Evaluating ST Segment Elevations

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Questions and Answers

What is the ST segment?

It is the interval between the end of ventricular depolarization (QRS complex) and the beginning of repolarization (T wave).

What does the ST segment represent?

The interval between the end of ventricular depolarization (QRS complex) and the beginning of repolarization (T wave).

What is a segment?

Areas of baseline between wave/complexes.

What is an interval?

Segments plus the preceding waves/complexes. Signup and view all the answers

What is the J-point?

The J point represents a change from the vertical QRS wave to the horizontal ST segment. Signup and view all the answers

To find the J-point, locate the end of the QRS complex and identify the point where it makes a sudden or sharp change in direction; the point in which the QRS ends and the direction changes is the ______.

J-point Signup and view all the answers

What should the ST segment be compared to, to determine elevation or depression?

The upper edge of the PR segment and the upper edge of the ST segment at the J point. Signup and view all the answers

Why is determining the location of the J point critical to the diagnosis of ST segment elevation?

It is an essential landmark for determining eligibility for fibrinolytic therapy in the setting of myocardial infarction. Signup and view all the answers

What is the TP segment?

The end of the T wave to the beginning of the P wave. Signup and view all the answers

What is another way to identify the ST segment?

Amount of elevation or depression, in mm, relative to the TP segment & morphology. Signup and view all the answers

What is one setback to measuring the ST segment with reference to the TP segment as opposed to the PR segment?

Atrial repolarization resulting in a large negative P wave can result in an inaccurate measurement of the ST segment elevation. Signup and view all the answers

What is a normal ST segment?

Usually isoelectric, but may vary from 0.5 mm below to 1 mm above baseline in limb leads. Signup and view all the answers

What are the ST segment morphologies?

Concave upward, convex upward, horizontal, down sloping, and up sloping. Signup and view all the answers

What is a nonspecific ST segment?

Slight (< 1mm) ST segment depression or elevation. Signup and view all the answers

What is ST segment elevation?

It should be measured at the Y point, at 40 ms from the J point. Signup and view all the answers

When the acute ischemia is transmural, what happens to the ST vector?

The ST vector usually shifts in the direction of the outer (epicardial) layers, producing ST elevations. Signup and view all the answers

Profound ST elevation or depression in multiple leads usually indicates what?

Very severe ischemia. Signup and view all the answers

How is the division of acute myocardial infarction into ST-segment elevation and non-ST elevation types useful?

The efficacy of acute reperfusion therapy is limited to the ST-segment elevation group. Signup and view all the answers

When ischemic ST elevations occur as the earliest sign of acute infarction, they typically are followed by what?

Evolving T-wave inversions and often by Q waves occurring in the same lead distribution. Signup and view all the answers

How do ST segment elevations associated with reversible transmural ischemia differ from those of acute infarction?

Coronary vasospasm may cause transient ST-segment elevations without development of Q waves. Signup and view all the answers

Study Notes

ST Segment Overview

The ST segment is the interval between the end of ventricular depolarization (QRS complex) and the beginning of repolarization (T wave).
It is represented as a horizontal line along the baseline of the PR or TP intervals.

Segments and Intervals

A segment refers to areas of baseline between waves/complexes.
An interval includes segments plus the preceding waves/complexes.

J-Point

The J-point marks the transition from the QRS complex to the ST segment, indicating the end of ventricular depolarization.
Critical for identifying ST segment changes, essential in diagnosing conditions like myocardial infarction (MI).

Measuring ST Segment Changes

Normal ST segment comparison is done from the PR segment to the ST segment at the J-point.
ST segment elevation or depression indicates pathophysiological changes.

Importance of Accurate Measurement

Accurate location of the J-point is crucial, as the criteria for elevation is 1 mm, impacting treatment eligibility for fibrinolytic therapy during MI.

TP Segment

The TP segment is the interval from the end of the T wave to the beginning of the P wave.

ST Segment Identification

The amount of ST segment elevation or depression is assessed relative to the TP segment and its morphology.
Relying on the TP segment may lead to inaccuracies, particularly with negative P waves.

Normal ST Segment Characteristics

Typically isoelectric, can range from 0.5 mm below to 1 mm above baseline in limb leads, and up to 3 mm elevation in precordial leads during early repolarization.

ST Segment Morphologies

Different morphologies include concave upward, convex upward, horizontal, downsloping, and upsloping patterns.

Non-Specific Changes

A nonspecific ST segment may show slight changes (< 1 mm) and does not indicate acute ischemia.

Measuring ST Elevation

ST elevation should be measured at the Y point, specifically 40 ms from the J-point (J40).

Effects of Transmural Ischemia

In cases of transmural ischemia, the ST vector shifts toward the epicardial layers, often resulting in ST elevations and hyperacute T waves.

Clinical Implications

Profound ST elevation or depression across multiple leads typically suggests severe ischemia.
Acute myocardial infarction is divided into ST-segment elevation and non-ST elevation types, guiding reperfusion therapy decisions.

Evolving ST Changes

ST elevations occurring as acute infarction signs are followed by T-wave inversions and potential Q waves evolving over hours to days.

Reversible Ischemia vs. Acute Infarction

ST segment elevations due to reversible transmural ischemia (e.g., coronary vasospasm) may resolve quickly and do not always lead to Q wave development.

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Description

This flashcard quiz focuses on understanding the ST segment in electrocardiograms (ECGs). It covers definitions and concepts related to ST segment elevations, which are crucial for diagnosing cardiac conditions. Test your knowledge on this important aspect of cardiac physiology.