6: Rhythm Identification Flashcards
What distinguishes sinus node reentry from sinus tachycardia?
It is only the abrupt onset and offset that distinguishes sinus node reentry from sinus tachycardia.
What is the difference between Mobitz 1 and 2?
In both there are dropped QRS Complexes, but only in Mobitz 1 is there a lengthening of the PR Interval.
Looking at different leads helps make the diagnosis. Delayed and abnormal activation of the left ventricular myocardium and a diffuse slowing of conduction throughout the left ventricle lead to the following changes on the ECG: there is a tall monophasic and broadened R wave in leads I, aVL, and V6 instead of a septal Q wave; there is a QS complex which is abnormal and widened in V1, instead of a small initial R wave, due to septal activation; the QRS interval is prolonged >0.12 seconds; myocardial repolarization changes, including T-wave inversion and ST segment depression, are evident.
Complete LBBB
Every other beat is a PVC in a regular pattern.
Ventricular Bigeminy
Sinus rhythm with a rate between 60 and 100.
Normal Sinus Rhythm
Looking at different leads helps make the diagnosis. The initial myocardial activation is normal; thus, there is
a normal septal q wave in leads I and V6, followed by a
tall R wave. Similarly, there is a normal initial septal R
wave followed by a deep S wave in leads aVR and V1.
However, the subsequent abnormal right ventricular
activation occurs from left to right and goes through the ventricular myocardium instead of the His-Purkinje
system; thus, there will be a tall and broad secondary R
wave (R’) in leads aVR and V1 (a RSR’ complex), and
a deep and broad S wave in leads I and V6. The width
of the QRS complex is >0.12 seconds.
Complete RBBB
Impulses discharged in the SA node are either not conducted to the atria or are done so with a delay.
Sinoatrial Exit Block
Every 3rd beat is a PVC in a regular pattern.
Ventricular Trigeminy
What do you look for on an EKG in atrial flutter?
Flutter waves, which have a predictable, sawtooth appearance.
What causes PACs?
Different states of excitability promote occurrence.
Delay of conduction through the left bundle leads to slight prolongation of the QRS Complex (0.10-0.12 seconds). Initial septal activation is normal and the QRS Complexes resemble those associated with normal conduction.
Incomplete LBBB
What causes a sinus pause?
Intermittent failure of the sinus node impulse generation.
Complete loss of P Wave functioning. Narrow QRS. Slower rhythm.
Junctional Dysrhythmias
AV node gets excited and causes HR >100.
Junctional Tachycardia
Progressive lengthening of the PR Interval followed by a dropped QRS Complex.
Second-Degree Block 1 (Mobitz 1, Wenckebach)
Can occur when the backup pacemaker fails and now using the backup backup. Ventricles fire at a regular rate. QRS Complexes are wide and no P Waves.
Accelerated Idioventricular Rhythm
P Wave fires prematurely. A very early one can block the QRS Complex or cause it to be aberrantly conducted.
Atrial Premature Complexes (APCs or PACs)
Is second-degree Mobitz 1 or 2 more alarming?
Mobitz 2, b/c it often needs a pacemaker if the rhythm can’t be reversed.
A negative QRS complex in lead I and positive QRS complex in aVF is characteristic. The QRS duration is normal.
Left Posterior Hemiblock
Manifests as a long RR cycle length, which is longer than the RR interval of the underlying sinus rhythm.
Sinus Pause
Short PR Interval (<0.12 seconds) which represents a fusion beat. Delta Wave. Broad QRS Complex.
Wolff-Parkinson-White Syndrome
The AV junctional rate speeds up to 61-99 and takes over the pacemaking function.
Accelerated Junctional Rhythm
PR Interval is prolonged (>0.20). Delay in conduction.
First-Degree AV Heart Block
P Waves and QRS Complexes dissociated. Both march along at their own rhythm. Usually requires pacemaker.
Third-Degree (Complete) Heart Block
Can be normal in athletes or when sleeping.
Sinus Bradycardia
Why is a left anterior hemiblock more common that a left posterior hemiblock?
This is because the left posterior hemifascicle is much thicker than the anterior hemifascicle. It also has a dual blood supply (from the left and right coronary arteries), whereas the anterior hemifascicle does not.
Sinus rhythm with a rate greater than 100, but less than approximately 160-180.
Sinus Tachycardia
The junctional rate in an adult is 40-60. The rhythm rises because the SA node is either delayed or fails in its pacemaking function.
AV Node Escape Rhythm
Normal in young children and elderly adults.
Sinus Arrhythmia
What drug toxicity might you suspect if the AV nodal escape rhythm is faster than the normal 40-60?
Digoxin (digitalis) toxicity
P Wave circling around through the atria. There may be regular QRS Complexes that follow (but not always). More of a regularly irregular pattern.
Atrial Flutter
Twisting pattern of V-Tach.
Torsades de Pointes
The only heart block where the P Waves can be buried.
Third Degree Heart Block
When is SVT paroxysmal (PSVT)?
When it starts and stops on its own (independent, abrupt starting and stopping).
Complete chaos with the rhythm. Distorted QRS Complexes. No pattern to it.
V-Fib
A run of 3 or more PVCs in a row.
Ventricular Tachycardia
How do you tell the difference in PAC and PVC?
A narrow QRS complex indicates the conduction starts at the AV node (not below it), indicating a PAC.
Accelerated heart rate (150-250) originating above the ventricles.
Supraventricular Tachycardia (SVT)
AV node fires independently, without stimulation from above. Leads to absence of P Wave (or inverted P Wave).
Premature Junctional Contraction
This arrhythmia has a sudden onset and offset with a rate that is usually 100 to 160 beats per minute. A P wave precedes each QRS complex and has a morphology identical to the sinus P wave. The PR interval is also similar to that of sinus rhythm. Looks like a skipping pattern.
Sinus Node Reentry
Variability in HR based on breathing pattern. Seen as variability between successive P Waves.
Sinus Arrhythmia
How do you differential V-Tach from A-Flutter, since they both have a sawtooth pattern?
V-Tach has no QRS in between the flutters, b/c this F Wave is the QRS Complex, unlike in A-Flutter where there is a QRS Complex b/c the F Wave replaces the P Wave.
Caused d/t vagal inhibition.
Sinus Tachycardia
How do you differentiate V-Tach and V-Fib?
V-Tach may have a pulse with a chaotic rhythm, but V-Fib will never have a pulse.
Complete stopping of P Wave firing.
Sinus Arrest
Which node acts as the backup pacemaker and is programmed at a slower baseline rate?
AV Node (SA Node is the natural pacemaker)
What is a high risk PVC that can set you up for Torsades?
R-on-T
Affected bilaterally. Wide QRS Complexes.
Bilateral BBB (has characteristics of both RBBB and LBBB)
How does a sinoatrial exit block look on EKG?
Loss of P Waves (loss of atrial activation) and consequently loss of QRS Complexes (loss of ventricular depolarization).
Sinus rhythm with a rate less than 60.
Sinus Bradycardia
Blocked P Waves of varying degrees, without progressive lengthening of PR Interval (as indicated by a dropped QRS Complex).
Second-Degree Block 2 (Mobitz 2)
What often causes Torsades?
Magnesium deficiency, so often associated with alcoholism.
This is d/t continuous activity or reentry within the sinus node or the sinoatrial junction.
Sinus Node Reentry
In sinus arrhythmia, the heart rate _____ with inspiration and _____ with expiration.
In sinus arrhythmia, the heart rate increases with inspiration and decreases with expiration.
Results in a long pause and a complete skipped beat.
Sinus Arrest
