SUPRAVENTRICULAR TACHYCARDIA

OVERVIEW

Mechanism

Abnormal automaticity: inappropriate sinus tachycardia, ectopic atrial tachycardia
Abnormal repolarization activity: atrial premature contraction, multifocal atrial tachycardia (MAT)
Reentry: atrioventricular reentrant tachycardia (AVRT), atrioventricular nodal reentrant tachycardia (AVRT), atrial flutter.

RECOGNITION AND DIAGNOSIS

QRS duration <120milliseconds in all surface leads: likely supraventricular SVT may result in a wide complex tachycardia when there is a bundle branch block or intraventricular conduction delay
Irregularly irregular QRS complexes most commonly signify fibrillation.
Rapid irregularly irregular wide QRS tachycardia may represent atrial fibrillation with preexcitation over an accessory pathway (AP) (wolf Parkinson's/white syndrome)
Organize continues atrial activity faster than 240 beats per minutes is classified as atrial flutter.

GENERAL MANAGEMENT OF SVTs

Assess patient stability
Identify sinus tachycardia and MAT: treat the underlying causes and control heart rate.
Prompt direct current (DC) cardioversion

Electrical cardioversion should be synchronized atrial flatter and other SVTs are usually terminable with a single 50 to 100 J countershock. Atrial fibrillation often requires 200 to 300J

Stable patients

Vagal maneuvers: carotid sinus massage or a valsalva manoeuvre.
Adenosine 6- 12 mg IV push.
IV verapamil, diltiazem B-blockers may be used.
Atrial flutter and atrial fibrillation are unlikely to terminate with these measures.
Type 3 antiarrhythmic agent may be used for conversation alone or in combination with DC cardioversion

SPECIFIC ARRHYTHMIAS AND THERAPIES

Atrial fibrillation

Atrial fibrillation is the most common
Acute treatment

Unstable: synchronized DC cardioversion is the treatment of choice
Stable pharmacologic rate control

B1-selective adrenergic receptor antagonist in nonasthmatic patients.
Nondihydropyridine calcium channel blockers ( e.g. verapamil, diltiazem) may be used in absence of ventricular dysfunction.
Digitalis may be used with relative safety in patients with poor ventricular function but provides only modest control of ventricular rate.
Amiodarone effectively controls ventricular rate response during atrial fibrillation when administered IV and is safe for use in patients

Stop offending drugs
Correct electrolyte abnormalities
Attend to other cardiac, endocrine ( particularly thyroids) and pulmonary disease.
Correct/treat severe metabolic stress, severe on cardiac disease, and other hyperadrenergic states.
Rate control and anticoagulation are reasonable approaches in stable patients with limited symptoms
Patient in atrial fibrillation <48 hours or who have been anticoagulated (INR) <2 for at least 3 weeks. Candidates for early cardioversion.
Pharmacologic cardioversion - amiodarone.
Unanticoagulated patients in atrial fibrillation for <48 hours (or an uncertain duration) are at elevated risk of thromboembolism. These patients require anticoagulation before conversion from atrial fibrillation an alternative approach is to exclude left atrial thrombus with anticoagulation, and proceed to DC cardioversion, followed by oral anticoagulants for at least 4 weeks.
Patient with recurrent atrial fibrillation should be considered for anticoagulation

Atrial Flutter

The clinical presentations and management of atrial flutter are very similar to those of atrial fibrillation. However, rate control can be more difficult to achieve.
Rare control, especially before attempting chemical cardioversion.
The risk of thromboembolism from atrial flutter is significant. Atrial flutter warrants anticoagulation in the same manner as for atrial fibrillation.

AV Nodal reentry tachycardia

AVNRT is most common cause of rapid regular, SVT
Paroxysmal rapid regular narrow complex tachycardia with heart rate often 150 to 250 beats per minute and P waves either buried within the QRS complex or visible at its termination.
Symptoms; palpitation, pounding in the neck, lightheadedness, shortness of breath, chest pressure, weakness and fatigue.
Acute treatment; same as atrial fibrillation acute management mentioned above

Atrioventricular reentry tachycardia

AVNRT is common form of regular SVT, accounting for up to 30% of patients
During tachycardia, the QRS usually appears normal, and waves is visible, will be seen at the end of the QRS complex, within the ST segment or within the T wave
Acute treatment: same as atrial fibrillation acute management mentioned above

Wolf- Parkinson/white syndrome

The wolf-Parkinson/ white syndrome (WPW) consists of a short interval and ventricular pre-excitation (delta wave) due to an AP, with symptoms of palpitations.
The most common arrhythmia associated with WPW is AVRT.

The accessory track may also participate in arrhythmogenesis by allowing rapid ventricular rates during atrial fibrillation. The AP may permit very rapid ventricular fibrillation.

Patients with WPW may be at risk for sudden cardiac death, although the overall risk is rather low, on the order of 0.15% per patient-year
Fast pre-excited ventricular response to atrial fibrillation (irregular rhythm with varying QRS complexes) should undergo electrical cardioversion.
Stable pre-excited atrial fibrillation may be treated with class 1a 1c or 111drugs or procainamide (10 to 15 mg/kg ) may be effective
During rapid pre-excited atrial fibrillation, AV Nodal blocking drugs are contraindicated (digoxin, adenosine, calcium channel blockers, and B- blockers) due to the potential for more rapid ventricular rates.

Ectopic atrial tachycardia

Narrow complex tachycardia with an RP interval that is usually, but not always longer than the PR interval.
The P wave morphology may or may not be visibly different from sinus.
Ectopic atrial tachycardia may occur in short runs, may be sustained.
May be associated with underlying disease (coronary artery disease, myocardial infarction, ethanol ingestion, hypoxia, theophylline toxicity, digitalis toxicity, or electrolyte abnormalities)
Acute treatment