INTRAVENOUS MAGNESIUM FOR ACUTE TERMINATION OF MONOMORPHIC
VENTRICULAR TACHYCARDIA. HMO. Farouque*, P. Sanders, GD. Young
& LJ. Mahar. Cardiovascular Investigational Unit, Royal
Adelaide Hospital, Adelaide, SA. There is little data on the antiarrhythmic
efficacy of intravenous magnesium sulfate (IVMS) in terminating sustained
monomorphic ventricular tachycardia (SMVT).
The primary aims of this study were to determine the effects of IVMS on
ventricular refractoriness and whether this therapy could revert SMVT induced
by programmed stimulation. Methods: 18 normomagnesaemic patients (pts) with repeatedly
inducible haemodynamically stable SMVT were studied (mean age 61±12
years; 16 male). 16 pts had an ischaemic aetiology for their
arrhythmia. Once SMVT was established, 2.5 grams of IVMS was
infused over 90 seconds. Pts were observed for 5 minutes and
if reversion had not occurred, SMVT was pace terminated. Reinduction
of SMVT was then attempted. The parameters measure before
and after IVMS included cycle length of tachycardia (CL), right
ventricular effective refractory period (RVERP), mean intra-arterial
blood pressure (BP) and serum magnesium concentration (Mg). Results:
The data obtained are presented below (mean±SD). CL
(msec) RVERP
(msec) BP
(mmHg) Mg
(mmol/) Pre
IVMS 342±66 251±28 78±15 0.85±0.07 Post
IVMS 357±78 246±25 80±17 1.35±0.15 p
value 0.06 0.36 0.35 <0.001 IVMS terminated SMVT in only 2 of 18 pts
(11%). The morphology of SMVT was
unchanged after IVMS. The same rhythm
was reinduced in all pts after IVMS.
Generalised flushing was reported by all pts during the infusion. Conclusion: IVMS as used in this study, though safe, has limited efficacy in
terminating haemodynamically stable SMVT.
It cannot be recommended for the emergency treatment of SMVT as it may
delay the initiation of more effective antiarrhythmic therapy.
