Sinus Rhythms
Normal Sinus Rhythm
| Parameter | Definitions |
|---|---|
| HR | Between 60 and 100 |
| Regularity | Regular |
| P | Upright, regular P waves |
| QRS | Narrow QRS complexes |
| P:QRS Ratio | 1:1 |
Normal sinus rhythm is a common finding in all adults and children regardless of underlying etiology. As Hudson and Brady (2023) puts it, "normal sinus rhythm neither confirms nor rules out any acute process or injury." However, in the absence of any other cardiovascular signs or symptoms, it can be a fairly safe move to direct your attention to other body systems.
Sinus Bradycardia
| Parameter | Definitions |
|---|---|
| HR | Less than 60 |
| Regularity | Regular |
| P | Upright, regular P waves |
| QRS | Narrow QRS complexes |
| P:QRS Ratio | 1:1 |
Sinus Bradycardia can result from a variety of conditions that targets the SA node, such as electrolyte abnormalities or an inferior MI. Certain medications such as beta-blockers can lower the heart rate at the SA node. As well, vagal nerve stimulation can induce a bradycardia. Increased vagal tone is often the reason given for the lower resting heart rate in athletes.
Most people can tolerate a low heart rate less than 60. Even at rates of 20-30, a person with a relatively robust cardiovascular system can increase their cardiac output enough to compensate for the lower heart rate.
In the emergency department, Sinus Bradycardia is treated as per ACLS guidelines.
Sinus Tachycardia
| Parameter | Definitions |
|---|---|
| HR | Greater than 100 |
| Regularity | Regular |
| P | Upright, regular P waves |
| QRS | Narrow QRS complexes |
| P:QRS Ratio | 1:1 |
Sinus Tachycardia is often a physiological response to some sort of stressor such as exercise, infection, and dehydration. Certain substances (such as salbutamol/albuterol and caffeine) can also cause an increase in heart rate.
The mainstay "treatment" is to treat the underlying cause, or at least monitor that there's no ill effect if it was a known medication that caused this. Very rarely is sinus tachycardia idiopathic or inappropriate - in those cases, consult to cardiology for follow-up and possible intervention.