Supraventricular tachycardia (SVT)

Vignette says a 28 year old female presents to the emergency department with a sudden onset of palpitations that started 30 minutes ago while she was studying for an exam; She describes the sensation as her "heart racing" and feels lightheaded but denies chest pain, shortness of breath, or syncope; She states that she had similar episodes in the past that resolved spontaneously; She has no significant past medical history and takes no medications; She drinks 2–3 cups of coffee daily; Vital signs show pulse rate of 180 beats/min, blood pressure of 110/70 mm of Hg, respiratory rate of 16 breaths/min, oxygen saturation of 96% in RA and temperature of 98.2 F; The patient appears anxious but is alert and oriented; ECG shows a narrow QRS complex tachycardia at 180 bpm with absent visible P waves in lead II; Diagnosis?

Diagnosis is Supraventricular tachycardia (SVT). Supraventricular tachycardia (SVT) is a tachyarrhythmia originating at or above the atrioventricular node and is defined by a narrow complex (QRS < 120 milliseconds) at a rate > 100 beats per minute (bpm).

Types:-

1. AV nodal reentry tachycardia (AVNRT)

2. Atrioventricular reentry tachycardia (AVRT)

3. Atrial tachycardia (AT)

Presents with symptoms such as palpitations, chest discomfort, dyspnea, dizziness, light-headedness, presyncope, syncope, or anxiety.

Diagnosis:-

1. ECG

2. Cardiac monitoring

3. EP studies

Treatment of SVT:- 

1. If the patient is hemodynamically unstable, consider synchronized cardioversion. 

2. If the patient is hemodynamically stable:- 

• Apply vagal maneuvers (e.g. carotid massage, ice water immersion, modified valsalva maneuver i.e. the modified Valsalva maneuver (mVm) has been shown to have a higher success rate in converting hemodynamically stable SVT to normal sinus rhythm (NSR) when compared to sVm (REVERT trial)).
• Pharmacological therapy includes adenosine, beta blockers (metoprolol), calcium channel blockers (verapamil, diltiazem).

3. Radiofrequency ablation. When to refer to ablation?

• Recurrent episodes despite medications.
• Medication intolerance
• High-risk occupations (pilots, commercial drivers)
• WPW syndrome

ECG of AVNRT shows sinus tachycardia, normal QRS complex (<120ms) complex and P wave inversion in leads II, III and aVF.

Figure:- ECG showing AVNRT