EKG Overview

Heart Walls Inferior Wall Septal Wall Anterior Wall Lateral Wall Posterior Wall

Inferior Wall II, III, aVF I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 View from Left Leg  inferior wall of left ventricle I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Septal Wall V1, V2 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 Along sternal borders Look through right ventricle & see septal wall I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Anterior Wall V3, V4 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 Left anterior chest  electrode on anterior chest I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Lateral Wall V5 and V6 I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 View from Left Arm  lateral wall of left ventricle I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Lateral Wall I and aVL I II III aVR aVL aVF V1 V2 V3 V4 V5 V6 View from Left Arm  lateral wall of left ventricle I II III aVR aVL aVF V1 V2 V3 V4 V5 V6

Key Principles of Electrocardiography There are 12 leads. The six that reflect electrical activity in the fontal plane are I, II, III, AVL, AVR and AVF. The six reflecting the horizontal plane are V1 through V6.

Summary of EKG Leads In summary, the 12 standard leads are: Limb leads I, from the right arm (-) toward the left arm (+) II, from the right arm toward the left leg III, from the left arm toward the left leg Augmented Leads aVR, augmented lead toward the right (arm) aVL, augmented lead toward the left (arm) aVF, augmented lead toward the foot

Summary of EKG Leads In summary, the 12 standard leads are: Chest Leads V1 through V6, starting over the right atrium with V1, and placed in a semi-circle of positions leftwards, to the left side of the left ventricle. V1 and V2, on the right and left sides respectively, are placed just off the sternum at the 4th intercostal spaces (the space between the 4th and 5th ribs, which can be felt through the skin) and the others travel around to V6 under the armpit, as shown in the diagram.

Summary of EKG Leads

12 Lead Paper and Measurements At one end of each ECG strip there is usually a step-like structure called a calibration box. The standard box is 10 mm high and 0.20 seconds wide. The calibration box is there to confirm that the ECG conforms to the standard format.

12 Lead Paper and Measurements The easiest way to calculate the rate is to use the method of separated boxes. Find a QRS complex that starts on a thick line. The best is to use the tip of the tallest wave on the QRS complex- R wave. This will be a starting point. As a second step, find the next QRS complex or any other spot- your end point. Then just count the thick lines in between the two spots, and calculate the rate from memorized numbers 300, 150, 100, 75, 60, 50, where each number represents one of the previous rates.

12 Lead Paper and Measurements

12 Lead Paper and Measurements

EKG Complex: PQRSTU

12 Lead EKG Workshop If any acute changes are present. One of the most important reasons for obtaining an ECG is to help evaluate the patient who presents with new-onset chest pain.  By doing so we hope to determine: If any acute changes are present. If there is evidence of prior infarction.

12 Lead EKG Workshop Specifically, we want to determine if the patient being evaluated is acutely infarcting or ischemic. If so, what area of the heart is involved, how extensive is the involvement, are other abnormalities present (i.e., AV block, conduction defects, arrhythmias) and most importantly, is the patient a candidate for acute intervention (i.e., with thrombolytic therapy or angioplasty)?

Acute Infarction: What are the Changes? There are 4 principal ECG indicators of acute infarction: ST segment elevation T wave inversion Development of Q waves Reciprocal ST segment depression.

Acute Infarction: What are the Changes? A and B show a normal QRS complex before any changes develop.   

Acute Infarction: What are the Changes? Picture C shows the "hyperacute" stage, which is the earliest change of Acute MI, in which the T wave becomes broader and peaks (almost as if "trying" to lift the ST segment).  This change may be subtle (and easy to miss!); it usually is short-lived.    

Acute Infarction: What are the Changes? Picture D shows conventional ST elevation follows (with ST coving/"frowny" shape) and developing Q waves.

Acute Infarction: What are the Changes? Picture E and F show Q waves becoming bigger, ST elevation is maximal, and T wave inversion begins. T waves evolve as ST segments return to baseline (in F).

Acute Infarction: What are the Changes? Picture G shows ST-T wave abnormalities resolving (or nearly resolving) but there is persistence of Q waves.

KEY Points regarding the ECG with Acute MI: Not all patients with Acute MI develop ECG changes.  As many as 1/3 do not develop changes, especially if MI occurs in electrically silent areas of the heart. The A thru F sequence in the figure above represents the "typical" evolution of Acute MI. Variations on this theme are common (i.e., ST depression or T wave inversion may be the only change, Q waves don't always develop, Q waves sometimes resolve with time, etc.).

Rhythm Identification: P Waves Are there visible P waves? Does a QRS follow EVERY P wave? If not, how many P waves are before each QRS? Is it a consistant number of P waves before each QRS?

Rhythm Identification: PR Interval Time interval from start of P wave to start of QRS 0.12 - 0.20 sec. In length

Rhythm Identification: QRS (reg or irreg) Next, look at the QRS. Is it narrow or wide? Ask yourself again, do they occur at regular or irregular intervals? If irregular, is the rhythm regularly irregular or irregularly irregular?

Blocks The leads to look in first for right bundle branch block (RBBB for short) are leads V1 & V2. In RBBB, the QRS complex has two R-waves which give the QRS a double-peaked appearance. This is called the “R-S-R1” wave. “R-S-R1” wave

The leads to look in first for left bundle branch block (LBBB) are leads V5, V6, and I. If the QRS is wide, mostly upright, and the T waves are inverted, then you are most likely looking at LBBB. Blocks

Inferior MI: The leads to look in are leads II, III, & AVF. MI Identification Inferior MI: The leads to look in are leads II, III, & AVF.

Septal MI: Look at leads V1-V2 for MI’s. MI Identification Septal MI: Look at leads V1-V2 for MI’s.

Anterior MI: Look at leads V3-V4 for MI’s. MI Identification Anterior MI: Look at leads V3-V4 for MI’s.

MI Identification Lateral MI: The leads to look in for lateral MI are leads I, AVL, V5, & V6.

MI Identification Posterior MI: This one is tricky, and the EKG is not the definitive diagnostic tool for this type of MI. Look for tall R waves and ST depression as sign to suspect Posterior MI in V1 & V2.

MI Identification Posterior MI: If you suspect Posterial MI then need to perform a “right sided EKG”

MI Identification Posterior MI: Label the new leads that you changed to either V7, V8, V9 or V4R, V5R, V6R.

Heart Walls and Lead Correlation Lateral Wall Inferior Wall Septal Wall Anterior Wall