Supraventricular tachycardia: Clinical sciences

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Introduction 0:00–0:55

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.

Unstable patient 0:55–1:59

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.

Stable patient 1:59–2:35

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.

ECG analysis: Regular Rhythm 2:35–3:02

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.

Sinus tachycardia 3:02–3:36

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.

Physiologic causes3:36–4:03

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.

Non-physiologic causes 4:03–5:16

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.

Focal atrial tachycardia 5:16–5:58

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. In some individuals, ECG might reveal P waves buried in the QRS complexes, which you’ll notice as the absence of P waves; or they might be just before or after the QRS.

Typical AVNRT5:58–7:16

In this case, diagnose typical atrioventricular nodal reentrant tachycardia, or typical AVNRT, which occurs when there’s a reentry circuit within the AV node.
Here’s a clinical pearl! Patients with typical AVNRT usually report “neck pounding,” and on physical exam you could recognize this as neck pulsations.
Management of typical AVNRT includes vagal maneuvers, such as Valsalva, carotid massage, or ice immersion; or IV adenosine if vagal maneuvers fail.
If the tachycardia abruptly terminates, this is highly suggestive of typical AVNRT. If ineffective, you might need to add beta-blockers or non-dihydropyridine calcium channel blockers, or even provide synchronized cardioversion.
Finally, if the AVNRT becomes persistent, treatment might require catheter ablation. Next, ECG findings associated with P waves that always follow the QRS are highly suggestive of orthodromic atrioventricular reciprocating tachycardia, or orthodromic AVRT.

Orthodromic AVRT7:16–8:42

In this type, an electrical impulse travels normally through the AV node to the ventricle, but then conducts abnormally back to the atria through an accessory atrioventricular pathway, creating a P wave that follows after the QRS.
The QRS is narrow, because the ventricles are depolarized normally. Management consists of vagal maneuvers or adenosine, but if ineffective, consider beta-blockers or non-dihydropyridine calcium channel blockers.
If the rhythm still persists, provide synchronized cardioversion and consider catheter ablation of the accessory pathway.
Here’s a high-yield fact! A classic example of an accessory pathway predisposing to orthodromic AVRT is Wolff-Parkinson White syndrome, or WPW.
In WPW, the resting ECG has a distinct pattern, including a short PR interval, delta waves, and a QRS over 110 milliseconds.
Moving to atrial flutter with rapid ventricular response! In these individuals, ECG reveals an atrial rate of 250 or more with negative sawtooth flutter waves in leads II, III, and aVF.

Atrial flutter with rapid ventricular response 8:42–9:33

Additionally, the conduction to the ventricles is typically in a 2:1 or 3:1 ratio. In this case, diagnose atrial flutter with a rapid ventricular response.
Management involves beta-blockers or non-dihydropyridine calcium channel blockers for rate control, with elective synchronized cardioversion for rhythm control.
Some patients may also need anticoagulation. Finally, your patient might need long-term control with catheter ablation.
Alright, let’s go back to the assessment of QRS duration. If the rhythm is regular and the QRS complex is wide, meaning 120 milliseconds or more, consider an alternative diagnosis, such as SVT with aberrancy, or monomorphic ventricular tachycardia.

Wide complex tachycardia 9:33–11:06

Now, here’s a high-yield fact! While SVTs usually produce a narrow QRS, if there’s an intraventricular conduction delay, such as a right or left bundle branch block, the QRS might be wide.
If there’s supraventricular electrical activity, like P waves preceding each QRS, you’re dealing with SVT with aberrancy.
However, if there’s no supraventricular electrical activity, suspect monomorphic ventricular tachycardia! And another high-yield fact!
In addition to orthodromic AVRT, there’s also antidromic AVRT. In antidromic AVRT, the accessory atrioventricular pathway allows abnormal antegrade conduction, while the AV node allows abnormal retrograde conduction back to the atria.
This causes the ventricles to contract early, known as ventricular pre-excitation, which can trigger a wide-complex reentrant tachycardia that resembles monomorphic ventricular tachycardia.
Okay, switching our focus to SVT with an irregular rhythm. In this case, again, assess the QRS duration.

Irregular rhythm / Narrow complex 11:06–12:35

If the QRS is narrow, meaning less than 120 milliseconds, diagnose SVT, and assess atrial activity on the ECG. No obvious P waves and an irregular ventricular response is suggestive of atrial fibrillation, or A-fib, with a rapid ventricular response.
Treatment involves beta-blockers or non-dihydropyridine calcium channel blockers for rate control. Additionally, consider antiarrhythmics or cardioversion to achieve rhythm control, as well as anticoagulants since these patients are at risk for developing left atrial appendage thrombus.
On the other hand, if the ECG reveals P waves with 3 or more distinct morphologies, diagnose multifocal atrial tachycardia, or MAT.
This is often seen in pulmonary conditions, as well as hypomagnesemia and theophylline use. Management is based on treating the underlying condition, and giving intravenous magnesium.
If needed, give verapamil or metoprolol for rate control, but remember to avoid beta-blockers in patients with pulmonary disease.
Lastly, if the QRS is wide, consider alternative diagnoses, like A-fib or MAT with aberrancy, polymorphic ventricular tachycardia, or torsades de pointes.

Irregular rhythm, wide complex 12:35–12:48

Alright, as a quick recap… Supraventricular tachycardia refers to tachyarrhythmia that originates from or above the atrioventricular node.

Review 12:48–13:29

On ECG, you’ll see a narrow QRS complex, meaning less than 120 milliseconds. Based on additional ECG findings, SVTs can be subdivided into SVTs with regular cardiac rhythm, which include sinus tachycardia, focal atrial tachycardia, typical AVNRT, orthodromic AVRT, and atrial flutter; and SVTs with irregular cardiac rhythm, which include atrial fibrillation,