Supraventricular Tachycardia

Introduction

• SVT is a term used to describe tachycardia with a rate greater than 100 bpm with a mechanism originating at or above the Bundle of His.¹
• SVT encompasses several distinct arrhythmias, which may be grouped into three major categories.
  • 1. Involvement of the atrioventricular (AV) node:
    • AV nodal reentrant tachycardia (AVNRT): AVNRT is the most common SVT and is defined as a reentrant tachycardia involving 2 functionally distinct pathways, generally referred to as “fast” and “slow” pathways, that originates at the AV node.
  • 2. Involvement of an accessory pathway:
    • Accessory pathway-mediated AV reentrant tachycardia (AVRT): This reentrant tachycardia requires an accessory pathway in the atrium, AV node (or second accessory pathway), or ventricle.

• • • Wolff-Parkinson-White (WPW) Syndrome: a type of AVRT that combines the presence of a congenital accessory pathway, known as the Bundle of Kent, and episodes of tachyarrhythmia. Please see the OA summary on WPW syndrome for more details.(will add link when published)
  • 3. Involvement of other atrial tissue:
    • Atrial tachycardia (focal and multifocal AT): This rhythm arises at a focal point in the atria and is characterized by regular, organized atrial activity with discrete P waves (in focal AT) or by ≥3 distinct P-wave morphologies and/or patterns of atrial activation at different rates (in multifocal AT)
    • Atrial flutter: This rhythm is characterized by a fast atrial rate with a fixed or variable ventricular rate
    • Junctional tachycardia: This is a non-reentrant SVT that arises from the AV junction, which can present as tachycardia or bradycardia
• In the general population, the prevalence of SVT is 2.25/1000 persons, and the incidence is 35/100,000 person-years. Women have a risk of developing SVT that is two times greater than that of men, and persons aged 65 years and older have more than five times the risk of developing SVT than younger individuals.²
• In a prospective cohort study, the incidence of persistent SVT was 2% during surgery and 6% in the postoperative period.³ In noncardiac surgery, perioperative arrhythmias are more likely to be supraventricular than ventricular in origin4. Atrial arrhythmias occur most frequently 2–3 days postsurgery and are likely related to sympathetic stimulation associated with an inflammatory response.⁵
• There are many risk factors for SVT in the perioperative period, including.⁶
  • Anesthetic factors (e.g., local anesthetic toxicity, inotropes, shock)
  • Surgical factors (e.g., pain, trauma, anemia)
  • Medical factors (e.g., electrolyte disturbances, pneumonia, sepsis)
  • Chronic medical conditions (e.g., hypertension, cardiomyopathy, malignancy)

Clinical Presentation and Diagnosis

• Patients may present with palpitations, chest pressure, dizziness, fainting, shortness of breath, or a sense of unease. In some instances, they may present in a state of shock, with low blood pressure or clinical evidence of heart failure, especially if the SVT has been ongoing for many hours or days. Symptoms usually begin and end suddenly and are often triggered by stress, whether physical or emotional.
• A physical examination may detect a rapid resting heart rate, increased respiratory rate, pallor, or sweating.⁷

ECG Features of Different Types of SVT

• Slow-Fast AVNRT: P waves are often hidden – being embedded in the QRS complexes, pseudo r’ wave may be seen in V1, pseudo S waves may be seen in leads II, III or arteriovenous fistula (aVF).

• Fast-Slow AVNRT: QRS -P-T complexes, P waves are visible between the QRS and T wave.

• Orthodromic AVRT: Regular, narrow complex tachycardia

• WPW: PR interval < 120ms, Delta wave: slurring slow rise of initial portion of the QRS, QRS prolongation > 110ms, discordant ST-segment and T-wave changes.

• Focal AT: Consistent, abnormal P wave morphology indicating an ectopic focus

• Multifocal AT: Rapid irregular rhythm > 100 bpm. At least 3 distinctive P-wave morphologies (arrows).

• Atrial flutter: Narrow complex tachycardia, regular atrial activity at ~300 bpm, loss of the isoelectric baseline, “saw-tooth” pattern of inverted flutter waves. Please see the OA summary on atrial fibrillation and flutter for more details. Link

• Junctional Tachycardia: Narrow complex tachycardia, retrograde P waves — inverted in II, III, and aVF and upright in V1 and aVR, short PR interval (< 120 ms) indicates a junctional rather than atrial focus.

Management

• Management of medical comorbidities and correction of electrolyte imbalances are essential for the treatment and prevention of perioperative SVT. Arrhythmias should be stabilized preoperatively since surgery and anesthesia can worsen them.
• Beta-blockers and nondihydropyridine calcium channel blockers should be continued when possible, as they reduce the incidence of perioperative SVT.
• In patients with AF at high thromboembolic risk, therapeutic anticoagulation should be held, with consideration of bridging using therapeutic-dose low-molecular-weight heparin before and after surgery.⁶
• For acute intraoperative SVT, the underlying cause should be assessed before initiating therapy, except in cases of severe hemodynamic instability, where immediate synchronized cardioversion is required.⁸