Chapter 1: The Basics

Introduction to EKG and Cardiac Electrophysiology

The electrocardiogram (EKG or ECG) is a diagnostic tool that records the electrical activity of the heart. It is essential for evaluating cardiac rhythm, conduction, and detecting abnormalities.

• EKG Function: Records electrical signals, not cardiac output or blood pressure.

• Key Ions: Sodium (Na+) and Potassium (K+) are crucial for cardiac depolarization and repolarization.

• Resting Membrane Potential: Maintained by potassium efflux; typical value is -90 mV.

• Automaticity: The ability of cardiac cells to self-depolarize and generate impulses without external stimulation.

• Standard EKG Paper: One small square = 0.04 seconds; one large square = 0.20 seconds.

• Standard Recording Speed: 25 mm/sec.

• Amplitude: One large box vertically = 0.5 mV; 10 mm = 1 mV.

• Electrodes: Placed on the body surface to detect electrical potentials.

• Artifact: EKG artifact can be caused by muscle tremor, poor electrode contact, or electrical interference.

Key Properties of Cardiac Cells

• Excitability: Ability to respond to stimuli.

• Conductivity: Ability to transmit impulses.

• Contractility: Ability to contract.

• Automaticity: Ability to generate impulses spontaneously.

EKG Components and Interpretation

• P wave: Atrial depolarization.

• QRS complex: Ventricular depolarization.

• T wave: Ventricular repolarization.

• PR interval: Time from onset of atrial depolarization to onset of ventricular depolarization.

• ST segment: Time between ventricular depolarization and repolarization.

• QT interval: Total time for ventricular depolarization and repolarization.

Example Table: EKG Wave Components

Important Formulas

• Heart Rate Calculation:

• Standard Calibration:

Chapter 2: The Cells of the Heart

Types of Cardiac Cells

The heart contains three major types of cells: pacemaker cells, electrical conducting cells, and myocardial cells. Each plays a distinct role in cardiac function.

• Pacemaker Cells: Located in the sinoatrial (SA) node, these cells possess automaticity and initiate the heartbeat through spontaneous depolarization.

• Electrical Conducting Cells: Form pathways such as the His bundle and Purkinje network, rapidly transmit impulses throughout the heart.

• Myocardial Cells: Responsible for contraction and pumping blood; do not initiate impulses but respond to them.

Key Points

• Automaticity: Pacemaker cells can depolarize spontaneously.

• Conduction System: Includes SA node, AV node, bundle of His, bundle branches, and Purkinje fibers.

• Resting Membrane Potential: Maintained by sodium-potassium pump ().

Example Table: Cardiac Cell Types and Functions

Chapter 3: The Parts of the QRS Complex

QRS Complex Overview

The QRS complex represents ventricular depolarization and is a critical component of the EKG. Its duration, amplitude, and morphology provide information about ventricular conduction and possible pathology.

• Q wave: Initial negative deflection; may indicate septal depolarization.

• R wave: First positive deflection; represents main ventricular depolarization.

• S wave: Negative deflection following the R wave.

• Normal QRS Duration:

• Prolonged QRS: suggests bundle branch block or ventricular origin.

Clinical Significance

• Wide QRS: Indicates abnormal ventricular conduction (e.g., bundle branch block).

• Narrow QRS: Suggests supraventricular origin.

• Pathologic Q waves: May indicate previous myocardial infarction.

Chapter 4: The Waves and Straight Lines of the EKG

EKG Waveforms and Segments

Each EKG waveform and segment corresponds to a specific phase of cardiac electrical activity.

• P wave: Atrial depolarization.

• QRS complex: Ventricular depolarization.

• T wave: Ventricular repolarization; normally upright and asymmetric.

• U wave: May represent repolarization of the Purkinje fibers; often absent.

• PR interval: ; reflects AV nodal conduction.

• ST segment: Should be isoelectric; elevation or depression indicates pathology.

• QT interval: Varies with heart rate; prolonged QT increases risk of arrhythmias.

Example Table: Normal EKG Intervals

Chapter 5: The 12 Views of the Heart

EKG Leads and Cardiac Views

The standard 12-lead EKG provides multiple perspectives of the heart's electrical activity, aiding in localization of pathology.

• Limb Leads: I, II, III, aVR, aVL, aVF

• Precordial Leads: V1-V6

• Lead Placement: Limb leads on arms and legs; precordial leads on chest.

• Axis Determination: Based on limb leads; helps identify deviations.

Example Table: EKG Lead Views

Additional info:

Some context and terminology have been expanded for clarity and completeness, including definitions, normal ranges, and clinical applications. The notes cover foundational concepts in cardiac anatomy, physiology, and EKG interpretation, suitable for college-level Anatomy & Physiology students.