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 arm Lead II: Left leg to right arm Lead III: Left leg to left arm

Waveforms

What do they mean? P Wave. QRS Complex. Q Wave. T 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

ECG paper

How to read an ECG systematically Rate Rhythm Axis Interval

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.

Abnormalities Bradycardia: Heart rate < 50 beats/min Tachycardia:

What is the heart rate? www.uptodate.com (300 / 6) = 50 bpm

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

2. Rhythm 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

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

Lead II : sinus arrhythmia in a healthy 26 year-old woman 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 enlargement Conduction 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 Approach 1. 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 Approach 2. 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 The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/ Negative in I, positive in aVF  RAD

Quadrant Approach: Example 2 The Alan E. Lindsay ECG Learning Center http://medstat.med.utah.edu/kw/ecg/ Positive in I, negative in aVF  Predominantly positive in II  Normal Axis (non-pathologic LAD)

4. Intervals 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

What are these? ST elevation

T waves 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

QT interval QT interval decreases when HR increases http://www.slideshare.net/cksheng74/tutorial-in-basic-ecg-for-medical-students QT interval decreases when HR increases Should not be more than half of the interval between adjacent R waves (R-R interval)

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 A 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. Chronic anterior wall myocardial infarction

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