment is often needed.
• Second-degree AV block Type I (Mobitz I/Wenckebach): PR interval gradually lengthens until a P wave is not followed by a QRS complex. Can be caused by medications and CAD.
• Second-degree AV block Type II (Mobitz II): PR interval does not lengthen and there is a random absence of QRS complexes. This needs careful monitoring for complete block and possible permanent pacing.
• Third-degree AV block (Complete Heart Block): P waves and QRS complexes are completely independent. Causes often include CAD, MI, and other conditions. Usually requires pacemaker.

Pacemakers

• Temporary: Transcutaneous or transvenous. Deliver a pulse to the heart to help with bradycardia.
• Permanent: Epicardial. Implanted devices that help trigger the heartbeat if conduction is failing.

Other Lethal Arrhythmias

• Asystole: Absence of electrical activity and therefore a heartbeat.
• Pulseless Electrical Activity (PEA): Electrical activity is present, but there is no heartbeat. Requires immediate intervention.

This quiz explores the anatomy and physiology of the heart's conduction system, including the roles of different cardiac intervals and rhythms. Test your understanding of heart rate, rhythm, and the conduction pathways crucial for effective heart function.