EKG Basics | How to Read & Interpret EKGs: Updated Lecture

The Physics Behind Electrical Signals in Myocardium Understanding EKGs begins with grasping the physics and physiology behind them. When a section of ventricular myocardium is stimulated, it undergoes depolarization as positive ions flood into cells, creating an electrical signal that propagates through gap junctions. This flow of positive charges towards a positive electrode results in upward deflections on an EKG reading; conversely, if the charge moves away from the electrode, downward deflections occur.

Deflection Patterns: Understanding Upward Deflections and Isoelectric Lines When negative charges move toward a negative electrode during repolarization phases or when there’s no net movement of electrical activity (perpendicular to lead axes), this can also produce upward deflections or flat lines respectively. An isoelectric line indicates either equal amplitude movements canceling each other out or lack of significant electrical activity at that moment.

Mapping Atrial Depolarization Using Lead II Focusing on Lead II for mapping EKG waveforms reveals how atrial depolarization initiates within the SA node located near where blood enters from veins. The action potentials spread throughout both atria towards the AV node below them while generating mean vectors pointing downwards and leftward—indicating directionality crucial for interpreting readings accurately.

The isoelectric line on an EKG indicates a lack of net electrical activity or that the activity is perpendicular to the lead's axis. This flat line occurs after the P wave, where depolarization from the SA node reaches and activates the AV node. The AV node slows down conduction for about 0.1 seconds before transmitting signals to the ventricles, resulting in no directional deflection during this period. Understanding this segment involves distinguishing between two key components: PR segment (the flat portion) and PR interval (from start of P wave to end of PR segment).

Understanding Cardiac Electrical Activity The P wave represents the SA node firing and generating a mean vector towards the AV node, which holds electrical activity before conducting it down to the bundle of His. The left bundle branch is primarily responsible for depolarizing the interventricular septum, creating small vectors that point rightward and slightly upward due to heart orientation. This results in a net depolarization vector moving away from lead II's positive electrode, causing a negative deflection known as the Q wave.

Significance of Normal vs Pathological Q Waves The Q wave signifies septal depolarization; its normal presence on an EKG indicates physiological function. However, if Q waves become excessively wide or deep, they may be classified as pathological signals requiring further investigation. Recognizing these variations is crucial since not all 12-lead EKGs will display visible Q waves under standard conditions.

Understanding Upward Deflection: Electrical Activity Dynamics The upward deflection in an EKG indicates the movement of electrical activity from the SA node, which sends a depolarization vector downward and to the left towards the AV node. This process involves atrial depolarization followed by conduction through bundle branches, particularly affecting how vectors are generated as they move toward both ventricles. The thicker left ventricle generates stronger action potentials than the right ventricle due to its greater myocardium mass, resulting in more intense positive deflections on an EKG.

Mean QRS Vector and Its Significance The mean QRS vector represents a combination of electrical activities from both ventricles; it leans towards the larger left ventricular vector because it is significantly thicker than that of the right ventricle. When this net flow of positive charge moves toward lead II's positive electrode, it results in a notable upward deflection known as R wave on an EKG tracing. Thus, understanding these vectors helps interpret heart function accurately during electrocardiography.

Understanding Atrial and Ventricular Depolarization The PR interval consists of the P wave and the PR segment, representing atrial depolarization initiated by the SA node. The AV node briefly holds this electrical activity before transmitting it down through the bundle branches to initiate ventricular depolarization. This process generates distinct waves: Q for septal depolarization, R for left ventricle dominance in vector direction, and S as a downward deflection indicating further ventricular activation.

Significance of ST Segment Stability The ST segment appears isoelectric on an EKG when all myocardial tissue has fully depolarized but not yet repolarized. During this phase, there’s no net movement of charge resulting in a flat line on the graph; it's crucial for identifying potential pathologies later discussed in medical contexts.

Ventricular Repolarization Dynamics Repolarization begins after full ventricular contraction during which positive charges inside cells revert back to their resting negative state. As each section repolarizes sequentially from inner myocardium outward towards electrodes, it creates vectors that lead to an upward T wave deflection indicative of ventricles returning to rest post-contraction.

Understanding the 12 Leads in EKG The EKG consists of 12 leads, with Lead II being the most commonly used for rhythm strips. These include three limb leads (I, II, III), three augmented unipolar limb leads (aVR, aVL, aVF), and six precordial or chest leads (V1-V6). Understanding each lead's orientation is crucial as they provide different views of heart activity through vector analysis.

Einthoven’s Triangle Explained Einthoven’s triangle illustrates how electrodes are placed on the body to create axes for Leads I-III. Each lead has specific positive and negative electrode placements that define its axis relative to heart position: Lead I looks horizontally at the left ventricle; Lead II diagonally from right arm to left leg; and Lead III from left arm downwards towards left leg.

Waveform Consistency Across Primary Leads Leads I-III generally produce similar waveforms due to their directional similarities toward electrical activity in various parts of the heart. The P wave typically shows an upward deflection while QRS complexes vary slightly based on their respective vectors but maintain overall consistency across these primary limbs' readings.

Insights into Augmented Unipolar Limb Leads 'Augmented unipolar limb leads' enhance understanding by using one positive electrode against two negatives creating unique perspectives without complex physics involved. For instance, aVR focuses on right-sided cardiac activities while maintaining opposite waveform characteristics compared to standard Limb Leas like II which serves as our reference point for normal patterns

Differentiating Views Among Augmented Unipolar Leaders 'AVR provides insights about interventricular septum function alongside aspects related specifically towards right ventricular performance whereas AVL mirrors high lateral wall observations akin those seen via traditional Limbs leading us back again confirming consistent interpretations between them all except AVR which stands apart distinctly showcasing differing results altogether.'

Importance and Placement of Precordial Leads Precordial leads are crucial in ECG analysis, providing insights into cardiac pathology. These unipolar leads are placed on the chest at specific locations: V1 at the right fourth intercostal space near the sternal angle, V2 to the left fourth intercostal space parasternal line, and others extending across various positions up to V6 in mid-axillary line. They capture electrical activity from a horizontal plane of heart anatomy.

R Wave Progression Across Precordials Understanding R wave progression is essential for interpreting precordial lead data. As you move from V1 to V6, R waves should increase due to stronger depolarization signals primarily originating from the left ventricle while S waves decrease as they indicate movement away from positive electrodes. This ratio shift provides critical information about ventricular health.

Interpreting Heart Regions via Lead Activity The relationship between R and S wave amplitudes reveals significant details regarding heart function; typically less than 1 for early leads (V1-V3) but greater than 1 for later ones (V5-V6). The first three precordial leads focus mainly on right ventricular activity while transitioning through anterior wall representation before reaching lateral wall assessment with higher numbers like AVL contributing additional context during ST elevation scenarios.

'STEMI' Detection Through Lead Analysis 'STEMI' detection relies heavily on understanding which portions of myocardium each lead represents—right ventricle by V1-V3; basal septum also noted here alongside AVR readings; anterior walls covered by both sides leading towards central areas represented predominantly by middle numbered channels such as AVF or AVL when assessing lateral aspects effectively too!