6: Rhythm Identification

Question 1

What distinguishes sinus node reentry from sinus tachycardia?

Answer 1

It is only the abrupt onset and offset that distinguishes sinus node reentry from sinus tachycardia.

Question 2

What is the difference between Mobitz 1 and 2?

Answer 2

In both there are dropped QRS Complexes, but only in Mobitz 1 is there a lengthening of the PR Interval.

Question 3

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.

Answer 3

Complete LBBB

Question 4

Every other beat is a PVC in a regular pattern.

Answer 4

Ventricular Bigeminy

Question 5

Sinus rhythm with a rate between 60 and 100.

Answer 5

Normal Sinus Rhythm

Question 6

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.

Answer 6

Complete RBBB

Question 7

Impulses discharged in the SA node are either not conducted to the atria or are done so with a delay.

Answer 7

Sinoatrial Exit Block

Question 8

Every 3rd beat is a PVC in a regular pattern.

Answer 8

Ventricular Trigeminy

Question 9

What do you look for on an EKG in atrial flutter?

Answer 9

Flutter waves, which have a predictable, sawtooth appearance.

Question 10

What causes PACs?

Answer 10

Different states of excitability promote occurrence.

Question 11

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.

Answer 11

Incomplete LBBB

Question 12

What causes a sinus pause?

Answer 12

Intermittent failure of the sinus node impulse generation.

Question 13

Complete loss of P Wave functioning. Narrow QRS. Slower rhythm.

Answer 13

Junctional Dysrhythmias

Question 14

AV node gets excited and causes HR >100.

Answer 14

Junctional Tachycardia

Question 15

Progressive lengthening of the PR Interval followed by a dropped QRS Complex.

Answer 15

Second-Degree Block 1 (Mobitz 1, Wenckebach)

Question 16

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.

Answer 16

Accelerated Idioventricular Rhythm

Question 17

P Wave fires prematurely. A very early one can block the QRS Complex or cause it to be aberrantly conducted.

Answer 17

Atrial Premature Complexes (APCs or PACs)

Question 18

Is second-degree Mobitz 1 or 2 more alarming?

Answer 18

Mobitz 2, b/c it often needs a pacemaker if the rhythm can’t be reversed.

Question 19

A negative QRS complex in lead I and positive QRS complex in aVF is characteristic. The QRS duration is normal.

Answer 19

Left Posterior Hemiblock

Question 20

Manifests as a long RR cycle length, which is longer than the RR interval of the underlying sinus rhythm.

Answer 20

Sinus Pause

Question 21

Short PR Interval (<0.12 seconds) which represents a fusion beat. Delta Wave. Broad QRS Complex.

Answer 21

Wolff-Parkinson-White Syndrome

Question 22

The AV junctional rate speeds up to 61-99 and takes over the pacemaking function.

Answer 22

Accelerated Junctional Rhythm

Question 23

PR Interval is prolonged (>0.20). Delay in conduction.

Answer 23

First-Degree AV Heart Block

Question 24

P Waves and QRS Complexes dissociated. Both march along at their own rhythm. Usually requires pacemaker.

Answer 24

Third-Degree (Complete) Heart Block

Question 25

Can be normal in athletes or when sleeping.

Answer 25

Sinus Bradycardia

Question 26

Why is a left anterior hemiblock more common that a left posterior hemiblock?

Answer 26

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.

Question 27

Sinus rhythm with a rate greater than 100, but less than approximately 160-180.

Answer 27

Sinus Tachycardia

Question 28

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.

Answer 28

AV Node Escape Rhythm

Question 29

Normal in young children and elderly adults.

Answer 29

Sinus Arrhythmia

Question 30

What drug toxicity might you suspect if the AV nodal escape rhythm is faster than the normal 40-60?

Answer 30

Digoxin (digitalis) toxicity

Question 31

P Wave circling around through the atria. There may be regular QRS Complexes that follow (but not always). More of a regularly irregular pattern.

Answer 31

Atrial Flutter

Question 32

Twisting pattern of V-Tach.

Answer 32

Torsades de Pointes

Question 33

The only heart block where the P Waves can be buried.

Answer 33

Third Degree Heart Block

Question 34

When is SVT paroxysmal (PSVT)?

Answer 34

When it starts and stops on its own (independent, abrupt starting and stopping).

Question 35

Complete chaos with the rhythm. Distorted QRS Complexes. No pattern to it.

Answer 35

V-Fib

Question 36

A run of 3 or more PVCs in a row.

Answer 36

Ventricular Tachycardia

Question 37

How do you tell the difference in PAC and PVC?

Answer 37

A narrow QRS complex indicates the conduction starts at the AV node (not below it), indicating a PAC.

Question 38

Accelerated heart rate (150-250) originating above the ventricles.

Answer 38

Supraventricular Tachycardia (SVT)

Question 39

AV node fires independently, without stimulation from above. Leads to absence of P Wave (or inverted P Wave).

Answer 39

Premature Junctional Contraction

Question 40

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.

Answer 40

Sinus Node Reentry

Question 41

Variability in HR based on breathing pattern. Seen as variability between successive P Waves.

Answer 41

Sinus Arrhythmia

Question 42

How do you differential V-Tach from A-Flutter, since they both have a sawtooth pattern?

Answer 42

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.

Question 43

Caused d/t vagal inhibition.

Answer 43

Sinus Tachycardia

Question 44

How do you differentiate V-Tach and V-Fib?

Answer 44

V-Tach may have a pulse with a chaotic rhythm, but V-Fib will never have a pulse.

Question 45

Complete stopping of P Wave firing.

Answer 45

Sinus Arrest

Question 46

Which node acts as the backup pacemaker and is programmed at a slower baseline rate?

Answer 46

AV Node (SA Node is the natural pacemaker)

Question 47

What is a high risk PVC that can set you up for Torsades?

Answer 47

R-on-T

Question 48

Affected bilaterally. Wide QRS Complexes.

Answer 48

Bilateral BBB (has characteristics of both RBBB and LBBB)

Question 49

How does a sinoatrial exit block look on EKG?

Answer 49

Loss of P Waves (loss of atrial activation) and consequently loss of QRS Complexes (loss of ventricular depolarization).

Question 50

Sinus rhythm with a rate less than 60.

Answer 50

Sinus Bradycardia

Question 51

Blocked P Waves of varying degrees, without progressive lengthening of PR Interval (as indicated by a dropped QRS Complex).

Answer 51

Second-Degree Block 2 (Mobitz 2)

Question 52

What often causes Torsades?

Answer 52

Magnesium deficiency, so often associated with alcoholism.

Question 53

This is d/t continuous activity or reentry within the sinus node or the sinoatrial junction.

Answer 53

Sinus Node Reentry

Question 54

In sinus arrhythmia, the heart rate _____ with inspiration and _____ with expiration.

Answer 54

In sinus arrhythmia, the heart rate increases with inspiration and decreases with expiration.

Question 55

Results in a long pause and a complete skipped beat.

Answer 55

Sinus Arrest