Quick reference:
- is patient unstable or stable?
- unstable -> ACLS
- Stable? continue.
- Attempt to identify underliying trigger for event
- Attempt vagal maneuver
- Attempt adenosine
- Cardiovert
Description
Supraventricular tachycardia is a general term for dysrhythmias originating at or above the atrioventricular node, characterized by a narrow QRS complex (<120 ms) with a heart rate exceeding 100 bpm, typically ranging from 150 to 220 bpm. Supraventricular tachycardia includes various conditions, including atrial, junctional (ectopic), and atrioventricular tachycardias.
EKG Findings:
- No discernable P waves
- Narrow QRS
- Rate: Tachy (usually >140-150)
Treatment
Treatment of Unstable Patients
For unstable patients, the heart fills during diastole, which typically accounts for two-thirds of the cardiac cycle. A rapid heart rate significantly shortens the time for the ventricles to fill, decreasing blood flow from the heart during systole. This reduction in blood ejection results in lower cardiac output, leading to hypotension.
As cardiac output drops, patients may exhibit symptoms such as hypotension, hypoxia, chest pain, dyspnea, altered mental status, or other signs of shock. These symptoms are more common when the heart rate exceeds 150 bpm. In cases where the patient is unstable, immediate synchronized cardioversion should be considered.
A defibrillator must be set to sync mode, typically indicated by a marker on the device’s screen highlighting each QRS complex. This synchronization ensures that the shock is delivered in line with the QRS complex, preventing delivery during the T wave, which could trigger ventricular fibrillation, known as the R on T phenomenon.
For patients with supraventricular tachycardia, the appropriate shock voltage for cardioversion is between 50 and 100 J. In children, the initial dose for cardioversion is between 0.5 and 1 J/kg, which can be increased to 2 J/kg if necessary (see Image. Supraventricular Tachycardia Termination on Electrocardiogram Tracing). If time permits, anxiolysis or analgesia may be considered before cardioversion, but this should be done once the patient is stabilized.
Treatment of Stable Patients
In stable patients, vagal maneuvers can be attempted while in the supine position as a preliminary approach before preparing for chemical cardioversion. These maneuvers stimulate the parasympathetic nervous system, helping to slow impulse formation at the sinus node, reduce conduction velocity at the atrioventricular node, and increase the refractory period of the atrioventricular node.
Although the Valsalva maneuver is generally accepted, carotid sinus massage should be avoided in both pediatric and adult populations, particularly in patients with bruits, a history of cerebrovascular disease, transient ischemic attacks, or those who have undergone endarterectomy. The Valsalva maneuver and the application of ice to the face can effectively treat hemodynamically stable supraventricular tachycardia in infants and children. When performed correctly, these techniques can be applied rapidly and safely without affecting any follow-up treatments if they prove unsuccessful.
The oculocardiac reflex refers to a moderate bradycardic response to ocular pressure elicited by tension on the extraocular muscles. Although it has been used as a vagal maneuver, it is now avoided due to the risk of ocular injury.
Pharmacotherapy with Adenosine
If vagal maneuvers are not effective, pharmacotherapy becomes necessary. The first-line medication for supraventricular tachycardia is adenosine, an endogenous nucleoside that creates a transient blockade of the adenosine A1 receptors. This blockage interrupts conduction through the atrioventricular node, disrupting the reentry circuit and allowing for restoration of the sinus rhythm.
Continuous ECG monitoring during adenosine administration can help diagnose the mechanism of tachycardia in patients suspected of having focal atrial tachycardia. Adenosine is rapidly metabolized in the body and should be administered as a rapid intravenous push, preferably through a large peripheral vein.
The adverse effects of adenosine are typically self-limited due to its short duration of action and quick metabolism. These adverse effects may include flushing, chest discomfort, and dyspnea. After administration of adenosine, transient arrhythmias may occur, such as sinus pauses, sinus bradycardia, asystole, and premature atrial or ventricular depolarizations. There have been case reports of bronchoconstriction following adenosine administration, particularly in patients with preexisting obstructive lung disease.
Notably, methylxanthines, such as caffeine and theophylline, can negate the effects of adenosine. Adenosine is not contraindicated in pregnant or lactating patients, as it is believed to be rapidly metabolized and poses a low risk to a fetus or nursing infant due to its natural presence in the body.
Synchronized Cardioversion
Intravenous or oral β-blockers, diltiazem, or verapamil are suitable options for the acute treatment of hemodynamically stable patients with supraventricular tachycardia. For hemodynamically stable patients with atrioventricular nodal reentrant tachycardia, intravenous amiodarone may be considered when other therapies are ineffective or contraindicated. Synchronized cardioversion is recommended for hemodynamically stable patients with atrioventricular nodal reentrant tachycardia if pharmacological treatment does not terminate the tachycardia or is inappropriate.
If these measures are ineffective, overdrive pacing—where the heart is paced at a faster rate than its natural rhythm—can help terminate supraventricular tachycardia. However, this approach carries an increased risk of ventricular tachycardia or fibrillation; therefore, it should be used cautiously, with cardioversion readily available.
Patients with recurrent supraventricular tachycardia without preexcitation may require long-term maintenance therapy with oral β-blockers or calcium channel blockers to maintain sinus rhythm. In patients with recurrent supraventricular tachycardia who also have structural or ischemic heart disease, the use of flecainide or propafenone may be beneficial. Intravenous amiodarone may be considered for the acute treatment of hemodynamically stable adults and pediatric patients with supraventricular tachycardia when other therapies are ineffective or contraindicated.
Notably, adenosine does not terminate supraventricular tachycardias when the atrioventricular node is not part of the reentry circuit, such as in cases of atrial ectopic tachycardia, atrial flutter, and atrial fibrillation. In addition, adenosine is typically ineffective in terminating ventricular tachycardia.