The Incidence of Pacemaker Dysfunction During Helicopter Air Medical Transport ROBERT E. FROMM, JR, MD,**t DIANE HOPKINS TAYLOR,* LAURA CRONIN,* WILLIAM 6. G. McCALLUM, MD,**? ROBERT L. LEVINE, Mb*,+
A number of recent publications have raised concern regarding in-flight pacemaker dysfunction during air medical transport. Unfortunately the clinical importance of this problem is unknown. The authors’ purpose was to examine the incidence of pacemaker use and malfunction during helicopter air medical transpott, using an incidence (cohort) study of an air medical service of a tertiary-care teaching hospital. During the study period, April 1, 1987 through December 31, 1991 2,388 patients were air-transported. Cardiac patients constituted 72% of the total population. Pacemakers were used in 44 patfents, temporary transvenous pacemakers in 35, permanent transvenous in five, and transcutaneous pacers in four patients. No rate-responsive pacemakers were transported. No episodes of pacemaker malfunction were observed (95% confidence Interval 0 to .002 for the population as a whole). The authors conclude that pacemaker dysfunction during air medical transport is a very rare occurrence, in parl due to the infrequent transport of patients requiring these devices. (Am J Emerg Mad lgg2;10:333-335. Copyright 0 1992 by W.8. Saunders Company)
The number of patients transported by air medical helicopters is increasing annually.’ Air medically transported patients are exposed to additional physical factors manifest in the aviation environment. In addition to affecting the patient and flight personnel, these factors may effect medical equipment.* Cardiovascular illness represents a substantial proportion of the transported population. The potential for in-flight pacemaker malfunction in these patients has been the subject of a number of recent publications.3T4 The patient dependent on a pacemaker for cardiac performance could be devastated by an in-flight malfunction when limited remedial capabilities are present. Unfortunately, the incidence of pacemaker use and malfunction during air medical evacuation is unknown and therefore the clinical importance of this problem unclear. It was the purpose of this study to examine the incidence of pacemaker use and malfunction during air medical evacuation performed by a cardiology-based air medical progr*. From ‘the Department of Emergency Services, The Methodist Hospital, Houston, TX; and the tDepartment of Medicine, Baylor College of Medicine, Houston, TX. Manuscript received October 31,199l; revision accepted February 6, 1992. Presented in part at the Annual Scientific Session, The Association of Air Medical Services, Tampa, FL, October, 1991. Address reprint requests to Dr Fromm, MS 8101 The Methodist Hospital, Houston, TX 77030. Key Words: Helicopter transport, pacemaker. Copyright 0 1992 by W.B. Saunders Company 07356757/92/l 004-0014$5.00/0
METHODS Aeromedical Services of the Methodist Hospital (Houston, TX) is a cardiovascular-based transport service using a Sikorsky S-76A helicopter to provide critical care transport services within a 200-mile radius of the Texas Medical Center in Houston. All patients transported by Aeromedical Services from April 1, 1987, through December 31, 1991, were eligible for the study. Demographic data, interventions, and complications were entered into the computerized database of all transported patients established by the Sakowitz Computer Laboratory of Baylor College of Medicine (Houston, TX). All patients receiving cardiac pacemaker therapy were identified and classified as receiving temporary transvenous pacing, permanent transvenous pacing, permanent epicardial pacing, or transcutaneous pacing. Patients prophylactically connected to transcutaneous pacing devices, but not paced, were not included. Pacemaker malfunction was defined as failure to capture, failure to sense, or the requirement to change pre-takeoff pacemaker settings while in flight. Statistical
Analysis
Record identification and cross tabulation were performed using the Analysis Programs for Attribute System Databases. Descriptive statistics are presented as mean -C standard deviation unless otherwise noted. The 95% confidence intervals were estimated using the normal approximation methods as reviewed by Berry.’ RESULTS During the study period 2,388 patients were transported. Of these, 1,715 patients (72%) were classified as “cardiac patients” at the time of transport. Of the transported population, 67.9% were male with a mean age of 56.6 ? 15.0 years, and 32.1% were female with a mean age of 60.9 + 16.8 years (P < .OOl). Pacemakers were used by 44 patients during transport. Temporary transvenous pacemakers were used by 35 patients, permanent transvenous pacemakers by five patients, and transcutaneous pacers were used by four patients. All pacemakers were operated in the ventricular pacedventricular inhibited mode. Underlying diagnoses at the time of transport included: 20 (45%) acute myocardial infarction (45%), six unstable angina (140/o), six status postresuscitation from sudden death, (14%), three ventricular tachycardia (7%), three syncope (7%), and six other (14%). Males num-
333
334
AMERICAN
JOURNAL
OF EMERGENCY
bered 27 of the pacemaker patients (61%), and 17 were female (39%). Pacemaker patients tolerated transport well with no inflight deaths. No incidents of pacemaker malfunction occurred during flight, yielding a 95% confidence interval of pacemaker malfunction for the transported population as a whole of 0 to 402, and 0 to .07 for transported patients using pacemakers. Hospital mortality for the pacemaker patients was 25% (11 deaths) none of which were attributed to pacemaker dysfunction. DISCUSSION Air medical transport exposes patients and medical equipment to additional forces, or forces of increased magnitude from those experienced by nontransported patients. Unfortunately, the effect of the aviation environment on medical equipment has not been fully determined. The recent publication of two case reports detailing in-flight dysfunction of cardiac pacemakers raises concerns about the prevalence of this problem. This study from a cardiovascular-based transport program demonstrated no incidence of pacemaker dysfunction during the transport of 2,388 consecutive patients, with an upper limit of the 95% confidence interval for the proportion of patients experiencing in-flight pacemaker dysfunction of .002. This observation suggests that it is unlikely for a busy air medical transport service to observe even a single incident of pacemaker malfunction. Part of the explanation for this low probability of in-flight pacemaker malfunction is the relatively infrequent occurrence of transport of patients requiring pacemaker therapy. This is true for our program despite its cardiovascular orientation. Cardiac pacemakers are complicated devices which can malfunction on the basis of a number of physical factors present during air transport. Mitchell et al6 demonstrated interference with pacemaker function from exposure to the main beam of pulsed and continuous aviation radar units at distances of up to 1 mile or greater during in vitro tests. Responses ranged from asystole (five consecutively missed beats) to no apparent effect. Effects varied by pacemaker model, individual pacemaker unit, and the characteristics of the radar source, including distance from the antenna. Furman et al’ examined the response of 10 different pacemakers to the in vitro application of low frequency voltages to the pacemakers leads. They also examined other electromagnetic field sources including: the spark of an automobile coil, subthreshold of perception AC currents applied to the patient’s extremities, and three different electric shaver units. They demonstrated a variety of responses including the in-
TABLE 1. North American Pacemaker Code
Society
of Pacing
Characteristic 0 A V D
= = = =
none atrium ventricle dual (A + V)
0 A V D
= = = =
none atrium ventricle dual (A + V)
W Volume
10, Number
4 W July 1992
duction of asystole. Responses varied for different pacemaker models and also varied for different pacing modes. As pacing technology has advanced, new modes of operation have been introduced. A nomenclature for simply communicating the operating characteristic of cardiac pacemakers, the North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group Generic Pacemaker Code, describes pacing mode by a five-position code as noted in Table 1. A 1987 modification to the code introduced the use of the “R” designation in position IV to indicate “rate adaptive pacemakers.“’ These devices have been developed to allow physiologic increases in cardiac rate in response to exercise and other stresses. Rate-adaptive pacemakers sense one of a number of indicators of metabolic demand (ie, Q-T interval, respiratory rate, minute ventilation, venous oxygen saturation, venous temperature) and accelerate their pacing rate as appropriate. One indicator of metabolic demand, body movement or vibration, is used by the most common rate adaptive pacemaker in use today, the Activitrax (Medtronics, Inc, Minneapolis, MN).9 Environmental vibrations from several forms of transport including aircraft have been known for a number of years to induce increases in this pacemaker’s rate, as can direct pressure on the generator case.“.” One of the recently reported pacemaker “dysfunctions” during air medical transport was essentially the normal response of the pacemaker unit to sensed vibration.’ No patients in our study population received rate-adaptive pacing. If acceleration of pacemaker rate to programmed levels by sensed vibration is a criterion for pacemaker dysfunction, then increased use of vibrationsensing pacemakers in the future may result in more episodes of in-flight pacemaker dysfunction than suggested by our study. Clearly it is important for air medical transport services to ascertain the pacemaker type and mode of operation prior to patient transport. Options to prevent vibrationinduced acceleration include reprogramming the device to a non rate-adaptive mode or placing a magnet over the device to place the pacemaker into a fixed rate mode. Transcutaneous pacing technology actually preceded cardiac pacing by endocardial electrodes.‘2 but patient discomfort limited its widespread continued use after introduction of transvenous devices. Improvements in the technology of transcutaneous pacingI has led to its resurgence, and it has penetrated the transport arena substantially in the past decade. The ease of application of this devices makes it ideal for prehospital operations. As noted above, we experienced no episodes of dysfunction of transcutaneous pacing devices and, equally important, observed no dysfunction of commu-
and Electrophysiology/British
II Chamber(s) Sensed
I Chamber(s) Paced
Position
MEDICINE
Pacing
Ill Response to Sensing 0 = none I = inhibited T = triggered D = dual
and Electrophysiology
Group
IV Rate Modulation, Programability 0 S M C R
= = = = =
None simple programmable multiprogramable communicating rate modulation
Generic
Cardiac
V Antitachycardia Functions 0 P S D
= = = =
None antitachycardis shock dual (P + S)
pacing
FROMM ET AL n PACEMAKER DYSFUNCTION
nication or navigation instruments associated with the use of this pacing technology. Complications of transcutaneous pacing are not infrequent despite technical advances and include discomfort in conscious patients and failure to capture the myocardium.‘4 CONCLUSION In-flight cardiac pacemaker dysfunction is a very rare event during air medical transport. Rate-adaptive pacemakers using vibration sensing can be expected to accelerate their rate during air medical transport, and increased use of these devices in the future may increase the proportion of air medical transports with pacemaker dysfunction if this nonphysiologic rate acceleration is deemed dysfunctional. Air medical transport programs should ascertain the type of pacemaker and mode of operation of all transported patients receiving this therapy. REFERENCES 1. Collett HM: Annual transport statistics. J Air Med Transport 1991;10(3):11 2. Fromm RE, Duvall JO. Medical aspects of flight for civilian aeromedical transport. Problems in Critical Care 1990;4(4):495507 3. French RS, Tillman JG: Pacemaker function during helicopter transport. Ann Emerg Med 1989;18:305-307 4. Sumachai A, Sternbach G, Eliastam M, et al: Pacing hazards in helicopter air medical transport. Am J Emerg Med 1988; 6:236-240
335
5. Berry CC: A tutorial on confidence intervals for proportions in diagnostic radiology. AJR 1989;154:477-480 6. Mitchell JC, Hurt WD, Walters WH, et al: Empirical studies of cardiac pacemaker interference. Aerospace Med 1974;45(2): 189-195 7. Furman S, Parker B, Krauthamer M, et al: The influence of electromagnetic environment on the performance of artificial cardiac pacemakers. Ann Thorac Surg 1968;6:90-95 8. Bernstein AD, Camm AJ, Fletcher RD, et al: The NASPU BPEG Generic Pacemaker Code for antibradyarrhythmia and adaptive-rate pacing and antitachyarrhythmia devices. PACE 1987;10:794-799 9. Lau C, Camm A: Rate-responsive pacing: Technical and clinical aspects. In El-Sherif N, Samet P (eds): Cardiac Pacing and Electrophysiology. Philadelphia, PA, Saunders, 1991, pp 524-544 10. Stangl K, Wirtzfeld A, Heinze H, et al: Activitrax pacemaker: Physiologic rate response with a nonphysiologic sensor? In Sartini M, Pistolese M, Alliegro A (eds): Proceedings of the International Symposium on Progress in Clinical Pacing. Rome, Italy, Centro Editoriale Publicitario Italiano, 1986, pp 124132 11. Toff WD, Leeks C, Joy M, et al: The effect of aircraft vibration on the function of an activity-sensing pacemaker. Br Heart J 1987;57:573-574 12. 2011PM: Resuscitation of the heart in ventricular standstill by external electric stimulation. N Engl J Med 1952;247:788-771 13. 2011RH, 2011PM, Belgard AH: External noninvasive electric stimulation of the heart. Crit Care Med 1981;9:393-394 14. 2011PM, Zoll RH, Falk RH, et al: External noninvasive temporary cardiac pacing: Clinical trials. Circulation 1985;71:937944
A number of recent publications have raised concern regarding in-flight pacemaker dysfunction during air medical transport. Unfortunately the clinical importance of this problem is unknown. The authors’ purpose was to examine the incidence of pacemaker use and malfunction during helicopter air medical transpott, using an incidence (cohort) study of an air medical service of a tertiary-care teaching hospital. During the study period, April 1, 1987 through December 31, 1991 2,388 patients were air-transported. Cardiac patients constituted 72% of the total population. Pacemakers were used in 44 patfents, temporary transvenous pacemakers in 35, permanent transvenous in five, and transcutaneous pacers in four patients. No rate-responsive pacemakers were transported. No episodes of pacemaker malfunction were observed (95% confidence Interval 0 to .002 for the population as a whole). The authors conclude that pacemaker dysfunction during air medical transport is a very rare occurrence, in parl due to the infrequent transport of patients requiring these devices. (Am J Emerg Mad lgg2;10:333-335. Copyright 0 1992 by W.8. Saunders Company)
The number of patients transported by air medical helicopters is increasing annually.’ Air medically transported patients are exposed to additional physical factors manifest in the aviation environment. In addition to affecting the patient and flight personnel, these factors may effect medical equipment.* Cardiovascular illness represents a substantial proportion of the transported population. The potential for in-flight pacemaker malfunction in these patients has been the subject of a number of recent publications.3T4 The patient dependent on a pacemaker for cardiac performance could be devastated by an in-flight malfunction when limited remedial capabilities are present. Unfortunately, the incidence of pacemaker use and malfunction during air medical evacuation is unknown and therefore the clinical importance of this problem unclear. It was the purpose of this study to examine the incidence of pacemaker use and malfunction during air medical evacuation performed by a cardiology-based air medical progr*. From ‘the Department of Emergency Services, The Methodist Hospital, Houston, TX; and the tDepartment of Medicine, Baylor College of Medicine, Houston, TX. Manuscript received October 31,199l; revision accepted February 6, 1992. Presented in part at the Annual Scientific Session, The Association of Air Medical Services, Tampa, FL, October, 1991. Address reprint requests to Dr Fromm, MS 8101 The Methodist Hospital, Houston, TX 77030. Key Words: Helicopter transport, pacemaker. Copyright 0 1992 by W.B. Saunders Company 07356757/92/l 004-0014$5.00/0
METHODS Aeromedical Services of the Methodist Hospital (Houston, TX) is a cardiovascular-based transport service using a Sikorsky S-76A helicopter to provide critical care transport services within a 200-mile radius of the Texas Medical Center in Houston. All patients transported by Aeromedical Services from April 1, 1987, through December 31, 1991, were eligible for the study. Demographic data, interventions, and complications were entered into the computerized database of all transported patients established by the Sakowitz Computer Laboratory of Baylor College of Medicine (Houston, TX). All patients receiving cardiac pacemaker therapy were identified and classified as receiving temporary transvenous pacing, permanent transvenous pacing, permanent epicardial pacing, or transcutaneous pacing. Patients prophylactically connected to transcutaneous pacing devices, but not paced, were not included. Pacemaker malfunction was defined as failure to capture, failure to sense, or the requirement to change pre-takeoff pacemaker settings while in flight. Statistical
Analysis
Record identification and cross tabulation were performed using the Analysis Programs for Attribute System Databases. Descriptive statistics are presented as mean -C standard deviation unless otherwise noted. The 95% confidence intervals were estimated using the normal approximation methods as reviewed by Berry.’ RESULTS During the study period 2,388 patients were transported. Of these, 1,715 patients (72%) were classified as “cardiac patients” at the time of transport. Of the transported population, 67.9% were male with a mean age of 56.6 ? 15.0 years, and 32.1% were female with a mean age of 60.9 + 16.8 years (P < .OOl). Pacemakers were used by 44 patients during transport. Temporary transvenous pacemakers were used by 35 patients, permanent transvenous pacemakers by five patients, and transcutaneous pacers were used by four patients. All pacemakers were operated in the ventricular pacedventricular inhibited mode. Underlying diagnoses at the time of transport included: 20 (45%) acute myocardial infarction (45%), six unstable angina (140/o), six status postresuscitation from sudden death, (14%), three ventricular tachycardia (7%), three syncope (7%), and six other (14%). Males num-
333
334
AMERICAN
JOURNAL
OF EMERGENCY
bered 27 of the pacemaker patients (61%), and 17 were female (39%). Pacemaker patients tolerated transport well with no inflight deaths. No incidents of pacemaker malfunction occurred during flight, yielding a 95% confidence interval of pacemaker malfunction for the transported population as a whole of 0 to 402, and 0 to .07 for transported patients using pacemakers. Hospital mortality for the pacemaker patients was 25% (11 deaths) none of which were attributed to pacemaker dysfunction. DISCUSSION Air medical transport exposes patients and medical equipment to additional forces, or forces of increased magnitude from those experienced by nontransported patients. Unfortunately, the effect of the aviation environment on medical equipment has not been fully determined. The recent publication of two case reports detailing in-flight dysfunction of cardiac pacemakers raises concerns about the prevalence of this problem. This study from a cardiovascular-based transport program demonstrated no incidence of pacemaker dysfunction during the transport of 2,388 consecutive patients, with an upper limit of the 95% confidence interval for the proportion of patients experiencing in-flight pacemaker dysfunction of .002. This observation suggests that it is unlikely for a busy air medical transport service to observe even a single incident of pacemaker malfunction. Part of the explanation for this low probability of in-flight pacemaker malfunction is the relatively infrequent occurrence of transport of patients requiring pacemaker therapy. This is true for our program despite its cardiovascular orientation. Cardiac pacemakers are complicated devices which can malfunction on the basis of a number of physical factors present during air transport. Mitchell et al6 demonstrated interference with pacemaker function from exposure to the main beam of pulsed and continuous aviation radar units at distances of up to 1 mile or greater during in vitro tests. Responses ranged from asystole (five consecutively missed beats) to no apparent effect. Effects varied by pacemaker model, individual pacemaker unit, and the characteristics of the radar source, including distance from the antenna. Furman et al’ examined the response of 10 different pacemakers to the in vitro application of low frequency voltages to the pacemakers leads. They also examined other electromagnetic field sources including: the spark of an automobile coil, subthreshold of perception AC currents applied to the patient’s extremities, and three different electric shaver units. They demonstrated a variety of responses including the in-
TABLE 1. North American Pacemaker Code
Society
of Pacing
Characteristic 0 A V D
= = = =
none atrium ventricle dual (A + V)
0 A V D
= = = =
none atrium ventricle dual (A + V)
W Volume
10, Number
4 W July 1992
duction of asystole. Responses varied for different pacemaker models and also varied for different pacing modes. As pacing technology has advanced, new modes of operation have been introduced. A nomenclature for simply communicating the operating characteristic of cardiac pacemakers, the North American Society of Pacing and Electrophysiology/British Pacing and Electrophysiology Group Generic Pacemaker Code, describes pacing mode by a five-position code as noted in Table 1. A 1987 modification to the code introduced the use of the “R” designation in position IV to indicate “rate adaptive pacemakers.“’ These devices have been developed to allow physiologic increases in cardiac rate in response to exercise and other stresses. Rate-adaptive pacemakers sense one of a number of indicators of metabolic demand (ie, Q-T interval, respiratory rate, minute ventilation, venous oxygen saturation, venous temperature) and accelerate their pacing rate as appropriate. One indicator of metabolic demand, body movement or vibration, is used by the most common rate adaptive pacemaker in use today, the Activitrax (Medtronics, Inc, Minneapolis, MN).9 Environmental vibrations from several forms of transport including aircraft have been known for a number of years to induce increases in this pacemaker’s rate, as can direct pressure on the generator case.“.” One of the recently reported pacemaker “dysfunctions” during air medical transport was essentially the normal response of the pacemaker unit to sensed vibration.’ No patients in our study population received rate-adaptive pacing. If acceleration of pacemaker rate to programmed levels by sensed vibration is a criterion for pacemaker dysfunction, then increased use of vibrationsensing pacemakers in the future may result in more episodes of in-flight pacemaker dysfunction than suggested by our study. Clearly it is important for air medical transport services to ascertain the pacemaker type and mode of operation prior to patient transport. Options to prevent vibrationinduced acceleration include reprogramming the device to a non rate-adaptive mode or placing a magnet over the device to place the pacemaker into a fixed rate mode. Transcutaneous pacing technology actually preceded cardiac pacing by endocardial electrodes.‘2 but patient discomfort limited its widespread continued use after introduction of transvenous devices. Improvements in the technology of transcutaneous pacingI has led to its resurgence, and it has penetrated the transport arena substantially in the past decade. The ease of application of this devices makes it ideal for prehospital operations. As noted above, we experienced no episodes of dysfunction of transcutaneous pacing devices and, equally important, observed no dysfunction of commu-
and Electrophysiology/British
II Chamber(s) Sensed
I Chamber(s) Paced
Position
MEDICINE
Pacing
Ill Response to Sensing 0 = none I = inhibited T = triggered D = dual
and Electrophysiology
Group
IV Rate Modulation, Programability 0 S M C R
= = = = =
None simple programmable multiprogramable communicating rate modulation
Generic
Cardiac
V Antitachycardia Functions 0 P S D
= = = =
None antitachycardis shock dual (P + S)
pacing
FROMM ET AL n PACEMAKER DYSFUNCTION
nication or navigation instruments associated with the use of this pacing technology. Complications of transcutaneous pacing are not infrequent despite technical advances and include discomfort in conscious patients and failure to capture the myocardium.‘4 CONCLUSION In-flight cardiac pacemaker dysfunction is a very rare event during air medical transport. Rate-adaptive pacemakers using vibration sensing can be expected to accelerate their rate during air medical transport, and increased use of these devices in the future may increase the proportion of air medical transports with pacemaker dysfunction if this nonphysiologic rate acceleration is deemed dysfunctional. Air medical transport programs should ascertain the type of pacemaker and mode of operation of all transported patients receiving this therapy. REFERENCES 1. Collett HM: Annual transport statistics. J Air Med Transport 1991;10(3):11 2. Fromm RE, Duvall JO. Medical aspects of flight for civilian aeromedical transport. Problems in Critical Care 1990;4(4):495507 3. French RS, Tillman JG: Pacemaker function during helicopter transport. Ann Emerg Med 1989;18:305-307 4. Sumachai A, Sternbach G, Eliastam M, et al: Pacing hazards in helicopter air medical transport. Am J Emerg Med 1988; 6:236-240
335
5. Berry CC: A tutorial on confidence intervals for proportions in diagnostic radiology. AJR 1989;154:477-480 6. Mitchell JC, Hurt WD, Walters WH, et al: Empirical studies of cardiac pacemaker interference. Aerospace Med 1974;45(2): 189-195 7. Furman S, Parker B, Krauthamer M, et al: The influence of electromagnetic environment on the performance of artificial cardiac pacemakers. Ann Thorac Surg 1968;6:90-95 8. Bernstein AD, Camm AJ, Fletcher RD, et al: The NASPU BPEG Generic Pacemaker Code for antibradyarrhythmia and adaptive-rate pacing and antitachyarrhythmia devices. PACE 1987;10:794-799 9. Lau C, Camm A: Rate-responsive pacing: Technical and clinical aspects. In El-Sherif N, Samet P (eds): Cardiac Pacing and Electrophysiology. Philadelphia, PA, Saunders, 1991, pp 524-544 10. Stangl K, Wirtzfeld A, Heinze H, et al: Activitrax pacemaker: Physiologic rate response with a nonphysiologic sensor? In Sartini M, Pistolese M, Alliegro A (eds): Proceedings of the International Symposium on Progress in Clinical Pacing. Rome, Italy, Centro Editoriale Publicitario Italiano, 1986, pp 124132 11. Toff WD, Leeks C, Joy M, et al: The effect of aircraft vibration on the function of an activity-sensing pacemaker. Br Heart J 1987;57:573-574 12. 2011PM: Resuscitation of the heart in ventricular standstill by external electric stimulation. N Engl J Med 1952;247:788-771 13. 2011RH, 2011PM, Belgard AH: External noninvasive electric stimulation of the heart. Crit Care Med 1981;9:393-394 14. 2011PM, Zoll RH, Falk RH, et al: External noninvasive temporary cardiac pacing: Clinical trials. Circulation 1985;71:937944
