J. ELECTROCARDIOLOGY 12 (4), 1979, 407-410

The Precordial ECG Belt for Obtaining Rapid Reproducible Precordial Leads

BY HAROLD MILLS, M.D., HERBERT I. STEIN, M.D. AND WILLIAM J. MANDEL, M.D.

S U M M A R Y A new, stretchable precordial ECG belt is described. It represents an excellent

method for obtaining reproducible, accurate precordial ECGs and is especially useful in women and individuals with abnormal chest configurations.

For years physicians reading serial ECGs have recognized tha t significant voltage vari- ation between precordial complexes resulted from varying precordial lead placement. Yet, few articles addressing this problem have been published. Kerwin, et al., 1 noted tha t technicians marked the chest position with < lcm. variation in only 40-50% of male and only 15-20% of female subjects. Recently, Rautaharju, et al., 2 described an ECG elec- trode locator designed to more accurately de- f ine p record ia l e lec t rode pos i t ions . The method is extremely accurate but too tedious and time consuming for use in a hospital where hundreds of ECGs are taken daily. The best technicians cannot place electrodes with daily precision. The chest landmarks appear different when viewed from either side of the body. Furthermore, the barrel-shaped chest, the hairy chest, the large breasted woman and the thin, emaciated subject all present problems in positioning the electrodes. Often

From the Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center and the UCLA School of Medicine, Los Angeles, California. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accord- ance with 18 U.S.C. w 1734 solely to indicate this fact. Reprint requests to: Publications Office, Division of Car- diology, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Los Angeles, CA 90048

a technician will knowledgeably misplace a chest electrode because it is impossible to ob- ta in electrode adherence at the correct spot. With the advent of the three-channel ECG recording system all six leads are placed si- multaneously, often inaccurately, in haste. Frequently, the electrodes slip off, requiring multiple (and expensive), inadequate records before a satisfactory tracing is obtained. Be- cause of these problems it was felt t ha t a rapid, accurate, reproducible, nonslippable method of electrode placement would be most useful and therefore the precordial ECG belt was developed. The purpose of this prelimi- nary report is to describe this precordial belt and to present initial studies val idat ing its accuracy and reproducibility.

M A T E R I A L S A N D M E T H O D S The precordial electrode belt (Fig. 1)* is a thin

(0.005") natural rubber belt, 21" by 3-3/4", sup- ported by three vertical braces to prevent stretch distortion. Six apertures are prestamped for elec- trode placement. The belt is snap-attached to a pair of 2 pound weights and is easily stretched across the chest. The weights placed on the bed hold the electrodes in place. The stretch characteristics of the belt allow the placement of electrodes in the correct precordial position with only a few mil- limeters variation, particularly in the Vs-V~ posi- tion. Belts for children and large chests (greater than 44" in circumference) are available for use

407

4O8 MILLS ET AL

FIG. 1. A) The simple method of placing the precordial belt is dem- onstrated. B) Electrodes are top- loaded with electrode gel with the belt in place.

when indicated. The special electrodes* used con- sist of a plastic body with a silver alloy center tube merging into a concave disc cup. The electrode is designed for top-loading with electrode gel. The technician simply positions the belt with the elec- trodes in the V1 and V2 positions, stretches it hori- zontally across the chest and the V3 through V6 electrodes assume their correct positions with the weights on each end holding them firmly in place. Consecutive ECGs were obtained on 100 patients, using the standard method with suction cup elec- trodes, followed by the precordial belt method. The ECGs were recorded by a three-channel machine. These records were coded by computer, read and compared by two trained electrocardiographers. In addition, twenty medical ly stable subjects (ten male and 10 female) had ECGs taken on consecu- tive days by both the standard and precordial belt methods. Each daily set of ECGs was taken by one

*Gamma Medical Products Corporation, 2011 Fort Drive, Alexandria, Virginia 20307.

of three trained technicians instructed to position electrodes carefully. The technic ians were re- minded repeatedly regarding the research nature of these tracings so tha t electrodes were placed with extreme accuracy. The ECGs obtained on con- secutive days were taken by different technicians simulat ing common hospital practice. The ECGs taken by the standard method were obtained utiliz- ing a flat precordial electrode held in place by a leaded rubber belt. A suction cup electrode was not used because the residual chest indentation could influence the technicians, and because accurate suction cup placement is difficult in females. The chest circumferences ranged from 34-46" in the male and 33-47" in the female subjects.

The chest lead R and S voltages obtained by the standard and precordial belt methods were mea- sured (to 0.5 mm accuracy) and then compared. The results of this la t ter study, for which all ECGs were recorded by a single channel ECG machine, appear in Tables 1-3. For all studies the ECGs were standardized at 10 mm. deflection per 1 mv.

J. ELECTROCARDIOLOGY, VOL 12, NO. 4, 1979

P R E C O R D I A L ECG BELT 409

TABLE 1

A Males (N = 10)

Mean R Deflection Mean S Deflection B I 8.092 +- 0.767* 5.325 _+ 0.728 D II 8.000 _+ 0.811 5.667 -- 0.773 ST I 8.417 _+ 0.831 5.433 +_ 0.736 ST II 8.230 _+ 0.732 5.483 + 0.732

B Females (N=10)

Mean R Deflection Mean S Deflection B I 7.408 _+ 0.646 5.325 _+ 0.728 B II 7.117 _ 0.614 5.667 _+ 0.773 ST I 7.667 _+ 0.661 5.433 + 0.736 ST II 7.367 _+ 0.592 5.483 __+ 0.732

The mean and standard error of R and S deflections (mm.) are listed. The values recorded on consecutive days are not significantly different. In this and subsequent tables, B represents the precordial belt method and ST the standard method.

*Standard error of mean (SEM)

RESULTS For the initial study the ECGs obtained by

both the standard (utilizing suction cup elec- trodes) and belt methods were coded by com- pu te r and read by a t ra ined electrocardi- ographer. Ninety-two percent of the records resulted in QRS configurations which were essentially identical. In 8% of the consecutive records moderate variation in the QRS and T wave voltage was noted without significantly affecting comparative interpretation. It was repeatedly observed that in patients with un-

u sua l ches t con f igu ra t ions and in large- breas ted women, electrode p lacement was more accurate when the precordial belt was used.

To validate the reliabili ty and reproducibil- ity of the precordial belt, the second s tudy was performed in which consecutive records were obtained using a s tandard precordial elec- trode application and the application of elec- trodes by the precordial belt method. Table 1 lists the mean and standard error of R and S deflections (mm.) for the ECGs taken by each method on consecutive days (I and II). The differences are not significant. Table 2 sum- marizes the absolute differences of R and S deflections for the ECGs on consecutive days. Analysis of these values reveals that in males the absolute differences of the deflections are not s ign i f i can t ly d i f fe ren t when the two methods are compared. In contrast, the abso- lute differences of the deflect ions for the R(P=0.010) and S(P=0.003) are significantly different in females . Table 3 summar izes these total differences between R and S de- flections (mm.) in all precordial leads for each pair of records obtained by both methods. It should be emphasized that comparison of all four records taken on each patient reveals no significant differences which would affect in- terpretation; however, it is readily seen that the belt method resulted in lower total pre- cordial voltage differences between the con- secutive ECGs. In no instance were the total R and S deflections greater than 25 mm. using the belt, whereas this occurred in five in- stances using the standard method. Four of these five subjects with large deflection dif- f e rences were females . The m a r k e d and statistically significant differences noted in the females would be expected because appli- cation of precordial electrodes is made dif- ficult as a result of skin slippage and breast mobility.

TABLE 2

Males (N= 10) B ST P Value

R absolute deviation 1.408 -+ 0.199 ~ 1.650 -+ 0.227 0.366 S absolute deviation 1.125 _+ 0.189 1.350 _+ 0.318 0.495

Females (N= 10) R absolute deviation 1.425 __ 0.206 2.233 _+ 0.327 0.910 S absolute deviation 1.142 _+ 0.202 1.958 _+ 0.258 0.003

The absolute deflection differences (mm.) between days I and II are listed for both methods. This represents the absolute values of the differences between the R and S measures on consecutive days. Statistically significant greater differences are noted in females when the ST method is used.

*Standard error of the mean (SEM)

J. ELECTROCARDIOLOGY, VOL 12, NO. 4, 1979

410 MILLS ET AL

TABLE 3

R & S Diff. B M/F ST M/F

0-10 4 2/2 3 3/0 11-15 7 4/3 4 3/1 16-20 5 2/3 6 1/5 21-25 4 2/2 2 2/0 26-30 1 0/1 31-35 2 1/1 >35 2 g/2 This table summarizes the total absolute differences be- tween R and S deflections (ram.) in all precordial leads for each pair of records obtained on consecutive days with the belt and standard methods. The number of subjects falling into each group is listed. M/F represents male/ female ratio.

DISCUSSION The precordial ECG belt allows t ra ined

technicians to rapidly place the precordial electrodes in a manner which results in an accurate reproducible ECG. Even with the skilled ECG technicians in our hospital, sig- nificant variations in serial ECGs are often noted, occasionally leading to misinterpreta- tion of the records. Thus, increased voltage could be interpreted as hypertrophy and de- creased voltage as possible infarction. In addi- tion, significant ST and T wave changes can also occur. Many technicians misplace elec- trodes by applying them in haste or simply by " eyeba l l i ng" the app ropr i a t e l a n d m a r k s . Furthermore, with use of the suction chest e l e c t r o d e s and t h e m u l t i - c h a n n e l E C G machine, t racings were frequent ly aborted

because the suction electrodes dislodged, a problem, obviated by the ECG belt. Our pre- l iminary data and observations suggest that the precordial ECG belt will al leviate the p rob lems so genera ted . If the t echn ic ian places the electrodes properly in the V1 and V2 positions, and then horizontally stretches the belt fixed in place by the weights, it is vir tually impossible to place the electrodes more than a few mill imeters away from the appropriate precordial position. Thus, repro- ducible, reliable serial ECGs can be obtained, a l levia t ing the impact improper electrode placement or electrode slippage can have on serial ECGs. This would be especially true for females and patients with unusual chest con- figurations.

In summary we have found the precordial belt to be an accurate, reproducible, rapid method for recording precordial ECG leads. It would seem to be a useful tool, particularly when mated to a three-channel ECG machine.

Acknowledgment: We are grateful to Amy C. Kwan, Biostatistician, Cedar-Sinai Medical Center, for performing statistical analyses of our data.

REFERENCES 1. KERWIN, A J, MCLEAN, R, AND TEGELAAR, H: A

method for placement of chest electrodes in the taking of serial electrocardiographic tracings. Canad. MAJ 82:258, 1960.

2. RAUTAHARJU, P M, WOLF, H K, EIFLER, W J AND BLACKBURN, H: A simple procedure for position- ing precordial ECG and VCG electrodes using an electrode locator. J Electrocardiol, 9:35, 1976.

J. ELECTROCARDIOLOGY, VOL 12, NO. 4, 1979