Determine the following:
P waves: _______________________________________
PR interval: _______________________________________
QRS complex: _______________________________________
What's your interpretation?
(Answers on next page)
Name that strip: Answers
Rate: 45 beats/minute
P waves: Sinus
PR interval: 0.16 to 0.18 second
QRS complex: 0.08 to 0.10 second
Interpretation: Sinus bradycardia
Sinus bradycardia is a dysrhythmia that originates in the sinoatrial (SA) node, with electrical impulses discharged regularly at a rate between 40 and 60 beats/minute. The P waves are normal in size, shape, and direction and positive in lead II (a positive lead), with one P wave preceding each QRS complex. The duration of the PR interval and the QRS complex is within normal limits. The distinguishing feature of this dysrhythmia is the SA node origin and a heart rate between 40 and 60 beats/minute.
Sinus bradycardia is the normal response of the heart to relaxation or sleeping when the parasympathetic effect on cardiac automaticity dominates the sympathetic effect. It is common among trained athletes who may have a resting or sleeping pulse rate as low as 35 beats/minute. Mild bradycardia may actually be beneficial in some patients, such as in the setting of an acute myocardial infarction (AMI), because of resultant decreased myocardial workload and oxygen consumption.
Sinus bradycardia may occur with any of the following:
- during sleep and in healthy, well-conditioned individuals such as athletes
- in AMIs especially those involving the right coronary artery, which usually supplies the SA node
- as a reperfusion dysrhythmia after percutaneous coronary intervention or fibrinolytic therapy
- sick sinus syndrome
- obstructive sleep apnea
- decreased metabolic states, such as hypothermia and hypothyroidism
- pericarditis and viral myocarditis
- exaggerated vagal activity, such as carotid sinus stimulation, vomiting, coughing, and Valsalva maneuver
- sudden movement from a recumbent to an upright position (common in older adults)
- intracranial hypertension
- drugs such as digoxin, beta-blockers, or calcium channel blockers.
Sinus bradycardia does not require treatment unless the patient has serious signs and symptoms related to the low heart rate, such as hypotension, decreased mentation, and syncope. The initial treatment of choice is I.V. atropine, a drug that increases the heart rate by decreasing parasympathetic tone. If the bradycardia is atropine refractory, other treatment options include a transcutaneous pacemaker, dopamine infusion, or epinephrine infusion. The patient may require transvenous pacing. All medications that cause a decrease in heart rate should be reviewed and discontinued if indicated. For chronic symptomatic bradycardia, permanent pacing may be indicated.
Sinus bradycardia: Identifying ECG features
Rate: 40 to 60 beats/minute
P waves: Normal in size, shape, and direction; positive in lead II; one P wave precedes each QRS complex
PR interval: Normal (0.12 to 0.20 second)
QRS complex: Normal (0.10 second or less)