Helicopter transport of patients during acute myocardial infarction

Helicopter Transport of Patients During Acute Myocardial Infarction RAYE L. BELLINGER, MD, ROBERT M. CALIFF, MD, DANIEL 6. MARK, MD, MPH, RITA A. WEBER, RN, MS, PATRICIA COLLINS, RN, JANICE STONE, RN, HARRY R. PHILLIPS, Ill, MD, LAWRENCE GERMAN, MD, and RICHARD S. STACK, MD

Initial experience with a regional system of emergency helicopter transport of patients with acute myocardlal infarction (AMI) referred for emergent cardiac catheterization and percutaneous transiuminai coronary angioplasty (PTCA) is described. Two hundred fifty patients with AMI were transported from within a 150-mile radius to Duke University Medical Center over a 15month period. Ail patients were within 12 hours of onset of symptoms. Thrombolytic therapy was administered to 240 (96 % ) patients (72% before or in-flight). The tlme to administration of thromboiytic therapy ranged from 30 to 120 minutes (median 180), while the time to arrival in the interventional catheterization laboratory ranged from 105 to 815 minutes (median 300). The flight time was 12 to 77 minutes (median 31). Most patients had l- or 2-vessel coronary artery disease; the baseline ejection fraction ranged from 27 to 70 % (median 42). Transient hypotension was the most common complication both pre-flight and in-

flight. Third-degree atrioventricular block and nonsustained ventricular tachycardia were the next most common complications. Ventricular fibrillation or sustained ventricular tachycardia occurred before takeoff in 38 patients (15 % ). No patients had ventricular fibrillation, asystole or respiratory arrest during transport. Fluid boluses for hypotension were the most common intervention. Five patients required cardiopulmonary resuscitation in-flight; 3 before liftoff and 2 required a brief period of cardiopulmonary resuscitation during sustained ventricular tachycardia. Fourteen patients had pressor therapy, military antishock trousers or both to malntain adequate blood pressure. Neither cardioversion, defibrillation nor intubation were performed in-flight. Thus, inflight complications are infrequent and can be managed en route to an intervention center. The overall benefit of regional helicopter transportation relative to its cost has yet to be determined. (Am J Cardiol 1988;61:718-722)

From the Division of Cardiology, Department of Medicine, Duke University Medical Center, Durham, North Carolina. This work was supported by NRSA training grant 5T 32 HL07101-09 from the National Institutes of Health, Bethesda, research grants HS-04873 and HS-05635 from the National Center for Health Services Research, Rockville, research grant HL-17670 from the National Heart, Lung, and Blood Institute, Bethesda, training grant LM-07003 and grant LM-03373 from the National Library of Medicine, Bethesda, Maryland, and grants from the Andrew W. Mellon Foundation, New York, New York, and from Genentech, Inc., San Francisco, California. Manuscript received July 20, 1987; revised manuscript received November 30, 1987, and accepted December 4. Address for reprints: Robert M. Califf, MD, Division of Cardiology, Department of Medicine, P.O. Box 31123, Duke University Medical Center, Durham, NC 27710.

T

herapies designed to achieve early and sustained coronary reperfusion in patients with acute myocardial infarction (AMI) decrease in-hospital mortality1 and improve left ventricular function2y3 compared with standard therapy. Intravenous thrombolytic therapy alone has 2 major shortcomings. First, a significant number of patients fail to achieve reperfusion. Second, a significant atherosclerotic plaque often remains after successful thrombolytic therapy, increasing the risk of recurrent infarction4 and periinfarction ischemia.5 Percutaneous transluminal coronary angioplasty (PTCA) provides a reasonable adjunct to thrombolytic therapy because it often achieves reperfusion where thrombolysis fails6 and it increases the Iuminal diameter narrowed by the residual atherosclerotic plaquep7

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An interventional program including thrombolytic therapy, acute cardiac catheterization, PTCA and coronary artery bypass surgery is beyond the means of many hospitals. However, patients admitted to such institutions may benefit from a regional system that includes immediate thrombolysis followed by rapid transportation of patients with AMI to a nearby intervention center. While a helicopter is the most efficient means of transportation for distances up to 150 miles, concerns have arisen about the safety of such transportation for potentially unstable AMI patients. This study examines our initial experience with a regional system of helicopter transport of patients in the early stages of AMI with particular attention to the complications encountered.

Methods The Duke LifeFlight Helicopter Service began transporting critically ill patients in March 1985. Many patients were transported for interventional cardiac catheterization during AMI. Because of established referral patterns with community hospitals and the limited range of the helicopters used, most flights stayed within a 150-mile radius of our medical center. Patients were considered to have an AMI if they met the following criteria: (1) a compatible clinical history of chest pain or equivalent of <12 hours in duration; [2) at least 1 mm of ST elevation in at least 2 of 6 anterior leads (V, through Vs), 2 of 3 inferior leads (11,111, aVF] or both lateral leads (I, aVL]; (3) no resolution of ST elevation with 0.4 mg sublingual nitroglycerin in 3 consecutive doses. Once patients fulfilled the criteria for AMI, thrombolytic therapy was usually administered after intravenous premeditation with 50 mg diphenhydramine and 300 mg cimetidine. Patients who were at high risk of bleeding or had other known contraindications to thrombolytic therapy did not receive thrombolytic agents. Streptokinase was the predominant thrombolytic agent used; 1.5 million units of streptokinase mixed in 250 cc of 5% dextrose and water was infused intravenously over a 30- to 45-minute period. During the course of this study, recombinant tissue-type plasminogen activator was made available to patients with the entry requirements of the Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) trial. The study protocol and dosing regimen for the recombinant tissue-type plasminogen activator infusion have been described previously.8 Patients were designated as meeting the criteria for AM1 by their referring physicians. The referring physicians then notified either the Duke cardiologist oncall or the Duke LifeFlight medical control officer oncall to arrange transfer of the patient. A helicopter and flight crew consisting of an experienced pilot and 2 flight nurses with previous critical care experience were dispatched to the referring hospital. If the weather conditions were adverse (20% of flight requests), alternative transport by ambulance was arranged or the patient was not transferred. At the discretion of the referring physician and the Duke accepting physician,

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TABLE I

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719

Patient Data: Quartiles

Age W Time to thrombolytic therapy (min)’ Time to catheterization (min)+

25%

Median (50%)

75%

47 130

58 185

63 280

240

304

403

* Time from the onset of chest pain to the start of thrombolytic therapy. t Time from the onset of chest pain to the start of cardiac catheterization.

thrombolytic therapy was started either at the community hospital, during air transport or at Duke University Medical Center. Vasoactive, antiarrhythmic and other specialized therapy was initiated by the referring physician as needed. After acceptance of the patient, the flight crew radioed the patient’s status to the Duke medical control officer and, during the transport, notified the medical control officer of any changes in the patient’s status so that existing therapy could be modified or new therapy initiated. Changes in patient status and interventions were documented by the flight team. Upon arrival at Duke, all patients underwent diagnostic cardiac catheterization and, when clinically indicated, coronary angioplasty or coronary artery bypass grafting. Each patient’s flight record and in-patient chart were reviewed to ascertain complications and interventions during transport and throughout the hospitalization.

Results From March 1, 1985, through June 30, 1986, 1,597 critically ill patients were transported from community hospitals to Duke University Medical Center. Within the group transported for cardiac reasons [n = 896), 250 patients met the study criteria for AMI. Most patients (96%) were given thrombolytic therapy: intravenous streptokinase was administered to 77%; intravenous recombinant tissue plasminogen activator was administered to 19%; and 4% (lo/2501 of patients did not receive thrombolytic therapy because of contraindications Thrombolytic therapy was started at the referral hospital in 70% (168/240), in-flight in 5% (l2/ 240) and at Duke University Medical Center in 25% (60/240) of patients. Tables I and II summarize the clinical and transport-related variables. Thrombolytic therapy was started early in most patients (median of 3 hours from symptom onset) and cardiac catheterization was performed within 2 hours of thrombolytic therapy treatment in most patients, All patients underwent emergency coronary arteriography and ventriculography upon arrival at Duke. Only 3 (l%] patients were found to have insignificant coronary artery disease (i.e., 150% diameter stenosis in all major coronary vessels). One hundred and seven (43%) patients had l-vessel coronary artery disease, 93

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Data: Quartiles Median

(50%)

25% Distance by air (miles)’ Time from call to arrival (min)+ Time in air (min)+ Estimated ground distance (miles)

75%

40

61

98

95

136

172

21

31

50

57

81

109

* Distance by air from Duke Hospital to community hospitals. + Time from a call received by the LifeFlight dispatcher until the patient arrived at Duke Hospital. + Time required to transport patient from community hospital to Duke University Medical Center by air.

TABLE Ill Complications During Helicopter with Acute Myocardial Infarction Pre-Flight (n) Sinus bradycardia (HR <40 beats/min) Atrial fibrillation/flutter Ventricular fibrillation Ventricular tachycardia sustained Ventricular tachycardia nonsustained Asystole Third-degree AV block Second-degree AV block type I Second-degree AV block type II Transient hypotension” Sustained hypotension+ Respiratory arrest

Transport

of Patients

In-Flight (n)

Total (n)

10

4

14

3 19 19

3 0 3

6 19 22

6

7

13

1 19 2 3 30 20 9

0 a

1 27 2 3

0 0 21 4 0

51 24 9

* Defined as a systolic blood pressure of <90 mm Hg for I hour. AV = atrioventricular; HR = heart rate.

(37%) had Z-vessel disease and 48 [19%) had &vessel disease. The baseline ejection fraction was 42%. Five percent of patients had coexistent left main disease. One hundred and eighty-eight (75%) patients underwent PTCA during their admission; 176 (94%) were performed emergently (i.e., at the time of the cardiac catheterization]. Persistent reperfusion (i.e., sustained angiographic perfusion of the infarct-related artery) was obtained in 94% of the patients who underwent emergent coronary angioplasty. Forty-five (18%) patients underwent coronary artery bypass grafting during admission for either severe 3-vessel disease, coexistent left main disease or failed reperfusion by PTCA. Seventeen (7%) patients were reperfused with thrombolytic therapy alone and, because of no significant residual coronary stenosis in the infarct-related artery after thrombolysis, did not undergo either coronary angioplasty or coronary artery bypass grafting.

Table III summarizes the pre-flight and in-flight complications encountered during the transport of patients with AMI. Transient hypotension (systolic blood pressure of <90 mm Hg for
Discussion The most important finding of our study is the relatively small number of complications encountered by our patients while they were being transported from

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their community hospitals. The low complication rate is especially remarkable in view of the large number of complications they experienced before transfer. Patients who suffered complications before transport may, in fact, have benefitted more from helicopter transfer than other patients because of the greater risk that a long ground trip to a tertiary center poses to an unstable patient. The rarity of both ventricular tachycardia and fibrillation during flight may, have resulted from the frequent use of antidysrhythmic prophylaxis before takeoff. Nonsustained ventricular tachycardia was treated with a bolus infusion of either lidocaine or procainamide; patients who did not respond were given bretylium. All 3 patients developing sustained ventricular tachycardia in-flight spontaneously converted to sinus rhythm prior to direct current countershock. Two of the 3 patients received brief cardiopulmonary resuscitation by 1 crewmember while the other crewmember was preparing to administer a direct current countershock. All 3 patients had received lidocaine therapy before liftoff. Patients who developed severe bradyarrhythmias (severe sinus bradycardia or high grade second- or third-degree atrioventricular block) were first treated with atropine. If a transcutaneous external pacemaker was available, the patient was paced externally as needed; in the absence of an external pacemaker, or if the patient did not respond to atropine, isoproterenol was infused. None of the 3 patients developing atria1 fibrillation or flutter required therapy during transport. The helicopter transport system used in this study has certain advantages over conventional ambulance transport. The care given in the helicopter by 2 highlytrained critical care nurses in constant radio communication with a physician at the tertiary center is likely to be more effective than care rendered in an ambulance. Even when a physician accompanies a patient during ground transport, the environment lacks the physical stability possible within a helicopter, which allows for careful monitoring and control of blood pressure, cardiac rhythm and therapeutic infusions. When specific interventions, such as volume, antidysrhythmic and inotropic infusions are required, the medical flight team can maintain precise control with physician guidance by radio communication. While the total amount of time from referral to arrival at the tertiary center may not be less with helicopter transport, the amount of time the patient spends travelling between hospitals is markedly diminished. The patient remains under the careful management of the referring physician until the arrival of the helicopter, minimizing the time in a less controlled environment. This aspect of helicopter transport also preserves local emergency medical transport resources, making it unnecessary for a physician or nurse from the community hospital to accompany the patient to the tertiary hospital, as is frequently the case with ambulance transport. The loss of medical personnel and equipment, especially in smaller communities, im-

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TABLE IV Interventions During Helicopter with Acute Myocardial Infarction Pre-Flight (n) 34 24 12 29 0 3 15 13 3 196 6 7 30 6 0

CPR Cardioversion/defibrillation lntubation Fluid bolus MAST External pacer Transvenous pacer Atropine lsoproterenol Lidocaine Procainamide Bretylium Dopamine Dobutamine Levophed CPR = cardiopulmonary

resuscitation;

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Transport of Patients

In-Flight tn)

Total m)

5 0 0 24 7 3 0 7 2 10 0 2 5 0 2

39 24 12 53 7 6 15 20 5 206 6 9 35 6 2

MAST = military antishock trousers.

pairs the ability of the local medical services to respond to other emergencies. Helicopter transport with constant radio communication also makes it possible for the tertiary center to prepare for the patient being transported, based on information passed between helicopter and hospital about the status of the patient. Many of the potential advantages of this system pertain more to the personnel and equipment for communication than to the specific mode of transport. A similar system could be developed for specialized ambulance and fixed-wing transport. Aircraft safety is an important and controversial issue, which has major ramifications for the transport of critically ill patients. From 1980 to 1986, there have been 66 aeromedical helicopter crashes; 21 people have died and 16 have been injured. At present, there are approximately 171 aeromedical helicopter services operating throughout the U.S. For 1986, the accident rate for medidal helicopters was 17.7/1OO,OOO patient transports9 Documented causes of these crashes include catastrophic mechanical failures and pilot error during operation in marginal weather conditions. Recently, the American Society of Hospital-Based Air Medical Services has published guidelines concerning pilot and crew standards, aircraft operating and equipment and maintenance standards in order to improve safety during aeromedical transports.lO Details of our safety standards have been published elsewhere.ll Intravenous thrombolytic therapy is the most common technique used in clinical practice today for rapid reperfusion of infarct-related vessels. It is especially suited to community hospitals, which may not have the resources to support a full-time interventional cardiac catheterization facility capable of acute coronary angioplasty and emergency coronary bypass surgery. Intravenous thrombolytic therapy has a reperfusion rate of 30 to 70% in well-controlled trials. For the 30 to 70% of patients who do not respond to thrombolytic therapy in a community hospital without interventional facili-

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ties, transportation of the patient to a specialized interventional center will improve the chances of infarctvessel patency.

References 1. Gruppo It&no Per Lo Studio Della Streptochinasi Nell’Infarto Miocardice (GISSI). Effectiveness of intravenous thrombolytic treatment in acute myocardial infarction. Loncet 1986:1:397-401. 2. The I.S.A.M. Study Group. A prospective trial of intravenous streptokinase in acute myocordjal infarction [I.S.A.M.). N Engl J Med 1985;313:1384-1389. 3. Mathey DG, Sheehan FH, Schof& J, Dodge HT. Time from onset of symptoms to thromboIytiC therapy: a major determinant of myocardial salvage in patients with acute transmural infarction. TACC 1985;6:518-525. 4. The TIMI Study Group. The thrbmbolysis in myocardiol infarction [TIMI) trial. N Engl / Med 1985;312:932-936, 5. O’Neill W, Timmis G. Bourdillon P, Lai P, Ganghadarhan V, Walton 1, Ramos R, Laufer N, Gordon S, Schork MA, Pitt B. A prospective randomized clinical trial of introcoronary streptokinose versa.3 coronary angioplasty ther-

apy of acute myocordial infarction. N Engl J Med 1986;314:812-828.

6. FungAY, Lai P, Top01EJ, Bates ER, Bourdillon PDV, Walton JA, Mancini J, Kryski T, Pitt B, O’Neill WW. Value of percutaneous transfuminal coronary angioplasty after unsuccessful intravenous streptokinase therapy in acute myocardial infarction. Am J Cardiol 198(X58:686-691. 7. Gold Hi(, Cowley MJ, Palacios IF, Vetrovec GW, Akins CW, Block PC, Leinbach RC. Combined introcoronary streptokinase and coronary angioplosty during acute myocardiol infarction. Am r Cardiol 1984;53:122C-125C. 8. Topd EJ, Califf RM, George BS, Kereiakes DJ, Abbottsmith CW, Candela RJ, Lee KL. Pitt B, Stack RS, O’Neill WW and the Thrombolysis and Angioplasty in Myocardial Infarction (TAMI) Study Group. A multicenter, randomized trial of intravenous recombinant tissue plasminogen activator and emergency coronary angioplasty in acute myocardial infarction. N Engl r Med 1987;317:581-588. 9. Collett HM. Aeromedical accident trends. Hospital Aviation. February, 1987. 10. American Society of Hospital-based Air Medical Services (ASHBEAMS). Guidelines for operation of aeromedical helicopters, March 1986. 11. Califf RM, Bellinger RL. A regionalized approach to acute coronary intervention. In: Top01EJ, ed. Acute Coronary Intervention. New York: Alan Ft. Lisa 1987:231-253.