Supraventricular tachycardia: Clinical sciences

Supraventricular tachycardia, or SVT, refers to tachyarrhythmia that originates from or above the atrioventricular node.

An SVT can be physiologic due to physical exercise or emotional stress, or pathologic, which results from abnormal electrical activity outside the sinoatrial node.

Based on 12-lead ECG findings, pathologic SVTs can be subdivided into

SVTs with regular cardiac rhythm, like sinus tachycardia, focal atrial tachycardia, typical AVNRT, orthodromic AVRT, and atrial flutter; and

SVTs with irregular cardiac rhythm, such as atrial fibrillation and multifocal atrial tachycardia.

Now, if a patient presents with a chief concern suggesting SVT, perform an ABCDE assessment to determine if they’re unstable or stable.

If unstable and have a pulse, follow the ACLS guidelines for Tachycardia with a Pulse. Stabilize their airway, breathing, and circulation, and obtain IV access. Put your patient on continuous vital sign monitoring including blood pressure, heart rate, and pulse oximetry, as well as cardiac rhythm monitoring. Finally, if needed, provide supplemental oxygen!

Next, assess for signs and symptoms of unstable tachycardia, which include signs of shock, hypotension, altered mental status, ischemic chest pain, and acute heart failure.

If your patient has these features, diagnose unstable tachycardia and proceed with immediate synchronized cardioversion!

Now, let's go back and discuss stable patients. Start with a focused history and physical examination.

Patients typically report palpitations, exercise intolerance, lightheadedness, and sometimes syncope.

Additionally, if the physical exam reveals a heart rate of over 100 beats per minute, diagnose stable tachycardia.

Next, obtain a 12-lead ECG and assess the heart rhythm. Start by evaluating the consistency of the R to R interval.

If the R to R interval is the same from beat to beat, the rhythm is regular your next step is to assess the width or duration of the QRS complex.

If the QRS complex is narrow, meaning under 120 milliseconds, there’s a narrow complex tachycardia, which indicates that the pacing originates above the ventricles. In this case, diagnose SVT.

Once you diagnose SVT, determine the type by assessing the atrial activity on the ECG. If the ECG shows typical “sinus” P waves preceding QRS complexes that are upright in leads I, II, and aVF, and biphasic in V1, diagnose sinus tachycardia. This means that tachycardia is originating from the sinoatrial node. Next, assess the cause of sympathetic stimulation. First, let’s start with the physiologic causes.

These can be subdivided into non-pathologic causes, like anxiety, pain, and exercise; and pathologic causes, like infection, hypovolemia, and anemia. In this case, diagnose physiologic sinus tachycardia and be sure to remove physiologic triggers and treat any underlying conditions! There’s also non-physiologic causes of sympathetic stimulation.

If the workup reveals no physiologic stressors or signs of acute illness, and the individual reports palpitations, fatigue, or syncope, you should evaluate for heart rate changes related to posture. Check the patient’s heart rate when they move from a supine to a standing position.

Once they stand up, if their heart rate increases by 30 beats per minute from baseline, or if it exceeds 120 beats per minute within 10 minutes, in the absence of postural hypotension, diagnose postural orthostatic tachycardia syndrome.

Treatment is based on increasing salt and fluid intake, exercise training, and the use of compression stockings. Additionally, consider oral fludrocortisone, as it can reduce symptoms by increasing plasma volume.

On the other hand, if the sinus tachycardia is symptomatic but unrelated to postural changes, diagnose inappropriate sinus tachycardia and treat it with medications, such as ivabradine and beta blockers. Let’s go back to the atrial activity and take a look at focal atrial tachycardia.

If the ECG shows P waves that are abnormal in morphology or deflection, but consistent in appearance, diagnose focal atrial tachycardia. This means the electrical impulse is coming from a spot in the atrium that’s outside of the SA node.

Treatment includes rate control medications, like beta blockers or non-dihydropyridine calcium channel blockers, such as verapamil or diltiazem. Additionally, consider catheter ablation for patients with persistent tachycardia that is refractory to medications.