When a patient’s heart beats too fast and starts to affect blood pressure or consciousness, immediate treatment becomes critical. Unstable tachycardia is a serious and life-threatening condition that demands fast recognition and decisive action from healthcare providers. Left untreated, it can quickly lead to cardiac arrest, organ failure, or death.
The first line treatment for unstable tachycardia plays a major role in stabilizing the patient and restoring proper blood flow to vital organs. Early intervention can prevent complications and improve the chances of survival.
This guide from Heart Start CPR covers what unstable tachycardia means, the signs you need to look for, and the key steps that must be taken to respond to this emergency with confidence.
What Is Unstable Tachycardia?
Unstable tachycardia occurs when a patient’s heart beats too fast for the body to maintain adequate blood pressure and perfusion. Unlike stable tachycardia, which may not show any outward symptoms, unstable tachycardia is a true emergency. The rapid heart rate disrupts the heart’s ability to pump blood and leads to life-threatening conditions like hypotension, shock, and cardiac ischemia.
It’s important to understand that “unstable” refers to the effect the arrhythmia has on the patient’s circulation and mental status, not just the heart rate itself. Even a moderately elevated heart rate can be considered unstable if it causes serious symptoms.
Unstable tachycardia can be triggered by a variety of underlying rhythms, including supraventricular tachycardia (SVT), atrial fibrillation with rapid ventricular response, ventricular tachycardia, and others.
Also read: tachycardia ACLS algorithm
Signs and Symptoms of Unstable Tachycardia
Unstable tachycardia presents with a combination of clinical signs that reflect poor blood flow and cardiac dysfunction. Common indicators include:
- Hypotension (low blood pressure)
A drop in blood pressure can suggest that the heart is not pumping effectively. - Altered mental status
Symptoms such as confusion, restlessness, or unresponsiveness may point to inadequate brain perfusion. - Chest discomfort or pain
Reduced coronary perfusion can cause pressure, tightness, or pain in the chest. - Shortness of breath or respiratory distress
Difficulty breathing can develop as the heart struggles to meet the body’s oxygen demands. - Signs of shock
Look for pale, cool, or clammy skin and weak peripheral pulses, all classic signs of poor circulation. - Rapid heart rate
Typically greater than 150 beats per minute in adults, though clinical symptoms matter more than the exact number.
First Line Treatment for Unstable Tachycardia
The first line treatment for unstable tachycardia is immediate synchronized cardioversion. This procedure involves delivering a controlled electrical shock to the heart. The shock is timed precisely to reset the heart’s rhythm back to normal.
Synchronized cardioversion is different from defibrillation as it detects the patient’s QRS complex and delivers the shock at the optimal time to avoid causing a dangerous arrhythmia. It is specifically used for conditions like supraventricular tachycardia (SVT), atrial fibrillation with rapid ventricular response, and monomorphic ventricular tachycardia with a pulse.
Immediate cardioversion helps restore stable circulation quickly, relieve symptoms, and prevent cardiac arrest. If time allows, sedation can be provided to make the procedure more comfortable for the patient.
Understanding Synchronized Cardioversion
Synchronized cardioversion works by interrupting the abnormal electrical pathways in the heart. The device (monitor/defibrillator) “syncs” the shock with the patient’s own heartbeat, avoiding delivery during a vulnerable period of the cardiac cycle, which could trigger ventricular fibrillation.
The process involves applying adhesive electrode pads to the chest, connecting to a monitor-defibrillator capable of synchronized mode, and delivering the shock at the precise moment the heart can safely reset. Proper technique, equipment preparation, and clear team communication are essential for success.
Cardioversion Energy Levels Based on Rhythm
Cardioversion energy levels refer to the amount of electrical energy delivered to the heart during the cardioversion procedure. The appropriate energy level depends on the type of arrhythmia being treated. The goal is to reset the heart’s rhythm back to normal without causing further harm or complications.
Here’s how energy levels are set for different types of tachyarrhythmias:
- Narrow regular rhythms (e.g., SVT, atrial flutter):
Initial dose of 50–100 Joules. - Narrow irregular rhythms (e.g., atrial fibrillation):
Initial dose of 120–200 Joules (biphasic). - Wide regular rhythms (e.g., monomorphic ventricular tachycardia):
Initial dose of 100 Joules. - Wide irregular rhythms (e.g., polymorphic VT or ventricular fibrillation):
Unsynchronized high-energy shock (defibrillation) is required.
If the initial shock is unsuccessful, energy levels can be increased according to ACLS guidelines.
Also Read: Differences between Ventricular Fibrillation and Pulseless Ventricular Tachycardia
Key Actions Before and After Cardioversion
Here are the critical steps you’ll want to follow before and after delivering the shock:
Before Cardioversion:
- Manage the airway and oxygenation.
Make sure the airway is secure and monitor oxygen levels closely. Good oxygenation helps improve outcomes.
- Connect the patient to a cardiac monitor and get baseline vitals.
You’ll want to see what’s happening with their heart rhythm and blood pressure before proceeding.
- Establish IV access if possible.
Having an IV line ready gives you a fast way to administer medications if needed.
- Sedate the patient if time allows.
If the patient is awake and stable enough, light sedation can make the procedure much more comfortable.
- Set the defibrillator to synchronized mode.
Always confirm that the sync markers are showing on the ECG — this ensures the shock is delivered safely at the right point in the cardiac cycle.
After Cardioversion:
- Monitor continuously.
Keep the cardiac monitor and vitals going. Watch closely for any recurrence of arrhythmias or signs of hemodynamic instability.
- Be ready for follow-up care.
Some patients may need additional treatment depending on how they respond after cardioversion, especially if blood pressure remains low or rhythms become unstable.
How Heart Start CPR Prepares You for Emergency Response
At Heart Start CPR, we emphasize real-world preparation for cardiac emergencies. Our ACLS certification courses cover the recognition and management of unstable tachycardia, with special focus on practical skills like synchronized cardioversion. Students have the opportunity to practice using advanced equipment in simulation scenarios.
Our training goes beyond the textbook. We prepare you to assess patients quickly, work effectively as part of a resuscitation team, and make critical decisions under stress. Whether you’re a healthcare provider, first responder, or clinical team leader, Heart Start CPR ensures you are ready to deliver life-saving interventions when every second counts.
Join us at Heart Start CPR and take the next step toward improving your emergency response skills.
