The Journal of Emergency Medicine, Vol. 24, No. 2, pp. 131–139, 2003 Copyright © 2003 Elsevier Science Inc. Printed in the USA. All rights reserved 0736-4679/03 $–see front matter
ACCURACY OF THE PRECORDIAL V-QUICK姞 PATCH IN PERSONS WITH CARDIAC OR PULMONARY DISEASE Linda S. Baas,
RN, PhD, ACNP,*
Theresa A. Beery, RN, PhD,* Gordon A. Allen, PhD,† Susan Ware, Sumant Lamba, MD, FACC,§ and William T. Abraham, MD, FACC§
*University of Cincinnati College of Nursing, Cincinnati, Ohio, †Miami University, Oxford, Ohio, ‡Department of Neurology, Cincinnati VA Medical Center, Cincinnati, Ohio, and §Division of Cardiology, Ohio State University Medical Center, Columbus, Ohio Reprint Address: Linda S. Baas, PhD, RN, University of Cincinnati College of Nursing, PO Box 210038, 3110 Vine Street, Cincinnati, OH 45221-0038
e Abstract—The aim of this study was to demonstrate the equivalence of 12-Lead Electrocardiograms (EKG) obtained with the new V-Quick威 patch and traditional tabstyle electrodes. Using a within-subject design, a convenience sample of 100 subjects with either cardiac or pulmonary disease underwent two 12-lead EKGs, one with the traditional tab-style electrodes and one with the precordial patch. Computer-generated measurements of waveform axes and amplitude were obtained for both EKGs. Comparison of mean and 95% confidence intervals revealed no significant differences in Q, R or S wave amplitude across the six precordial leads. Furthermore, a fourfactor ANOVA found no significant difference (p > 0.05) in the Q, R and S wave amplitude between the type of electrode, gender and type of disease. A subset of 29 EKGs read by three experts found intra- (.90) and inter-rater (.84) reliability to be strong. In conclusion, the precordial VQuick威 patch provided equivalent EKGs to those obtained using standard tab-style electrodes. © 2003 Elsevier Science Inc.
intervention, increased survival, and preserved myocardial function is rapid diagnosis. Rapid diagnosis is essential because the maximal clinical benefits of acute interventions using thrombolytic agents or emergent angioplasty are obtained when the patient is treated within 90 min from the time symptoms first occur (1–3). Therefore, all treatment delays must be minimized. This preliminary study examined the accuracy of a contained set of electrocardiogram (EKG) leads for the precordium that was designed to facilitate the process of obtaining a 12-lead EKG. Along with history and cardiac enzymes, the 12-lead EKG has become a standard diagnostic tool in the detection of AMI (1–3). Currently, national standards strongly recommend that all patients experiencing chest pain receive a 12-lead EKG as soon as possible in the pre-hospital setting or emergency department (ED) (1– 3). This is of special concern for Emergency Medical System (EMS) providers in the pre-hospital care setting, who are encouraged to decrease on-scene times and still obtain essential screening information, including 12-lead EKGs (4 –11). The aim of this initial investigation was to demonstrate the efficacy of a new precordial (V1–V6) V-Quick威 patch (Figure 1) through comparison to traditional 12lead EKG systems in persons with heart or lung disease. Because the primary purpose of the V-Quick威 patch is detection of myocardial infarction, it is important to
e Keywords—12-lead electrocardiogram; electrodes; prehospital EKG
INTRODUCTION For the 1.5 million Americans who suffer an acute myocardial infarction (AMI) each year, the key to early
RECEIVED: 20 June 2001; FINAL ACCEPTED: 24 June 2002
17 May 2002; 131
L. S. Baas et al.
Figure 1. The V Quick Patch姞 with the six precordial leads placed on a mylar template. The leads can be moved along tracks placed on the template to facilitate correct placement and be adjusted to fit the chest.
assess the performance of this new precordial electrode system in a sample of persons with known heart disease. This would allow comparisons of performance of the V-Quick威 patch with standard tab-style electrodes in persons with varied cardiac dysrhythmias, bundle branch blocks, chamber enlargement, and old myocardial infarctions. We included a sample of persons with lung disease for two reasons. First, these individuals have a high incidence of EKG abnormalities such as dysrhythmias and chamber enlargement. Second, those with pulmonary disease develop changes in thoracic diameter over time. It is possible that this change may influence the ability to obtain accurate and precise EKGs due to difficulty in identifying landmarks, variations in the chest diameter, and differences in the distance between the heart and the skin. The purpose of this study of the patch electrode system was to see whether under ideal circumstances, in persons with known disease, the EKG would be equivalent to that obtained with traditional electrodes. We examined equivalence in two ways: first, with computergenerated measurements of waveform amplitude, then
using an expert clinical review in a subset of the sample. The specific research questions posed in this study were: 1. In a sample of men and women with known cardiac or pulmonary disease, are there significant differences in the Q, R or S wave amplitude in the precordial leads between EKGs recorded with standard tab-style electrodes and the V-Quick威 patch electrode system? 2. What is the inter-rater and intra-rater agreement for interpretation of EKGs obtained with the two electrode systems in a subset of the sample?
MATERIALS AND METHODS Subject Recruitment Subjects were recruited from cardiac and pulmonary rehabilitation programs, cardiac and pulmonary office settings, and by personal referrals. Stable men and women with known heart disease comprised the cardiac group and those with known lung disease comprised the
Accuracy of V-Quick Patch
pulmonary group. Convenience, purposeful sampling provided near equal disease type and gender representation, as well as a wide range in height and weight, representing underweight to obese body sizes. Eligible subjects were 21 years of age or older, capable of understanding spoken English, and able to lie flat without difficulty for a period of 15 min for the extensive skin preparation performed for the two EKGs. Subjects were not excluded based on the type of cardiac rhythm or electrical abnormality. However, subjects with spinal abnormalities that distort the chest wall and interfere with the ability to lie supine were excluded. Electrodes The electrodes on the V-Quick威 patch were commercially available post-style composed of Silver/Silver Chloride (Ag/AgCl). The standard electrode system used disposable tab-style electrodes (5500 Q-Trace威 Gold) manufactured by Graphic Controls Corporation (Buffalo, NY). Both electrodes meet the Association for the Advancement of Medical Instrumentation standards and are commercially available. The same brand and style of electrodes was used for the precordial and limb leads. Thus, both electrode systems had matching direct current offset potentials, reducing interference and ensuring quality recordings (5). 12-Lead EKG Machine A PhysioControl Life Pack 11 Monitor/Defibrillator威 was used to obtain all 12-lead EKGs. This is a portable, multiple-channel, 12-lead EKG machine that also serves as a cardiac monitor and defibrillator. It conforms to current recommendations and safety standards of the American Heart Association and the Association for the Advancement of Medical Instrumentation (5). This machine uses a computerized EKG analysis system developed by the Mortara Instrument Corporation, in accordance with the 10th Bethesda Conference on Optimal EKG (12). This system uses criteria based on: heart rates; wave amplitudes and durations; and P, QRS and T wave axis. Interpretation is based on 10 s of data obtained simultaneously from each of the 12 leads. This device was selected to obtain all 12-lead EKGs in this study because it is currently used by a large number of EMS personnel to obtain pre-hospital EKGs. Procedure We decided to conduct this initial study using the ideal procedure for obtaining the EKG with a sample of pa-
tients who were likely to have abnormal tracings, but were not experiencing acute symptoms. Using this approach, we could examine the accuracy of tracing obtained with the new and traditional lead systems as well as the more meaningful question of consistency among clinicians interpreting the tracings. A clinical study of actual patients in acute settings experiencing symptoms was not appropriate for the initial investigation, as it could delay treatment for persons with actual cardiac problems. After signed informed consent was obtained, subjects were asked to complete a brief questionnaire about medications, medical history, height, and clothing size. Measurement of weight and total body fat were obtained using bioelectrical impedance analysis with the Tanita TBF-105威 (13). If a subject had a pacemaker or ICD, this measurement was deferred, as it would likely be inaccurate due to the metal box within the chest. Subjects received either the patch or the standard tab-style 12-lead EKG first, by drawing marked electrode packets from a shuffled stack. A consistent procedure was used to prepare the skin and apply electrodes (14). This preparation consisted of a 30 s isopropyl alcohol wipe, followed by 2 min drying time and mild abrasion using a standard EKG skin preparation paper. Electrode placement was based on the American College of Cardiologist Standards (15,16). Electrodes were removed at the completion of the first EKG and the skin was prepared again using the same procedure to remove any remaining electrode residue. Both EKGs were printed and placed in the subject record. The following measures were taken to ensure quality EKGs and prevent muscle voltage interference: a firm surface such as a bed or table was used for full body support; a pillow was provided for increased comfort; and a comfortable room temperature was maintained to prevent shivering. Measures to prevent alternating current interference included: use of a surge protector, straightening lead wires, moving the table or bed away from walls with power outlets, and ensuring that the subjects had no contact with metal surfaces (5,15,16). Two investigators and two research assistants, experienced in performing 12-lead EKGs, collected all of the data. To assure consistency in procedure, paired investigators-research assistants collected most of the data, and these pairings were varied.
Data Management The voltage of the Q, R and S waves in all leads of the 12-lead EKGs from standard tab and patch recordings were measured by the computer software program of the PhysioControl Lifepack 11威. PhysioControl LifeNet威 Software package was used to download the saved EKGs
L. S. Baas et al.
Table 1. Measures of Body Size for Men and Women with Cardiac and Pulmonary Disease (N ⴝ 100) Men
Height Weight Body Mass Index Body Fat% Impedance
70.4 191.7 26.6 20.1 381.3
68.7 186.4 27.2 23.8 441.4
62.7 162.5 28.1 38.5 455.7
64.2 157.9 26.6 36.9 486.4
67.2 (4.6) 177.1 (35) 27 (4.4) 28.3 (11.7) 432.8 (100.2)
and waveform measurements from the recording device to a personal computer using a direct-link cable. After downloading, the waveform measurements were printed and the data were manually entered into an Excel 97娀 spreadsheet. Demographic data were included in the database. During the process of downloading the computer-generated data from the PhysioControl Lifepack 11威, a total of 10 EKGs from 8 subjects were lost. For these EKGs with lost computer data, the same research assistant manually measured the original copy of the 12-lead EKG recording. The manually measured data were then added to the spreadsheet that contained the computer-generated measurements.
Analyses The data from the spreadsheet were imported into SPSS PC娀 Version 10.0 for all statistical analyses. The demographic data were analyzed using descriptive statistics. The first research question was answered by first examining the mean and 95% confidence intervals for the computer calculated amplitude of the Q, R and S waveforms for each precordial lead. Next, a Repeated Measures Analysis of Variance (RM-ANOVA) was performed with the type of electrode (patch or standard tab-style) and waveform (Q, R or S) amplitude examined as within-subject factors. Gender and type of disease were included as the between-subjects factors so we could examine for interaction effects with type of electrode in each lead. A statistically significant difference in waveform (Q, R, and S) was expected as the amplitude of each varies both normally and in most abnormal EKG interpretations. That is, the R wave was expected to increase in amplitude from V1 to V6. At all steps in analysis, the data were examined for the effect of outliers and extreme cases. Once identified, these cases were reviewed and the raw data examined for a pattern to explain differences. One investigator purposefully selected pairs of EKGs obtained from 29 subjects for use in the agreement phase of the study. These subjects were selected to provide a representative sample of various EKG interpretations,
medical histories and body size. The EKGs were copied so that all identifying information and computer-generated measurements and interpretations were removed. The EKGs were shuffled and renumbered, for the manual reading and interpretation. Three expert reviewers examined both EKGs for all subjects in the subset. Two readers were board-certified cardiologists with clinical, academic and research experience. The third reader was an acute care nurse practitioner who has taught nationally sponsored 12-lead EKG interpretation classes for more than a decade. Intra-rater agreement was the percent of times that each expert reviewer provided the same interpretation for the EKGs obtained with the V-Quick patch and the standard tab-style electrode for each subject. This provided an evaluation of consistency of each reviewer across the pairs, and therefore reflected similarity in the tracing provided by the two types of electrode. Inter-rater agreement was the degree of consistency among the three experts and the computer interpretations of the two EKGs obtained for each subject.
RESULTS Subjects A total of 100 subjects (men ⫽ 54; women ⫽ 46) were enrolled in the study. These included both cardiac (n ⫽ 54) and pulmonary (n ⫽ 46) patients; the cardiac and pulmonary patients were approximately equally divided among males and females. Mean age was 60.8 years (SD 12) with a range of 28 – 84 years. Most of the subjects were European-American (69%), with the majority of the remaining being African-American. Measures of weight, height, body fat, and body mass index are presented in Table 1. Men and women with pulmonary disease had slightly lower body mass index and weight than those with cardiac disorders. Subjects with cardiac diseases reported that they had diagnoses of old myocardial infarctions, hypertension, heart failure and valvular disorders. Pulmonary diagnoses included chronic bronchitis, emphysema and asthma. Table 2 provides a summary of
Accuracy of V-Quick Patch
Table 2. Interpretation of the Pairs of EKGs Performed on the Subjects (N ⴝ 100) Rhythm Sinus rhythm Sinus tachycardia Sinus bradycardia Atrial fibrillation Paced rhythm Ectopic beats EKG findings Chamber enlargement Old myocardial infarction Bundle branch block
71% 5% 4% 3% 1% 19% 21% 19% 13%
the number and types of dysrhythmias and findings noted on the EKGs examined in this study.
Comparison of Computer-Generated Measurement of Waveform Amplitude
formed with type of electrode (patch and standard tabstyle), lead (V1 through V6), and waveform (Q, R and S) as the repeated measure factors and sex and disease as the between-subject factors. There was no statistically significant overall difference (F[10, 87] ⫽ .79, p ⫽ 0.64). The anticipated significant difference in waveform (Q, R, and S) and lead (V1-V6) was found, but there was no difference between electrode type, gender, or disease. Next, we examined the cases with the most extreme differences in waveform amplitude. Most of the subjects with the greatest differences had either intraventricular conduction defects or ectopic beats. The EKG machine identification of QRSR waveforms was not always consistent and led to some of the differences in reported amplitude. None of these pairs of EKGs had distinguishable differences when reviewed by the investigators. No gender, disease or body size differences could explain a pattern in these extreme cases. Clinician Agreement
The mean amplitude of the Q wave, obtained with the two types of electrodes, across the precordial leads (V1– V6) is depicted in Figure 2. The largest difference was found in V4 (0.4 mm) and the smallest in V2 (0.001 mm). These are minute differences that are not significantly. Figure 3 depicts the mean R wave amplitude, with the greatest difference found in V5 (1.3 mm) and the least in V1 (0.04). The S wave is depicted in Figure 4; again, the largest difference was in V4 (0.26 mm). Table 3 provides the average difference in amplitude for each waveform in each of the 12 leads. A five-factor Repeated Measures ANOVA was per-
This subset of the overall sample reviewed by the three expert clinicians included 20 men and 9 women. The mean age of this sample was 34 years (SD 13.2) with a range of 21 to 82 years. Sixty-seven percent of subjects were white, while the remainder were African-American. Height ranged from 50 to 75 inches tall (mean 68.3, SD 5.3) and weight ranged from 109 to 254 pounds (mean 183.7, SD 38.1). Body mass index ranged from 17.9 to 34.7 (mean 26.8, SD 3.9). Because the two EKGs were performed sequentially, two subjects had normal physiological changes on one
Figure 2. Q-wave amplitude in precordial leads. Mean and 95% confidence interval.
L. S. Baas et al.
Figure 3. R-wave amplitude in precordial leads. Mean and 95% confidence interval.
EKG that were not found on the second EKG. The first had a heart rate of 62 beats/min that was read as sinus rhythm on one EKG, whereas the second EKG had a rate just below 60 beats/min and therefore was read as sinus bradycardia. In a second case, one EKG had premature ventricular beats but the second did not. These changes were not included as reader differences in the subsequent analyses because they were actual changes and not disagreements in interpretation. Intra-rater agreement was the percent of times that
each expert reviewer and the computer provided the same interpretation for the EKGs obtained with the VQuick威 patch and the standard tab-style electrode for each subject. So, the intra-rater agreement was an evaluation of consistency of each reviewer across the pairs and therefore reflected similarity in the tracing provided by standard and V-Quick威 patch electrodes. Overall, there were 29 pairs of EKGs that were evaluated by three investigators and the computer. Thus, there were 116 possible pairs for intra-rater agreement.
Figure 4. S-wave ampitude in precordial leads. Mean and 95% confidence interval.
Accuracy of V-Quick Patch
Table 3. Mean Differences in Millimeters of Q, R, and S Waves Amplitudes for Each EKG Lead Lead
I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
.028 .004 .358 .080 .018 .045 .088 .001 .320 .394 .006 .002
.021 .219 .148 .002 .013 .228 .039 .157 .069 .207 1.303 .234
.155 .156 .087 .205 .137 .052 .034 .167 .186 .302 .013 .092
Actual agreement was found in 104 paired comparisons. This provided an overall agreement rate of 89.7%. Table 4 describes the nature of the intra-rater disagreements. Of the nine pairs in which there was disagreement, there was one subject in whom three paired interpretations disagreed. In another subject there were two reviewers with disagreement on paired interpretations. Five of the remaining disagreements involved only one reader. Inter-rater agreement is the degree of consistency between the expert and computer interpretations. Determination of inter-rater agreement was first performed in the most conservative manner by looking for like readings on the more specific disorders, like bundle branch block or old myocardial infarction, as well as the less definitive comments such as “nonspecific ST-T wave changes” or “possible atrial enlargement.” When this was computed, the overall inter-rater agreement was .67. When possible atrial enlargement was excluded, the inter-rater reliability increased to .74. In the most liberal
interpretation, when both possible left atrial enlargement and nonspecific ST-T wave changes were excluded, the inter-rater reliability reached .84. Of interest, the first and second reviewers more frequently made the interpretation of nonspecific ST-T wave change than the third reviewer or the computer. The third reviewer read more instances of left atrial enlargement than the other reviewers and the computer. These were deemed to be differences that could be due to the small size of the original print-out of the EKG (4 ⫻ 10 inches), faded ink on the original EKG, and reproduction of the original EKG by photocopying. All are factors that make subtle changes like atrial enlargement and nonspecific ST-T wave changes difficult to detect. In two subjects, the nonspecific ST-T wave changes were read on only one of the EKGs and this occurred once with the traditional electrodes and once with the precordial patch. The change in these subjects may have been due to the fact that the EKGs were not obtained simultaneously. Despite the difficulty in identification, nonspecific ST-T wave changes are of concern in patients with acute symptoms and must be considered along with history and diagnostic test results.
DISCUSSION The results from this study demonstrate that the tracings obtained from the patch and standard tab-style electrodes were equivalent. Once equivalence is established, ease of use becomes the driving factor in selection of EKG electrodes. In this study, we did not examine ease of use or time for typical application in a busy Emergency Department. However, the V-Quick威 patch provides a one-piece template for the placement of all six precordial
Table 4. Expert Reader Disagreements in Interpretations of the 12-Lead Electrocardiograms Obtained with the V-Quick Patch and Standard Tab-Style Electrodes Subject 26
51 48 118 4 7 10 49 106
V-Quick Patch EKG
Standard Tab Electrode EKG
1 2 3 Computer 2 3 Computer Computer 2 2 3 3 3
Normal Possible right atrial enlargement, ST changes ST changes Normal Left ventricular enlargement Intraventricular conduction defect Incomplete LBBB, possible lateral ischemia RBBB, left atrial enlargement Incomplete RBBB Diffuse T wave inversion Nonspecific ST changes* RBBB Left atrial enlargement
Incomplete RBBB Incomplete RBBB Possible RBBB Normal Normal* Intraventricular conduction defect, Left ventricular enlargement Possible old septal infarct** Right axis deviation, Intraventricular conduction defect* Normal* Incomplete RBBB** Intraventricular conduction defect Left atrial enlargement, LBBB* Intraventricular conduction defect*
* Other interpretations agreed with this finding. ** Other interpretations were normal sinus rhythm. RBBB ⫽ right bundle branch block.
leads that may make application easier. The personnel using the V-Quick威 Patch must reach for only a single item instead of six separate items to place all six chest leads. As noted in the description in the appendix, the patch has characteristics that enable it to conform to variations in thoracic dimensions while retaining the ability to accurately place the electrodes. Because the template provides cues for lead placement, it is possible that initial training and retraining time might be reduced. Whereas the initial intent of the precordial patch was to develop a lead system that would be accurate and provide rapid application for the pre-hospital setting, the V-Quick威 patch has the potential to be used anywhere a 12-lead EKG is needed. For instance, it might be used in office settings, occupational health clinics or in-patient areas. The sample included in this study represented the population of people who need to have 12-lead EKGs, especially in the pre-hospital setting. These men and women had a variety of abnormal as well as normal EKGs. The tracings were equivalent. The extreme differences in computer-measured amplitude that did occur were due to errors in the recognition of waves and the measurement of waveform amplitude performed by the EKG machine. Small variations of 1– 4 mm can occur due to thoracic changes from the respiratory cycle (16). The largest mean difference in voltage was 1.3 mm and this appeared in V5, a lead that generally has a tall R wave. This difference was neither statistically nor clinically significant. If a person had borderline voltage criteria for left ventricular enlargement, this 1-millimeter difference could perhaps enable the person to meet criteria for the EKG finding, but it would not result in a difference in clinical management of the individual. Furthermore, greater differences in waveform amplitude have been found when precordial electrodes are moved as little as a centimeter either vertically or horizontally from the designated position on the chest (16). In this study, the degree of agreement in interpretation of the pairs of EKGs across all reviewers was high. Examination of the differences revealed that the areas of disagreement were relatively minor and would not alter patient treatment in most clinical situations. What is of interest is that in past studies of expert readings of 12-lead EKGs, the rate of agreement has been much lower than the agreement found in this study. Inter-rater reliability was only .337 when the interpretations of 40 primary care physicians were compared to computer interpretations (17). Nine EKGs were presented to 44 residents, 32 senior residents, 15 staff physicians and 9 consultants. The percentage of correct answers ranged from a low of 18% of house officers able to correctly identify supraventricular tachycardia, to 86% for a paced rhythm. Acute myocardial infarction and bundle branch
L. S. Baas et al.
block had higher correct identification (18). Even lower levels of both intra-rater and inter-rater reliability were reported when eight cardiologists were asked to independently read shuffled pairs of 12-lead EKGs obtained from 105 subjects (19). It should be noted that the number of reviewers in this study was lower than in previous research; however, inflation of correlation coefficient has been reported when the number of reviews is increased (20). Observational research often relies on three to five reviewers for inter-rater reliability measurement (21). Based on this study and a previous study, there seems to be no reason to limit the use of the V-Quick威 patch. The sample in this study and the larger sample found in the previous studies included persons with a small body size as well as those who meet the qualification for Stage 2 Obesity. A high degree of agreement in clinical interpretations as well as computer analysis of waveform amplitude was found in this sample of adult men and women of various body sizes. This sample included those with known cardiac and pulmonary disease who had normal as well as abnormal EKGs. We deliberately included a large number of women in the sample so that we could look for gender differences. Breast tissue may pose a problem with electrode placement or cause artifact during recording of the EKG. In this study, we found the V-Quick威 patch to be equally effective in men and women. During data collection, no problems were reported related to inability to use the V-Quick威 patch due to chest size, configuration, or breast size.
Summary In this sample of persons with heart or lung disease, the precordial (V1–V6) V-Quick威 patch provided EKGs that were equivalent to the EKGs obtained using standard precordial tab-style electrodes. Safety and efficacy were demonstrated in both men and women diagnosed with cardiac or pulmonary disease. The subjects in this study represent the type of patients who usually need urgent 12-lead EKGs performed. In this sample, QRS waveform analysis and clinician interpretation were not different. Efficacy and safety were demonstrated for both men and women, with varying age and body size. Based on the results of this study, and the one conducted by Ware (“Accuracy of the precordial V-Quick patch ECG.” Unpublished masters thesis, University of Cincinnati, College of Nursing and Health, 1997), the V-Quick威 patch is equivalent to standard tab-style electrodes and is safe for use in healthy individuals as well as persons with cardiac or pulmonary disease.
Accuracy of V-Quick Patch
Acknowledgments—The authors thank the following people who assisted in the recruitment of subjects: Marci Moreno, RN, MSN, Sharon Balkanhol, RN, MSN and Sandy Doman, RN, MSN. In addition, we would like to thank Nezam Al-Nsair, RN, MSN and Virginia Hedger, RN, MSN for their assistance in data collection. Funding for this study was provided by VQ Corporation.
REFERENCES 1. American Heart Association. Guidelines 2000 Conference on CPR and ECC. Circulation 2000;102(Suppl 1):I172–I203. 2. Ryan TJ, Antman EM, Brooks NH, et al. 1999 update: ACC/AHA guidelines for the management of patients with acute myocardial infarction. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Acute Myocardial Infarction). J Am Coll Cardiol 1999;34:890 –911. 3. National Heart, Lung and Blood Institute. Emergency department: Rapid identification and treatment of patients with acute myocardial infarction. (NIH Publication No. 95-3278). Washington, DC: U.S. Government Printing Office, 1995. 4. Phalen T. Advanced prehospital ECG. Emerg Med Serv 1994;23: 51– 60. 5. Laks MM, Arzbaecher R, Bailey JJ, Geselowitz DB, Berson AS. Recommendations for safe current limits for electrocardiographs. A statement for healthcare professionals from the committee on electrocardiography, American Heart Association. Circulation 1996;93:837–9. 6. Karagounis L, Ipsen ST, Jessop MR, et al. Impact of field-transmitted electrocardiography on time to in-hospital thrombolytic therapy in acute myocardial infarction. Am J Cardiol 1990;66: 786 –91. 7. Aufderheide TP, Hendley GE, Thakur RK, et al. The diagnostic impact of prehospital 12-lead electrocardiography. Ann Emerg Med 1990;19:1280 –7. 8. Gibler WB, Kereiakes DJ, Dean EN, et al. Prehospital diagnosis and treatment of acute myocardial infraction: a north-south perspective. Am Heart J 1991;121:1–11. 9. Kereiakes DJ, Gibler WB, Martin LH, Pieper KS, Anderson LC. Relative importance of emergency medical system transport and the pre-hospital ECG on reducing hospital time delay to therapy for acute myocardial infarction: A preliminary report from the Cincinnati Heart Project. Am Heart J 1992;123:835– 40. 10. Weaver WD, Cerqueira M, Hallstrom AP, et al. Prehospital-imitated vs hospital-initiated thrombolytic. JAMA 1993;270:1211– 6. 11. Canto JG, Rogers WJ, Bowlby LJ, French WJ, Pearce DJ, Weaver WD. The prehospital electrocardiogram in acute myocardial infarction: is its full potential being realized? J Am Coll Cardiol 1997;29:498 –505.
139 12. Rautaharju PM, Ariet M, Pryor TA, Arzbaecher RC. The quest for optimal electrocardiography. Task force III: Computers in diagnostic electrocardiography. Am J Cardiol 1978;41:158 –70. 13. Davies PSW, Jagger SE, Reilly JJ. A relationship between bioelectrical impedance and total body water in young adults. Ann Hum Biol 1990;17:445– 8. 14. Clochesy JM, Cifani L, Howe K. Electrode site preparation techniques: a follow-up. Heart Lung 1991;20:27–30. 15. Rautaharju PM. Electrocardiography in epidemiology and clinical trials. In: MacFarlane PW, Awry TD, eds. Comprehensive electrocardiology: theory and practice in health and disease, Vol 2. New York: Pergamon; 1989:1219 – 68. 16. Chou TC. Electrocardiography in clinical practice, 4th edn. Philadelphia: Saunders; 1996. 17. Hillson SD, Connelly DP, Liu Y. The effects of computer-assisted electrocardiographic interpretation on physician’s diagnostic decisions. Med Decis Making 1995;15:107–12. 18. Kahn MA, King D, Davies KN, Silas JH. Practical cardiological skills and ECG interpretation amongst doctors. Br J Clin Pract 1993;47:183– 4. 19. Weston MJ, Bett JH, Over R. Consensus opinion and observer accuracy in electrocardiography with reference to coronary arteriographic information. Aust NZ J Med 1973;6:429 –32. 20. Cronbach, L.J. Essentials of psychological testing, 2nd ed. New York: Harper & Row; 1984. 21. Carmines EG, Zeller RA. Reliability and validity assessment. Newbury Park, CA: Sage Publishers; 1980.
APPENDIX Description Of The V-Quick威 Patch The V-Quick威 Patch has a disposable backing constructed of a Mylar base with adhesive post style Silver/ Silver Chloride (Ag/AgCl) electrodes that slide along the marked template to allow proper placement. This template provides prompts for correct placement of leads so that the accuracy may be increased for practitioners who perform 12-lead EKGs infrequently. Leads are grouped into sections and individual electrodes can be moved along tracks on the template to provide for individual variation in chest dimensions. The template itself is pliable and will pleat to fit a smaller size chest and unfold to accommodate a larger individual. The V-Quick威 patch is composed of materials previously used in patient monitoring systems and meets the standards of the Association for the Advancement of Medical Instrumentation.