Efficiency of a physician-operated mobile intensive care unit for prehospital thrombolysis in acute...

Efficiency of a Physician-Operated Mobile Intensive Care Unit for Prehospital Thrombolysis

in Acute Myocardial Infarction Hans-Richard Arntz, MD, Richard Stern, MD, Thomas Linderer, MD, and Rolf SchrOder, MD

The effklemy of an emergency medical system for routinely performed prehospital thrembolysis is evahuhted for 1 of the 7 physician-staffed mobile intensive care units (MICU) in former West Berlin. Duri~ 19 consecutive months the MICU had 4,926 missions, and 1,226 patknts had chest pain of presumed cardiac origin. The diagnosis at hospital discharge was acute myocardial infarc- tion (AMI) in 408 patiemts and ‘*itipted” in- farctionin llpatlents(total417).Correcton- scene waphic diagnosis of acute in- jury was made in 288 patients (84%) and was false-positive in 4 patknts (1%). In 8%, pressnt ST eiemtions were not recognized. In 27%, the electrocardiogram on scene was nondbgnestic (18% with no ST elevation, 11% with bundle branch block). of all 417 patients with later hospi- tal evidence of AMI, 317 (76%) wore seen by the MICU physkian wwn 4 hours, and 173 (41%) within the ftrst hour from symptom onset. Two hundred three patients seen within 4 hours had di- agnosticSTelevationonthescenet,ofwhom124 (6l%)Mceivd pmhospMthrombolysis(74pa- tients [36%] wHMn the first hour). There was no’ pmhospbldeath;hmpitalmortalitywas6.3%. 8ecause >SO% of all patients in the community, hospitalkedbecauseofAMI,madeuseofthe MICU and ?4 of them had called witMn 4 hours from symptom onset, a large proper&n of all pa- tients with AMI wero candidates for and actually received pldmspkl thromboiysis.

(Am J Cardtol193~70~17-420)

From the Department of Cardiology, Klhikum Steglitz, Free. Universi- ty Berlin, Germany. Manuscript received January 24, 1992; revised manuscript received April 29.1992, and accepted May 1.

Address for reprints: Rolf Schrikler, MD, Department of Cardiolc+ gy, Khikum Steglitz, Free University Berlin, Hmdenburgdamm 30, D- 1000 Berlin 45, Germany.

I n-hospital thrombolysis for acute myocardial infarc- tion (AMI) reduces mortality.1-3 The benefit is re lated to the interval between onset of symptoms and

initiation of thrombolysis. ly2 Prehospital thrombolysis is feasible, safe and time-saving, as controlled studies in selected patients groups have shown.“8 However, when prehospital thrombolysis is performed on a routine ba- sis, its efficiency will depend on the proportion of all patients with AM1 in the community correctly identi- fied and properly treated already in the field. Based on the results of a pilot study4 in West Berlin, prehospital thrombolysis is performed routinely since 1987. The present study was performed in order to evaluate its ef- fectiveness.

MEIWODS s-ofthswest8erlln~nledled

systemr The emergency medical system of former West Berlin (population approximately 2 million) is coordi- nated by the fire department. Fifty-five emergency medical technician-staffed ambulances, operating from 33 fire stations distributed throughout the city, respond to patient-initiated emergency calls. Experienced dis- patchers receive the call and decide, by using a key word system, whether in addition to the ambulance the nearest of 7 mobile intensive care units (MICUs) staffed with 1 emergency physician and 2 emergency medical technicians has to bc called. Key words are: chest pain, respiratory distress, unconsciousness, severe injury, severe bleeding and shock.

Prehospital thrombolysis is performed by 6 of the 7 MICUs. The emergency physician records clinical sta- tus, duration of symptoms, diagnosis (including a 12- lead electrocardiogram), contraindications to thrombol- ysis, complications and therapeutic measures during prehospital care on a special report form. Generally, pa- tients are transported to the nearest hospital with an intensive care unit. During the study period, the modes of admission were evaluated for all patients hospitalized because of AMI. Data from 1 MICU (Klinikum Steg- litz, serving about 350,000 people) are reported. The re sults can be regarded as representative for the West Berlin emergency system, since all MICUs have similar standards and strategies.

W~-mwJ=Y adgmwnb All assign- ments during 19 consecutive months (April 1988 to Oc-

ROUTINE PREHOSPITAL THROMBOLYSIS 417

TABLE I On-Scene Diagnosis and Hospital Evidence of Acute Myocardial Infarction in 4,920 Consecutive Missions of the Mobile Intensive Care Unit

MICU Missions n = 4,920

I Chest pain of

presumed cardiac origin (n = 1,226)

Diagnosis of I \ emergency AMI Suspected AMI physician or unstable AP

n = 272 (22%)

I I .

n = 404 (33%) n = 550 (45%)

Hospital evidence of AMI n = 268* n= 105 n = 44

‘Eleven with “interrupted” ischemic event included. AMI = acute myocerdiel infarction; AP = angina pectoris; MICU = mobile intensive

cam unit.

tober 1989) with in-field diagnosis of chest pain of pre sumed cardiac origin were analyzed. The emergency physician had to decide on 1 of .3 diagnostic categories: (1) AMI, (2) suspected AM1 or unstable angina pecto- ris, and (3) angina pectoris. Hospital charts of all pa- tients were analyzed and the discharge diagnosis was used to determine patients with AMI.

RWuutbn of sums: The prehospital electrocardiographic recordings of patients, in whom the emergency physician had diagnosed AMI, were reevalu- ated throughout the study. During the last 7 study months, on-scene electrocardiograms from all patients with chest pain of presumed cardiac origin (n = 472) were reevahtated without knowledge of the emergency

Pat. (4;)

50 1

40

30

20

IO

0 0 1 2 3 4

hrs

11 hr n = 173 (41%) 1 -2hrs n = 86 (21%) 2 - 3 hrs n = 36 ( 9%) 3 - 4 hrs n = 22 ( 5%) ----------------------------- 4 - 6 hrs n = 27 ( 6%) > 6hrs n= 73(18%)

physician’s or the final in-hospital diagnosis. Acute inju- ry was defined when 12 continuous leads in a group location displayed ST elevation >O.l mV or tall peaked T waves in the absence of bundle branch block or ven- tricular pacing.

Pr&ospN Wembelyais: Patients aged <76 years seen within 4 hours from symptom onset without con- traindications were candidates for prehospital thrombol- ysis. ST elevations had to persist after 5 minutes of sub lingual nitroglycerin. Patients with bundle branch block were excluded. Streptokinase (1.5 million U) was in- fused intravenously in 30 minutes in 79 patients, and 44 patients received an intravenous injection of anisoylated plasminogen streptokinase activator complex (30 mg) in 3 to 5 minutes. Three patients who had previously re ceived streptokinase therapy were given 3 million U of urokinase preceded by 5,000 IU of heparin intrave nously.

RESULTS During the study period, 70% of all patients in the

community hospitalized because of AM1 had come through the emergency system, and 51% by the MICU.

PaWapiWandhospIW&gnosk(TabIeI):During 19 consecutive months the MICU had 4,920 missions, 1,226 patients (25%) had chest pain of presumed cardi- ac origin. The emergency physician diagnosed AM1 in 272 patients, of whom 268 (including 11 with “inter- rupted” AMI) had diagnosis confiied in the hospital. Of 404 patients with in-field suspected AM1 or unstable angina pectoris, 105 (26%) developed hospital evidence of AMI. Of 550 patients with an in-field diagnosis of angina pectoris, 44 (6%) eventually developed AMI. Thus, a total of 417 patients had hospital evidence of AMI.

Arrivals of the MICU, subdivided by time from symptom onset for these 417, are shown in Figure 1. Three hundred seventeen patients (76%) were seen by the emergency physician within the first 4 hours, and 173 had called so promptly that they were reached by the MICU within the fast hour from symptom onset. Median time delay for all patients was 1.3 hours, mean delay 4.6 f 7.4 hours.

Saminacutamyocudkllnfarctbn andacamcyofbl4ieldi~ The prehospital diagnosis of acute injury was confiumed in 268 of 272 cases (99%). Eleven patients with diagnostic ST eleva- tion on the scene subsequently developed negative T waves, but cardiac enzymes did not exceed twice the upper normal range. Obviously they have had an inter- rupted ischemic event as confiied by subsequent coro- nary angiography.

In 4 patients the diagnosis of the emergency physi- cian was wrong. The in-hospital diagnosis was esophagi- tis in 2 patients, old anterior myocardial infarction with Menike’s disease and acute pancreatitis in the 2 other patients.

In a subset of 472 consecutive patients with chest pain of presumed cardiac origin, accuracy of all in- field electrocardiographic interpretations was checked by second readings. Injury of AM1 was seen retrospec- tively in 109 patients and had been identified in the field

418 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70 AUGUST 15. 1992

in 100 patients. The electrocardiograms of the 363 pa- tients without diagnostic ST elevation were correctly in- terpreted in the field. Therefore, in this subset of pa- tients, the overall accuracy of the in-field interpretation was 98%, sensitivity 92% (correct identification of diag- nostic ST elevation) and speciticity 100% (correct inter- pretation of no ST elevation).

Of the 146 subset patients who developed in-hospital evidence of AMI, 106 (73%) have had diagnostic ST elevations in the prehospital electrocardiogram, 24 (16%) had nondiagnostic ST-T changes or a normal electrocardiogram, and 16 (11%) had bundle branch block.

M thrombolysIs: Of the patients seen with- in 4 hours from symptom onset, 205 had an in-field di- agnosis of AMI; 126 of these (61%) had prehospital thrombolysis. Two misdiagnosed patients had an un- eventful course, and no bleeding complications oc- curred.

The main reason for exclusion was age >75 years in 43 patients (21%), suspected bleeding risk in 25 (12%), and other reasons in 11 (5%) patients. Adverse events outside of the hospital included 3 cases of ventricular fibrillation, managed by electrical defibrillation and 2 of symptomatic bradyarrhythmias, controlled by atropine. There were no bleeding complications or death outside hospital. In-hospital mortality was 6.3% (8 of 126 pa- tients). Five patients died from cardiogenic shock or cardiac failure, 1 from cardiac rupture, and 1 suddenly. Two patients had intracranial hemorrhages, lethal in 1 and minor bleeding without significant disability in the other. Six patients had nonfatal reinfarction, 23 elective coronary angioplasty, and 15 bypass surgery.

Table II subdivides MICU arrival times and propor- tion of prehospital thrombolysis for the first 4 hours from pain onset. In 74 patients with prehospital throm- bolysis the emergency physician was on the scene within the fust hour (i.e., 23% of the 317 patients with later in- hospital evidence of AM1 had very early prehospital thrombol ysis) .

In-field times for AM1 patients with prehospital thrombolysis were compared to those without it. Re sponse time averaged 8 f 3 minutes in both groups. After arrival, 26 f 8 minutes elapsed until initiation of thrombolysis. Total in-field times were 48 f 10 minutes for patients receiving thrombolytic therapy and 39 f 10 minutes for those who did not. Thus, about 10 minutes are additionally required to perform prehospital throm- bolysis.

DISCUSSION Very early treatment has the potential to maxi-

mize the beneficial effects of thrombolytic therapy in AMI.119-11 In former West Berlin, most patients in the hospital because of AM1 had made use of the MICU. They usually seek medical attention very early (Figure 1) and thus are candidates for thrombolytic therapy outside hospital. In our study, 41% of all patients who developed hospital evidence of AM1 had called prompt- ly, enough to be reached by the MICU within 1 hour from symptom onset. For these patients immediate pre hospital thrombolysis is advocated. Even fast admission

TABLE II Patients Seen by Emergency Physicians Within Four Hours, Subdivided by Time from Pain Onset and Proportion of Prehospital Thrombolysis

Hospital Evidence of AMI Prehospital Thrombolysis

A (n) B(n) B (%A) C(n) C(%A) C(% B)

First hour 173 115 66% 74 43% 64% Second hour 86 47 55% 31 36% 66% Third tofourth 58 41 71% 19 33% 46%

hour

Total 317 203 64% 124 39% 61% A = hospital evidence of AMI; B = injury of AMI correctly diagnosed in the field; C =

prehospital thmmtmlysis.

to the hospital would not ensure prompt therapy. At least 1 hour delay is still typical and reflects the many impediments to rapid thrombolytic therapy in the hospi- ta1.8J2J3 Previous studies in selected patients demon- strate that prehospital thrombolysis is feasible, safe and associated with significant time gain.4-8 Our fmd- ings showed that this holds true also when prehospital thrombolysis is performed routinely. Within the time window of 4 hours from symptom onset of AMI, 61% of all patients with recognized acute injury had thromboly- sis initiated on the scene, and mostly so within the first hour. Decision to treat on the scene was correct in 124 of 126 patients. Under clinical conditions thrombolysis likewise will be performed in some misdiagnosed pa- tients.14 Not all patients with diagnostic ST elevation on the scene develop definite infarction. They may have ex- perienced an interrupted myocardial ischemic event.i4 Bleedings are principal complications of thrombolysis but not a consequence of prehospital initiation of thera- PY-

The main reason thrombolytic drugs were not ad- ministered out of the hospital was advanced age. In ad- dition, patients with bundle branch block had been ex- cluded. However, because older patients and those with bundle branch block not only have the highest mortal- ity risk but also benefit most from early thromboly- ~is,~v~J~J~ we now perform prehospital thrombolysis also in these patients.

In keeping with our findings, several studies have shown that in approximately 20 to 30% of patients with later evidence of AMI, ST elevations are not present in the initial electrocardiogram.6~8J7-19 However, thii is no disadvantage so far as early prehospital thrombolysis is concerned, because these patients in general are not candidates for thrombolytic therapy. Recent trials have shown that only patients with ST elevation (or bun- dlel @tt$i block) clearly benefited from thromboly- &,>, 7

Selection of patients with suspected AM1 for throm- bolytic therapy is based on the evaluation of symptoms, exclusion of potential risk of serious bleeding, and elec trocardiographic findings on the initial electrocardio- gram. On-scene electrocardiograms may be interpreted by the MICU physician, after cellmar transmission by a basestation physician,8 or a portable computer electro cardiographic system may verify the diagnosis.i9 Elec- trocardiographic accuracy of infarct diagnosis compar-

ROUTINE PREHOSPITAL THROMBOLYSIS 419

TABLE III Patients with Chest Pain of Presumed Cardiac Origin identified in the Field, Hospital Evidence of AMI and Prehospital Thrombolysis Initiated by the Emergency Physician (Berlin) or Potentially Eligible for Prehospital Thrombolysis by Paramedics (Seattle)*

Berlin- Seattle No. of Pts. No. of F’ts.

Chest pain of 1,226 100% 2,473 100% presumed cardiac origin

Hospital evidence 417 1

34% of AMI 453 1 18%

Prehospital 124 30% 10% 105 23% 4% thrombolysis

*Comparison between our findings and those of Weaver et aL8 AMI = acute myccardial infarction.

ing interpretation by a computer algorithm, an electro- cardiographer or an emergency ward physician had shown that, like our MICU physicians outside hospital, the emergency ward physician and the computer had high specificity in excluding patients without deftite acute injury of AMT. The skilled electrocardiographer, although slightly more sensitive by using less stringent criteria, had an overall incidence of 5% false-positive di- agnoses.19

Cllnk4 N With an effective emergency medical system, most patients with hospital evidence of AM1 in a community are first seen outside the hospital by the physician of a MICU, and a large proportion of these patients are candidates for thrombolytic therapy. Our fmdings in Berlin are similar to those obtained in Gateborg, Sweden.2ol21 The emergency physician can select appropriate patients and initiate thrombolysis on the scene often within the first hour of symptom onset. However, less favorable results are recently reported from a study in which a paramedic-operated emergency medical system was used.22

Prehospital thrombolysis is not necessarily linked to a physician-attended MICU. Weaver et al* developed an algorithm that allows trained paramedics, under the direction of a hospital-based physician, to identify in the field patients eligible for thrombolytic therapy. The re cently reported experience of the Myocardial Infarction Triage and Intervention project is similar to our experi- ences in Berlin (Table III). However, the proportion of all patients in the community with hospital evidence of AM1 already identified in the field by paramedics is not reported.

The true benefit of earlier therapy will be estab lished only with randomized controlled trials of suffi- cient sample size. The European Myocardial Infarction Project, designed specifically to address this problem? and the ongoing Myocardial Infarction Triage and In- tervention Phase II trial may help to answer the ques- tion of whether instituting major programs for at-home thrombolysis is justified. However, because greatest benefit from thrombolysis is expected within the first 60 to 90 minutes from symptom onset,1*8-10 it seems rea- sonable to perform prehospital thrombolysis whenever proper logistic preconditions are given or can be institut-

ed easily, and provided a sufficient proportion of all pa- tients with AM1 in a community make use of the emer- gency medical system.

REFERENCES 1. Gruppo Italian0 Per Lo Studio Della Streptochinasi Nell’Infarto Miocardico (GISSI). Effectiveness of intravenous thromtolytic treatment in acute myocardial infarction. Lowet 1986;1:397-402. 2. ISIS-2 Collaborative Group. Randomized trial of intravenous stmptokinase, oral aspirin, both or neither among 17187 cases of suspected myocardiil infare tion: ISIS-2. Lancer 1988;2:349-360. 3. Wilcox RG, von der Lippe G, Olsson CG, Jensen G, Skene AM, Hampton JR. Effects of alteplase in acute myccardial infarction: 6-month results from the ASSET study. Lancer 1990;335:1175-1178. 4. Schr6der R. Importance of time window in thrombolytic treatment. In: Cham- berlain DA, Julii DG, Sleight P, eds. The Management of Acute Myocardial Ischaemia. London: Chapman and Hall Medical, 1990~69-75. 5. Castaigne AD, HervC C, Duval-Moulin AM, Gaillard M, Duboii-Ronde JL, Boesch C, Wolf M, Lellouche D, Jan F, Vemant P, Huguenard P. Prehqital use of APSAC: results of a placetintrolled study. Am J Ciwdiol 1989;64: 30A-33A. 6. E.M.I.P. Subcommittee. Potential time saving with prehospital intervention in acute myocardiil infarction. Eur Hearr J 1989;9:118-124. 7. Roth A, Barhash GJ, Hod H, Miller HI, Rath S, Mcdan M, Har Zahav Y, Keren G, Baasan S, Koplinsky E, L&ado S. Should thrombolytic therapy be administered in the mobile intensive care unit in patients with evolving myocardii infarction? A pilot study. J Am Coil Cardiol 1990,15:932-936. 8. Weaver WD, Eisenberg MS, Martin JS, Litwin PE, Shader SM. Ho MT, Kudenchuk P, Hallstrom AP, Cerequeira MD, Copass MK, Kennedy W, Cobb LA, Ritchie JL. Myocardial Infarction Triage and Intervention Project-Phase I: ptient characteristics and feasibility of prehospital initiation of thromholytic therapy. J Am Co11 Cardiol 1990;15:925-931. 9. Karen G, Weiss AT, Hasin Y, Appelbaum D, Welber S, Rozeman Y, Lotan C, Sapoznikow D, Luria MH, Gotsman MS. Prevention of myocardiil damage in acute myccardial ischemia by early treatment with intravenous streptokinase. N Engl J Med 1985;313:1384-1389. 10. Lmderer T, Arntz HA, Schr6der R. P&lb&he Thrombolyse bei akutem Myokardinfarkt. D~sch Med !+‘ochenschr 1991;116:1881-1887. 11. McNeiU AJ, Cu~ingham SR, Flannery DJ, Dalzell GWN, Wilson CM, Campbell NPS, Kban MM, Patterson GC, Webb SW, Adsey AAJ. A double blind placebo controlled study of early and late administration of recombiit tissue plasminogen activator in acute myocardial infarction. Er Heart J 1989; 61:316-321. 12. Doorey AJ, Michelson EL, Weber FJ, Dreiius LS. Tbromkolytic therapy of acute myocardiil infarction: Emerging challenge of hnplemmtation. J Am Call Cardiol 1987;10:1357-1360. 13. Braunwald E. optimizing thrombolytic therapy of acute myocardial infarc- tion. Circularion 1990;82:1510-1513. 14. Topol EJ, Bates ER, Walton JA Jr, Baumann G, Wolfe S, Maino J, Bayer L, German L, Kline EM, O’Neill WW, Pitt B. Community hospital administration of intravenous tissue plaaminogen activator in acute myocardiil infarction: im- proved timing, thromholytic efficacy and ventricular function. J Am ColI Gardiol 1987;10:1173-1177. 15. Grines CL, DeMaria AN. Optimal utilization of thrombolytic therapy for acute myocardiil infarction: concepts and controversies. J Am CON Cardiol 1990;16:223-231. 16. Yusuf S, Sleight P, Held P, McMahon S. Routine medical management of acute myocardial infarction. Circulation 1990;82(suppl 11):11-l 17-11-134. 17. Eisenberg MS, Ho MT, Shaeffer S, Litwin P, Larsen MP, Hallstrom AP,

Weaver DW. A community survey of the potential use of tbrombolytic agents for acute myccardii infarction. Ann Emerg Med 1989;18:838-841. 18. Karlson BW, Herlitz J, Wiiund 0, Richter A, Hjabnarson A. Early predic- tion of acute myocardial infarction from clinical history, examination and electr+ cardiogram in the emergency room. Am J Gudiol 1991;68:171-175. 19. Kudenchuk PJ, Ho MT, Weaver WD, Litwin PE, Martin JS, Eisenberg MS, Hallstrom AP, Cobb LA, Kennedy JW, MIT1 Project Investigators. Accuracy of computer-interpreted el&rocardio8raphy in selecting patients for thrombolytic therapy. J Am toll Gudiol 1991;17:1486-1491. 20. Herlitz J, Hjabnarson A, Holmherg S, Richterova A, Wennerblom B. Mor- tality and morbidity in suspected acute myocardial infarction in relation to ambu- lance transport. Eur Heart J 1987;8:503-509. 21. The Thrombolysis Early in Acute Heart Attack Trial Study Group. Very early thrombolytic therapy in suspected acute myocardiil infarction. Am J Car- diol 1990;65:401-407. 22. Gibler B, Kereiakea DJ. Dean EN, Martin L, Anderson L, Abbottsmith CW, Blanton J, Blanton D, Morris JA, Gibler CD, Erb RE, Teichman SL, and investigators of the Cincinnati Heart Project and the Nashville Prohospital TPA Trial. Prehospital diagnosis and treatment of acute myocardial infarction: a North-South perspective. Am Heart J l991;121:1-11.

420 THE AMERICAN JOURNAL OF CARDIOLOGY VOLUME 70 AUGUST 15. 1992