To Treat or Not to Treat (Out‐of‐hospital) Paroxysmal Supraventricular Tachycardia, That Is the Question

Abstract

REFERENCESGausche et al. also evaluated the efficacy and feasibility of the use of adenosine for the treatment of PSVT in the out-of-hospital setting. These investigators defined PSVT as a narrow-complex tachycardia with a rate of 2140 beatdmin. Adenosine was administered in a 12-mg followed by 12-mg dosing regimen. Eighty-five of 107 tachycardic patients (79%) were subsequently found to be in PSVT, and 85% of these patients converted to sinus rhythm with adenosine. The recurrence rate was 1.6% and the complication rate was 11%. The authors also noted that 60 of 85 (71%) of the patients in PSVT were unstable (chest pain, hypotension, rales) and that adenosine treatment resulted in improved hemodynamic status. ' Furlong et al. and Lozano et al. confirmed the efficacy and safety of adenosine use for PSVT in EMS systems in which adenosine was administered without direct medical c~ntrol.~" Similar to the current study's design, Madsen et al. reported the use of adenosine prospectively and the use of verapamil retrospectively over a 12-month period in San Francisco.Treating Out-of-hospital PSVT, Gausche 565Of 102 patients in presumed PSVT, only 17 (17%) were treated with verapamil, whereas 64 of 89 (72%) patients believed by paramedics to be in PSVT were treated with adenosine.7 Conversion rates were similar for the 2 drugs (82% for verapamil vs 78% for adenosine), although the sample size for the verapamil group was small. Complication rates were higher in the adenosine group (45% vs 29%) but were more transient than the complications in the verapamil group. One patient receiving verapamil remained hypotensive for 16 minutes. Misdiagnosis of the initial cardiac rhythm by paramedics was as high as 41% during the adenosine study period. These authors concluded that base-station physicians were significantly more likely to order adenosine than erap pa mil.^ Although Shaw et al., in an outof-hospital study of verapamil use reported a successful conversion rate of only 50% for 24 patients in PSVT, other in-hospital investigators have shown comparable conversion rates of 93% with adenosine and 91% with verapamil.6.8 The out-of-hospital study of Shaw et al. had no major complication with the use of verapamil.In the current study with direct medical control over drug use, Brady et al. reported that the conversion rates for adenosine (69%) and verapamil (83%) were not significantly different.' Again, adenosine was significantly more likely to be ordered by base-station personnel for the treatment of PSVT (83%) than was verapamil (49%); p < 0.001. Basestation personnel may have applied stricter criteria before approving drug use during the verapamil intervention period, thus creating a biased (elevated) conversion rate in the verapamil group. This finding also highlights the problem with patient selection bias that may occur with retrospective studies. The conversion rate for adenosine was much lower in the study by Brady et al. (69% vs 85%) than it was for other EMS studies.'.' It is not clear why the conversion rate was l...