SVT Flashcards
What is the most common type of paroxysmal supraventricular tachycardia (SVT)?
AV nodal reentrant tachycardia (AVNRT).
What is the primary mechanism of AVNRT?
A reentrant circuit within the AV node due to dual conduction pathways.
What is the most common risk factor for AVNRT?
Idiopathic, with onset typically in young adulthood.
What are the common clinical symptoms of AVNRT?
Palpitations, dizziness, dyspnea, and sometimes syncope.
What does the ECG show in AVNRT?
Narrow-complex tachycardia without visible P waves or with retrograde P waves.
What is the first step in evaluating a patient with tachyarrhythmia?
Assess airway, breathing, circulation (ABCs), secure the airway if necessary, and check hemodynamic stability.
What is the stepwise approach for treating narrow QRS tachycardias?
If stable, use vagal maneuvers, then adenosine, then beta-blockers or calcium channel blockers. If unstable, perform synchronized cardioversion.
What is the first-line treatment for hemodynamically unstable SVT?
Synchronized cardioversion, also called direct countershock (DC cardioversion).
What are the indications for synchronized cardioversion in SVT?
Severe hypotension, ischemic chest pain, altered mental status, or signs of shock (<90 mmHg SBP).
What is the initial management for hemodynamically stable SVT?
Vagal maneuvers such as Valsalva, carotid massage, or ice pack application (in children).
What is the next step if vagal maneuvers fail in stable SVT?
Intravenous adenosine.
What is the dosing protocol for adenosine in SVT?
Initial dose of 6 mg IV push, followed by 12 mg if the first dose is ineffective.
What is the effect of adenosine on the AV node?
Temporarily blocks conduction, terminating AVNRT and unmasking atrial activity.
What are contraindications to adenosine use?
Asthma due to risk of bronchospasm, and severe hypotension.
What are common side effects of adenosine?
Facial flushing, hypotension, shortness of breath, and transient bradycardia.
What is the next step if adenosine fails to terminate SVT?
Beta-blockers such as metoprolol or calcium channel blockers like diltiazem or verapamil.
What is an alternative medication for SVT in patients with asthma?
Calcium channel blockers such as verapamil or diltiazem, or digoxin in select cases.
What is the difference between AVNRT and AVRT?
AVNRT is due to a reentrant circuit within the AV node, while AVRT involves an accessory pathway outside the AV node.
What are the two types of AVRT?
- Orthodromic AVRT (narrow QRS).
- Antidromic AVRT (wide QRS).
How does atrial fibrillation appear on ECG compared to AVNRT?
Irregularly irregular rhythm with no distinct P waves in AFib, whereas AVNRT is regular.
What is the hallmark ECG finding in atrial flutter?
Sawtooth flutter waves in leads II, III, and aVF.
Which SVT has an irregularly irregular rhythm?
Atrial fibrillation.
What are the key differences in management between AVNRT and atrial fibrillation?
AVNRT is managed with vagal maneuvers and adenosine, while atrial fibrillation requires rate control and anticoagulation if indicated.
Why are P waves often absent in AVNRT?
They are buried within the QRS complex due to simultaneous atrial and ventricular activation.
What ECG findings suggest orthodromic AVRT?
Narrow-complex tachycardia with retrograde P waves after the QRS complex.
What ECG findings suggest antidromic AVRT?
Wide-complex tachycardia due to conduction through an accessory pathway.
How do you manage sinus tachycardia?
Identify and treat the underlying cause rather than suppressing the rhythm.
How does metoprolol work in SVT?
Beta-blockade decreases AV nodal conduction, slowing ventricular response.
How do calcium channel blockers like diltiazem work in SVT?
They inhibit slow calcium channels, reducing AV nodal conduction.
Which antiarrhythmic drug can be used in pharmacologic cardioversion of atrial fibrillation?
Ibutilide, a Class III antiarrhythmic.
Which antiarrhythmic drug is used for monomorphic ventricular tachycardia?
Lidocaine, a Class Ib antiarrhythmic.
What is the definitive treatment for recurrent AVNRT?
Catheter ablation of the slow pathway in the AV node.
What lifestyle modifications can help prevent SVT episodes?
Avoiding stimulants like caffeine and alcohol, managing stress, and staying hydrated.
A 38-year-old man presents to the emergency department due to palpitations and shortness of breath for the past two hours. The patient has never experienced an episode like this and has no family history of heart disease. He was in his usual state of health prior to this episode. The patient has no significant past medical history and takes no medications. Vital signs and ECG are obtained by nursing staff while you examine the patient. The patient appears anxious and uncomfortable. Palpation of the radial pulse reveals a regular and rapid heart rate. After reviewing the electrocardiogram you suspect AV nodal reentrant tachycardia. Which of the following findings is most likely to be seen on ECG?
A) Prolonged QT interval and progressive sinusoidal alterations of the QRS axis
B) QRS <120 ms and P waves buried in the QRS complexes
C) The absence of typical P waves and sawtooth waves in leads III and aVF
D) QRS >120 ms and atrioventricular dissociation
E) QRS <120 ms, irregular R-R intervals, and no visible P waves
Tachyarrhythmias can be classified based on the rhythm as regular or irregular. They can then be classified based on the width of the QRS complexes (narrow complex QRS <120 ms or wide complex QRS ≥120 ms). These distinctions along with specific morphologies seen on the ECG can establish the diagnosis of the tachyarrhythmia. This patient presents with palpitations, shortness of breath, and tachycardia with a regular rhythm. Given that this patient is young and healthy with no prior heart disease, no recent illnesses, and he is not taking any medications, this symptomatic regular rapid heart rate most likely indicates AV nodal reentrant tachycardia. The first step after stabilizing a patient with a tachyarrhythmia is to obtain an electrocardiogram (ECG), which is usually done at the same time as the history and physical examination are being performed. The ECG in AV nodal reentrant tachycardia will have a QRS <120 ms and P waves buried in the QRS complexes. Tachyarrhythmias are divided based on the rhythm as regular or irregular. The QRS duration is used to classify them further. The QRS complex is, either narrow (<120 ms) or wide (≥120 ms). In general, electrical impulses generated above the ventricles (i.e. supraventricular) produce narrow QRS complexes; and impulses generated below the ventricles produce wide QRS complexes. Irregular tachyarrhythmias are more likely to occur in patients with significant cardiac or pulmonary disease. Classification and causes of tachyarrhythmias: 1) Regular rhythm with narrow QRS complexes: sinus tachycardia, atrial tachycardia, AV nodal reentrant tachycardia (AVNRT), AV reentrant tachycardia, and atrial flutter. 2) Regular rhythm with wide QRS complexes: monomorphic ventricular tachycardia, and SVT with aberrancy (a supraventricular tachyarrhythmia occurring in a patient with a bundle branch block). 3) Irregular rhythm with narrow QRS complexes: atrial fibrillation and multifocal atrial tachycardia (typically associated with severe lung disease). 4) Irregular and wide QRS complexes: tachyarrhythmias most commonly represent polymorphic ventricular tachycardia (of which torsades de pointes is a specific subtype).
