ECG review!
AV junctional rhythms
(in lead II) Are formed when dysrhythmias arise from the AV junctional tissue. - as well as from lower-right atrium near the AV node or in the left atrium *Can occur before, during, or after the QRS complex* -P waves may be *buried in the QRS complex, inverted or absent*
9 Step Process of Analyzing an ECG
*1. Heart rate*: is it normal, fast, or slow *2. Regularity* *3. P waves*: Asses the P waves (is there a p wave preceding each QRS complex?) *4. QRS complexes*: Assess the QRS complexes (Are they normal/ w/in normal limits?) *5. PR interva*l: Are they identifiable? w/in normal limits? constant in duration? *6. ST segment*: Is it a flat line? is it elevated or depressed? *7. T waves*: are the slightly asymmetrical? Are the normal in height? Is it oriented in the same direction as the QRS *8. QT intervals*: Are they within normal limits? *9. U waves*: look for U waves
Biphasic P waves
*normal in lead V1* Have an initial positive deflection (reflecting right atrial depolarization) followed by a negative deflection (reflecting left atrial depolarization)
Methods for approximating HR
- 6 second interval x 10 method - 300, 150, 100, 75, 60 method - 1500 method
ECG lead
- Each configuration or positioning of lead wires is referred to as a _________. - Many leads are used to view as much of the heart as possible -Each lead provides a different view of the heart -Bipolar or unipolar
Regularity (Step 2/9)
- Normlly heart beats should be regular and rhythmmic. The distance between p waves and QRS complexes should be the same: if not the rhythm is *irregular* *Irregularity may be occasionally, slightly or very irregular. It can also be patterned or TOTALLY irregular*
ECG electrodes
- Placed on the patient's skin to detect the heart's electrical activity which is then transferred to the ECG machine; - represent electrical poles: positive or negative charges; - Positioning the ECG electrodes in various positions on the patient's body give us different views of the heart.
PR interval
- Representing depolarization of the heart *from the SA node through the atria, AV node, and HIS-Purkinje system*. - Total amount of time between the contraction (depolarization) of the atria to the start of ventricular contraction; *2 parts*= P wave + PR segment
Sinus Rhythm
- Waveforms and intervals that appear at regular intervals at a a rate of 60-100 bpm (adult) - Upright and slightly asymmetricl P waves, each followed by a QRS complex of normal upright contour, duration, and configuration. - PR interval of normal duration that precedes each QRScomplex - A flat ST segment followed by an upright and slightly asymmetrical T wave - a normal QT interval - Sometimes the presence of a U wave
ECG uses
- continuous monitoring of the heart rhythm - identify developing or existing cardiac and non cardiac conditions such as MI, inflammation, enlargement and/or hypertrophy of the heart muscle - identify changes in or blockage of the heart's conduction system, accumulation of fluid in the pericardial sac -identify electrical effects of medication and electrolytes, -conduct assessments such as stress testing and to obtain a baseline recording before, during, and after medical procedures
Methods used to determine regularity of a rhythm include ____________________________________________________.
-Paper and Pen method - Caliper method - Counting the small quares method - Using a rate calculator
Small horizontal square
0.04 seconds in duration
Large horizontal box
0.20 seconds in duration (Made up of 5 small squares) - *5 large boxes= 1 second*
Small vertical box
1 mm or 0.1 mV
Large vertical box
5 mm or 0.5 mV
Aberrant Conduction
A *brief* failure of the R or L bundle branch to normally conduct an electrical impulse. -can occur when electrical impulses, such as (supraventricular) early beats and tachycardias, travel down one unaffected bundle branch while stimulation of the other bundle branch follows.
Bipolar lead
A ________________ records the flow of the electrical impulse between the two selected electrodes. They have a 3rd (and often 4th) electrode called a *"ground"*
Occasionally irregular rhythms
A rhythm that appears mostly regular, but from time to time you see an area where it is irregular. The irregularity may be so infrequent that you might not see it at first.
Very irregular rhythms
A rhythm that has many areas of irregularity. A common cause is frequent early beats .
Initial assessment of P waves
ASK: Are P waves present? Do they appear normal (upright and normal in size)? Is there one P wave preceding each QRS complex?
*Short* (< 0.5mm) narrow and symmetrically peaked P waves
Abnormal P wave associated with: - *hyper*kalemia
Notched or wide (greater than 0.12 seconds) P waves
Abnormal P wave associated with: - P mitrale: a condition of *increased left atrial pressure and left atrial enlargement* - conduction block in the interatrial conduction tract (b/w the R and L atria)
Tall (> 2.5mm), narrow, and symmetrically peaked P waves
Abnormal P wave associated with: -P Pulmonale: a condition of *increased right atrial pressure and right atrial enlargement* - sinus tachycardia - *hypo*kalemia
Irregularly (Totally) irregular rhythm
Also called chaotically or grossly irregular rhythm; is one with no consistency to irregularity. -may be hard to find an R-R interval that is the same as others -*typically one condition*: in which the atria fires in excess of 350 beats/min and from multiple sites. This bombards the AV node at a rate in which it can not respond to all the impulses and only allows some to get through to the ventricles
Early beats
Also called premature beats or ectopy; Impulses that occur before the SA node has a chance to fire or initiate the impulse. *They can arise from any of the cells of the heart*, including the atria, AV junctional tissue, or ventricles. *R-R interval appears shorter* than normal. Considered occasionally irregular if beats occur only a few times a minute and frequently irregular if the early beats are more frequent. *likely to progress to tachycardia*
Patterned irregularity
Also called regularly irregular, occurs when the irregularity occurs over a cyclic fashion. Early beats occurring at regular intervals: when the HR speeds up and slows down in a cyclic way, and one type of conduction blockage are all characterized as being regularly irregular. - *Bigeminy*: one early beat every other (second) complex - *trigeminy*: one early beat every third complex - *Quadrigeminy*: One early beat every 4th complex -Can be a result of speeding up and slowing of the HR as it *corresponds to resp. cycle*. - Can occur as a result of a conduction block in which the AV node is weakened and tires more and more with each conducted impulse until it fails to conduct through to the ventricles resulting in a *dropped ventricular beat*.
Muscle artifact
Appears as *high frequency, low amplitude, relatively irregular distortion of the baseline* and QRS complexes. - Often caused by poorly supported or tense muscles in the arms and legs or shivering... can also be caused by loose, dried out or out of date electrodes
Wandering baseline
Appears as a low frequency, high amplitude artifact. May be observed during deep inhalations and exhalation, patient movement, or the acceleration forces of a moving vehicle
Abnormal QRS
Are produced by abnormal depolarization of the ventricles.
P waves (Step 3/9)
Assessing P waves can tell us if the impulse that initiated the heart beat arose from the SA node. Normal: its *amplitude is 0.5 to 2.5 mm* (½ to 2 ½ small vertical boxes) and its duration is *0.06 to 0.10 seconds ( 1 ½ - 2 ½ small horizontal boxes)*
Saw-toothed waveforms
Atrial wave forms that appear saw toothed are produced by rapid firing impulses that arise from the atria. - fire at a rate of 250-350 bpm - normal p waves absent- instead F waves are seen
Chaotic looking baseline
Atrial waveform that produces a chaotic looking baseline produced by rapid firing impulses that arise from the atria. - fire at a rate grater than 350 bpm - no discernable p waves- uneven baseline
Abnormal PR interval
Considered abnormal if: - they are shorter than 0.12 seconds - longer than 0.20 seconds - absent - if they vary in duration
QRS Complexes (Step 4/9)
Consists of up to 3 parts: The Q wave, the R wave, and the S wave. *appearance depends on lead* - Q wave: first downward deflection; less than 0.04 sec; *not always present* - Duration: Normally *0.06 -0.10 secs (1 ½ - 2 ½ small boxes)* - Amplitude: 5 to 30 mm high (1 -6 large vertical boxes)
1st step in ECG analysis
Determine the HR - First, estimate if the HR is fast, slow, or normal by looking at the space between the QRS complexes -Then, determine the actual or approximate HR
PR interval (Step 5/9)
Distance from the beginning of the P wave to the beginning of the Q wave. *2 parts*= P wave + PR segment A normal PR interval is *0.12 - 0.20 (3-5 small squares)* seconds in duration; - A short PR interval (less than 0.12 secs) is seen when electrical impulse arises close to the AV junction, - A longer PR interval an even greater delay in conduction of impulse through the AV junction known as an *AV heart block*.
ST segment
During this period the ventricles are preparing to repolarize
ST segment (Step 6/9)
During this period the ventricles are preparing to repolarize.
Atrial Dysrhythmias/ P prime waves
Dysrhythmias that arise outside of the SA node, from the atrial tissue or in the internal pathways. *Produce P prime waves* - How the P prime waves look depends on where it originates and the direction of the electrical impulse. - *the closer the site of origin is to the SA node, the more it looks like a normal P wave. - P prime waves coming from one site will look similar while P prime waves that continuously change in appearance indicate that the impulse is arising from different locations in the atria.
ECG tracing
ECG rhythm printed out onto graph paper which show electrical activity which has already occured
Dynamic ECG
ECG rhythm shown on an oscilloscope which represent real time electrical activity
ECG lead placing
Each configuration or positioning of lead wires is referred to as a "lead"
P prime waves seen with early atrial beats
Early atrial beats preceded by a P prime wave have a different morphology than other normal beats. - Appearance depends on where the ectopic beat arise from. - the P prime wave may be obscured and/or buried in the T wave of the preceding beat; result in in a short P-P interval
Wide QRS complexes of *supraventricular* origin
Even though a cardiac rhythm originates from a supra ventricular site, the subsequent conduction of the impulses through the ventricles can be impaired which can result in wide, bizarre QRS. Associated with: - Intraventricular Conduction Defect - Abberant Conduction - Ventricular Preexcitation - Pacemaker induced QRS
Artifact
Factors that interfere with the signal being detected and transferred to the ECG machine.
U waves (Step 9/9)
In about 50%- 75% of ECGs except in lead aV1
Limb leads
Include 4 electrodes placed on the arms and legs or on the upper torso at least 10 cm from the heart. I, II, III: bipolar leads aVR, aVL, AVF: unipolar leads
horizontal plane leads
Is a transverse (sup/inf) cut through the middle of the heart. The leads arranged on this plane *provides with anterior, lateral and posterior views*. Also called precordial leads or V leads
ECG Frontal plane
Is a vertical (ant/post) cut through the middle of the heart. The leads arranged in the frontal plane *view the inferior, superior and lateral sides of the heart*. Also referred to as *limb leads*
T Waves (Step 7/9)
It is larger than the P wave; the peak is close to the end than the beginning. Normally, the T wave is not more than 5 mm in height in the limb leads or 10 mm in the precordial lead
P waves in AV heart block
More P waves than QRS complexes indicate that the impulse was initiated in the SA node or another ectopic site in the atria but was blocked and did not reach the ventricles.
Lead II
Most commonly used to monitor for emergencies or existing cardiac dysrhythmias. It is a combination of a positive lead wire (LL), negative lead wire (RA), and one or two ground lead wires (LA)
If the ectopic pacemaker arises from the upper- or middle- right atrium, depolarization occurs in a _______________ direction.
Normal
QT interval (Step 8/9)
Normal Duration: *0.36 - 0.44 sec* Varies according to age, sex, HR- the faster the HR, the shorter the QTinterval.
Longer PR intervals
Occur when the impulse is delayed beyond normal as it passes through the AV junction. *Associated with: AV heart block*
Pause or Arrest of the Sinus Node
Occurs when the *SA node fail to initiate an impulse*. Usually observed as a *sudden* absence of a P wave, QRS complex, and T wave *followed by recovery* of the SA node which fires another impulse. If the SA node frequently fails to fire, then there will be many pauses, causing the rhythm to look frequently (very) irregular. *frequent pauses are likely to lead to a bradycardic HR*
Varying PR intervals
Occurs when the pacemaker site in the atria changes from beat to beat. Also occurs in one form of AV heart block *(Mobitz 1)*, where the *PR interval becomes increasingly longer* until finally a QRS complex is dropped.
If we suspect that the P wave is not originating in the SA node, we refer to this shortened PR interval as ______________.
P prime R interval
Count atrial rate by counting ________ _________.
P waves
To assess atrial regularity, we asses _____________
P-P intervals
Ventricular Preexcitation
Premature depolarization of the ventricles that occurs when an impulse arises from a site above the ventricles but *travels through accessory conduction pathways to the ventricles* (by passes the av node, purkinje system and bundle branches) - Has an abnormal slurring and sometimes notching at its onset, known as *delta waves*
Wide, Bizarre QRS complexes
Produced by ventricular dysrhythmias. - Preceded by a P wave -T wave is in the opposite direction as the R wave Caused by: -Early beats: Associated with a compensatory pause - Escape Rhythm: characteristic feature are rate or 20-40 bpm
Count ventricular rate by counting __________ __________.
QRS complexes
To assess ventricular regularity, we assess ______________.
R-R intervals *if the R wave is not present, then use either the Q or S wave (whichever is tallest).
If the P prime wave follows the QRS complex (sometimes seen in dysrhythmias from the AV junction), it is referred to as the _________.
RP prime interval
PR segment
Represents the impulse traveling through the HIS-Purkinje system and is seen as a flat line between the P wave and Q wave.
If the impulse arises from the lower- right atrium near the AV node or in the left atrium, depolarization occurs in a __________ direction.
Retrograde (meaning the impulse conducts upward [backward] through the heart) *results in an inverted P wave*
Absent QRS
Seen in Ventricular Fibrillation and asystole
Paper and pen method
Simple and quick method used to determine regularity: To employ this method, place marks on a paper above two consecutive P or R waves. Then move the paper across the tracing, matching the marks on the paper against subsequent consecutive P waves or R waves.
P-P interval
The distance between consecutive P waves. (normal/regular= they should be the same)
R-R interval
The distance between consecutive QRS complexes. (normal/regular= they should be the same). *a slight variance of one small square (0.04 sec) is still considered normal*
Vertical Lines
The distance between lines, or boxes, running vertically represents *amplitude in millimeters (mm)* or *voltage in millivolts (mV)*
Horizontal Lines
The distance between the lines or boxes running horizontally represent *time or duration*. *Horizontal measurements are used to determine heart rate*
Conduction ratio
The number of atrial waveforms (P waves) to ventricular waveforms (QRS complexes). Normally 1 to 1 irregularity can result from dysrhythmias that have a varying conduction ratio.
300, 150, 100, 75, 60 method
Used to determine HR Also called countdown; involves locating the R wave (which is usually the most prominent deflection of the QRS complex) on a bold line on the ECG paper, assigning that R wave as the "starting point", then find the next consecutive R wave. If it is on a *bold line* then the HR is the value of that line (300, 150, 100, 75, 60) - in some cases the S wave may be most prominent deflection, in which case you would use the S wave as the starting point. - *advantage*: it is quick and easy; requires no tools, calculations or rulers; is fairly accurate - *disadvantage: can only be used if the rhythm is regular*
6 second interval x 10 method
Used to determine HR Involves multiplying by 10 the number of QRS complexes found in a 6 second portion of the ECG tracing. ECG paper typically has markings on the top and/or bottom indicating each 3-sec block of time: the fore 2 consecutive blocks of time = 6 seconds - *Effective for assessing the rate of an irregular rhythm* - *advantage*: quick and easy; does not require any tools - *disadvantage*: not as accurate
1500 method
Used to determine HR: Involves counting the number of small squares between two consecutive R waves divide 1500 by that number.
Rate calculators
Used to determine HR: simple plastic devices about the size of a book mark that can be overlaid on an ECG tracing to show the HR. *advantage*: quickly identifies HR disadvantage: must have it available anytime you need to calculate a pts HR *can also be used to determine regularity*
Caliper method
Used to determine regularity: To employ this method, place one leg on the starting point and extend the second leg to the next consecutive waveform being assessed, then compare this distance across the ECG. *If the R-R or P-P interval is is irregular the point will be situated before or after the identified waveform
Counting the small squares method
Used to determine regularity: Performed by counting the number of small squares on the ECG paper between the peaks of two consecutive R or P waves and then compare it to other R-R (or P-P) intervals.
Intraventricular Conduction Defect
Usually occurs as a result of R or L bundle branch block. A block in one bundle branch cause the ventricle on that side to be depolarized later than the other. -Partial (incomplete) block: less of a delay; QRS complex greater than 0.10sec but less than 0.12sec & does not appear completely normal -Other causes: MI, fibrosis, hypertrophy, electrolyte imbalance, excessive cardiac drugs
P prime waves seen with Tachycardia
When tachycardia arises from the atria the P waves have a different morphology and *may be buried* in the T wave of the preceding beat. *supraventricular tachycardia*:tachycardias with normal QRS complexes and no discernible P waves
Unipolar leads
________________ only use one positive electrode and a reference point calculated by the ECG machine. The reference point lies in the center of the heart's electrical field located left to the inter ventricular septum and below the AV junction.
Paroxysmal
a term used to describe a dysrhythmia that has a sudden, or rapid onset and resolution. *Irregularity can result from sudden rapid acceleration or deceleration of HR*.
QRS complex
corresponds with: Ventricular contraction *should be narrow and sharp (no longer/wider than 3 small squares)*
P wave
corresponds with: atrial contraction
T wave
corresponds with: ventricular repolarization
As electricity heads away from the lead it causes an ___________ deflection
downward/negative
Occasionally or very irregular rhythms occur due to _______________________________.
early beats or pause in or arrest of the impulse arising from the *SA node*.
Very tall QRS complexes are usually caused by __________.
hypertrophy of one or more ventricles or an aberrantly conducted beat, or an abnormal pacemaker.
Short PR interval
less than 0.12 sec: Occur when the impulse that initiates the Heart beat originates outside the SA node- in the lower atria, AV junction, or an accessory pathway. *The shorter the distance the impulse has to travel the shorter the PR interval*
QT interval
measures the time of ventricular depolarization and repolarization
Low voltage or abnormally small QRS complexes may be seen in ____________________.
obese patients, hyperthyroid patients, and patients with Pleural Effusion
Slightly irregular
occurs when the P-P or R-R intervals vary just a bit. The difference between slightly irregular and occasionally irregular rhythms is that *slightly irregular rhythms are continuous throughout the ECG tracing*; with occasionally irregularity, the rhythm is mostly regular but there are areas where it is irregular. *caused by: initiation of the heart beat (pacemaker) within the atria changes from sight to site with each beat* instead of arising from the SA node;
Electromagnetic interference
originates outside the patient and is caused by interference from electronic sources such as power cords, insufficiently grounded alternating current powered equipment, ad nearby use of portable radios
Cardiac axis
the general direction of electricity through the heart
P waves can also be absent if
the impulse arises from the ventricles
precordial leads
unipolar leads
As electricity heads towards the lead it causes an ___________ deflection
upward/positive
Measuring QRS
width: First identify the complex with the longest duration and most distinct beginning and ending.
