How to Analyze a Rhythm

Rhythm Analysis

• Step 1: Calculate rate.• Step 2: Determine regularity.• Step 3: Assess the P waves.• Step 4: Determine PR interval.• Step 5: Determine QRS duration.

Step 1: Calculate Rate

• Option 1– Count the # of R waves in a 6 second rhythm strip,

then multiply by 10.

Interpretation?

9 x 10 = 90 bpm

3 sec 3 sec

Step 1: Calculate Rate

• Option 2

– Find a R wave that lands on a bold line.– Count the # of large boxes to the next R wave. If

the second R wave is 1 large box away the rate is 300, 2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc. (cont)

R wave

Step 1: Calculate Rate

• Option 2 (cont)

Interpretation?

300

150

100

75

60

50

Approx. 1 box less than 100 = 95 bpm

Step 2 : Determine Regularity

• Regular: If the difference between the longest R-R interval in the ECG and the shortest R-R interval is less than 0.12 second

• Irregular: If the difference between the longest R-R interval in the ECG and the shortest R-R interval is greater than 0.12 second

Step 2: Determine regularity

• Look at the R-R distances (using a caliper or markings on a pen or paper).

• Regular? Occasionally irregular? Regularly irregular? Irregularly irregular?

Interpretation? Regular

R R

Step 3: Assess the P waves

• Are there P waves?• Do the P waves all look alike?• Do the P waves occur at a regular rate?• Is there one P wave before each QRS?Interpretation?

Normal P waves with 1 P wave for every QRS

Step 4: Determine PR interval

• Normal: 0.12 - 0.20 seconds. (3 - 5 boxes)

Interpretation? 0.12 seconds

Step 5: QRS duration

• Normal: 0.04 - 0.12 seconds. (1 - 3 boxes)

Interpretation?0.08 seconds

Rhythm Summary

• Rate 90-95 bpm• Regularity regular• P waves normal• PR interval 0.12 s• QRS duration 0.08 sInterpretation?

Normal Sinus Rhythm

NSR Parameters

• Rate 60 - 100 bpm• Regularity regular• P waves normal• PR interval 0.12 - 0.20 s• QRS duration 0.04 - 0.12 s

Generation of the Electrocardiogram

1. A wave of depolarization traveling towards a positive electrode results in a positive deflection in the ECG trace.

2. A wave of depolarization traveling away from a positive electrode results in a negative deflection.

3. A wave of repolarization traveling toward a positive electrode results in a negative deflection.

4. A wave of repolarization traveling away from a positive electrode results in a positive deflection.

Key Points to Remember regarding Vector Analysis

Atrial Depolarization and the Inscription of the P-wave

Delay (no electrical activity) before the beginning of ventricular depolarization due to AV node function

0

90

SA node

AV node

Ventricular Depolarization and the Inscription of the QRS complex

1. The depolarizes from the inside out and the resulting depolarization wave m oves away from the electrode recording Lead II

septum

2. The rest of the depolarizes counter-clockwise from the inside out and creates the (large arrow) which is essentially, the algebraic sum of all of the sm all depolarization vectors (including the small contribution from the ) . In a normal heart, this vector is always moving directly toward Lead II, generating a mostly positive QRS com plex

left ventricle

m ain cardiac vector

right ventricle

Lead II electrode60 downwardrotation angle from the horizontal 0

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Note: compared tothe left ventricle, the right ventric le is muchsm aller and contributeslittle to the overall m ainvector of depolarization

60o

Ventricular Repolarization and the Inscription of the T-wave

Flow of Electrical Currents in the Chest Around the Heart

• Ventricular depolarization starts at the ventricular septum and the endocardial surfaces of the heart.

• The average current flows from negative to positive in the direction in the direction from the base of the heart to the apex.

• At the very end of depolarization the current reverses from 1/100 second and flows toward the outer walls of the ventricles near the base (S wave).

Flow of Electrical Currents in the Chest Around the Heart

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Mean Vector Through the Partially Depolarized Heart

ECG leads and their Axis

The ECG is measured by placing skin electrodes on the body surface at different locations and connecting these electrode in different configurations to a voltage amplifier and recorder

ECG Leads

The standard ECG 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.

Three Bipolar Limb Leads • To record limb lead I, the negative terminal of the electrocardiograph

is connected to the right arm and the positive terminal to the left arm

• To record limb lead II, the negative terminal of the electrocardiograph is connected to the right arm and the positive terminal to the left leg

• To record limb lead III, the negative terminal of the electrocardiograph is connected to the left arm and the positive terminal to the left leg

Leads I, II, & III together(“Einthoven’s triangle”)

Normal Electrocardiograms Recorded from the Three Standard Bipolar Limb Leads

• Recordings of the electrocardiograms in leads I, II, and III.

Augmented Unipolar Limb Leads

• In this type of recording, two of the limbs are connected through electrical resistances to the negative terminal of the electrocardiograph, and the third limb is connected to the positive terminal.

• When the positive terminal is on the right arm, the lead is known as the aVR lead

• when on the left arm, the aVL lead

• and when on the left leg, the aVF lead

0o

LEAD AVR LEAD AVL

LEAD AVF

LEAD II

LEAD I

LEAD III

60o

90o120o

-30o-150o

Each of the limb leads (I, II, III, AVR, AVL, AVF) can be assigned an angle of clockwise or counterclockwise rotation to describe its position in the frontal plane. Downward rotation from 0 is positive and upward rotation from 0 is negative.

Summary of the “Limb Leads”

Chest Leads (Precordial Leads)

V1 - 4th intercostal space - right margin of sternum V2 - 4th intercostal space - left margin of sternum V3 - linear midpoint between V2 and V4 V4 - 5th intercostal space at the mid clavicular line V5 - horizontally adjacent to V4 at anterior axillary line V6 - horizontally adjacent to V5 at mid- axillary line

Chest Leads (Precordial Leads)• In leads V1 and V2, the QRS

recordings of the normal heart are mainly negative because, the chest electrode in these leads is nearer to the base of the heart than to the apex.

• Conversely, the QRS complexes in leads V4, V5, and V6 are mainly positive because the chest electrode in these leads is nearer the heart apex, which is the direction of electropositivity during most of depolarization

Determining the electrical axis from standard lead electrocardiograms

Plotting the mean electrical axis of the ventricles from two electrocardiographic leads (leads I and III)

Left axis deviation in a hypertensive heart (hypertrophic left ventricle)

High-voltage electrocardiogram in congenital pulmonary valve stenosis with right ventricular hypertrophy. Intense right axis deviation and a slightly prolonged QRS complex also are seen