The Heart
What is the heart?
The heart is the muscle responsible for the process by which blood is pumped throughout the body. The journey begins through two large veins, the inferior and superior vena cava which returns deoxygenated blood to the heart. Deoxygenated blood arrives at
Pericardium
The layer or sac that surrounds the heart.
Myocardium
The middle layer.
Endocardium
The innermost layer.
Epicardium
The top layer.
Conduction System of the Heart
The heart consists of three layers: the pericardium, the myocardium, the epicardium and the endocardium. Located within the myocardium is the electrical conduction system. This is the system responsible for the regulation of the pumping action of the hear
How does the conduction system work?
The conduction system begins in the sinoatrial (SA) node, or the pacemaker. Here, the impulse is initiated, and then travels through the intermodal pathway, passing through several passages such as the interatrial and interventricular septums, finally end
Myocardial infarction
Commonly known as a heart attack, is a term that refers to an obstruction to the myocardial tissue. This obstruction causes an interruption of the blood supply to part of the heart which causes the heart cells to die.
Myocardial ischemia
Also known as angina, is a condition caused by a lack of oxygen-rich blood in the heart.
Arrhythmia
A term used to refer to any disorder of your heart rate or rhythm.
Fundamentals of the Electrocardiogram
An electrocardiogram, also known as the ECG or EKG, is a tool used to record the electrical activity of the heart. An electrocardiograph is a device that amplifies low-voltage electric impulses detected on the skin and produces a printed record of that el
Limb Leads
1. Lead I: Records electrical activity from right arm to left arm
2. Lead II: Records electrical activity from right arm to left leg
3. Lead III: Records electrical activity from left arm to left leg
Augmented Leads
1. aVR: Records electrical activity away from midpoint between left arm and left leg to right arm (across heart to right shoulder)
2. aVL: Records electrical activity from midpoint between right arm and left leg to left arm (across heart to left shoulder)
Chest or Precordial Leads
1. V1: Records electrical activity between center of heart and the chest wall where V1 electrode is placed
2. V2: Records electrical activity between center of heart and the chest wall where V2 electrode is placed
3. V3: Records electrical activity betwee
ECG Leads
Each lead is marked with a different color and lead number. The right arm lead is white and marked RA, the left arm lead is black and marked LA, the right leg lead is green and marked RL, and the left leg is red and marked LL. Limb leads are usually place
Interpreting Waveforms
The results of the electrocardiogram are printed on a special graph paper which travels through the electrocardiogram at a rate of about 25 millimeters per second. The graph paper has both horizontal and vertical lines which serve to divide the paper into
Isoelectric line
A term used to describe a straight line on the ECG strip with illustrates the resting state of the myocardial cells. The isoelectric line represents the beginning and ending point of the five major waves of the cardiac cycle.
The Cardiac Cycle
Begins with the firing of the SA node, which is represented by a P wave on the ECG. The p wave, which represents the depolarization of both the right and left atria, can be characterized as a smooth, upward deflection which is approximately 0.10 second in
The Five Steps for Analyzing an ECG
Heart rate, regularity, P-waves, QRS complex, and P-R interval.
The 6 Second Interval x 10 Method
This involves counting the number of QRS complexes on a 6 second rhythm and multiplying that number by 10, this is the only method that can be used on an irregular rhythm.
The 300, 150, 100, 75, 60, 50 Method.
This involves locating an R-wave on a bold line on the ECG paper then finding the next consecutive R wave and counting down from 300 on the subsequent bold lines to determine the rate.
1500 Method
Count number of small squares between two consecutive R-waves and divide that number by 1500, it is the most accurate method of obtaining the heart rate but can only be used on regular rhythms.
Rate Calculators
Rate calculators are devices that you use to measure between R-waves and it gives you the rate. You count the QRS complexes to get the Ventricular rate and count the P-waves to determine the atrial rate.
Regularity
The second step in analyzing an ECG. To find this you measure the distance between all the R-R waves on the strip and if they are all the same the rhythm is called regular, if not the rhythm is called irregular and irregular rhythms are considered abnorma
Calipers
This involves using a device called a caliper to measure the intervals, which is the quickest and easiest method.
Paper and Pen Method
This involves using a piece of paper and marking an R-wave, then marking the next R-wave and using that to judge the R-waves of the rest of the rhythm.
Counting the Squares
Count the small squares between each R-R interval and see if they are all the same, this method takes longer but does not require any equipment to use.
Irregularly (totally) Irregular
This means there is no consistency to the rhythm such as atrial fibrillation.
Patterned Irregularity
The irregularity repeats over and over such as AV-heart blocks.
Slightly Irregular
There is an abnormality that does not occur very often such as one PVC in a rhythm strip.
Very Irregular Rhythms
There are multiple occurrences of an abnormality such as a PVC or PAC in one rhythm strip.
P-Waves
A normal P-wave is upright and rounded in Leads I, II, avf, and V2 thru V6; they should have a duration of o.06 to o.10 sec. and an amplitude of o.5 to 2.5mm. P-waves signify the pulse initiating at the SA node and depolarizing the atria. Abnormal P-waves
Separating the P-Waves
You can separate the P-wave into two parts the first half of the P-wave is the depolarization of the right atrium and the second half is the depolarization to the left atrium. If there is a dilation of the right atrium then the P-wave will have higher amp
Q-Wave
The Q-wave is the first negative deflection from the base line after the P-wave.
R-Wave
The R-wave is the first positive deflection from the base line after the P-wave.
S-Wave
The S-wave is the first negative deflection that extends below the base line after the R-wave.
Normal QRS Complexes
Normal ORS complex should be 0.06 to 0.12 sec. in duration and 5mm to 30mm in amplitude. A normal QRS complex indicates the impulse originated above the ventricles and traveled through the ventricles in a normal fashion. Normal QRS complexes are those tha
Abnormal QRS Complexes
Abnormal QRS complexes are produced by abnormal depolarization of the ventricles. The duration of abnormal complexes is usually greater than .12 sec. abnormal QRS complex varies widely and can have strange, wide, and bizarre shapes. Very tall QRS complexe
P-R Intervals
The P-R interval is the distance from the beginning of the P-wave to the beginning of the Q-wave or R-wave. It signifies the depolarization of the heart from the SA node through the atria and AV node. The duration of the P-R interval should be .12 to .20s
Sinus Dysrhythmia
The SA node fires at various speeds. The P wave, Pr interval, and QRS complex are normal. The pulse is usually normal at 60-100 BPM. The only abnormality is irregular P-P intervals. There must be 0.12 or more difference in the longest and shortest P-P int
Atrial Dysrhythmia
Atrial dysrhythmias originate outside the SA node in the atrial tissue or in the intermodal pathways. The three mechanisms responsible for atrial dysrhymias are:
1.Increased automaticity-the atrial cells spontaneously depolarize and initiate impulses befo
Premature Atrial Complexes
Rate: Depends on the underlying rhythm
Regularity: depends on the number of PAC's present
P-waves: may be upright or inverted, will appear different than those of the underlying rhythm
QRS complexes: Normal
PR interval: may be normal, shortened, or prolon
Atrial tachycardia
Rate: 150-250 beats per minute
Regularity: regular
P-waves: may be upright or inverted will appear different from underlying rhythm
QRS-complex: Normal
PR interval- may be normal, shortened, or prolonged
Wandering Atrial Pacemaker
Rate: Usually between 60-100bpm
Regularity: Slightly irregular
P-waves: continuously change in appearance
QRS-complex: Normal
PR interval: varies
Atrial Flutter
Rate: atrial between 250-350, ventricular rate can vary
Regularity: may be regular or irregular
P-wave: absent (flutter waves)
QRS-complex: normal PR-interval: absent
Atrial fibrillation
Rate: atrial rate over 350bpm, ventricular rate can vary
Regularity: irregularly (totally) irregular
P-wave: absent (chaotic baseline)
QRS-complex: normal
PR-interval: absent
Junctional Dysrhythmias
Junctional dysrhythmias originate in the AV junction around the AV node or Bundle-of-His.
Major characteristics of Junctional complex are P-waves that may be inverted, follow the QRS-complex, or absent and PR-intervals that will be shortened or absent.
Premature Junctional Complex
Rate: depends on the underlying rhythm
Regularity: occasional or frequently irregular depends on the number of PJCs
ORS-complex: Normal
PR Interval: short or absent
Junctional Escape Rhythm
Rate: 40 to 60bpm
Regularity: Regular
P-wave: inverted, absent, or occur after the QRS-complex
QRS-complex: normal
PR-interval: short or absent
Junctional Tachycardia
Rate: 100 to 180bpm
Regularity: regular
P-wave: inverted, absent, or occur after the QRS-complex
PR-interval: short or absent
Ventricular dysrhythmias
Ventricular dysrhythmias originate in the ventricles below the Bundle of His. Some may be benign while some may be life threatening.
Major characteristics of ventricular dysrhythmias are absent P-waves and wide bizarre QRS-complexes.
Premature ventricular complexes
Rate: depends on the underlying rhythm
Regularity: occasionally irregular or very irregular depends on the number of PVC's
P-wave: absent at the PVC
QRS-complex: the PVC will have a wide bizarre looking QRS
PR-interval: absent
Two PVC's in a row are calle
Idioventricular Rhythm
Rate: 20-40bpm
Regularity: regular
P-wave: absent
QRS-complex: wide and bizarre
PR-interval: absent
Accelerated Idioventricular Rhythm
Rate: 40-100bpm
Regularity: regular
P-wave: absent
QRS-complex: wide and bizarre
PR-interval: absent
Ventricular tachycardia (may have a pulse or may not)
Rate: 100-250bpm
Regularity: regular
P-wave: absent
QRS-complex: wide and bizarre
PR-interval: absent
Polymorphic ventricular tachycardia (Torsades de Pointes)
QRS complexes alternate between upright and downward deflections.
Ventricular fibrillation (produces no effective cardiac output)
Rate: 200-500bpm
Regularity: totally chaotic
P-wave: absent
QRS-complex: wavy line
PR-interval: absent
The only effective treatment for Ventricular fibrillation is defibrillation
Asystole
Total absence of cardiac activity (Flat line).
Pulseless Electrical Activity
Organized electrical activity that should result in a pulse but there is no pulse.
Artifacts
Any electric activity on an EGC that is non-cardiac in origin and represents unwanted marks is characterized as an artifact. This unwanted electrical activity, whether it is intentional or unintentional, can be prevented by either changing outlets or movi