PSVT (Paroxysmal Supraventricular Tachycardia)
Supraventricular Tachycardia 2006 (NEJM)
See also WPW Syndrome
Increase vagal tone: carotid sinus massage, induction of gagging by
touching the posterior phryns with a tongue blade, valsalva maneuver.
IV Adenosine 6-12 mg bolus. If the initial 6 mg is ineffective, a
second bolus of 9 mg can be given after 2-3 min. Transient sinus pauses,
aV nodal block, & atrial fibrillation as well as systemic side effects,
such as flushing, headache, dyspnea, chest pressure, & nausea, are common
with adenosine. They are usually not serious, however, and resolve rapidly.
IV Verapamil 5-10 mg (0.075 to 0.15 mg/kg) bolus over 1-3 min.
Conversion to sinus rhythm usually occurs within 10 min. If no effect is
observe, vagal maneuvers should be repeated, & if ineffective, the same
dose may be repeated in 30 min.
Cardiovasc. side effects associated with its use include sinus bradycardia
& transient asystole on conversion (esp. in pts with preexisting sinus
node dysfunction), AV block, hypotension, & exacerbation of heart failure.
The drug should be be used IV in conjunction with beta-blocking agents, in
pts with sick sinus syndrome (unless a pacemaker is in place), or in pts
with heart failure unrelated to the rapid heart rate.
IV beta-blocking agents.
Propranolol 1 mg IV, with increments of 1 mg every 5 min until conversion
occurs or a total dose of 0.1 mg/kg (5-10 mg in the average adul) has been
Metoprolol, a more cardioselective beta blocker, can be used IV in similar
Esmolol, a B-blocker with an ultrashort half-life, can also be used, about
Digoxin rapid IV digitalization - 0.5 to 0.75 mg.
Other antiarrhythmic drugs as Flecainide 300 mg PO, IV procainamide
100 mg q2 min to conversion or to a total dose of 2 gm, PO propafenone,
Electrical cardioversion or external pacemaker with rapid atrial
Wolff-Parkinson-White (with/without CHF)
(avoid adenosine, beta blockers, calcium channel blockers, digoxin)
Rate Control *amiodarone
Reentry is the mechanism responsible for the vast majority of cases of PSVT:
AV nodal reentry through the Beta pathway of His bundle ( no P waves are
AV nodal reentry using a concealed bypass tract (inverted retrograde P waves
on the T waves)
In WPW synd. the bypass tract conduct antegradely instead of retrogradely.
AV Nodal Reentrant Tachycardia - the most common cause of PSVT:
It usually presents as a narrow QRS complex with regular rates
ranging from 120-250 beats/min. PACs that initiate the arrhythmia are almost
always associated with a prolonged PR interval. Retrograde P waves may be
absent, buried in the QRS complex, or appear as distortions at the terminal
parts of the QRS complex.
Vagal maneuvers (if no hypotension) as carotid sinus massage, can terminate
the arrhythmia in 80% of cases.
If hypotension is present, raising the BP by the cautious use of IV phynylephrine
in 0.1 mg increments may terminate the arrhythmia lone or in combination
with carotid sinus pressure. if thse Rx are unsuccessful, then
IV adenosine 6-12 mg or verapamil 2.5-10 mg. - agents of first choice.
IV propranolol 0.05-0.2 mg/kg to slow or terminate the tachycardia - agent
of second choice.
digoxin has a lower onset of action & should not be used for acute Rx.
Prevention of AV nodal reentry: digoxin, B-blocker, calcium channel blockers,
quinidine, flecainide, amiodarone.
Radiofrequency catheter modification of AV nodal function for those who require
chronic med. Rx..
Concealed AV bypass tract retrograde Reentrant Tachycardia
These pts manifest the same type of PSVT as in WPW synd, but the bypass tract
cannot conduct in an antegrade direction during sinus rhythm or other atrial
Alteration of the QRS complexes &/or T wave occurs in about 1/3 of such
tachycardias. The P wave usually occurs after the QRS complex, because atrial
activation must follow vent. activation during AV reentry.
RX: similar to that for AV Nodal Rentry Tachycardia above.
POL Outlines in Clinical Medicine 1998
Most are re-entrant tachycardias with concealed bypass tracts
Adenosine 6-12mg most effective for diagnosis of SVT and usually breaks
ß-Blockers preferred in post-MI setting or in ischemic disease
Verapamil is now the preferred agent in stable SVT control
Electrophysiology Study (EPS) guided conduction system ablation may also
EPS guided ablation uses radiofrequency emitting catheters
Accessory tracts or part of the AV node are selectively ablated
Radiofrequency waves induce tissue necrosis