1. Fast & Easy ECGs – A Self-Paced Learning Program8
Sinus Dysrhythmias
Fast & Easy ECGs – A Self-Paced Learning Program Q I A

2. Identifying Dysrhythmias
Examination of the ECG rhythm must be done in a systematic, organized way
Instructional point:
A dysrhythmia is an ECG rhythm that differs from normal sinus rhythm. I

3. 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

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

5. 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

6. Sinus Bradycardia Instructional point:
It often occurs naturally as a means of conserving energy during times of rest or sleep. I

7. 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

8. Sinus Tachycardia
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. Sinus Tachycardia Instructional point:
When the stimulus for the tachycardia is removed, the dysrhythmia spontaneously resolves. I

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

12. 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

13. Sinus Dysrhythmia
Can occur naturally in athletes, children, and older adults
Can also occur in:
Patients with heart disease or inferior wall myocardial infarction
Individuals receiving certain drugs such as digitalis and morphine
Conditions where there is increased intracranial pressure

14. 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

15. Sinus Arrest Occurs when the SA node transiently stops firing
Causes 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

16. 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

17. Sinus Arrest 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

18. Sinus Arrest

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. Summary
A dysrhythmia is an ECG rhythm that differs from normal sinus rhythm (NSR).
Examination of the ECG rhythm must be done in a systematic, organized way.
Rhythms originating from the SA node are called sinus rhythms.

29. Summary
Normal sinus rhythm has a heart rate of 60 to 100 BPM (in the average adult).
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.

30. 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.