Intro to EKG Interpretation - QRST Changes

Summary

This video provides a comprehensive guide to understanding QRS-T wave abnormalities on an ECG, focusing on the distinction between pathologic and non-pathologic Q waves, R-wave progression, and common ST segment and T-wave abnormalities. It explores the causes behind these changes, including myocardial infarctions, conduction abnormalities, and other rare conditions. The video emphasizes the importance of clinical context in diagnosing ECG findings, clarifying that morphology alone is not always a definitive indicator of pathology. Key abnormalities discussed include ST elevation patterns, T-wave inversions, low voltage, and electrical alternans, making it an essential resource for interpreting ECGs.

Takeaways

• 😀 Q waves can be non-pathologic due to left-to-right depolarization of the septum, often seen as small deflections in most leads.
• 😀 A pathologic Q wave is identified by a duration of 30+ milliseconds, presence in leads V1-V3, or depth exceeding 1/3 or 1/4 of the R-wave height.
• 😀 Common ideologies of pathologic Q waves include previous myocardial infarctions (MI), conduction abnormalities, and infiltrative diseases like amyloidosis.
• 😀 R-wave progression refers to the gradual increase of the R to S ratio across the precordium, with delayed or absent progression linked to conditions like anterior MI or COPD.
• 😀 ST segment elevation can be either concave (smiley face) or convex (frowny face), with the latter being more indicative of acute MI.
• 😀 The presence of ST elevation is a critical diagnostic feature for ST-elevation myocardial infarction (STEMI), but early repolarization can present similarly and requires careful interpretation.
• 😀 ST depression can be horizontal, downsloping, or upsloping, with potential causes including ischemia, infarction, tachycardia, and electrolyte imbalances.
• 😀 T-wave abnormalities include inversion (normal in some leads), flattening, or peaking, with conditions such as hypokalemia, myocardial infarction, and hypothyroidism being potential causes.
• 😀 Low voltage in EKG waveforms is defined by reduced amplitude in all limb leads (<5 mm) and/or precordial leads (<10 mm), associated with conditions like obesity, COPD, or pericardial effusions.
• 😀 Electrical alternans, characterized by beat-to-beat variations in waveform amplitude, is a significant indicator of a large pericardial effusion, though not necessarily indicative of tamponade.

Q & A

What are septal Q waves and why are they considered non-pathologic?

Septal Q waves are small downward deflections seen in the early part of the QRS complex in most leads. They are due to the left-to-right depolarization of the septum, which is a normal process and is not a cause for concern in most individuals.

What is a pathologic Q wave, and what are its defining characteristics?

A pathologic Q wave is a significant downward deflection in the QRS complex, often indicating underlying cardiac pathology. It is characterized by a duration of 30 milliseconds or more, a presence in leads V1, V2, or V3, or a depth that exceeds 1/3 or 1/4 of the R-wave height.

Why is the presence of a Q wave in lead V1 controversial?

The presence of a Q wave in lead V1 is debated because some sources consider it normal, while others classify it as potentially indicative of pathology. It may be linked to conduction abnormalities but does not necessarily point to a prior myocardial infarction (MI).

What are some common causes of pathologic Q waves aside from myocardial infarction?

Pathologic Q waves can also be caused by left bundle branch block, left anterior fascicular block, right ventricular hypertrophy, infiltrative diseases (such as amyloidosis), and conditions like myocarditis and myocardial contusion.

What does R-wave progression refer to in an EKG?

R-wave progression refers to the gradual increase in the R-to-S ratio across the precordial leads (V1 to V6). This reflects the normal transition from a negative to a positive deflection as depolarization moves through the ventricles.

What is poor R-wave progression, and what are its causes?

Poor R-wave progression refers to an abnormal delay or absence of the typical increase in R-wave amplitude across the precordial leads. It can be caused by conditions like an old or subacute anterior MI, left ventricular hypertrophy (LVH), right ventricular hypertrophy (RVH), or misplacement of the electrodes.

What is reverse R-wave progression, and when might it be seen?

Reverse R-wave progression occurs when the maximal R-to-S ratio is seen in V1 or V2, which is atypical. It may be seen in conditions like right bundle branch block, certain subtypes of RVH, or dextrocardia.

What are the two major morphologies of ST-segment elevation?

The two major morphologies of ST-segment elevation are concave upwards and convex upwards. Concave ST elevation is commonly associated with early repolarization, while convex ST elevation, often described as 'tombstoning,' is typically indicative of an acute myocardial infarction (MI).

How do you differentiate between benign and dangerous ST elevation based on morphology?

Concave upward ST elevation is generally considered benign and often seen in early repolarization, while convex upward (tombstone) morphology is more indicative of a large acute MI. However, clinical context is more important than morphology alone when assessing ST elevation.

What are some causes of ST depression in EKG, and how is it classified?

ST depression can be classified into three morphologic subtypes: horizontal, downsloping, and upsloping. Common causes include myocardial ischemia, tachycardia, hypokalemia, conduction system disease, and ventricular hypertrophy. The 'strain pattern' is a specific form of ST depression seen in certain hypertrophy cases.

What does low voltage in an EKG indicate, and what are some potential causes?

Low voltage in an EKG refers to QRS amplitudes less than 5 mm in the limb leads or less than 10 mm in the precordial leads. Causes include obesity, COPD, pericardial or pleural effusion, myocardial infiltration, and hypothyroidism.

What is electrical alternans, and what is its most significant cause?

Electrical alternans refers to beat-to-beat variations in the appearance of waveforms, such as a tall R-wave alternating with a short one. It is most commonly caused by a large pericardial effusion, where the heart rocks back and forth within a distended pericardial sac.