Intravenous adenosine as first-line prehospital management of narrow ...

Original Contributions

Intravenous Adenosine as First-Line Prehospital Management of Narrow-Complex Tachycardias by EMS Personnel Without Direct Physician Control RICHARD FURLONG, MD,* ROBERT T. GERHARDT, MD, MPH,§ PAMELA FARBER, RN, REMTP,:~ KATHLEEN SCHRANK, MD,* REGINA WlLLIG, REMTP,::I:JUAN PITTALUGA, MD'I" This study was conducted to evaluate the safety and efficacy of intravenous adenosine therapy for prehospital treatment of narrow-complex tachycardias with a presumptive field diagnosis of paroxysmal supraventricular tachycardia (PSVT) by paramedics without direct physician control. A ten-month prospective case series was designed in an urban EMS system that has paramedics operating under standing orders before physician radio contact. All patients with PSVTfield diagnosis were included. Diagnosis of PSVT was made by regular, narrow-complex tachycardia with a heart rate greater than 160 beats/min by field ECG. Interpretation was performed solely by paramedics; ECG transmission was not available. In hemodynamically stable patients, vagal maneuvers were followed by intravenous placement and administration of adenosine as recommended by the manufacturer. If three adenosine boluses failed to convert the arrhythmia, patients were monitored and transported, with electrical cardioversion available. Data collection included demographics, history, medications, vital signs, and ECG tracings. Of 41 included patients, 31 were correctly diagnosed with PSVT (75.6%), with mean ventricular rate of 205 beats/min (SD 7 beats/min); one had sinus tachycardia; nine had atrial fibrillation (AF) (22%). Of the 31 cases correctly

From the *Emergency Medicine Section and the "l'Division of Cardiology, Department of Medicine, University of Miami School of Medicine, and the :~City of Miami Fire Department, Miami, FL; and the §Department of Emergency Medicine, Darnall United States Army Community Hospital, Fort Hood, TX. Manuscript received March 21, 1994; revision accepted October 7, 1994. Supported by a Medical Student Research Award from the Emergency Medicine Foundation/Society for Academic Emergency Medicine. Presented at the Emergency Medicine Foundation Showcase, Scientific Assembly of the American College of Emergency Physicians, Seattle, WA, September 19-21, 1992. The viewpoints and conclusions of the authors as reported herein do not necessarily reflect the official opinion of the United States Army, the Department of Defense, or the US Government. Address reprint requests to Dr Gerhardt, Department of Emergency Medicine, Darnall Army Community Hospital, Fort Hood, TX 76544. Key Words: Adenosine, narrow-complex tachycardia, emergency medical services. This is a US government work. There are no restrictions on its use. 0735-6757/96/1304-0001 $0.00/0

diagnosed as PSVT, 28 converted to sinus rhythm after adenosine (90.3%). Of those converted, 16 required a single dose (57.1%), nine required one additional dose (32.1%), and three required two additional doses (10.8%). None reverted to PSVTafter adenosine conversion during the study period (conversion to arrival at emergency department). No significant difference in length of asystolic pause or in outcome was detected between the true PSVTcases and the AF cases receiving adenosine. There were no significant deleterious side effects in the adenosine group. It was concluded that adenosine is effective for prehospital treatment of narrow-complex tachycardias, and its safety profile appears to allow paramedic administration without "requisite" physician control. It should be used as directed by the manufacturer and may prove to be a valuable prehospital diagnostic adjunct in AF and hemodynamically stable abberant PSVT masked as wide-complex tachycardia. (Am J Emerg Med 1995;13:383-388. This is a US government work. There are no restrictions on its use.)

Paroxysmal supraventricular tachycardia (PSVT) is a narrow-complex (QRS duration less than 0.12 second) cardiac dysrhythmia with a regular, rapid ventricular rate usually greater than 150 beats/min, arising from atrioventricular reentry or an ectopic pacing focus above the bifurcation of the bundle of His.~ Although this condition does not usually present as an immediate life-threatening disorder, PSVT possesses the potential to cause significant hemodynamic compromise and is associated with deterioration to potentially lethal ventricular arrhythmias in select cases, z Thus, PSVT is considered to be a medical emergency, warranting prompt diagnosis and treatment. Adenosine is a naturally occurring purine nucleoside capable of converting symptomatic PSVT to sinus rhythm when administered by rapid intravenous infusion. Its mechanism of action is thought to be through transient atrioventricular nodal blockade and coronary vasodilatation. 3 Adenosine has demonstrated efficacy in PSVT of several etiologies, including atrioventricular nodal reentry, Wolff-ParkinsonWhite syndrome possessing a regular rhythm regardless of QRS duration, and concealed atrioventricular bypass tracts. 4 In addition, because it has neither a beneficial nor an adverse effect on the majority of ventricular dysrhythmias, adenosine has proven useful as a diagnostic adjunct in he383

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modynamically stable wide-complex tachycardias of questionable etiology. Hospital trials have indicated roughly a 90% success rate in termination of PSVTs. 5'6 Comparative trials with verapamil have demonstrated adenosine to be at least equal in effectiveness, often terminating PSVTs that were refractory to verapamil treatment, without the risk of inducing hypotension, and obviating the risk of verapamil administration for a tachycardia that is in fact ventricular in origin. 5 Because of its demonstrated effectiveness in terminating PSVT, its rapid onset of action, its short half-life, and its relative paucity of adverse effects, as well as its inherent heat stability (which facilitates storage aboard rescue vehicles), adenosine may be ideal for use in the prehospital environment by paramedical personnel under medical direction. A recent case series described the successful prehospital use of adenosine for PSVT by emergency medical service (EMS) personnel after evaluation and approval by base station medical controlT; however, the question remains whether field diagnosis of PSVT and subsequent adenosine administration may be performed in a prehospital setting without obligatory physician control and electrocardiogram (ECG)-telemetry confirmation. This study was undertaken to investigate and define adenosine's role as a potential first-line therapeutic adjunct in prehospital cardiac care. This evaluation included adenosine's potential as a "protocol-driven" intervention whereby trained EMS personnel are authorized to diagnose and administer emergency field treatment without compulsory advance physician evaluation unless such evaluation is warranted by the situation in the paramedic's judgment. Further, dosage requirements were investigated by comparing the rate of conversion from the initial 6-mg intravenous bolus with rates of conversion from the higher 12-mg dosage after initial treatment failure.

gaged in EMS operations underwent a two-hour in-service educational block in which PSVT etiology, pathophysiology, and diagnosis were reviewed and in which adenosine was introduced. Adenosine pharmacology, dosing schedule, route of administration, indications, contraindications, side effects, and precautions were discussed. After the didactic session, a practical seminar was conducted demonstrating the correct administration of adenosine, emphasizing rapid bolus of adenosine followed by a rapid flush of the intravenous line. The specific protocol for intravenous adenosine infusion used as the standing orders of the EMS medical director in this study is depicted in Figure 1. Briefly, field diagnosis of PSVT was made by physical signs and symptoms (complaint of palpitations or chest tightness, rapid pulse, hypotension relative to patient's baseline, if known, dyspnea, cyanosis, and/or diaphoresis) followed by ECG confirmation of a regular, narrow-complex tachycardia with a rate equal to or greater than 160 beats/min. After presumptive diagnosis of PSVT, intravenous access was established, with a large-bore antecubital cannulation preferred, while vagal maneuvers were attempted. Paramedics were instructed to consider patients showing signs of severe hemodynamic instability (defined as a systolic blood pressure 160 Regular, Narrow QRSComolexECG

VagalManeuvers ContinuousECGMonitoring Peripheral I.V. Access (Antecubital)

Systolic BP > 90 mm ttg?

v~'- Electrfcal't~-cli6versldn

Yes ~ Adenosine 6 mg BoJus

and 5cc N-,.~. / i ~ FJ~,.%b

METHODS Subjects included in this study consisted of all patients with a prehospital diagnosis of PSVT who were transported within Miami, FL by advanced life support (ALS) units of the City of Miami Department of Fire Rescue and Inspection Services (MFR) between July 21, 1991 and April 30, 1992 and who did not respond to vagal maneuvers. All subjects were transported for definitive care to local emergency departments (EDs). Subjects were excluded from adenosine treatment if they were known to be pregnant, were younger than 14 years of age or older than the age of 85 years, or if they had a history of recent ingestion of dipyridamole or carbamazepine. A concurrent placebo-controlled study design was not feasible. Under State of Florida Statutes, randomized placebo-controlled studies require full informed written consent before entry (ie, treatment). This was deemed ethically unacceptable in view of adenosine's demonstrated efficacy and MFR's documented short average transport time to EDs. The study was approved by the University of Miami School of Medicine Human Studies Committee. Specifically, data collection included the ALS unit number and personnel responding, subject age, sex, chief complaint, elapsed field treatment time, 8 prehospital diagnosis, serial vital signs, continuous ECG rhythm strips both before and during treatment, a detailed log of medications and other interventions employed, subject disposition on arrival at definitive care, and location of definitive care. All data were reviewed by the study coordinator and cardiology consultant. Before releasing adenosine for use, all firefighter/paramedics en-

Conversion?

Yes Monitor and Transport

Re~.sses.% Adenosine 12 ms Bolus and 5cc N5 / LR Flush

Conversion ?

Yes

Monitor and T~'n%;/',~%

Reassess Adenosine 12 mg Bolus and 5cc NS / LR Flush

Conversion ?

Yes

No ~

Monitor and Transport v

Reassess Consider Electrical C a r d i o v e r s i o n Monitor and Transport

FIGURE 1. Prehospital adenosine treatment protocol.

FURLONG ET AL • PREHOSPITAL IV ADENOSINE

crushing substernal chest pain, or altered mental status) as having a diagnosis of "unstable PSVT," in which case they would receive expeditious prehospital electrical cardioversion in accordance with standard ACLS guidelines. In the absence of hemodynamic instability and if vagal maneuvers failed to convert the dysrhythmia, subjects were advised of side effects to be expected, and a rapid intravenous bolus of 6 mg adenosine (over 1 to 2 seconds) was administered, followed by a rapid flush using 5 mL of normal saline or lactated Ringer's solution. If PSVT failed to convert to sinus rhythm within 2 minutes, adenosine was administered a second time at a dose of 12 mg (over 1 to 2 seconds) followed by flush. If PSVT failed to convert to sinus rhythm within 2 minutes of the second dosage, a third rapid intravenous bolus consisting of 12 mg adenosine was given, followed by rapid saline flush. After conversion, or in the event of adenosine therapeutic failure after the prescribed three doses, paramedics then contacted their base station physician by radio to summarize treatment, continued monitoring the patient, provided volume support or electrical therapy if required, and transported the patient to definitive care as soon as possible. Significance was defined as an alpha error (P) of less than .05. Statistical analyses included: unpaired two-tailed Student's t tests to assess the significance of the difference in asystolic pause in both unmatched PSVT and AF patients with 6-mg and 12-rag doses, respectively; paired two-tailed Student's t tests to assess the difference in asystolic pause in patients who received both 6-mg and 12-mg adenosine boluses because of initial 6-mg dose failure; and two-way repeated-measures analysis of variance (ANOVA) to assess the significance of differences in asystolic pause between the PSVT and AF groups, at both 6-mg and 12-mg doses, respectively. RESULTS

Descriptive demographic and therapeutic effect statistics for this study appear in Table 1 and Table 2, respectively. During the 10-month duration of this study, 43 subjects were diagnosed with PSVT and treated in the field with adenosine. Of these, two cases were excluded retrospectively. One was excluded because prehospital ECG records were unrecoverable, and one was excluded because of deviation from the study protocol (patient was in sinus tachycardia secondary to cocaine toxicity, received no vagal maneuvers, and was treated with one 6-mg adenosine bolus only). Thus, 95.3% of cases were evaluable. Neither of the excluded subjects suffered adverse outcomes. Of the 41 subjects included in the study, 31 were confirmed to have been diagnosed correctly as PSVT (75.6%) by a cardiologist's evaluation of field ECG strips. Of the 31 cases correctly diagnosed in the field, 28 converted to either normal sinus rhythm or sinus tachycardia after adenosine administration (90.3%). Of these, 15 required a single dose TABLE 1.

Prehospital Adenosine for Narrow-Complex

T a c h y c a r d i a Demographics

Category

Adenosine Treatment Group (-+SD)

Number Age (yr) Sex (female, male) Response time (min) Field treatment time (min) Initial ECG rate (beats/min) Initial systolic BP (mm Hg) Initial respirations (breaths/min)

41 52 (-+18) 26, 15 5.3 (-+1.6) 28 (-+7) 197 (-+26) 119 (-+34) 26 (---33)

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TABLE2.

Prehospital Adenosine for Narrow-Complex

T a c h y c a r d i a Adenosine Treatment

Group--Therapeutic Results Actual ECG Diagnosis*

No. (%)

Total Cases 41 (100) ParoxysmalSVT 31 (75.6) AF 9 (22) ST 1 (2.4) Adenosine Conversion to Sinus Rhythmt SVT 28 (90.3) Required 6-mg dose 16 (57) Required additional 12-mg dose 9 (32) Required two additional 12-mg doses 3 (11) AF 0 (0) ST 0 (0)

Ventricular Rate (beats/rain) 205 -+ 7 203 -- 25 180 ± 17 166

* All were field-diagnosed as PSVT by paramedics. ? Sinus rhythm is defined as sinus tachycardia or normal sinus rhythm.

(57.1%), 10 required one additional dose (32.1%), and three required two additional doses (10.8%). None reverted to PSVT after adenosine conversion, with the end point being ED arrival. Of the three patients failing to convert with adenosine therapy, one required electrical cardioversion in the ED to break the PSVT; a second received a new intravenous line in the ED (the original had infiltrated) and converted after two further doses of adenosine; the third converted, after 6 mg of adenosine, to A F with slower ventricular rate (a phenomenon described recently as occurring occasionally with verapamil therapyg). There were no reports of arrhythmias or ectopy lasting longer than one minute after administration; after this period, the condition of all patients either improved with conversion to sinus rhythm or returned to baseline before adenosine administration. Of the 10 cases diagnosed incorrectly, one had sinus tachycardia (ST) (2.4%), with a rate of 166 beats/rain at time of field ECG. After receiving adenosine, this patient experienced a sinus pause, then a transient slowing of ventricular rate followed by return to underlying ST at a rate of 150 beats/min. The remaining nine cases were later diagnosed as atrial fibrillation (AF) (22%). In each of these cases, adenosine administration was associated with an asystolic pause (mean 1.19 seconds, 95% confidence interval [CI] 0.96 to 2.48 seconds) associated with a jagged baseline consistent with A F , then resumption of the underlying arrhythmia. None of the A F cases treated with adenosine developed deleterious side effects. There were no cases of ventricular tachycardia misdiagnosed as PSVT, nor was there any case where the rate of PSVT appeared to increase after adenosine administration.I° The asystolic pause induced by both 6-mg and 12-mg adenosine treatment was evaluated in all adenosine-treated patients. This was defined as the single maximum interval between consecutive QRS complexes immediately after the respective adenosine dose as recorded on field single-lead ECG. The results are depicted in Table 3. A crude unmatched comparison was made of mean asystolic pause between all patients receiving 6-mg and 12-mg adenosine treatments regardless of actual rhythm, followed by analysis both within and between the groups later diagnosed with PSVT versus AF. Greater asystolic pauses were detected with the 12-mg dosage than with the 6-mg dosage, regardless of actual cardiac rhythm; this finding closely approximated signifi-

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TABLE3. Prehospital Adenosine for Narrow-Complex Tachycardia Adenosine Treatment Group--Ventricular Asystole Analysis Average Pause(s) at 6 mg

Average Pause(s) at 12 mg

Significance (P