Supraventricular tachycardia Flashcards
What is Supraventricular Tachycardia (SVT)?
SVT is a fast heart rate caused by abnormal electrical signals originating above the ventricles, often resulting in a self-perpetuating loop of electrical activity.
What is the normal pathway of electrical signals in the heart?
Electrical signals start in the sinoatrial node, travel through the atria, then the atrioventricular (AV) node, and down to the ventricles, causing them to contract.
How does SVT differ from normal electrical conduction?
In SVT, the electrical signal re-enters the atria from the ventricles, creating a continuous loop of electrical activity that leads to tachycardia.
What is a ‘narrow complex’ tachycardia?
Narrow complex tachycardia is when the QRS complex on an ECG lasts less than 0.12 seconds, typically seen in SVT.
How does SVT appear on an ECG?
SVT shows a series of QRS complexes followed immediately by T waves, with P waves often buried in the T waves.
What are the main differentials of narrow complex tachycardia?
- Sinus tachycardia
- Supraventricular tachycardia
- Atrial fibrillation
- Atrial flutter
How can you differentiate sinus tachycardia from SVT?
Sinus tachycardia has a gradual onset and more variability, while SVT has an abrupt onset and a very regular rhythm without variability.
What are the types of SVT?
- Atrioventricular nodal re-entrant tachycardia (AVNRT)
- Atrioventricular re-entrant tachycardia (AVRT)
- Atrial tachycardia
What is Wolff-Parkinson-White (WPW) syndrome?
WPW syndrome is characterized by an extra electrical pathway between the atria and ventricles, which can lead to SVT and cause abnormal ECG findings like a short PR interval, wide QRS complex, and a delta wave.
What are the ECG findings in WPW syndrome?
- Short PR interval (<0.12 seconds)
- Wide QRS complex (>0.12 seconds)
- Delta wave (slurred upstroke in the QRS complex)
What is the definitive treatment for WPW syndrome?
Radiofrequency ablation of the accessory pathway.
What is the management approach for SVT without life-threatening features?
- Vagal maneuvers
- Adenosine
- Verapamil or beta blockers
- Synchronised DC cardioversion
What are vagal maneuvers and how do they work?
Vagal maneuvers, like the Valsalva maneuver or carotid sinus massage, stimulate the parasympathetic nervous system to slow the heart rate and potentially terminate SVT.
When should adenosine be avoided?
Adenosine should be avoided in patients with asthma, COPD, heart failure, heart block, severe hypotension, or possible atrial arrhythmia with pre-excitation.
How is adenosine administered in the treatment of SVT?
Adenosine is given as a rapid IV bolus, starting with 6mg, followed by 12mg, and then 18mg if needed.
What is synchronised DC cardioversion?
A procedure where an electric shock is applied to the heart at the R wave to restore normal sinus rhythm.
How is paroxysmal SVT treated for long-term management?
- Beta blockers
- Calcium channel blockers
- Amiodarone
- Radiofrequency ablation
What is radiofrequency ablation and how does it treat SVT?
Radiofrequency ablation involves using heat to destroy abnormal electrical pathways in the heart, aiming to permanently resolve arrhythmias like SVT and WPW syndrome.
What is the risk of anti-arrhythmic medications in patients with WPW syndrome and atrial fibrillation?
Anti-arrhythmic medications like beta blockers and calcium channel blockers can increase the risk of life-threatening ventricular rhythms by promoting conduction through the accessory pathway.
What is the management for patients with WPW syndrome who develop atrial fibrillation or flutter?
Procainamide or electrical cardioversion is used for treatment, as adenosine, beta blockers, and calcium channel blockers are contraindicated.
