Supraventricular Tachycardia (SVT)
Patients with a heart rate greater than 100 beats a minute are tachycardic but, what differentiates sinus tachycardia from supraventricular tachycardia (SVT) and how are they treated? That is today’s Pass ACLS tip topic.
Sinus Tachycardia vs. Supraventricular Tachycardia (SVT)
Generally speaking, a rate of 150 or more differentiates SVT from sinus tachycardia. On the monitor both rhythms will have a narrow QRS complex less than 0.12 seconds (3 tiny boxes) preceded by an upright p wave.
If the rate is 100 to 149, it’s sinus tachycardia which, for most people with a healthy circulatory system, doesn’t usually cause problems significant enough to require intervention.
If the rate is 150 or more, the rhythm is SVT which could require immediate intervention if the patient is unstable.
Stable vs. Unstable SVT
First, review the patient’s history to identify underlying, treatable causes of tachycardia. Physical exertion, hypoxia, & hypovolemia are just a few examples of underlying, treatable conditions.
If a cardiac patient with SVT over 150 BPM exhibits any of these signs or symptoms, they should be considered unstable and in need of immediate intervention.
- Hypotension, as indicated by a systolic Blood Pressure less than 90 mm Hg;
- A sudden decrease in level of consciousness;
- Signs of shock (pale, cool & clammy skin, delayed capillary refill, or cyanosis);
- Signs of acute CHF; or
- Ischemic chest pain.
SVT Treatment Actions
If a patient in SVT doesn’t have any of the previously mentioned symptoms, they are “stable” (for now) and we have time to try things like oxygen, fluid challenge, vagal maneuvers, and Adenosine. If A-Fib or Flutter with RVR is identified after administration of Adenosine, we can use a beta blocker or calcium channel blocker. The full ACLS tachycardia algorithm is on your quick reference cards and is covered covered in another Pass ACLS Tip of the Day.
If any of the indicators of an unstable patient listed above are present after addressing underlying treatable causes, we’ll consider sedation (if appropriate & safe) and prepare for immediate cardioversion with a synchronized shock. We say to “consider sedation” because many of the medications used for sedation can cause a patient’s blood pressure to drop. So, sedation may not be appropriate for patients who are hypotensive or needed at all for patients that are unresponsive.
If we’re using a bi-phasic defibrillator we’ll use the devices’ suggested energy level. For older, (mono-phasic) defibrillators, 50-100 j is the suggested starting energy setting for cardioversion of unstable narrow complex tachycardias. (Pass ACLS Tips: defibrillation and cardioversion energy settings)
For the safety of your team, remember that delivery of a synchronized shock isn’t instant like when we defibrillate. Delivering a shock to a patient during ventricular repolarization as seen on the ECG as a T wave can result in a R-on-T and induce ventricular fibrillation; taking our patient with a pulse into cardiac arrest. To avoid this, when we’re in sync mode, the defibrillator will attempt to calculate when the next QRS should appear. To aid the defibrillator operator, a small icon will appear adjacent to each QRS when a monitor-defibrillator is in the sync mode. Because the defibrillator needs to calculate when to give the shock such that it will happen during ventricular depolarization, on a R wave and not on a T wave, there may be a few seconds lapse from the time you push the button to the time that the shock is delivered. The team leader should remind the team of this when performing synchronized cardioversion and ensure that nobody touches the patient until after the shock has been delivered. For an irregular rhythm like A-Fib with RVR, this delay can be even longer.
Most monitor/defibrillators will stay in sync mode until it’s turned off by the user. If a patient with a pulse who was cardioverted with a synchronized shock develops V-Fib or goes into pulseless V-Tach, immediate defibrillation is needed. We should deliver fast and deep chest compressions while we turn off the sync and begin charging the defibrillator to defibrillate with a non-synchronized shock as soon as safely possible.
For practice identifying computer-generated ECG rhythms, visit Dialed Medics online ECG Simulator.
