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Cardiology In Critical Care

Introducing The Electocardiogram (ECG, EKG)

The EKG Measures the Body's Electrical Activity
As it beats, the heart generates small electrical currents. A recording of this electrical activity is called an "EKG" (electrocardiograph). The terms EKG and ECG mean the same thing. EKG comes from the German language while ECG comes from English. A standard EKG is obtained by placing 12 small electrodes on the patient's body in a specific pattern. The EKG machine is then turned on, and the recording is made in just a few moments. The test is entirely painless.

Each of the heart's beats can be divided into three main parts. The first part is the small P wave which represents the atrial contraction. The second part is the tall QRS spike which represents the ventricular contraction. The third part is the large T wave which represents the relaxation of the ventricles. By analyzing the exact pattern of the EKG, doctors can learn a great deal about how the heart is working.

The Heart Beat: Contracting and Relaxing
The heart beat is usually divided into two main phases called "diastole" and "systole." During the first phase (diastole), the heart relaxes and fills with blood. During the second phase (systole), the heart contracts and pumps out the blood. The heart typically spends about 2/3 of its time in diastole and 1/3 of its time in systole. Keeping this activity well timed is the job of the heart's conduction system.

The signal to begin a contraction starts in a small region at the top of the right atrium called the "sinoatrial (SA) node." From this point, the contraction spreads over the two atria like a wave. The atrial contraction pumps the blood down into the ventricles. Next, the signal to contract reaches a small region of the heart called the "atrioventricular (AV) node." As its name implies, the AV node sits right between the atria and the ventricles. The AV node is smart, and it delays the signal just long enough to allow the atria to finish contracting. From here, the signal to contract travels down special fibers that connect to the bottom of the heart. This causes the ventricles to contract from the bottom to the top, and ensures that the blood is pumped up and out, into the lungs and the body. At the end of the cycle, the ventricles relax and the whole process begins again.

EKG Paper: What It means







The EKG: You Must Know What Happens When!

In order to adequately read EKGs you must know what is occuring during each wave. All rhythm interpretation must be correlated with other signs and the condition of the patient for successful outcome of any resuscitation attempt. Always remember the admonition "treat the patient, not the monitor". Is there a pulse?

When the P occurs, the SA node fires and atrial depolarization produces a sinus initiated rhythm. They P wave should not be longer than 0.20 seconds. A prolonged P waive may indicate a heart block.



P-Wave QRS. T-Wave.
Not greater than 0.20 seconds.
If it is longer may indicate first degree heart block.
SA Node fires.
Atrial Depolarization
Sinus initiated rhythm. Depolarization of the ventricles.
Ventricular Contraction.
Atrial Repoliarization.
(Can't always be seen on EKG) Ventricle repolarized.
May be affected by changes in serum K levels.


Rhythm Strip Analysis

Item Normal
Determine Heart Rate.
Count small boxes between two R waves.
Divide into1500 Gives BPM Normally 60-100 bpm in adults
90-100 bpm in children
Tachycardia
Eyeball rhythm Regular, Even.
Presence of P-Wave
Are there normal looking P waves? P-R interval 0.12 - 0.20 sec and consistant.
Each P wave followed by QRS
P to QRS ratio 1:1
Upright in Lead 2
Negative in AVR
Uniform size and contour from beat to beat.

Prolong when A-V Block present.
P-R interval.
What is the relationship between the P waves and the QRS complexes? 0.12 to 0.20
Each QRS preceeded by P wave
P to QRS ratio 1:1 R - R intervals may be slightly irregular esspecially in the young and elderly.
QRS Duration.
Are there normal-looking QRS complexes? At least 0.11 Sec QRS greater than 0.11 sec when Branch Block present.


S-T segment
QT interval.
Be aware of K levels. Normal K Level is 3-4.5 Low K will make patient more prone to Digoxin Toxicity.



Laboratory values after heart attack.
A. White Blood Cells - elevated after MI.
B. BUN, Creatine maybe elevated after MI.
C. Glucose maybe elevated after MI. (Bodies reaction to stress)
D. Coagulation Studies.
1. PT, PTT
2. PT normal 11-15 seconds.
3. Patient should be two times higher than control to be therapeutic.
4. PTT is used to monitor heparin.
Monitor Lead Plaeement
White Right arm
Black Left arm
Green Right leg
Red Left leg
Brown Chest

Dysrhythmias
RECOGNITION AND TREATMENT OF LIFE-THREATENING DYSRHYTHMIAS

Note: See ACLS ALGORITHMS for treatment protocols.

MI Locations
ST elevations in MI

I III AVF - Inferior Right
V1 V2 - Septial
V2 V3 V4 - Anterior LAD
V5 V6 AVL I - Lateral Circumflex
Left anterior descending affects V1 V2 V3 V4
Inferior Right Coronary Artery affects II III AVF
Lateral Left Circumflex Artery affects I AVL V5 V6
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