- Email: [email protected]
A Comparison of Adenosine and Verapamil for the Treatment of Supraventricular Tachycardia in the Prehospital Setting
E M S / O R I G I N A L CONTRIBUTION
A
Comparison of Adenosine and Verapamil for the Treatment of Supraventricular Tachycardia in the Prehospital Setting
From the City and County of San Francisco, Department of Public Health, Emergency Medical Services Agency, 5an Francisco, California.
Christopher D Madsen, EMT-P James E Pointer, MD, FACEP Thomas G Lynch, EMT-P
Receivedfor publication September 15, 1992. Revisions receivedJune 4, 1993;July 6, 1993; and August i2, 1994. Acceptedfor F~bltcationAugust 12, 1994. F@sawa Pharmaceutical Co provided funding assistancefor this study. Copyright © by the American College of Emergency Physicians.
Study objective: Tocompare the efficacy and base hospital physician use of adenosine with that of verapamil in the prehospital treatment of supraventricular tachycardia (SVT). Design: A 12-month prospective chart review of adenosine administration and a 12-rnonth retrospective chart review of verapamil administration.
Setting: A single-tier advanced life support emergency medical service system. Participants: Prehospital adult patients presenting with narrow-complex SVT.
Interventions: Field paramedics identified SVT.They then administered verapamil or adenosine under on-line physician medical control. Paramedics administered up to two IV doses of verapamil, 2.5 mg and 5 rng, or up to two IV doses of adenosine, 6 rng and 12 mg. They recorded ECG readings; blood pressure; pulse; respirations; and symptoms before, during, and after drug administration. Results: During the verapamil period, paramedics identified 102 cases of SVT and administered veraparnil to 17 patients. Review by a cardiologist revealed 6 of the 17 patients to have been in atrial fibrillation, atrial tachycardia, or sinus tachycardia. Of the remaining 11 patients, 7 (64%) converted from SVT to sinus rhythm. During the adenosine period, paramedics identified 89 cases of SVT, and they administered adenosine to 64 patients. Eight patients had no review because prehospital rhythm strips were lost. Of the remaining 56 patients, 24 were later determined to have been in atrial fibrillation, atrial tachycardia, sinus tachycardia, atrial flutter, or ventricular tachycardia. Of the remaining 32 patients who were in SVT, adenosine converted 25 (78%) to sinus rhythm. An important incidental finding was the misinterpretation of tachydysrhythrnias in 30 of 73 patients by paramedics and base hospital physicians.
MAY 199S
25:5
ANNALS OF EMERGENCY MEDICINE
649
SUPRAVENTRICULAR Madsen et al
TACHYCARDIA
Conclusion: Our study showed no difference in conversion rates between verapamil and adenosine. Base hospital physicians were more likely to order adenosine than verapamil. Paramedics and base hospital physicians often misinterpret tachydysrhythmias. [Madsen CD, Pointer JE, Lynch TG: Comparison of adenosine and verapamil for the treatment of supraventricular tachycardia in the prehospital setting. Ann EmergMed May 1995;25:649-655.] INTRODUCTION Treatment for the prehospital patient in supraventricular tachycardia (SVT) has included vagal maneuvers (Valsalva or carotid sinus massage), medication, and synchronized DC cardioversion. During the past 20 years, verapamil has been the drug of choice for treatment of SVT in the prehospital setting. However, Di Marco et al 1 have shown adenosine to be as effective as verapamil, with fewer side effects. Our study compared the safety and efficacy, as well as base hospital physician use, of adenosine with that of verapamil for the prehospital treatment of SVT.
MATERIALS AND METHODS The study included all patients more than 14 years old whom paramedics assessed as having narrow-complex tachycardias. We reviewed all prehospital records for the retrospective verapamil period---March 1, 1990, through February 28, 1991--and the prospective adenosine period--March 1, 1991, through February 28, 1992. Paramedics in San Francisco's single-tier emergency medical service (EMS) system administered the study drugs. The EMS system in San Francisco serves 1.4 million people during the workday, and the city has 725,000 inhabitants. Paramedics administered drugs only after consultation with a base hospital physician. The base hospital physician is a staff emergency physician at the city's only base hospital, San Francisco General Hospital. These emergency physicians have undergone 40 hours of specialized training in field telemetry, radio procedure, and EMS protocols. Paramedics used the following protocol for the assessment of narrow-complex QRS SVT: QRS duration of less than. 12 second and regular rhythm with a QRS rate between 160 and 240. Paramedics also rendered routine medical care consisting of patient assessment, cardiac
650
monitoring, oxygen administration, and IV therapy with D5W or Plasmalyte. If patients in SVT exhibited such signs of hypoperfusion as systolic blood pressure below 90 mm Hg, altered mental status, or diaphoresis; symptoms of chest pain; or possible myocardial infarction, paramedics carried out cardioversion in accordance with American Heart Association advanced cardiac life support guidelines. Patients without signs or symptoms of hypoperfusion were considered stable. Paramedics established on-line medical control by radio or telephone with a base hospital physician. In stable patients, paramedics first instructed the patient to perform a Valsalva maneuver. If the maneuver was unsuccessful, paramedics administered verapamil or adenosine by order of the base hospital physician. During the verapamil period, paramedics gave an IV bolus of 2.5 mg verapamil, followed by a 5.0-rag IV bolus after 5 minutes if SVT did not convert. During the adenosine period, paramedics administered adenosine as a rapid IV bolus of 6.0 rag, followed by a 12.0-rag rapid IV bolus after 1 to 2 minutes if the initial dose was unsuccessful. Each dose was followed by a 10-mL saline flush. Paramedics recorded initial pulse, blood pressure, respiratory rate, cardiac rhythm, age, sex, medications, symptoms, and a brief medical history before drag administration. They also recorded ECG rhythm strips--usually lead II-before, during, and after adenosine and before and after verapamil administration. Paramedics also took repeat blood pressure, pulse, and respiratory rate measurements after treatment and noted any side effects. The pulse rate was obtained by means of palpation of the radial pulse. Other data collected included patient care time, transport time, time of medication administration, and the time at which SVT converted. A cardiologist, blinded to the study's nature and objectives, retrospectively reviewed ECG rhythm strips. SVT was defined as sudden onset of atrioventricular nodal tachycardia or atrioventricular tachycardia between 160 and 240. These entities generally are responsive to verapamil and adenosine. Atrial tachycardia (AT) was defined as an intraatrial reentry rhythm generally not responsive to verapamil or adenosine. The null hypothesis of our study was that there should be no difference in the efficacy of verapamil or adenosine. This hypothesis was analyzed with the X2 test. For base hospital physician use, the null hypothesis (that there would be no difference in base hospital physician ordering of verapamil and adenosine) was tested with the %2 test. The mean age and number of men from each group were analyzed with an independent t test. Changes in
ANNALS OF EMER6ENCY MEDICINE
25:5
MAY 1995
SUPRAVENTRICULAR TACHYCARDIA Madset~et aI
blood pressure and pulse resulting from the study drugs were tested with two-way ANOVA with a multiple comparison test. Significance was assumed at the .05 level of probability. RESULTS
During the verapamil period, paramedics reported 102 cases of SVT; only the 17 patients who received verapamil (17%) had documentation or hard copies of ECG strips and were included for study of paramedic and base hospital physician ECG interpretation. In two patients, paramedics were unable to distinguish whether the rhythm was SVT or ventricular tachycardia (VT); base hospital physicians chose not to treat these patients with verapamil. Retrospective review of the 17 rhythm strips from patients treated with verapamil demonstrated that 4 patients were in atrial fibrillation (AF), 1 was in AT, 1 was in sinus tachycardia (ST), and 11 were in SVT. None of the patients in AP, AT, or ST converted. Verapamil converted 9 of the 11 patients (82%) determined to be in SVT (mean age, 56 years; range, 30 to 80 years; 5 men). Only seven (64%) were converted to sinus rhythms. Verapamil converted four patients (36%) to normal sinus rhythm, three (27%) to ST, and two (18%) to AE In the patients converted by verapamil, the pulse fell an average of 94 mm Hg (SD, 56; range, -36 to -112) (Figure 1), and mean systolic blood pressure (SBP) increased by 24- mm Hg (SD, 55; range, -30 to +120 mm Hg) (Figure 2). In nonresponders, the mean pulse decreased by 5 (SD, 7; range, 0 to -10); mean SBP was unchanged. The respiratory rate remained unchanged for Figure 1. Change in pulse rate: Responders versus nonresponders.
Changein BloodPressure 0 -
-
all patients. Of the four patients in AF, verapamil slowed the mean ventricular response to less than 100 in two. For patients in AE mean SBP increased 13 mm Hg (SD, 15; range, 0 to 30 mm Hg), and the ventricular response fell 53 (SD, 49; range, 28 to 112) compared with baseline. Paramedics administered verapamil to one patient through an IV line that had infiltrated. All patients in ST and AT had no significant changes in blood pressure, pulse, or respiratory rate after verapamil. Five of 17 patients (29%) experienced side effects after verapamil administration. One patient experienced a drop in systolic blood pressure from 110 mm Hg to 90 mm Hg that lasted at least 16 minutes. Another patient had two 10-second bursts of VT after 5.0 mg verapamil but converted to normal sinus rhythm 2 minutes later. One patient experienced atrial bigeminy, and one patient voided in the ambulance immediately after verapamil administration. Age and sex in the verapamil and adenosine populations were not statistically different. Paramedics reported 89 cases of SVT during the 12-month adenosine period and administered adenosine to 64 patients. The 64 patients treated with adenosine were initially enrolled in the study; however, 8 did not have field ECG rhythm strips available and so were excluded. Review of the ECG rhythm strips by a cardiologist determined that 32 of the 56 patients were in SVT, 11 in AF, 5 in AT, 5 in ST, 2 in VT, and 1 in atrial flutter. Paramedics were unable to distinguish VT from SVT in three patients. Base hospital physicians ordered adenosine for all three. Of these, one was later determined to be in Figure 2. Change in blood pressure: Responders versus nonresponders.
Changein BloodPressure
:':':':':':':'~ ::::::::::::::::: .:-:.:-:,:o:.:.: :::::::::::::::: :.:-:.:°:,:,:.:. .:.:.:-:.:.:,:-: :::::::::::::::: :-:.:.:.:-:.:.:.
-20
m
.:.:.:.:.:,:.:.: :-:.:-:,:.:.:.:. .-,..-,..-..,,.,
-4O
EEEiEEiEEEEEEEEE
n
::::::ti:it::::: ....o.....,
-60
iiiiiiiiiiii~ili
• Verapamil [] Adenosine
:~:~:~:~:~:~:i:i -80 --100
+
m
--m
i
Responders P=NS.
MAY 1995
• Verapamil [] Adenosine
25:5
ANNALS
OF E M E R G E N C Y
Nonrespenders
MEDICINE
P=NS.
Responders
Nonresponders
6 5 1
SUPRAVENTRICULAR TACHYCARDIA Madsen et aZ
AT and did not respond to adenosine. Two patients were later treated under the VT protocol with lidocaine after not responding to adenosine. Adenosine converted 25 of 32 patients (78%) (mean age, 51 years; SD, 18; range, 24 to 82 years; 19 men). Eleven converted to normal sinus rhythm, 13 to ST, and 1 to ST with bundle-branch block. Adenosine terminated SVT in 17 patients after the first 6-my dose and in 8 patients after the second 12-my dose. Among the patients converted by adenosine, mean pulse decreased by 72 (SD, 47; range, 16 to 180), and SBP increased by 11 mm Hg (SD, 24; range, -30 to 128 mm Hg) (Figure 2). In patients not converted by adenosine, mean pulse decreased by 2 (SD, 6; range, 0 to !.8) and SBP dropped by 4 mm Hg (SD, 20; range, 0 to 60 mm Hg) (Figures 1 and 2). The 12 patients in AF who received adenosine all remained in AF; however, the mean ventricular response for 2 patients fell from above 160 to below 100. The mean pulse fell by 16 after adenosine for patients in AE and mean SBP fell 5 mm Hg. Of the five patients in AT, two slowed to ST and one slowed to an atrial rhythm with a rate of 80. Mean SBP decreased by 5 mm Hg (SD, 20; range, 10 to 22 mm Hg), and the mean pulse fell by 37 (SD, 36; range, 0 to 80). One patient in ST experienced sinus slowing from a rate of 180 to 80; pulse rates in the other four patients remained unchanged after adenosine therapy, The patient in atrial flutter remained unchanged after adenosine therapy. The patients in VT did not convert immediately with adenosine; however, one patient did convert to a sinus rhythm without lidocaine therapy 4 minutes after the 12-my second dose of adenosine. Four patients experienced ventricular ectopic activity after conversion with adenosine, but the episodes were limited to the first 30 seconds after conversion. One patient experienced ventricular couplets and an R-on-T phenomenon that lasted 30 seconds. Adenosine terminated SVT in seven patients, who then experienced first- or second-degree AV blocks, none of which lasted longer than 1 minute. For seven of the eight patients who did not convert on adenosine, paramedics or the base hospital physician did not follow the established protocol. Three patients were initially hypotensive and should have undergone synchronized cardioversion. Two of these patients were subsequently cardioverted after adenosine was unsuccessful. Paramedics gave only a single 6-mg dose of adenosine to two patients and gave adenosine through an infiltrated IV line to one.
652
Two patients on oral theophylline received adenosine. One converted after a single 6-my dose; the other did not convert after 6-my and 12-my doses. One patient taking dipyridamole converted without complication after a single 6-my dose of adenosine. Twenty-nine of 64 patients (~b5%) experienced side effects; none required field or emergency department treatment. Seven patients had AV blocks lasting a mean of 7 seconds (SD, 2; range, 5 to 10 seconds), five had asystolic periods lasting an average of 6 seconds (SD, 4; range, 2 to 10 seconds), and four had ventricular ectopic activity after conversion. Four patients complained of chest discomfort during conversion, four had headache, and two felt weak. Four patients also reported flushing, three experienced dyspnea, and two had bronchospasm. None lost consciousness. One patient was 30 weeks pregnant and converted from SVT with adenosine without adverse effects. Base hospital physicians ordered adenosine treatment for 64 of 89 patients (72%) reported in SVT. They ordered verapamil treatment for 17 of 102 patients (17%) during the verapamil period. DISCUSSION McCabe and colleagues a found adenosine safe and effective for prehospital termination of SVT. Our study is the first to compare the efficacy of adenosine with that of verapamil for the prehospital termination of SVT. Prehospital health care providers treat SVT with vagal maneuvers, medication, or electricity. Mechanical vagal therapies (Valsalva maneuver, carotid sinus massage, dependent head-down body tilt position, and mammalian diving reflex) are approximately 50% effective for termination or conversion of SVT.3,40rnato 5 recommended that patients younger than 55 years be treated initially with vagal maneuvers but that these maneuvers were contraindicated in patients older than 55 years because of the risk of ventricular fibrillation and cerebrovascular accident. Singh 6 reported an 87% conversion rate for SVT with verapamil in the hospital setting. In the prehospital setting, Shaw r found that verapamil was effective in converting SVT in only 50% of patients in a busy urban EMS system. In our study, we were unable to find a difference in conversion rates between the two drugs. Our study's verapamil conversion rate (64%) may have been due in part to the judicious ordering of the drug by base hospital physicians. Base hospital physicians were significantly more likely to order adenosine treatment than verapamil for
ANNALS OF EMERGENCY MEDICINE
2 5 : 5 MAY 1995
SUPRAVENTRICULAR TACHYCARDIA Madsen et aI
any patient reported in SVT (P<.01), ahhough they did not necessarily prefer adenosine, as discussed below. When SVT could not be differentiated from VT, base hospital physicians were more likely to order adenosine for treatment. In two instances, the base hospital physician administered adenosine to rule out SVT before beginning the VT treatment protocol. Base hospital physicians may have been reluctant to order verapamil because of its side effects and safety profile. Our study had several important limitations. First, the small sample sizes in both groups of patients who converted prevented acceptance of the null hypothesis. To achieve a type I error of less than .05, a 19% difference in conversion rate must occur. Because the [3 error is .95 for these sample sizes, no conclusions can be made about the conversion rates. Furthermore, the fact that base hospital physicians treated SVT patients with verapamil in only 17% of cases, compared with 72% of cases for adenosine, resulted in a clear difference between the two populations. It cannot be determined whether the difference in the ordering rate was due to physician preference or to the fact that adenosine was being studied. Because the base hospital physicians generally were not aware of the study, we believe that the main difference was due to physician preference. A double-blind study was not possible because of the differences in medication administration routines; however, a randomized, prospective study design could have corrected some of these methodologic concerns. Our study used somewhat lower doses of verapamil than those recommended by current ACLS guidelines (first dose, 2.5 to 5.0 rag; second dose, 5 to 10 rag). These dosages were commonly used in California at the time of the study. As a calcium channel blocker, verapamil has side effects different from those of adenosine. Hypotension is commonly described, s In our study, only one patient who was treated with verapamil became significantly hypotensive. (SBP dropped from 110 to 90 mm Hg for at least 16 minutes, until the patient arrived at the hospital.) In contrast, no patient treated with adenosine became hypotensive (P=.20). None of the patients in either group had a history of congestive heart failure or presented with acute shortness of breath. Because of its negative inotropic action, verapamil is contraindicated in patients with left heart failure. Adenosine may be safer therapy for patients with history of heart failure, especially in the prehospital setting. It may induce bronchospasm or dyspnea. Three patients in our study felt dyspneic, and two experienced
MAY 1999 2 5 : 5 ANNALS OF EMERGENCY MEDICINE
bronchospasm (described by paramedics as wheezing) after adenosine. Inhaled adenosine has induced bronchospasm in asthmatic patients. 9 None of the patients in our study sustained serious respiratory complications, and none required further respiratory therapy, although all received supplemental oxygen. Although adenosine is competitively and reversibly antagonized by methylxanthines 1°, one of the two patients in our study taking theophylline converted with only a single 6-rag dose. The other patient on theophylline did not convert despite two doses of adenosine. The treatment effect may be dose dependent, and, unfortunately, paramedics did not indicate the patients' theophylline doses, nor were levels obtained. No patient in the verapamil group experienced any respiratory complication. Adenosine has not been shown to harm the patient in AF or atrial flutter. Paramedics treated twelve patients in AF or atrial flutter with adenosine without adverse outcomes, and two had significant slowing of the mean ventricular response (from above 160 to below 100). Clinical studies have described more transient arrhythmias after adenosine conversion of SVT than with verapamil 1~, and our study had similar findings. Paramedics have difficulty differentiating rapid AE atrial flutter, and other tachycardias from SVT in the field. Although SVT may occasionally be life threatening, paramedic training usually emphasizes the recognition of lethal dysrhythmias such as VT or third-degree atrioventricular heart block. Thus training may not be as thorough for differentiation of SVT as it is for rapid AE AT, or ST. Training in tachycardia recognition may also be hindered by paramedic instructors' lack of knowledge in 12-lead ECG interpretation. In retrospect, all cases of AF in our study could have been assessed by paramedics had they recognized the irregularity of the R-to-R interval. The use of calipers by paramedics may help this determination. In addition, some of the ST rhythm strips had P waves present, indicating a training issue. Every ECG rhythm that a base hospital physician interprets is transmitted by radio telemetry to the base hospital. The quality of radio reception varies with location, and in a moving ambulance the signal fidelity is extremely poor. Paramedics in San Francisco use lead II almost exclusively as a rhythm strip, with the physical placement of electrodes highly variable. Paramedics have been noted to place lead II electrodes incorrectly on the right shoulder and on the left shoulder. The modified chest lead I suggested by Marriott may provide better P- wave recognition, improve analysis of QRS morphology, and be easily
6 53
SUPRAVENTRICULAR TACHYCARDIA Madsen e~ a]
used as an adjunct to improve ECG rhythm identification. Finally, field equipment may be suboptimal for ECG analysis. Portable cardiac monitors have tiny screens. Most in use in San Francisco have screens less than 4 inches across. Radio telemetry screens in the base hospital are similarly sized. Paper tracings are often of poor quality because of patient movement and in a moving ambulance are almost always of poor quality and difficult to interpret. During the 24-month period, paramedics and base hospital physicians misdiagnosed 30 of 73 cases (41%) of SVT compared with the reading of the study cardiologist. It is important to note that retrospective ECG analysis was performed on 3- to 5-second lead II rhythm strips, some of poor quality. Paramedics consulted base hospital physicians for five patients presenting in wide-complex tachycardias that they could not distinguish from VT. Three were treated with adenosine without conversion (one was actually in AT). After finding no response to adenosine, the base hospital physician ordered treatment of two of the patients according to the VT protocol. In at least one instance, the base hospital physician intentionally used adenosine to rule out VT. The two patients presenting similarly during the verapamil period were not treated with verapamil. Although one study found adenosine to be 93% effective in hospital for converting SVT ~2, our study found it to be effective in 78% of patients. In a study of 99 patients with wide-complex QRS tachycardia, adenosine had a positive predictive value of 92% for differentiating junctional tachycardia, VT, or atrial arrhythmia; none of the 45 patients in VT had any hemodynamic deterioration after adenosine.13 These researchers concluded that adenosine is a valuable diagnostic test of wide-complex tachycardia. Neither of the two patients in our study who had VT suffered any detrimental effect from adenosine therapy. However, using verapamil to treat a patient in VT that has been incorrectly diagnosed as SVT with aberrant ventricular conduction may accelerate the heart rate or cause hypotension, sometimes with disastrous consequences. 14 In patients with Wolff-Parkinson-White syndrome, faster ventricular rates may develop, possibly increasing the likelihood of ventricular fibrillation. According to the work by Rinne et a115 in the hospital setting, the risk is small and should not discourage the use of adenosine as a diagnostic agent in wide-complex tachycardia with a regular rate. The recent advanced cardiac life support guidelines recommend adenosine as the drug of choice in the stable
654
patient with SVT and for the unstable patient awaiting cardioversion.16 Because of its patent status, adenosine is considerably more expensive than verapamfl. In the San Francisco Bay area, the cost to the pharmacy for adenosine for a 6-mg/ 2-mL ampule is $17.13. For verapamil, the cost for a 5-mg/2-mL ampule is $.27. Depending on the markup, the difference in cost to the patient could be significant. CONCLUSION
Verapamil has been the first-line therapy for SVT since the mid-1970s. Recent evidence has shown adenosine to be as effective as verapamil for hospital treatment of SVT. Because of the methodologic considerations discussed above, our study neither supports nor rejects the hypothesis that there is no difference in the conversion rates between the two drugs. Sixty-four patients were treated with adenosine without apparent major complications and with a reasonable success rate. Base hospital physicians ordered adenosine more frequently than verapamil because they preferred adenosine or because adenosine was being studied. Adenosine may aid treatment decisions in patients with wide-complex QRS tachycardias. Prehospital systems choosing to use drug therapy for SVT should carefully weigh the advantages and disadvantages of each drug. Paramedic and base hospital physician interpretation of tachydysrhythmias is often inaccurate. Better training, the use of simple tools such as calipers, and use of modified chest lead I may assist paramedics and base hospital physicians in ECG rhythm identification. REFERENCES 1. Di Marco JP, Miles W, ALtar M, et at: Adenosine for paroxysmal supraventricuier tachycardia: Dose ranging and comparison to verapamil. Ann InternMad 1998;113:104-110. 2. McOabe JL, Adhar GC, Menegazzi J J, et ai: Intravenous adenosine in the prehospitat treatment of paroxysmal supraventricular tachycardia. Ann EmergMad 1992;21:358-361. 3. Mehta D: Relative efficacy of various physical maneuvers in the termination of junctional tachycardia. Lancet1988;1:1181-1185. 4. Waxman MB: Vagal techniques for termination of paroxysmal supraventricular tachycardia. Am J Cardio11980;46:655-657. 5. Ornato JP: Treatment of paroxysmal supraventricular tachycardia in the emergency department by clinical decision analysis. Am J EmergMefl 1988;6:555-560. 6. Singh BN: Calcium antagonists: Clinical use in the treatment of arrhythmias. Drugs 1983;25:125-153. 7. Shaw LC: Prahospital use of intravenous verapemil. Am J ErnergMad 1986;5:287-210. 8. Weiss AT: The use of calcium with verapamii in the management of supraventricular tachycardias. Int J Cardio11983;4:275-280. 9. CusNey M J: Inhaled adenosine and guanosine on airway resistance in normal and asthmatic subjects. Br J Clin Pharrnacol1981 ;74:129-I36.
ANNALS OF EMERGENCY MEDICINE
25:5
MAY 1999
SUPRAVENTRICULAR TACHYCARDIA Madsen et aI
10. Cushley MJ: Adenosine induced bronchocenstriction in asthma: Antagonism by inhaled theophylline. Am RevRespirDis 1984;15:380-384. 11. BelhassenB. Glink A, Laniado S: Comparativeclinical and electrophysielogic effects of adenosine triphosphate and verapamil on paroxysmal reciprocating junctional tachycardia. Circulation 1988;77:795-805. 12. Garratt MB: Comparisonof adenosine and verapamil for termination of paroxysmaljunctional taehycardia.Am J Cordial 1989;84:1310-1316. 13. RankinAF, Oldroyd KG, Chang E, et a[: Value and limitations of adenosine in the diagnosis and treatment of narrow and broad complex tachycardias. Br HeartJ 1989;62:195-203. 14. Jacobs AS, Neilson DH, Gianelly RE: Fatal ventdcular fibrillation following verapamil in the Wolff-Parkinson-White syndromewith atrial fibrillation. Ann EmergMad1985;14:159-160. 15. Rinne C, Sharma AD, KIein GJ, et al: Comparative effects of adenosine triphosphate on accessorypathway and atrioventricular nodal conduction. Am HeartJ 1988;115:1042-I047. 16. EmergencyCardiac Care Committee and Subcommittees, American Heart Association: Guidelines for cardiopulmonary resuscitation and emergencycardiac care. JAMA 1992;268:22222225.
MAY 1995 25:5 ANNALS OF EMERGENCY MEDICINE
The authors thank Dr Tom Evans for his invaluable ass;stance with this study, as we]l as the paramedics and members of the EMS System of the City and County of San Francisco; and Margaret Madsen for her organizatiana] skills and encouragement.
Reprint no. 47/1/64006 Address for reprints: James E Pointer, MD, FACEP Coastal Emergency Services of Fort Lauderdale 6550 North Federal Highway Suite 300 Fort Lauderdale, Florida 33308 305-341-2488
655
A
Comparison of Adenosine and Verapamil for the Treatment of Supraventricular Tachycardia in the Prehospital Setting
From the City and County of San Francisco, Department of Public Health, Emergency Medical Services Agency, 5an Francisco, California.
Christopher D Madsen, EMT-P James E Pointer, MD, FACEP Thomas G Lynch, EMT-P
Receivedfor publication September 15, 1992. Revisions receivedJune 4, 1993;July 6, 1993; and August i2, 1994. Acceptedfor F~bltcationAugust 12, 1994. F@sawa Pharmaceutical Co provided funding assistancefor this study. Copyright © by the American College of Emergency Physicians.
Study objective: Tocompare the efficacy and base hospital physician use of adenosine with that of verapamil in the prehospital treatment of supraventricular tachycardia (SVT). Design: A 12-month prospective chart review of adenosine administration and a 12-rnonth retrospective chart review of verapamil administration.
Setting: A single-tier advanced life support emergency medical service system. Participants: Prehospital adult patients presenting with narrow-complex SVT.
Interventions: Field paramedics identified SVT.They then administered verapamil or adenosine under on-line physician medical control. Paramedics administered up to two IV doses of verapamil, 2.5 mg and 5 rng, or up to two IV doses of adenosine, 6 rng and 12 mg. They recorded ECG readings; blood pressure; pulse; respirations; and symptoms before, during, and after drug administration. Results: During the verapamil period, paramedics identified 102 cases of SVT and administered veraparnil to 17 patients. Review by a cardiologist revealed 6 of the 17 patients to have been in atrial fibrillation, atrial tachycardia, or sinus tachycardia. Of the remaining 11 patients, 7 (64%) converted from SVT to sinus rhythm. During the adenosine period, paramedics identified 89 cases of SVT, and they administered adenosine to 64 patients. Eight patients had no review because prehospital rhythm strips were lost. Of the remaining 56 patients, 24 were later determined to have been in atrial fibrillation, atrial tachycardia, sinus tachycardia, atrial flutter, or ventricular tachycardia. Of the remaining 32 patients who were in SVT, adenosine converted 25 (78%) to sinus rhythm. An important incidental finding was the misinterpretation of tachydysrhythrnias in 30 of 73 patients by paramedics and base hospital physicians.
MAY 199S
25:5
ANNALS OF EMERGENCY MEDICINE
649
SUPRAVENTRICULAR Madsen et al
TACHYCARDIA
Conclusion: Our study showed no difference in conversion rates between verapamil and adenosine. Base hospital physicians were more likely to order adenosine than verapamil. Paramedics and base hospital physicians often misinterpret tachydysrhythmias. [Madsen CD, Pointer JE, Lynch TG: Comparison of adenosine and verapamil for the treatment of supraventricular tachycardia in the prehospital setting. Ann EmergMed May 1995;25:649-655.] INTRODUCTION Treatment for the prehospital patient in supraventricular tachycardia (SVT) has included vagal maneuvers (Valsalva or carotid sinus massage), medication, and synchronized DC cardioversion. During the past 20 years, verapamil has been the drug of choice for treatment of SVT in the prehospital setting. However, Di Marco et al 1 have shown adenosine to be as effective as verapamil, with fewer side effects. Our study compared the safety and efficacy, as well as base hospital physician use, of adenosine with that of verapamil for the prehospital treatment of SVT.
MATERIALS AND METHODS The study included all patients more than 14 years old whom paramedics assessed as having narrow-complex tachycardias. We reviewed all prehospital records for the retrospective verapamil period---March 1, 1990, through February 28, 1991--and the prospective adenosine period--March 1, 1991, through February 28, 1992. Paramedics in San Francisco's single-tier emergency medical service (EMS) system administered the study drugs. The EMS system in San Francisco serves 1.4 million people during the workday, and the city has 725,000 inhabitants. Paramedics administered drugs only after consultation with a base hospital physician. The base hospital physician is a staff emergency physician at the city's only base hospital, San Francisco General Hospital. These emergency physicians have undergone 40 hours of specialized training in field telemetry, radio procedure, and EMS protocols. Paramedics used the following protocol for the assessment of narrow-complex QRS SVT: QRS duration of less than. 12 second and regular rhythm with a QRS rate between 160 and 240. Paramedics also rendered routine medical care consisting of patient assessment, cardiac
650
monitoring, oxygen administration, and IV therapy with D5W or Plasmalyte. If patients in SVT exhibited such signs of hypoperfusion as systolic blood pressure below 90 mm Hg, altered mental status, or diaphoresis; symptoms of chest pain; or possible myocardial infarction, paramedics carried out cardioversion in accordance with American Heart Association advanced cardiac life support guidelines. Patients without signs or symptoms of hypoperfusion were considered stable. Paramedics established on-line medical control by radio or telephone with a base hospital physician. In stable patients, paramedics first instructed the patient to perform a Valsalva maneuver. If the maneuver was unsuccessful, paramedics administered verapamil or adenosine by order of the base hospital physician. During the verapamil period, paramedics gave an IV bolus of 2.5 mg verapamil, followed by a 5.0-rag IV bolus after 5 minutes if SVT did not convert. During the adenosine period, paramedics administered adenosine as a rapid IV bolus of 6.0 rag, followed by a 12.0-rag rapid IV bolus after 1 to 2 minutes if the initial dose was unsuccessful. Each dose was followed by a 10-mL saline flush. Paramedics recorded initial pulse, blood pressure, respiratory rate, cardiac rhythm, age, sex, medications, symptoms, and a brief medical history before drag administration. They also recorded ECG rhythm strips--usually lead II-before, during, and after adenosine and before and after verapamil administration. Paramedics also took repeat blood pressure, pulse, and respiratory rate measurements after treatment and noted any side effects. The pulse rate was obtained by means of palpation of the radial pulse. Other data collected included patient care time, transport time, time of medication administration, and the time at which SVT converted. A cardiologist, blinded to the study's nature and objectives, retrospectively reviewed ECG rhythm strips. SVT was defined as sudden onset of atrioventricular nodal tachycardia or atrioventricular tachycardia between 160 and 240. These entities generally are responsive to verapamil and adenosine. Atrial tachycardia (AT) was defined as an intraatrial reentry rhythm generally not responsive to verapamil or adenosine. The null hypothesis of our study was that there should be no difference in the efficacy of verapamil or adenosine. This hypothesis was analyzed with the X2 test. For base hospital physician use, the null hypothesis (that there would be no difference in base hospital physician ordering of verapamil and adenosine) was tested with the %2 test. The mean age and number of men from each group were analyzed with an independent t test. Changes in
ANNALS OF EMER6ENCY MEDICINE
25:5
MAY 1995
SUPRAVENTRICULAR TACHYCARDIA Madset~et aI
blood pressure and pulse resulting from the study drugs were tested with two-way ANOVA with a multiple comparison test. Significance was assumed at the .05 level of probability. RESULTS
During the verapamil period, paramedics reported 102 cases of SVT; only the 17 patients who received verapamil (17%) had documentation or hard copies of ECG strips and were included for study of paramedic and base hospital physician ECG interpretation. In two patients, paramedics were unable to distinguish whether the rhythm was SVT or ventricular tachycardia (VT); base hospital physicians chose not to treat these patients with verapamil. Retrospective review of the 17 rhythm strips from patients treated with verapamil demonstrated that 4 patients were in atrial fibrillation (AF), 1 was in AT, 1 was in sinus tachycardia (ST), and 11 were in SVT. None of the patients in AP, AT, or ST converted. Verapamil converted 9 of the 11 patients (82%) determined to be in SVT (mean age, 56 years; range, 30 to 80 years; 5 men). Only seven (64%) were converted to sinus rhythms. Verapamil converted four patients (36%) to normal sinus rhythm, three (27%) to ST, and two (18%) to AE In the patients converted by verapamil, the pulse fell an average of 94 mm Hg (SD, 56; range, -36 to -112) (Figure 1), and mean systolic blood pressure (SBP) increased by 24- mm Hg (SD, 55; range, -30 to +120 mm Hg) (Figure 2). In nonresponders, the mean pulse decreased by 5 (SD, 7; range, 0 to -10); mean SBP was unchanged. The respiratory rate remained unchanged for Figure 1. Change in pulse rate: Responders versus nonresponders.
Changein BloodPressure 0 -
-
all patients. Of the four patients in AF, verapamil slowed the mean ventricular response to less than 100 in two. For patients in AE mean SBP increased 13 mm Hg (SD, 15; range, 0 to 30 mm Hg), and the ventricular response fell 53 (SD, 49; range, 28 to 112) compared with baseline. Paramedics administered verapamil to one patient through an IV line that had infiltrated. All patients in ST and AT had no significant changes in blood pressure, pulse, or respiratory rate after verapamil. Five of 17 patients (29%) experienced side effects after verapamil administration. One patient experienced a drop in systolic blood pressure from 110 mm Hg to 90 mm Hg that lasted at least 16 minutes. Another patient had two 10-second bursts of VT after 5.0 mg verapamil but converted to normal sinus rhythm 2 minutes later. One patient experienced atrial bigeminy, and one patient voided in the ambulance immediately after verapamil administration. Age and sex in the verapamil and adenosine populations were not statistically different. Paramedics reported 89 cases of SVT during the 12-month adenosine period and administered adenosine to 64 patients. The 64 patients treated with adenosine were initially enrolled in the study; however, 8 did not have field ECG rhythm strips available and so were excluded. Review of the ECG rhythm strips by a cardiologist determined that 32 of the 56 patients were in SVT, 11 in AF, 5 in AT, 5 in ST, 2 in VT, and 1 in atrial flutter. Paramedics were unable to distinguish VT from SVT in three patients. Base hospital physicians ordered adenosine for all three. Of these, one was later determined to be in Figure 2. Change in blood pressure: Responders versus nonresponders.
Changein BloodPressure
:':':':':':':'~ ::::::::::::::::: .:-:.:-:,:o:.:.: :::::::::::::::: :.:-:.:°:,:,:.:. .:.:.:-:.:.:,:-: :::::::::::::::: :-:.:.:.:-:.:.:.
-20
m
.:.:.:.:.:,:.:.: :-:.:-:,:.:.:.:. .-,..-,..-..,,.,
-4O
EEEiEEiEEEEEEEEE
n
::::::ti:it::::: ....o.....,
-60
iiiiiiiiiiii~ili
• Verapamil [] Adenosine
:~:~:~:~:~:~:i:i -80 --100
+
m
--m
i
Responders P=NS.
MAY 1995
• Verapamil [] Adenosine
25:5
ANNALS
OF E M E R G E N C Y
Nonrespenders
MEDICINE
P=NS.
Responders
Nonresponders
6 5 1
SUPRAVENTRICULAR TACHYCARDIA Madsen et aZ
AT and did not respond to adenosine. Two patients were later treated under the VT protocol with lidocaine after not responding to adenosine. Adenosine converted 25 of 32 patients (78%) (mean age, 51 years; SD, 18; range, 24 to 82 years; 19 men). Eleven converted to normal sinus rhythm, 13 to ST, and 1 to ST with bundle-branch block. Adenosine terminated SVT in 17 patients after the first 6-my dose and in 8 patients after the second 12-my dose. Among the patients converted by adenosine, mean pulse decreased by 72 (SD, 47; range, 16 to 180), and SBP increased by 11 mm Hg (SD, 24; range, -30 to 128 mm Hg) (Figure 2). In patients not converted by adenosine, mean pulse decreased by 2 (SD, 6; range, 0 to !.8) and SBP dropped by 4 mm Hg (SD, 20; range, 0 to 60 mm Hg) (Figures 1 and 2). The 12 patients in AF who received adenosine all remained in AF; however, the mean ventricular response for 2 patients fell from above 160 to below 100. The mean pulse fell by 16 after adenosine for patients in AE and mean SBP fell 5 mm Hg. Of the five patients in AT, two slowed to ST and one slowed to an atrial rhythm with a rate of 80. Mean SBP decreased by 5 mm Hg (SD, 20; range, 10 to 22 mm Hg), and the mean pulse fell by 37 (SD, 36; range, 0 to 80). One patient in ST experienced sinus slowing from a rate of 180 to 80; pulse rates in the other four patients remained unchanged after adenosine therapy, The patient in atrial flutter remained unchanged after adenosine therapy. The patients in VT did not convert immediately with adenosine; however, one patient did convert to a sinus rhythm without lidocaine therapy 4 minutes after the 12-my second dose of adenosine. Four patients experienced ventricular ectopic activity after conversion with adenosine, but the episodes were limited to the first 30 seconds after conversion. One patient experienced ventricular couplets and an R-on-T phenomenon that lasted 30 seconds. Adenosine terminated SVT in seven patients, who then experienced first- or second-degree AV blocks, none of which lasted longer than 1 minute. For seven of the eight patients who did not convert on adenosine, paramedics or the base hospital physician did not follow the established protocol. Three patients were initially hypotensive and should have undergone synchronized cardioversion. Two of these patients were subsequently cardioverted after adenosine was unsuccessful. Paramedics gave only a single 6-mg dose of adenosine to two patients and gave adenosine through an infiltrated IV line to one.
652
Two patients on oral theophylline received adenosine. One converted after a single 6-my dose; the other did not convert after 6-my and 12-my doses. One patient taking dipyridamole converted without complication after a single 6-my dose of adenosine. Twenty-nine of 64 patients (~b5%) experienced side effects; none required field or emergency department treatment. Seven patients had AV blocks lasting a mean of 7 seconds (SD, 2; range, 5 to 10 seconds), five had asystolic periods lasting an average of 6 seconds (SD, 4; range, 2 to 10 seconds), and four had ventricular ectopic activity after conversion. Four patients complained of chest discomfort during conversion, four had headache, and two felt weak. Four patients also reported flushing, three experienced dyspnea, and two had bronchospasm. None lost consciousness. One patient was 30 weeks pregnant and converted from SVT with adenosine without adverse effects. Base hospital physicians ordered adenosine treatment for 64 of 89 patients (72%) reported in SVT. They ordered verapamil treatment for 17 of 102 patients (17%) during the verapamil period. DISCUSSION McCabe and colleagues a found adenosine safe and effective for prehospital termination of SVT. Our study is the first to compare the efficacy of adenosine with that of verapamil for the prehospital termination of SVT. Prehospital health care providers treat SVT with vagal maneuvers, medication, or electricity. Mechanical vagal therapies (Valsalva maneuver, carotid sinus massage, dependent head-down body tilt position, and mammalian diving reflex) are approximately 50% effective for termination or conversion of SVT.3,40rnato 5 recommended that patients younger than 55 years be treated initially with vagal maneuvers but that these maneuvers were contraindicated in patients older than 55 years because of the risk of ventricular fibrillation and cerebrovascular accident. Singh 6 reported an 87% conversion rate for SVT with verapamil in the hospital setting. In the prehospital setting, Shaw r found that verapamil was effective in converting SVT in only 50% of patients in a busy urban EMS system. In our study, we were unable to find a difference in conversion rates between the two drugs. Our study's verapamil conversion rate (64%) may have been due in part to the judicious ordering of the drug by base hospital physicians. Base hospital physicians were significantly more likely to order adenosine treatment than verapamil for
ANNALS OF EMERGENCY MEDICINE
2 5 : 5 MAY 1995
SUPRAVENTRICULAR TACHYCARDIA Madsen et aI
any patient reported in SVT (P<.01), ahhough they did not necessarily prefer adenosine, as discussed below. When SVT could not be differentiated from VT, base hospital physicians were more likely to order adenosine for treatment. In two instances, the base hospital physician administered adenosine to rule out SVT before beginning the VT treatment protocol. Base hospital physicians may have been reluctant to order verapamil because of its side effects and safety profile. Our study had several important limitations. First, the small sample sizes in both groups of patients who converted prevented acceptance of the null hypothesis. To achieve a type I error of less than .05, a 19% difference in conversion rate must occur. Because the [3 error is .95 for these sample sizes, no conclusions can be made about the conversion rates. Furthermore, the fact that base hospital physicians treated SVT patients with verapamil in only 17% of cases, compared with 72% of cases for adenosine, resulted in a clear difference between the two populations. It cannot be determined whether the difference in the ordering rate was due to physician preference or to the fact that adenosine was being studied. Because the base hospital physicians generally were not aware of the study, we believe that the main difference was due to physician preference. A double-blind study was not possible because of the differences in medication administration routines; however, a randomized, prospective study design could have corrected some of these methodologic concerns. Our study used somewhat lower doses of verapamil than those recommended by current ACLS guidelines (first dose, 2.5 to 5.0 rag; second dose, 5 to 10 rag). These dosages were commonly used in California at the time of the study. As a calcium channel blocker, verapamil has side effects different from those of adenosine. Hypotension is commonly described, s In our study, only one patient who was treated with verapamil became significantly hypotensive. (SBP dropped from 110 to 90 mm Hg for at least 16 minutes, until the patient arrived at the hospital.) In contrast, no patient treated with adenosine became hypotensive (P=.20). None of the patients in either group had a history of congestive heart failure or presented with acute shortness of breath. Because of its negative inotropic action, verapamil is contraindicated in patients with left heart failure. Adenosine may be safer therapy for patients with history of heart failure, especially in the prehospital setting. It may induce bronchospasm or dyspnea. Three patients in our study felt dyspneic, and two experienced
MAY 1999 2 5 : 5 ANNALS OF EMERGENCY MEDICINE
bronchospasm (described by paramedics as wheezing) after adenosine. Inhaled adenosine has induced bronchospasm in asthmatic patients. 9 None of the patients in our study sustained serious respiratory complications, and none required further respiratory therapy, although all received supplemental oxygen. Although adenosine is competitively and reversibly antagonized by methylxanthines 1°, one of the two patients in our study taking theophylline converted with only a single 6-rag dose. The other patient on theophylline did not convert despite two doses of adenosine. The treatment effect may be dose dependent, and, unfortunately, paramedics did not indicate the patients' theophylline doses, nor were levels obtained. No patient in the verapamil group experienced any respiratory complication. Adenosine has not been shown to harm the patient in AF or atrial flutter. Paramedics treated twelve patients in AF or atrial flutter with adenosine without adverse outcomes, and two had significant slowing of the mean ventricular response (from above 160 to below 100). Clinical studies have described more transient arrhythmias after adenosine conversion of SVT than with verapamil 1~, and our study had similar findings. Paramedics have difficulty differentiating rapid AE atrial flutter, and other tachycardias from SVT in the field. Although SVT may occasionally be life threatening, paramedic training usually emphasizes the recognition of lethal dysrhythmias such as VT or third-degree atrioventricular heart block. Thus training may not be as thorough for differentiation of SVT as it is for rapid AE AT, or ST. Training in tachycardia recognition may also be hindered by paramedic instructors' lack of knowledge in 12-lead ECG interpretation. In retrospect, all cases of AF in our study could have been assessed by paramedics had they recognized the irregularity of the R-to-R interval. The use of calipers by paramedics may help this determination. In addition, some of the ST rhythm strips had P waves present, indicating a training issue. Every ECG rhythm that a base hospital physician interprets is transmitted by radio telemetry to the base hospital. The quality of radio reception varies with location, and in a moving ambulance the signal fidelity is extremely poor. Paramedics in San Francisco use lead II almost exclusively as a rhythm strip, with the physical placement of electrodes highly variable. Paramedics have been noted to place lead II electrodes incorrectly on the right shoulder and on the left shoulder. The modified chest lead I suggested by Marriott may provide better P- wave recognition, improve analysis of QRS morphology, and be easily
6 53
SUPRAVENTRICULAR TACHYCARDIA Madsen e~ a]
used as an adjunct to improve ECG rhythm identification. Finally, field equipment may be suboptimal for ECG analysis. Portable cardiac monitors have tiny screens. Most in use in San Francisco have screens less than 4 inches across. Radio telemetry screens in the base hospital are similarly sized. Paper tracings are often of poor quality because of patient movement and in a moving ambulance are almost always of poor quality and difficult to interpret. During the 24-month period, paramedics and base hospital physicians misdiagnosed 30 of 73 cases (41%) of SVT compared with the reading of the study cardiologist. It is important to note that retrospective ECG analysis was performed on 3- to 5-second lead II rhythm strips, some of poor quality. Paramedics consulted base hospital physicians for five patients presenting in wide-complex tachycardias that they could not distinguish from VT. Three were treated with adenosine without conversion (one was actually in AT). After finding no response to adenosine, the base hospital physician ordered treatment of two of the patients according to the VT protocol. In at least one instance, the base hospital physician intentionally used adenosine to rule out VT. The two patients presenting similarly during the verapamil period were not treated with verapamil. Although one study found adenosine to be 93% effective in hospital for converting SVT ~2, our study found it to be effective in 78% of patients. In a study of 99 patients with wide-complex QRS tachycardia, adenosine had a positive predictive value of 92% for differentiating junctional tachycardia, VT, or atrial arrhythmia; none of the 45 patients in VT had any hemodynamic deterioration after adenosine.13 These researchers concluded that adenosine is a valuable diagnostic test of wide-complex tachycardia. Neither of the two patients in our study who had VT suffered any detrimental effect from adenosine therapy. However, using verapamil to treat a patient in VT that has been incorrectly diagnosed as SVT with aberrant ventricular conduction may accelerate the heart rate or cause hypotension, sometimes with disastrous consequences. 14 In patients with Wolff-Parkinson-White syndrome, faster ventricular rates may develop, possibly increasing the likelihood of ventricular fibrillation. According to the work by Rinne et a115 in the hospital setting, the risk is small and should not discourage the use of adenosine as a diagnostic agent in wide-complex tachycardia with a regular rate. The recent advanced cardiac life support guidelines recommend adenosine as the drug of choice in the stable
654
patient with SVT and for the unstable patient awaiting cardioversion.16 Because of its patent status, adenosine is considerably more expensive than verapamfl. In the San Francisco Bay area, the cost to the pharmacy for adenosine for a 6-mg/ 2-mL ampule is $17.13. For verapamil, the cost for a 5-mg/2-mL ampule is $.27. Depending on the markup, the difference in cost to the patient could be significant. CONCLUSION
Verapamil has been the first-line therapy for SVT since the mid-1970s. Recent evidence has shown adenosine to be as effective as verapamil for hospital treatment of SVT. Because of the methodologic considerations discussed above, our study neither supports nor rejects the hypothesis that there is no difference in the conversion rates between the two drugs. Sixty-four patients were treated with adenosine without apparent major complications and with a reasonable success rate. Base hospital physicians ordered adenosine more frequently than verapamil because they preferred adenosine or because adenosine was being studied. Adenosine may aid treatment decisions in patients with wide-complex QRS tachycardias. Prehospital systems choosing to use drug therapy for SVT should carefully weigh the advantages and disadvantages of each drug. Paramedic and base hospital physician interpretation of tachydysrhythmias is often inaccurate. Better training, the use of simple tools such as calipers, and use of modified chest lead I may assist paramedics and base hospital physicians in ECG rhythm identification. REFERENCES 1. Di Marco JP, Miles W, ALtar M, et at: Adenosine for paroxysmal supraventricuier tachycardia: Dose ranging and comparison to verapamil. Ann InternMad 1998;113:104-110. 2. McOabe JL, Adhar GC, Menegazzi J J, et ai: Intravenous adenosine in the prehospitat treatment of paroxysmal supraventricular tachycardia. Ann EmergMad 1992;21:358-361. 3. Mehta D: Relative efficacy of various physical maneuvers in the termination of junctional tachycardia. Lancet1988;1:1181-1185. 4. Waxman MB: Vagal techniques for termination of paroxysmal supraventricular tachycardia. Am J Cardio11980;46:655-657. 5. Ornato JP: Treatment of paroxysmal supraventricular tachycardia in the emergency department by clinical decision analysis. Am J EmergMefl 1988;6:555-560. 6. Singh BN: Calcium antagonists: Clinical use in the treatment of arrhythmias. Drugs 1983;25:125-153. 7. Shaw LC: Prahospital use of intravenous verapemil. Am J ErnergMad 1986;5:287-210. 8. Weiss AT: The use of calcium with verapamii in the management of supraventricular tachycardias. Int J Cardio11983;4:275-280. 9. CusNey M J: Inhaled adenosine and guanosine on airway resistance in normal and asthmatic subjects. Br J Clin Pharrnacol1981 ;74:129-I36.
ANNALS OF EMERGENCY MEDICINE
25:5
MAY 1999
SUPRAVENTRICULAR TACHYCARDIA Madsen et aI
10. Cushley MJ: Adenosine induced bronchocenstriction in asthma: Antagonism by inhaled theophylline. Am RevRespirDis 1984;15:380-384. 11. BelhassenB. Glink A, Laniado S: Comparativeclinical and electrophysielogic effects of adenosine triphosphate and verapamil on paroxysmal reciprocating junctional tachycardia. Circulation 1988;77:795-805. 12. Garratt MB: Comparisonof adenosine and verapamil for termination of paroxysmaljunctional taehycardia.Am J Cordial 1989;84:1310-1316. 13. RankinAF, Oldroyd KG, Chang E, et a[: Value and limitations of adenosine in the diagnosis and treatment of narrow and broad complex tachycardias. Br HeartJ 1989;62:195-203. 14. Jacobs AS, Neilson DH, Gianelly RE: Fatal ventdcular fibrillation following verapamil in the Wolff-Parkinson-White syndromewith atrial fibrillation. Ann EmergMad1985;14:159-160. 15. Rinne C, Sharma AD, KIein GJ, et al: Comparative effects of adenosine triphosphate on accessorypathway and atrioventricular nodal conduction. Am HeartJ 1988;115:1042-I047. 16. EmergencyCardiac Care Committee and Subcommittees, American Heart Association: Guidelines for cardiopulmonary resuscitation and emergencycardiac care. JAMA 1992;268:22222225.
MAY 1995 25:5 ANNALS OF EMERGENCY MEDICINE
The authors thank Dr Tom Evans for his invaluable ass;stance with this study, as we]l as the paramedics and members of the EMS System of the City and County of San Francisco; and Margaret Madsen for her organizatiana] skills and encouragement.
Reprint no. 47/1/64006 Address for reprints: James E Pointer, MD, FACEP Coastal Emergency Services of Fort Lauderdale 6550 North Federal Highway Suite 300 Fort Lauderdale, Florida 33308 305-341-2488
655