Conduction and Arrythmias

FUNCTION AND CONDUCTION OF THE HEART

  • The heart serves as a vital organ for pumping blood throughout the body.

  • It is responsible for maintaining blood circulation, facilitating nutrient and oxygen transport, and removing carbon dioxide and waste products.

BLOOD FLOW AND HEART VALVES

  • Blood flow through the heart:

    • Superior/Inferior Vena Cava: Returns unoxygenated blood to the right atrium.

    • Tricuspid Valve: Blood flows from the right atrium to the right ventricle.

    • Pulmonic Valve: Blood exits the right ventricle into the pulmonary artery, which carries it to the lungs.

    • Pulmonary Vein: Returns oxygenated blood to the left atrium.

    • Mitral Valve: Blood flows from the left atrium to the left ventricle.

    • Aortic Valve: Blood exits the left ventricle into systemic circulation.

PULMONARY AND SYSTEMIC CIRCULATION

  • Pulmonary Circulation:

    • Characterized by low pressure.

    • Allows for gas exchange (oxygen and carbon dioxide exchange) in the lungs.

    • Involves the right side of the heart and pulmonary vessels.

    • Unique aspect: The pulmonary artery carries deoxygenated blood, while the pulmonary veins carry oxygenated blood.

  • Systemic Circulation:

    • Characterized by high pressure.

    • Transports oxygenated blood to all parts of the body.

    • Mean Arterial Pressure (MAP): ranges from 90-100 mmHg.

    • Involves the left side of the heart, aorta, and all tissue vessels.

    • Veins converge into the superior and inferior vena cava, which returns blood to the right atrium.

CARDIAC CONDUCTION

  • SA Node (Sinoatrial Node):

    • Acts as the pacemaker of the heart, initiating electrical impulses that set the rhythm for the heart.

  • AV Node (Atrioventricular Node):

    • Provides one-way communication from atria to ventricles, allowing for coordinated contraction.

  • Bundle of His:

    • A pathway through which impulse conduction slows before reaching ventricles.

  • Purkinje Fibers:

    • Responsible for conducting impulses throughout the ventricles, resulting in contraction.

  • Right and Left Bundle Branches:

    • Facilitate the distribution of electrical impulses to the respective ventricles.

  • Dysrhythmias/Arrhythmias:

    • Refers to abnormal heart rhythms that can arise from issues in conduction systems.

CARDIAC ACTION POTENTIALS

  • Depolarization:

    • Sodium ions (Na+) and calcium ions (Ca++) enter cardiac cells, reversing polarity from negative to positive.

    • This process initiates muscle contraction.

  • Repolarization:

    • Potassium ions (K+) exit the cell, aiding in the restoration of the membrane potential back to negative on the inside and positive on the outside.

  • Resting Potential:

    • The state when the membrane of an unexcited cell is polarized, ready to respond to the next impulse.

    • The role of sodium, potassium, and calcium ions as major electrical charge carriers in cardiac muscle cells is critical in this process.

ELECTROCARDIOGRAM

  • Electrocardiogram (ECG):

    • A recording of the electrical activity of the heart.

    • P Wave: Represents atrial depolarization (contraction of the atria).

    • QRS Complex: Represents ventricular depolarization (contraction of the ventricles).

    • T Wave: Corresponds to ventricular repolarization (relaxation of the ventricles).

    • The shape of these waves is determined by the direction in which impulses spread in relation to the placement of electrodes on the chest.

ARRHYTHMIAS

  • Defined as abnormal heart rhythms that can cause various concerns:

    • Tachyarrhythmias:

      • Rapid heart rates can reduce diastolic filling time, leading to decreased stroke volume, cardiac output, and myocardium perfusion.

      • Increases myocardium's oxygen demand.

    • Bradyarrhythmias:

      • Slow heart rates that can impair blood flow and reduce oxygen delivery to vital organs, particularly the brain.

    • Supraventricular Arrhythmias:

      • Originate above the ventricles and can have various causes and effects.

    • Ventricular Arrhythmias:

      • Originate in the ventricles and are typically more serious and life-threatening.

      • Include Ventricular Tachycardia (VT) and Ventricular Fibrillation.

ATRIOVENTRICULAR CONDUCTION

  • Refers to blockages in electrical conduction between the atria and ventricles:

    • First Degree AV Block:

      • Characterized by a prolonged PR interval (greater than 0.20 seconds) but with impulses still getting through.

      • Usually asymptomatic.

    • Second Degree AV Block:

      • Involves progressive lengthening of the PR interval; may require pacing for management.

    • Third Degree AV Block:

      • Complete block with no communication between atria and ventricles, necessitating a permanent pacemaker.

ATRIAL FIBRILLATION

  • A type of atrial arrhythmia that complicates normal impulse travel from the SA to the AV node.

  • Results in disorganized atrial contractions, often observed as an absence of P waves on an ECG.

  • Can lead to embolic strokes.

  • Treatment options include medications, anticoagulants, and ablation procedures.

VENTRICULAR ARRHYTHMIAS

  • Considered more dangerous compared to atrial arrhythmias due to their impact on the heart's pumping function:

    • Premature Ventricular Contractions (PVCs):

      • Occur when the ventricle generates a beat independently, leading to abnormal rhythms.

    • Ventricular Tachycardia (VT):

      • Characterized by the absence of both P and T waves and a rapid heart rate that can be hazardous.

VENTRICULAR FIBRILLATION

  • Involves rapid disorganized ventricular contractions resulting in a loss of effective pumping action.

  • Can lead to:

    • No cardiac output.

    • No pulse.

    • Cardiac arrest.

    • This condition is fatal if not corrected promptly.

  • Treatment option includes defibrillation to restore normal heart rhythm.

DIAGNOSTICS/TREATMENTS

  • Various methods and procedures to diagnose and treat cardiac conditions include:

    • Electrocardiogram (ECG): Used as a primary diagnostic tool to assess heart electrical activity.

    • Holter Monitoring/Implantable Loop Recorder: For prolonged monitoring of heart rhythms.

    • Exercise Stress Testing: Evaluates heart performance under stress conditions.

    • Electrophysiologic Studies: Assess electrical conduction system and arrhythmias.

    • Pacemaker: Device implanted to regulate heart rhythm.

    • Cardioversion: A procedure to restore normal heart rhythm using electrical shock.

    • Ablation: A technique to destroy areas of heart tissue that cause arrhythmia.

    • Surgical Intervention: May be necessary for complex arrhythmias or structural heart problems.

    • Medications: Used to manage heart rhythm, rate, and overall cardiac function.