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Three Part Question

In [patients with Unstable Paroxysmal Supraventricular Tachycardia] is [treatment with intravenous Adenosine] both [effective and safe]?

Clinical Scenario

A 40-year-old woman with known paroxysmal supraventricular tachycardia (PSVT) presents to the emergency department with an acute episode of palpitations, dizziness and chest tightness of sudden onset. She is found to have a further episode of supraventricular tachycardia on ECG and her systolic blood pressure is 55 mm Hg. Previous episodes have been terminated by DC cardioversion and you are aware of the algorithm recommending such treatment in the 2011 ALS course manual. However, the text also states that it is reasonable to give Adenosine to patients with regular narrow-complex tachyarrhythmias where there are adverse features while preparations are being made for synchronised cardioversion. You wonder whether it is really effective and safe to give adenosine first to unstable patients and whether this is so for children also.

Search Strategy

NHS Evidence Health Information Resources
Medline 1950 to week 1 October 2009; EMBASE 1980 to week 1 October 2009, Cochrane 1993 to week 1 October 2009.

[Exp Supraventricular Tachycardia, Paroxysmal Supraventricular Tachycardia, SVT, PSVT] and [Adenosine]

Search Outcome

A total of 711 articles were found. 8 papers were relevant to the question and these are detailed in table 1.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
McCabe et al. 1991. USA.	Total no. of adult patients 37. Total no. of adult patients with SVT 26. 7 were unstable. Setting: an urban Emergency Medical Services system (paramedics).	Prospective, consecutive case series.	Conversion rate to sinus rhythm in unstable patients with PSVT.	Overall success rate 88% and 100% in unstable patients with PSVT.	Small number of patients but otherwise well designed.
			Safety of Adenosine in unstable patients.	Recurrence rate 3%.
				Adverse effects occurred in16% of all patients and were transient (chest pain, flushing and dyspnoea). There was no differential rate of complications given for stable and unstable patients but there was no haemodynamic deterioration in any patient
Melio et al. 1992. USA.	12 adult patients with unstable PSVT over 2 yrs. Setting: university-affiliated hospital Emergency Department.	Retrospective chart review.	Conversion rate to sinus rhythm in unstable patients with PSVT.	Success rate 100%.	Retrospective Chart Review. Small number of patients.
			Safety of Adenosine in unstable patients.	Recurrence rate 0%.
				No complications encountered.
				Side effects were transient and were not clinically significant.
Marco et al 1994 USA	Total no. of adult patients 72. no. of patients with PSVT 46. 38 patients had unstable PSVT. Setting: an urban, university-affiliated Emergency Department.	Retrospective chart review.	Conversion rate to sinus rhythm.	Overall success rate 84.8%.	Retrospective chart review but otherwise well designed.
			Rate and significance of adverse effects of Adenosine.	Overall recurrence rate 4.1%.
				Side effects were transient and none were clinically significant(flushing, light-headedness, unsustained VT, chest discomfort, nausea).
Gausche et al 1994 USA	Total no. of adult patients 129. Total no. of adult patients with PSVT 85. 60 were unstable. Setting: large, urban, advanced life support Emergency Medical Services system (paramedics).	Prospective case series.	Conversion rate in unstable patients with PSVT.	Overall success rate 85%. (94% in patients with previous history of PSVT compared with 77% of those without such a history).	Well designed prospective study. This study was the first large series of unstable patients in PSVT who were successfully treated with Adenosine. Conversion rate of unstable patients with PSVT was not mentioned. Patients who presented with unstable PSVT had no increase in complication rate after administration of adenosine as compared to stable patients. Larger proportion than expected was stated to be unstable. The criteria for this were chest pain, systolic BP below 90 mmHg or pulmonary oedema.
			incidence of adverse events.	Overall incidence of adverse effects 10%. all transient and none serious
Lozano et al. 1995 USA	Total no. of adult patients 239 in study group. 228 in control group. Total no. of patients with PSVT 133 in study group, 88 in control group. Setting: large urban municipal Emergency Medical Services system (paramedics).	Prospective observational case series with historical controls.	Conversion rate to sinus rhythm in stable and unstable patients with PSVT. Criteria for treatment with adenosine were chest pain, evidence of myocardial ischaemia or shock	Success rate in unstable group of patients was 67.3%.	Historical controls. Not focused on side effects. Large number of patients lost to analysis mainly due to unavailability of records.
			SVT recurrence rate.	Overall recurrence rate 9% after using Adenosine.
Losek et al. 1998 USA	82 paediatric patients with total of 98 PSVT events. 52 prospective 46 retrospective pts events. Setting: 7 urban paediatric Emergency Departments.	Multicentre study with both prospective and retrospective patient entry.	Safety of Adenosine with unstable SVT.	Success rate 74.7%.	Paediatric pts with all types of medical and cardiac problems were included, including post cardiac surgery. The original design was prospective, but retrospective patients were added to increase the study population. The 2 centres that entered patients only prospectively may have missed eligible pts. Therefore, the results of this study might not be generalisable to the target population. Clinical factors not recorded in the medical records of patients entered into the study retrospectively were considered to be negative. Therefore, the true number of adverse effects may have been greater than reported although the rate of adverse events was similar for patients entered retrospectively compared with those entered prospectively.
			Incidence of adverse effects especially bronchospasm.	Success rate among 10 patients with multiple events 88%.
				Success rate in patients with PSVT and compensated heart failure 80%.
				Side effects occurred in 22% but none were severe (vomiting, chest pain, headache, flushing, transient arrhythmia). No sustained arrhythmia or bronchospam was observed. A greater incidence of side-effects occurred in patients aged 1 year or older or who had had cardiac surgery or who had no signs of cardiac shock.
				No bronchospasm reported in 13 asthmatic pts.
				Adenosine treatment of VT misinterpreted as SVT did not appear to be associated with serious adverse effects.
Clarke et al. 1987 UK	3 newborn infants and one older child. The 3 newborns were described as being severely ill and in cardiac failure due to long-term spontaneously occurring SVT. No data was given about the stability of the older child. Setting: hospital.	Prospective case series.	Conversion rate in unstable patients.	Success rate 100%.	Very small number of patients.
			Incidence of adverse events.	No untoward effects were observed.
Elkayam et al. 1994 USA	38 arrhythmic episodes (37 PSVT, 1 atrial flutter) in 33 pregnant women. Data were collected by four methods: 1. by Questionnaire. 2. Survey. 3. Medline review. 4. Data were obtained in 2 patients directly from LA county hospital.	Retrospective survey.	Conversion rate in pregnant women with SVT.	Success rate 89%.	Retrospective survey. Provides data indicating overall safety and efficacy of intravenous Adenosine for the rapid termination of PSVT during the second and third trimester of pregnancy. (Further study is necessary to determine the safety of Adenosine use during the first trimester of pregnancy). Did not mention the number of unstable pregnant women although some of the cases included in this survey were described as unstable in a case report.
			Incidence of side effects.	Side effects were temporary and none were clinically significant. (transient maternal bradycardia, short lasting uterine contraction).
			Outcome of pregnancy.	No effect on fetal heart rate.
				No late side effects -100% live born infants and no evidence for fetal growth retardation.
				The effective dose of Adenosine seems somewhat higher during pregnancy, possibly due to the expanded vascular volume.
				This study failed to find any evidence for an unfavourable acute effect of Adenosine on the fetus.

Comment(s)

No serious side-effects at all were reported in the eight papers we found looking at the safety and efficacy of using adenosine in patients with unstable PSVT. There were only short-lived, transient side-effects such as headache, flushing, transient arrhythmias and chest tightness, which are well recognised effects in stable patients anyway. In addition, the efficacy of adenosine in converting patients to sinus rhythm is similar for both stable and unstable patients, although some of the papers looked at in this review do not specifically compare the results in stable and unstable patients. In addition, the definition of stable varied between studies.

In view of the above and the speed and ease of giving adenosine to unstable patients as opposed to the need for and potential risks of anaesthesia in DC cardioversion, it seems sensible to use adenosine as first-line treatment in unstable patients. The evidence indicates that this is the case for both adults and children. However, there has not been a prospective randomised controlled trial comparing the two treatments.

Clinical Bottom Line

There is strong evidence to support the efficacy of using adenosine as first-line treatment in patients who present to emergency departments with unstable PSVT with no increased risk of complications. DC conversion could be used as an alternative treatment when adenosine is not successful.

References

1. McCabe JL, Adhar GC, Menegazzi JJ et al. Intravenous Adenosine in the prehospital Treatment of Paroxysmal supraventricular Tachycardia. Annals of Emergency Medicine. April 1992; 21:358-361.
2. Melio FR, Mallon WK, Newton E. Successful conversion of unstable supraventricular tachycardia to sinus rhythm with adenosine. Annals of Emergency Medicine. April 1993; 22:709-713.
3. Marco CA, Cardinale JF. Adenosine for the treatment of supraventricular tachycardia in the ED. American Journal of Emergency Medicine February 1994; 12:485-488
4. Gausche M, Persse DE, Sugarman T et al. Adenosine for the prehospital treatment of paroxysmal supraventricular tachycardia. annals of Emergency Medicine February 1994; 12:485-488.
5. Lozano M JR, Mcintosh BA, Giordano LM. Effect of adenosine on the management of supraventricular tachycardia by urban paramedics. Annals of Emergency Medicine. December 1995; 26: 691-696.
6. Losek JD, Endom E, Dietrich A et al. Adenosine and paediatric supraventricular tachycardia in the emergency department: Multicenter study and review. Annals of Emergency Medicine. February 1999; 33: 185-191.
7. Clarke B, Rowland E, Barnes PJ et al. Rapid and safe termination of supraventricular tachycardia in children by adenosine. The Lancet February 1987; 329:299-301.
8. Elkayam Uri, Murphy Goodwin T. Adenosine therapy for supraventricular tachycardia during pregnancy. American Journal of Cardiology March 1995; 75: 521-523.