Now let’s talk about Tachycardia both stable and unstable.
A heart rate in adults that is greater than 100 beats per minute is technically defined
as tachycardia.
Now many things can cause tachycardia like fever, shock, medications, stress, metabolic
dysfunction, or damage to the heart muscle and hypoxemia to name a few.
Perfusion problems may develop when the heart beats too fast and the ventricles are not
able to fully fill with blood, which is technically called ejection fraction compromise due to
the lack of pre-load before the heart fully contracts.
Now this can cause a decrease in cardiac output, poor perfusion and hemodynamic instability.
It’s important to quickly assess the patient's signs and symptoms and see if they are a result
of the tachycardia.
It’s important to find the underlying causes and treat them.
A patient with a heart rate of 100 to 150 beats per minute rarely has symptoms related
to the tachycardia.
Symptoms in this range are typically a result of another medical issue.
But, the higher the heart rate, the more likely tachycardia is the culprit of the patient’s
symptoms.
A thorough primary and secondary survey will help us properly assess the patient’s condition.
Now, when we have a patient with tachycardia the first step is to identify whether or not
the patient is stable.
A stable patient usually does not have any serious signs or symptoms as a result of the
increased heart rate.
In other words, there is no altered mental status, no chest pain, no hypotension, or
other signs of shock.
For a stable patient we would check patient vitals, monitor oxygen saturation, and give
oxygen as needed, get an ECG or a 12 lead, and identify the heart rhythm and start an
IV.
If the patient is determined to be unstable, synchronized cardioversion is the treatment
of choice and needs to be done immediately.
If time permits and the patient is conscious, we could consider sedation for discomfort
from the electrical therapy but if time doesn’t permit, we may need to defibrillate regardless
of sedation.
Now, if a patient does not have a pulse, we will treat the rhythm as if it were ventricular
fibrillation and follow the pulseless arrest algorithm.
The first step to identifying a tachycardic heart rhythm is to determine if the QRS is
wide or narrow.
A wide QRS complex is .12 seconds or greater, and a narrow QRS is less than .12 seconds.
Narrow complex tachycardias typically originate above the ventricles while wide complex tachycardias
typically originate in the ventricles and have a higher risk of deteriorating into cardiac
arrest.
For a patient with a regular narrow-complex stable tachycardia, it would be appropriate
to attempt vagal maneuvers first.
If that does not work then we may give adenosine 6 mg rapid IV push.
If the patient does not convert and remains stable, give a second dose of adenosine 12
mg rapid IV push.
Remember to remind the patient that after giving that adenosine, they may get a feeling
of breathlessness, or a flushed feeling, or as if their heart is skipping a beat.
This will pass quickly, and they should return to normal.
For a stable patient with an ECG rhythm that shows an irregular narrow-complex QRS tachycardia,
it is probably atrial fibrillation, atrial flutter, or multi-focal atrial tachycardia.
This would require expert consultation for treatment.
For a stable patient that has regular or irregular wide-complex QRS tachycardia, you would need
expert consultation as well.
Often antiarrhythmics are used to treat this such as procainamide or amiodarone.
However, the management and treatment of wide complex stable tachycardias requires advanced
knowledge of ECG rhythm interpretation and anti-arrhythmic therapy.