MASTER ECG/EKG INTERPRETATION: A Systematic Approach for 12 Lead ECG/EKGs

Systematic approach to interpreting a 12-lead EKG for mastery.

Understanding EKG Waveforms EKG waveforms consist of the P wave, PR segment, QRS complex, ST segment, and T wave. The P wave represents atrial depolarization from the SA node; the PR segment indicates AV node depolarization; and combining them gives us the PR interval. The QRS complex signifies ventricular depolarization followed by the ST segment representing still ventricular depolarization with no net movement of electrical activity. Finally, we have the T wave indicating ventricular repolarization.

Electrodes and Leads in EKGs The electrical activity of different parts of the heart is detected using electrodes placed on specific leads: 2-3-AVF for inferior part (right/left ventricle), 1-AVL-V5-V6 for lateral wall (left ventricle), V1-V2-AVR for right ventricle, and V1 to V4 for anterior/septal portion. There are a total of 12 leads used to determine electrical activity in various planes including three bipolar limb leads (I-II-III), three augmented unipolar limb leads (AVF-AVL-AVR) ,and six precordial chest leads(V1,V2,V3,V4,V5,andV6).

Determining Rate and Rhythm on a 12-Lead EKG In this chapter, we learn how to determine the rate and rhythm of a 12-lead EKG. We use methods like the box method or r waves times six to calculate the heart rate. Additionally, we look at the regularity of intervals and QRS complex width to identify bradycardia or tachycardia.

Systematic Approach for Narrow Regular Tachycardias We discuss a systematic approach for identifying narrow regular tachycardias using differential diagnosis techniques such as sinus tachycardia, atrial flutter with variable block, multifocal atrial tachycardia, SVT with bundle branch block, anti-dromic WPW syndrome; wide regular tacycardias including V-tac until proven otherwise; fast irregular rhythms with wide QRS indicating polymorphic V-tac or AFib with Wolf Parkinson's White Syndrome.

Understanding ST Segment Elevation The video discusses the importance of focusing on ST segment elevation in a 12-lead EKG to determine if there is any ischemia or infarction. It explains how to measure and classify ST segment elevation, emphasizing that it does not always indicate an MI. The potential differentials for ST segment elevation are highlighted, including benign early repolarization, pericarditis, vasospasm, pulmonary embolism, left ventricular hypertrophy among others.

Significance of ST Segment Depression This section covers three types of st segment depression: down sloping, horizontal and up sloping. It emphasizes the measurement criteria for identifying st depression and its implications as a sign of ischemia. Additionally,it highlights specific scenarios such as horizontal st depression being concerning signs of ischemia,and upsloping st depression indicating proximal LAD occlusion.The chapter also touches upon other conditions associated with St depressions like posterior MI,left bundle branch blocks,left ventricular hypertrophy,digoxin toxicity,j waves in hypothermia,hypocalcemia,and bragata syndrome.

T Wave Abnormalities Understanding the significance of T wave abnormalities in EKG interpretation. T waves can indicate arrhythmias, ischemia, and infarction which are life-threatening conditions. Specifically focusing on t wave inversions as a sign of impending inferior wall MI.

Different Types of T Waves Exploring various types of abnormal t waves including hyperacute, biphasic, flat, and peak t waves. Each type indicates different conditions such as early STEMI or electrolyte imbalances like hyperkalemia.

QRS Complex and Abnormalities The QRS complex is crucial for detecting arrhythmias, ischemia, and infarction. Wide QRS complexes can indicate bundle branch blocks, hyperkalemia, v-tachycardia, WPW syndrome or pacemaker rhythms. Pathological q waves in V1-V3 may signal acute MI or old ischemic events. Low voltage QRS complexes could suggest pericardial effusion or heart failure.

Bundle Branch Blocks Identification Left bundle branch block shows a wide 'M' shaped QRS in V5-V6 with deep S wave in V1-V2; right bundle branch block exhibits an RSR' pattern in V1-V2 and slurred S wave in V5-6. Pathological q waves should not be seen in particular areas on the EKG as they signify ischemia or old MI.

R Wave Progression and Hypertrophy Indicators 'Poor r wave progression' from v1 to v6 suggests anterior MI; dominant r wave (v1-v3) along with ST depression indicates posterior MI; LVH indicated by adding R+S heights >35mm (V5/V6 +V!/+V2); RVH indicated by adding R+S heights >10mm(VI+II &> 35).

The QT interval is important to assess for abnormalities, especially if it's prolonged. A prolonged QT interval can lead to a deadly arrhythmia called torsades de pointes, which presents as polymorphic ventricular tachycardia. Medications like anti-arrhythmics, antibiotics, antipsychotics, antidepressants, and antiemetics can affect the QT interval and should be discontinued if necessary. Electrolyte abnormalities such as low potassium or magnesium levels should be corrected to fix the QT interval. Ischemia from myocardial infarction is also a concern when dealing with a prolonged QT interval.

The systematic approach involves assessing the rate, rhythm, ST segment elevation/depression, T wave abnormalities, QRS wave abnormalities, and QT interval. Focus on identifying signs of atrial enlargement such as right atrial enlargement indicated by a P wave greater than 2.5mm in lead II or a biphasic P wave in V1. Left atrial enlargement is indicated by a bifid P wave with camel hump >0.04 seconds in lead II and biphasic P waves in V1.

Understanding Cardiac Axis The cardiac axis is determined by the R wave in lead I and AVF. If both have positive deflections, it's normal; if lead I is up and AVF down, check lead II for confirmation. Left axis deviation occurs when there's an upright R wave in lead I and a downward S wave in AVF with negative deflection in Lead II.

Abnormalities of Cardiac Axis Left axis deviation can be caused by left bundle branch block, LVH or hyperkalemia. Right axis deviation happens when there's a downward S wave in Lead I and upward R wave in AVF without checking Lead II. Extreme right-axis deviation may result from thick right ventricle, VTAC origin on the left side of heart or severe obesity pushing the diaphragm up.