ecg Flashcards
what are the characteristics of the P-Wave
The P-wave is a smooth, round, upright shape in lead II. It is the first of the waveforms in a Normal Sinus Rhythm.
PR Interval
Measure from the start of P-wave to the start of the QRS complex
Normally lasts 0.12 (3 small boxes) to 0.20 seconds (5 boxes). It is usually constant.
QRS
A normal QRS complex is narrow with sharply pointed waves and a duration of less than 0.12 seconds.
Q wave
It is any negative deflection that precedes an R wave.
A normal Q-wave, if present is small and usually seen in the lateral (left-sided) leads of a 12-lead ECG. If present represents electricity spreading Right to Left through the ventricular septum.
There is not always a Q-wave in lead II and a Q-wave that is greater than 1/3 the height of the QRS is abnormal.
ST Segment
The line between the QRS complex and the beginning of the T-wave
Normally isoelectric. An ST segment > 1 mm above or below the isoelectric line is highly suggestive of myocardial ischemia or injury though a 12-lead is required to determine significance.
Represents the interval between ventricular depolarization and repolarization.
T wave- 1st half represents?
Waveform after the QRS and represents ventricular repolarization.
Should be asymmetric.
1st half is the absolute refractory period where the ventricles have not sufficiently repolarized to enable another depolarization (NCECITS compares this to flushing a toilet -> if try to flush too soon, won’t flush). Nothing can stimulate the ventricles again.
Second half of T wave represent?
2nd half is the relative refractory period where some cells have repolarized sufficiently to depolarize again. A large stimulus can initiate depolarization of these cells and result in a dangerous rhythm.
TP Segment
Regarded as the isoelectric line or baseline.
Reference where we compare the J-point and ST Segment
J Point
The junction where QRS complex ends and ST segment begins.
QT Interval
Measured from the beginning of the QRS complex to the end of the T-wave.
Represents all the electrical activity of one complete ventricular cycle (depolarization and repolarization).
Length depends on heart rate and varies by gender and age. It can be affected by many factors.
A prolonged QT puts the heart at risk of lethal dysrhythmias.
As QT varies with rate, a formula is used to “correct” the QT and the result is the QTc. This “corrects” the QT to a rate of 60 and we become concerned when this number reaches greater than 450 ms).
approach to ECG
-Assess Regularity (Atrial and Ventricular)
-Assess Rate (Atrial and Ventricular)
Identify and examine waveforms
-Assess intervals (PR, QRS duration, QT) and examine the ST
Interpret rhythm and determine clinical significance.
Interpret Rhythm- include:
Specify site of origin (pacemaker) of the rhythm (sinus, atrial, junctional, ventricular).
Specify rate
Specify abnormalities (blocks, Wide QRS, Long QT, elevation or depression of T waves etc)
sinus rhythm includes?
A “normal” heartbeat starts with an electrical impulse in the Sinoatrial Node.
A rhythm that starts in the SA node has the following characteristics:
Positive P wave before each QRS (in lead II)
P-waves that are upright and look alike
Constant PR interval
Usually has a regular atrial and ventricular rate
SA block characteristics
-Irregular as a result of the pause(s). –the pause is the same or exact -multiple of distance between two other P-P intervals. Underlying rhythm is regular.
-Rate: Usually normal but varies due to pause
-P-Waves: Positive, 1:1 with QRS and -P-waves all look the same
-PR Interval: 0.12-0.20 seconds
-QRS Duration: < 0.12 seconds unless abnormally conducted.
what is an SA block?
Sinoatrial Block (aka Sinus Exit Block)
Pacemaker in the SA node initiate an impulse but it is blocked before it can exit the SA node resulting in an absent PQRST complex.
This is a disorder of impulse conduction as an impulse was initially generated.
How is sinus arrest different from a sinoatrial block?
Sinus Arrest is a disorder of impulse formation whereas SA block is a disorder of impulse conduction
The difference from a Sinus Exit Block is that the pause will not be an exact multiple of other P-P intervals.
what are the three main mechanisms that result in Atrial Dysrhythmias:
Abnormal Automaticity
Triggered Activity
Re-entry (aka Reactivation)
what is it called when a heart beat comes prematurely and is identified by the site of origin of the beat? (three possible complexes)
(Premature Atrial Complex, Premature Junctional Complex and Premature Ventricular Complex).
patterns seen in PAC
Couplet: Paired beats – 2 premature beats in a row
Run/Burst: 3 or more premature beats in a row
Bigeminy: Every other beat is a premature beat
Trigeminy: Every third beat is a premature beat
Quadrigeminy: Every fourth beat is a premature beat.
what causes a PAC?
PAC occurs when an irritable site within the atria fires before the next sinus impulse is expected.
describe how the p wave may appear in PAC’s
P-wave of the PAC may be:
Very similar to Sinus P if the irritable site is close to the SA node
Biphasic
Flattened
Pointed
Notched
Lost in preceding T-wave
Wandering Atrial Pacemaker (aka Multiform Atrial Rhythm)
There is a gradual shifting of the dominant pacemaker among the SA node, atria, and/or the AV junction. This results in variable-looking P-waves.
There need to be at least 3 different P-waves seen in the same lead for the diagnosis.
Characteristics of WAP
Usually irregular as the pacemaker site shifts
Rate is usually 60-100 but may be slower (if rate is greater than 100, this rhythm is known as Multifocal Atrial Tachycardia)
P-waves: Size, shape, and direction may change beat to beat. May be upright, inverted, biphasic, rounded, flat, pointed, notched, or buried in QRS.
PR interval: Varies as pacemaker site shifts
QRS duration: < 0.12s unless abnormally conducted.
Multifocal Atrial Tachycardia
Diagnosed when the wandering atrial pacemaker rate is greater than 100 beats per minute.
May be very fast and can be difficult to determine that there are variations.
characteristics of MAT
Irregular as pacemaker shifts but can be difficult to ascertain at very fast rates
Rate is > 100 bpm
P-waves: One before each QRS but may also be buried in the QRS. Need at least 3 different P-wave configurations.
PR Interval: Varies as the pacemaker shifts
QRS: Is usually < 0.12 unless abnormally conducted in the ventricles
what are Atrioventricular Nodal reentrant tachycardia (AVNRT) & Atrioventricular Reentrant Tachycardia
Regular, narrow complex tachycardias. In the emergency setting, in most cases won’t be able to differentiate.
AVNRT
Atrioventricular Nodal Reentrant Tachycardia: Is the most common and is caused by reentry circuit within or near the AV node allowing tachycardia to continue
AVRT
Atrioventricular Reentrant Tachycardia: An accessory pathway connects atria to ventricles and impulses can travel in similar circuit between AV node and accessory pathway. Wolff-Parkinson-White Syndrome (WPW) is an example of this.
characteristics of SVT
Very regular
Rate is > 100 beats/minute -> usually greater than 150 beats/minute
P-waves: Often not detectable as hidden in QRS.
PR Interval: Not usually measurable as unable to determine P-wave
QRS duration: < 0.12 seconds unless abnormally conducted.
Atrial Flutter
Reentrant rhythm in which irritable site in the atria fires regularly at a very rapid rate. This produces atrial waveforms that resemble teeth of a saw (commonly referred to as appearing “sawtooth”) which are called Flutter Waves or F waves.
A healthy AV node protects the ventricles from very fast rates and AV node usually can’t conduct more than about 180 impulses/minute. The rhythm may be regular or irregular depending on how the impulses are blocked in the AV node.
rates and characteristics of a flutter
-Atrial rate (F-waves) are regular. —ventricular rate may be regular or irregular depending on AV conduction and blockade
-Atrial rate is 240-300 bpm (F waves). -Ventricular rate varies but usually is not more than 180 bpm.
-P-waves: No P-waves but Flutter waves (F waves)
-PR Interval: Not measurable as no P waves
-QRS: < 0.12 seconds unless abnormally conducted or skewed by F-waves.