All things ECG

Basics - ECG Leads

The standard EKG has 12 leads:

3 Standard Limb Leads

3 Augmented Limb Leads

6 Precordial Leads

The axis of a particular lead represents the viewpoint from which it looks at the heart.

Basics – precordial leads

Precordial leads

Standard Limb Leads

Lead I: • Left arm to right armLead II: • Left leg to right armLead III: • Left leg to left arm

Waveforms

P Wave. Caused by depolarization of the atria. With normal sinus rhythm, the P wave is upright in leads I,

II, aVF, V4, V5, and V6 and inverted in aVR.

QRS Complex. Represents ventricular depolarization

Q Wave. The first negative deflection of the QRS complex (not

always present and, if present, may be pathologic). To be significant, the Q wave should be > 25% of the QRS

complex. T Wave.

Caused by repolarization of the ventricles and follows the QRS complex

Normally upright in leads I, II, V3, V4, V5, and V6 and inverted in aVR

What do they mean?

ECG paper

1. Rate 2. Rhythm3. Axis4. Interval

How to read an ECG systematically

1. Rate- Rule of 300

Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate

Although fast, this method only works for regular rhythms.

Bradycardia: Heart rate < 50 beats/min Tachycardia: Heart rate > 100 beats/min

Abnormalities

What is the heart rate?

(300 / 6) = 50 bpm

www.uptodate.com

What is the heart rate?

(300 / 1.5) = 200 bpm

The Rule of 300

It may be easiest to memorize the following table:

# of big boxes

Rate

1 300

2 150

3 100

4 75

5 60

6 50

Sinus Rhythms Normal: Each QRS preceded by a P wave (which is

positive in II and negative in aVR) with a regular PR and RR interval and a rate between 60 and 100 beats/min

2. Rhythm

http://www.bem.fi/book/19/19.htm

Lead II : sinus arrhythmia in a healthy 26 year-old woman. Note the marked variation in the P-P intervals induced by respiration. Courtesy of Morton Arnsdorf, MD.http://www.uptodate.com/contents/image?imageKey=CARD/2987

Normal rhythm strip in lead II. The PR interval is 0.15 sec and the QRS duration is 0.08 sec. Both the P and T waves are upright. Courtesy of Morton Arnsdorf, MD.http://www.uptodate.com/contents/image?imageKey=CARD/2987

3. The QRS Axis

The QRS axis represents the net overall direction of the heart’s electrical activity.

Abnormalities of axis can hint at:Ventricular enlargementConduction blocks (i.e. hemiblocks)

The QRS Axis

By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.

-30° to -90° is referred to as a left axis deviation (LAD)

+90° to +180° is referred to as a right axis deviation (RAD)

Determining the Axis

Predominantly Positive

Predominantly Negative

Equiphasic

The Quadrant Approach1. Examine the QRS complex in leads I and aVF to

determine if they are predominantly positive or predominantly negative. The combination should place the axis into one of the 4 quadrants below.

The Quadrant Approach2. In the event that LAD is present, examine lead II to

determine if this deviation is pathologic. If the QRS in II is predominantly positive, the LAD is non-pathologic (in other words, the axis is normal). If it is predominantly negative, it is pathologic.

Quadrant Approach: Example 1

Negative in I, positive in aVF RAD

The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/

Quadrant Approach: Example 2

Positive in I, negative in aVF Predominantly positive in II

Normal Axis (non-pathologic LAD)

The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/

PR <0.2 sec, QRS <0.12 sec, QT <0.4 sec P wave

Always positive in leads I and II Always negative in lead aVR <3 small squares in duration <2.5 small squares in amplitude

QRS A normal QRS width should be less than 0.12 s.

ST segment Normally isoelectric

4. Intervals

What are these?

ST elevation

Normal T wave is asymmetrical First half having more gradual slope than the

second half Amplitude rarely exceeds 10 mm Abnormal T waves are symmetrical, tall,

peaked, biphasic or inverted As a rule T waves follows direction of main

QRS deflection Normal T wave is always negative in lead

aVR and positive in lead II

T waves

QT interval decreases when HR increases Should not be more than half of the interval

between adjacent R waves (R-R interval)

QT interval http://www.slideshare.net/cksheng74/tutorial-in-basic-ecg-for-medical-students

Acute anterior wall ST elevation MI (STEMI) Note the marked ST elevations and hyperacute T waves in the anterior/lateral leads, including V2-V5, I and aVL.

Acute transmural anterior wall myocardial infarction

Chronic anterior wall myocardial infarctionA chronic anterior wall infarction is diagnosed by the presence of initial deep and broad Q waves in any of the precordial leads; in this case they are present in leads V1 to V4.

http://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis?source=related_link#H18

ECG made easy page 138 (7th edn.) has list of all problems and what to expect on an ECG