I.  Cardiac cycle

A. P wave

1. The first deflection of the cardiac cycle

2. Represents depolarization of the atria

3. Begins as the waveform begins to leave the baseline, and ends when it returns to baseline

4. Normal: Location - precedes every QRS complex
b) Amplitude - 0.5 to 2.5 mm high Rounded
c) Duration - 0.06 to 0.12 seconds
d) Configuration - small, rounded, similar in size and shape
e) Deflection - positive (upright) in lead II

5. Normal P waves indicate:

a) the electrical impulse originated in the SA node

b) that normal depolarization of the atria occurred

6. Abnormal P waves:

a) Inverted - indicates reverse (retrograde) conduction from the AV junction backward toward the atria

b) Peaked, notched or enlarged - the sinus impulse traveled through altered or damaged atria

c) Varying - the impulse may be coming from different sites

d) Absent - conduction by a route other that the SA node

e) Not preceding a QRS - heart block

B. PR interval

1. Represents the time required for the electrical impulse to leave the SA node and travel through the atria, AV node, bundle branches, and Purkinje fibers

2. Normal:

a) Location - from the beginning of the P wave to the beginning of the QRS complex, includes the P wave and the short flat (isoelectric) line that follows it

b) Amplitude - not measured

c) Duration - 0.12 to 0.20 seconds

3. Normal PR interval indicates that the electrical impulse leaving the SA node was conducted through the entire electrical system within a normal amount of time

4. Abnormal PR interval:

a) Short

(1) Electrical impulse was conducted through an abnormal pathway that bypasses the AV node, or

(2) The impulse originated in an ectopic site close to the AV junction

b) Long - indicates the electrical impulse is delayed traveling through the AV node and bundle of His

C. QRS complex

1. Represents ventricular depolarization

2. Measured from the beginning of the QRS as the first wave leaves the baseline to the J point

3. J point

a) The junction between the QRS and the ST segment

b) Where the last wave of the complex begins to flatten out at, above, or below the baseline

c) Elevation or depression of the ST segment can make finding the J point difficult

4. Normal:

a) Location - follows the PR interval

b) Amplitude  - varies greatly

c) Duration - 0.06 to 0.10

d) Configuration (use figure 3-6, p18, Huff)

(1) consists of the Q wave (the negative deflection before the R wave), the R wave (the first positive deflection after the Q wave), the S wave (the first negative deflection after the R wave)

(2) May not always see all three waves. 

(3) The second R or S waves are labeled R'(R prime) or S'(S prime)

e) Deflection - different in each lead

5. Normal QRS indicates that ventricular depolarization occurred within a normal amount of time

6. Abnormal (wide) QRS indicates that abnormal depolarization has occurred due to

a) Bundle branch block

b) Conduction through an abnormal pathway

c) The impulse originated in an ectopic site in the ventricles

D. ST segment

1. Represents the end of ventricular conduction

2. Normal:

a) Location - extends from the S wave to the beginning of the T wave

b) Deflection - usually isoelectric

3. Normal indicates the end of ventricular depolarization and the beginning of repolarization

4. Abnormal

a) Elevation is a sign of myocardial injury

b) Depression is most often associated with myocardial ischemia

E. T wave

1. Represents ventricular recovery or repolarization

2. Normal:

a) Location - follows the S wave

b) Amplitude - 0.5 mm, greater in MCL

c) Duration - duration 0.10 to 0.25 seconds

d) Configuration - rounded, slightly asymmetrical (ascends more slowly than the descent)

e) Deflection - usually positive

3. Abnormal T waves indicate abnormal repolarization has occurred

F. QT interval

1. Measures ventricular depolarization and repolarization

2. Normal:

a) Location - from the beginning of the QRS to the end of the T wave

b) Duration

(1) Varies according to heart rate, influence of medications, and other factors 

(2) Should not be greater than half the distance between two regular R waves

3. Abnormal:

a) Long - indicates that ventricular repolarization time has slowed, which means that the relative refractory period (the vulnerable period) of the cardiac cycle is longer, predisposing patients to potentially lethal ventricular dysrhythmias

b) Short - may result from digitalis toxicity or hypercalcemia

G. U wave

1. Represents the recovery period of the Purkinje fibers

2. Is not present of every rhythm strip, best seen with slow heart rates

3. Configuration is the most important characteristic

4. Normal:

a) Location - after the T wave and before the next P wave

b) Configuration - upright and rounded

c) Deflection - upright

5. Abnormal - prominent U waves may be due to hypercalcemia, hypokalemia or digitalis toxicity

V. Cardiac monitors – 2 types of recordings

A. Standard 12 lead (additional material regarding 12 lead recordings is outside the scope of this class)

1. Uses 10 electrodes to obtain a more complete view the heart

2. Records 12 different views of the heart, at different angles

3. Provides a complete picture of the hearts electrical activity

B. Single lead

1. Also known as rhythm monitoring

2. Provides continuous information about the hearts electrical activity

3. Chest leads pick up the electrical activity and displays it on a monitor

4. Electrodes are conductive gel discs that are placed on the patient's chest, these discs should be changed every 24 hours to avoid drying of the discs. Drying of the disc can cause poor tracings

A. Hard wire monitoring

1. Electrodes are attached to a cable which feed into a cardiac monitor

2. The monitor can be permanently attached in a patient room or can be portable

3. 3 leadwire system (used with portable monitors)

a) Made up of 3 leadwires

(1) white – right arm (RA)

(2) black – left arm (LA)

(3) red – left leg (LL)

b) Lead placement

(1) RA is placed right below the clavicle (2^nd intercostal space) right midclavicular line

(2) LA is placed right below the clavicle (2^nd intercostal space) left midclavicular line

(3) LL is placed on the left lower rib cage (8^th intercostal space, left midclavicular line)

c) Leads placed in this position will allow the monitoring in leads I, II, or III using the lead select on the monitor

d) To monitor MCL (V₁) – reposition the LL lead to the V₁ position (4^th intercostal space, right sternal border), and change the lead select on the monitor

4. 5 leadwire system (used mostly in the Critical Care Units)

a) Made up of 5 leadwires

(1) white – right arm (RA)

(2) black – left arm (LA)

(3) red – left leg (LL)

(4) green – right leg (RL)

(5) brown – chest lead (C)

b) Lead placement

(1) RA is placed right below the clavicle (2^nd intercostal space) right midclavicular line

(2) LA is placed right below the clavicle (2^nd intercostal space) left midclavicular line

(3) LL is placed on the left lower rib cage (8^th intercostal space, left midclavicular line)

(4) RL is placed on the right lower rib cage ( 8^th intercostal space, right midclavicular line)

(5) C is usually placed in the MCL or V₁ position (4^th intercostal space, right sternal border), but can be moved to any of the 6 chest lead positions

c) This configuration allows you to monitor any of the of the standard 12 leads using the lead selector on the monitor

B. Telemetry

1. The patient is attached to a small transmitter box

2. Radio waves transmit the tracing to a central monitor (this is when cell phones can interfere)

3. Telemetry systems

a) Also made up of 3 leadwires

(1) negative – usually white

(2) positive – usually red

(3) ground – usually black

b) The lead that will be monitored depends on the placement of the electrodes

c) Most commonly used leads are: (refer to lead placement handouts)

(1) lead II – NEGATIVE (white) @ 2^nd intercostal space, right midclavicular line, POSITIVE (red) @ 8^th intercostal space, left midclavicular line, GROUND (black) @ (2^nd intercostal space, left midclavicular line

(a) best lead for viewing the atrial activity –  P wave

(b) lead II tracing shows a positive or upward deflection since the electrical activity of the heart approaches the positive lead

(2) MCL – NEGATIVE (white) @ 2^nd intercostal space, left midclavicular line, POSITIVE (red) @ 4^th intercostal space, right sternal border, GROUND (black) @ 2^nd intercostal space, right midclavicular line

(a) best lead for differentiating ventricular arrhythmia

(b) MCL tracing shows a negative or downward deflection since the electrical activity of the heart move away from the positive lead

C. Applying electrodes

1. Prepare the skin

a) Shave the skin if necessary – hair interferes with the contact between the electrode disc and the skin

b) Remove skin oil – use a dry washcloth or soap and water

2. Attach electrode disc

a) Avoid placing over bony areas

b) Check to make sure electrode dics are not dry

A. Use calipers

B. 6 step method of interpretation

1. Check rhythm for regularity

a) Is the rhythm regular

b) Is the rhythm irregular

c) Is the rhythm regularly irregular

2. Calculate the ventricular rate (use one of the three methods)

a) If regular: divide 1500 by the number of small boxes between two R waves

b) If irregular: count the number of R waves on a 6 second strip and multiply by 10

c) Rapid method: start with an R wave that falls on a heavy black line and stop at the closest R wave counting 300, 150, 100, 75, 60, 50, 43, 37

3. Measure the QRS complex

a) Are all the complexes the same size and shape

b) Is the QRS complex normal, less than 0.10 seconds

4. Identify and examine the P waves

a) Do the P waves have normal configuration

b) Do all the P waves have the same size and shape

c) Is there only one P wave for each QRS

d) If more than one P wave for each QRS, what is the ratio

5. Measure the PR interval

a) Is the PR interval normal, 0.12 - 0.20 seconds

b) Is the PR interval constant

6. Identify the rhythm or rhythms