The Unstable Patient

The Unstable Patient: Medication

If the patient is unstable, there are two possible actions: medication or electricity.

The medication in this scenario is adenosine, but it should only be used if the QRS complex is:

1. Narrow or ≤ 0.12 seconds
2. Regular

Adenosine has a very short half-life and should be given as rapidly as possible into an intravenous site close to the heart, such as the antecubital fossa, and preferably through a large bore cannula.¹

The adenosine should be followed by a rapid normal saline flush of 20 mL to rush the drug to central circulation. The initial dose of adenosine is 6 mg. An additional dose of 12 mg can be given if the first dose is ineffective.

The patient should be warned that adenosine can cause symptoms such as lightheadedness, dizziness, and even chest pain, as it causes a temporary asystole (which lasts only seconds but will feel like an eternity for the patient and clinicians watching the cardiac monitor).

Adenosine is an antiarrhythmic drug. It can be used to attempt cardioversion.²

Related Video -Adenosine – ACLS Drugs

Read: Wide Complex Tachycardias

The Unstable Patient: Synchronized Cardioversion

Synchronized cardioversion is the treatment of choice for patients who are unstable and may or may not have been treated with adenosine. Whether to try adenosine first for regular narrow complex tachycardias is dependent on the patient’s condition. For patients who are very unstable, synchronized cardioversion is likely the best first option.

If there is time without compromising the patient’s condition, sedation should be given to patients with tachyarrhythmias undergoing synchronized cardioversion, as the shock is quite painful.

However, shock should not be delayed if the patient’s condition is rapidly deteriorating. Remember that it can take several minutes to start an intravenous line, draw up the necessary meds, inject them, and then wait for them to take effect.

Energy Settings for Synchronized Cardioversion

To perform synchronized cardioversion, set the biphasic energy level to 50–100 J for atrial flutter and other supraventricular tachycardias.³ If the monitor exhibits atrial fibrillation, a biphasic dose of 120–200 J is recommended. If the monitor shows monomorphic ventricular tachycardia, the biphasic dose is 100 J.

Related Video – ECG Rhythm Review – Atrial Flutter

Atrial Flutter — cardioversion with 50–100 J

Related Video – ECG Rhythm Review – Supraventricular Tachycardia (SVT)

SVT 50–100 J

Related Video – ECG Rhythm Review – Atrial Fibrillation

Atrial Fibrillation 120–200 J

Related Video – ECG Rhythm Review – Ventricular Tachycardia

Monomorphic Ventricular Tachycardia 100 J

Steps in Performing Synchronized Cardioversion

Performing synchronized cardioversion is a little different than defibrillating a patient.

First, the patient will likely be conscious, and sedation should be provided unless the patient is severely compromised and deteriorating quickly.

Second, there is a difference between synchronized cardioversion and defibrillation in terms of where in the cardiac cycle the electricity is delivered. In defibrillation, the shock can be delivered anywhere in the cardiac cycle.

However, in synchronized cardioversion, the electrical energy is delivered at the peak of the R wave, thus delivering energy at the vulnerable point in the cardiac cycle (on the T wave) is avoided, as this could cause the rhythm to deteriorate into ventricular fibrillation.⁴

Related Video – Synchronized Cardioversion for Tachycardia

The steps in synchronized cardioversion are as follows:

• Sedate the patient when feasible.
• Turn on the cardiac monitor or defibrillator.
• Attach the leads to the patient and ensure the rhythm is displayed clearly, then attach the defibrillation or pacing pads to the patient’s chest (for smaller patients, use anterior-posterior pad placement to avoid placement of pads over monitoring leads).
• Press the SYNC button on the monitor.
• Ensure there is a marker appearing above each R wave on the monitor. If necessary, adjust the gain until the markers appear above every R wave.
• Choose the energy level on the monitor or defibrillator.
• Clear the patient.
• Press the CHARGE button.
• Clear the patient again.
• Press the SHOCK button.
• Observe the patient’s rhythm to determine whether the shock was effective.

The shock may not be immediately delivered. It takes some time for the defibrillator to synchronize the energy dose delivery with the QRS complex of the cardiac cycle.

It is also important to note that synchronized cardioversion cannot be administered for tachyarrhythmias with polymorphic QRS complexes (i.e., torsades de pointes). In that case, higher energy levels are required, and the shock will be unsynchronized.

Summary

If the patient is refractory to initial interventions to address their tachyarrhythmia, the clinician must next determine if the patient is stable or unstable. In unstable tachyarrhythmias, the patient should be treated with medication or synchronized cardioversion, which is a shock of electrical energy that is delivered with the QRS complex within the cardiac cycle.