1. Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program11
Sinus Dysrhythmias
Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program

2. Sinus Rhythms
Rhythms originating from the SA node are called sinus rhythms
Instructional point:
Key characteristics of sinus rhythms include: Normal P wave preceding each normal QRS complex, and PR intervals that are within normal duration of 0.12 to 0.20 seconds and constant. I

3. Normal Sinus Rhythm (NSR)
During normal heart activity, SA node acts as the primary pacemaker
NSR has a heart rate of 60 to100 BPM (in the average adult)

4. Sinus Bradycardia
Has all the characteristics of NSR but the heart rate is < 60 BPM
Instructional point:
With sinus bradycardia there are longer R-R intervals and P-P intervals (making it appear like there are large spaces between the groups of complexes).
Question to ask the students “Which part of the autonomic nervous system is responsible for slowing the heart rate?”
Answer: the parasympathetic nervous system. Q I

5. Causes of Sinus Bradycardia
Often occurs naturally as body’s way to conserve energy during times of reduced demand for blood flow
Other causes include:
Instructional point:
It often occurs naturally as a means of conserving energy during times of rest or sleep. I

6. Effects of Sinus Bradycardia
Often insignificant and the patient is asymptomatic
Hypotension can result if the heart rate slows to the point where cardiac output drops sufficiently
Patients are less tolerant of rates < 45 BPM
Instructional points:
Cardiac output equals stroke volume X heart rate.
Typically, most adults are able to tolerate a heart rate of 45 to 59 beats per minute.
Hypotension occurs when the bradycardia occurs suddenly before the body compensates or when it reaches a point at which the body’s compensation is insufficient. I

7. Treatment of Sinus Bradycardia
Asymptomatic patients require no treatment but should be monitored in case there is a progression of the bradycardia
Symptomatic patients may improve with the administration of atropine, transcutaneous pacing, or administration of an IV infusion of dopamine or epinephrine

8. Sinus Tachycardia
Has same characteristics as NSR but has a rate >100 BPM
Instructional point:
It often occurs naturally as a means of increasing delivery of oxygen and nutrients and removing waste products during times of exertion, exercise or stress.
Question to ask the students “Which part of the autonomic nervous system is responsible for increasing the heart rate?”
Answer: the sympathetic nervous system. Q I

9. Causes of Sinus Tachycardia
Often occurs with physical labor, exercise, pain, fear, excitement, anxiety, and where increased sympathetic stimulation occurs in response to the need for more oxygen and nutrients at the cellular level
Other causes include those shown to the right:
Instructional point:
When the stimulus for the tachycardia is removed, the dysrhythmia spontaneously resolves. I

10. Effects of Sinus Tachycardia
Often of no clinical significance
Can increase myocardial oxygen consumption
which can aggravate ischemia (bringing on chest pain), and infarction, particularly in those with cardiovascular disease
Instructional point:
We often see sinus tachycardia in what are considered natural circumstances such as during physical labor, exercise, pain, fear, excitement or anxiety where increased sympathetic stimulation occurs in response to the need for more oxygen and nutrients at the cellular level and hence increased tissue perfusion. I

11. Treatment of Sinus Tachycardia
Asymptomatic patients require no treatment
However, patient should be encouraged to abstain from triggers such as alcohol, caffeine, and nicotine
Treatment for symptomatic sinus tachycardia is directed at treating the cause
Continued monitoring is indicated with an underlying medical or traumatic condition
For patients experiencing myocardial ischemia, consideration may be given to additional treatments that will slow the heart rate or vasodilate the coronary arteries

12. Sinus Dysrhythmia Same as NSR except there is a patterned irregularity
Described as a cycle of “slowing, then speeding up, then slowing again”

13. Sinus Dysrhythmia
The beat-to-beat variation produced by irregular firing of the SA node usually corresponds with the respiratory cycle and changes in intrathoracic pressure
Heart rate increases during inspiration and decreases during expiration

14. Causes of Sinus Dysrhythmia
Can occur naturally in athletes, children, and older adults
Other causes include:

15. Effects of Sinus Dysrhythmia
Usually of no clinical significance and produces no symptoms
In some patients and conditions it may be associated with palpitations, dizziness, and syncope

16. Treatment of Sinus Dysrhythmia
Provided the patient is asymptomatic, usually no treatment is needed
If unrelated to respirations, consideration may be given to treating the underlying cause

17. Sinus Arrest Occurs when the SA node transiently stops firing
Results in short periods of cardiac standstill until a lower-level pacemaker discharges or the SA node resumes its normal function
Instructional point:
The usual result of sinus arrest is a brief pause in all electrical activity. I

18. Sinus Arrest Most prominent characteristic is a pause in ECG rhythm
Produces an irregularity
Rhythm typically resumes its normal appearance after pause unless an escape pacemaker resumes the rhythm

19. Causes of Sinus Arrest
Results from marked depression in SA node automaticity
Causes include:
Instructional point:
Frequent or protracted episodes of sinus arrest can compromise cardiac output by decreasing heart rate and eliminating the atrial contribution to ventricular filling.
There is also a danger that sinus node activity will completely cease and an escape pacemaker may not take over pacing (resulting in asystole). I

20. Effects of Sinus Arrest
Becomes clinically significant with an extended pause or when there are frequent occurrences of the pause or arrest
Can lead to a drop in cardiac output and decreased blood pressure and tissue perfusion
There is also a danger that SA node activity will completely cease and an escape pacemaker may not take over pacing

21. Treatment of Sinus Arrest
Asymptomatic patients require no treatment
Symptomatic patients may be treated with administration of atropine or temporary or permanent ventricular pacing
Reasons to pace include the development of an AV junctional or ectopic ventricular pacemaker that is slow enough to result in such problems as syncope, CHF, angina, or frequent ventricular ectopic beats
As needed, drugs affecting SA node discharge or conduction, such as beta-adrenergic blockers, calcium channel blockers, and digoxin, should be discontinued

22. Sinoatrial Exit Block
Occurs when the SA node fires but conduction to the atria is delayed or blocked

23. Causes of Sinoatrial Exit Block
Include the following:

24. Effects of Sinoatrial Exit Block
Is usually insignificant
Can be clinically significant when there is an extended pause or when there are frequent occurrences of the dropped P waves (and subsequent QRS complexes)
Can lead to decreased heart rate, a drop in cardiac output, and decreased blood pressure and tissue perfusion

25. Treatment of Sinoatrial Exit Block
No treatment is indicated provided the patient is asymptomatic
If the patient is symptomatic, treatment includes administration of atropine or temporary or permanent ventricular pacing

26. Sick Sinus Syndrome
Is a group of abnormal rhythms that occur with malfunction of the sinus node
Bradycardia-tachycardia syndrome is one variant in which slow dysrhythmias and fast dysrhythmias alternate

27. Causes of Sick Sinus Syndrome
Is a moderately uncommon disorder
Causes include the following:

28. Effects of Sick Sinus Syndrome
Although many types are symptom free, patients may present with Stokes-Adams attacks, fainting, dizziness or lightheadedness, palpitations, chest pain, shortness of breath, fatigue, headache, and nausea

29. Treatment of Sick Sinus Syndrome
Bradydysrhythmias are well controlled with pacemakers whereas tachydysrhythmias respond well to medications
However, because both bradydysrhythmias and tachydysrhythmias may be present, drugs to control the rapid heart rates may worsen bradydysrhythmia
For this reason, a pacemaker is implanted before drug therapy is begun for the tachydysrhythmia

30. Sinus Rhythm as Underlying Rhythm
Sinus rhythm may be what is referred to as an underlying rhythm. What
that means is the sinus rhythm is seen, but then there is another dysrhythmia
or cardiac condition seen as well. For example, if there is a delay in
conduction through the AV node (referred to as first degree AV block, in
chapter 15) then we call it sinus rhythm with first degree AV block (Figure
11-9A). Similarly, if there are early beats, we call it sinus rhythm with
early beats

31. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 70 BPM, Ventricular rate 70 BPM, patterned irregularity (speeds up toward center of tracing and slows down again), normal and upright P waves, normal QRS complexes at 0.08 seconds, PRI seconds, QT seconds. Sinus dysrhythmia. I

32. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 86 BPM, Ventricular rate 86 BPM, regular rhythm, upright and normal P waves, QRS (more accurately described as QS) complexes at 0.08 seconds, PRI seconds, QT seconds. Sinus rhythm. I

33. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 125 BPM, Ventricular rate 125 BPM, regular rhythm, upright and tall P waves, QRS complexes at 0.08 seconds, PRI 0.16 seconds, QT 0.36 seconds. Sinus tachycardia. I

34. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 40 BPM, Ventricular rate 40 BPM, regular rhythm, normal and upright P waves, normal QRS complexes at 0.10 seconds, PRI seconds, QT seconds. Sinus bradycardia. I

35. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 70 BPM, Ventricular rate 70 BPM, patterned irregularity (slows down toward center of tracing and speeds up again), normal and upright P waves,
normal QRS complexes at 0.06 seconds, PRI seconds, QT seconds. Sinus dysrhythmia. I

36. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 130 BPM, Ventricular rate 130 BPM, regular rhythm, upright and tall P waves, QRS (more accurately described as RS) complexes at 0.08 seconds, PRI seconds, QT seconds. Sinus tachycardia. I

37. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 60 BPM, ventricular rate 60 BPM, patterned irregularity, normal and upright P waves, normal QRS complexes at 0.08 seconds, PRI 0.20
seconds, QT seconds. Sinus dysrhythmia. I

38. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 128 BPM, Ventricular rate 128 BPM, regular rhythm, upright and tall P waves, QRS complexes at 0.12 seconds, PRI 0.12 seconds, QT 0.32
seconds. Sinus tachycardia. I

39. Practice Makes Perfect
Determine the type of dysrhythmia
Answer: Atrial rate 60 BPM, Ventricular rate 60 BPM in the underlying rhythm (50 BPM with the pause), occasionally irregular, normal and upright P waves,
notched QRS complexes at 0.10 seconds, PRI seconds, QT seconds. Normal sinus rhythm with sinus arrest. I

40. Summary Rhythms originating from the SA node are called sinus rhythms.
Normal sinus rhythm has a heart rate of 60 to 100 BPM (in the average adult).

41. Summary
Sinus bradycardia has all the characteristics of normal sinus rhythm but the heart rate is less than 60 BPM.
Sinus tachycardia has the same characteristics as normal sinus rhythm but has a rate of greater than 100 BPM.

42. Summary
Sinus dysrhythmia is the same as sinus rhythm except there is the presence of a patterned irregularity. It can be described as a cycle of “slowing, then speeding up, then slowing again.”
With sinus arrest the ECG rhythm looks like normal sinus rhythm except there is a pause in the rhythm or an absence of the P, QRS, and T waveforms until a pacemaker site reinitiates the rhythm.

43. Summary
With sinoatrial exit block, there is a pause in the rhythm with an absence of the P, QRS, and T waveforms. Then the P wave (and associated QRS complex) reoccurs at the next expected interval
Sick sinus syndrome is a group of abnormal rhythms that occur with malfunction of the sinus node
Sinus rhythms may be what are referred to as an underlying rhythm. This is where the sinus rhythm is seen but then another dysrhythmia or cardiac condition is seen as well