The precordial lead in 104 normal adults

THE

PRECORDIAL

LEAD

.lN 104 NOK.MAL

ADlJL’lW

H. &IASTER, &I.I>. NEW YORK, N. Y.

I~RTHUR

T

HE use of the precordialt (“chest ” or “fourth “) lead in the diagnosis of heart disease is rapidly increasing. Before clinical application of the precordial lead readings can be of value, it is necessary to have tracings of normal people as controls. Katz and Kissinl have published the measurements from records of 25 individuals, but, a larger number is necessary before importance can be attached to the findings. These investigators placed their patients on the left side when taking the chest lead, but there is an objection to this procedure, as such a movement may shift and rotate the heart and hence change the electrocardiographic picture.

The 104 individuals whose records are reported in this paper were carefully examined at Cornell University Medical College in the years 1926, 27, 28. At that time the three standard leads of the electrocardiogram, and also anteroposterior and t,ransverse chest leads were taken. Everything possible was done to make certain that the individuals were normal. They had no complaints; physical examination was negative ; blood pressure tests, urine examinations, teleroentgenograms, electrocardiograms, exercise tolerance tests were all normal. The series consisted of 26 women ranging in age from twenty-eight to sixty-five years, the average age being forty years, and 78 men from twenty-seven to seventy-four years old, the average age being forty-four years. In other words, it was a series comprised of normal adults. The anterior electrode was placed near the lower end of the sternum, about the level of the apex of the heart and slightly to the left of the midline. The form of the electrocardiogram changed very little when this electrode was moved from the middle of the sternum to the region of the apex but not beyond. The posterior electrode was located on the back over the vertebral column at about the same level as the anterior or slightly higher. To the anterior electrode the wire from the right arm terminal of the galvanometer and to the posterior electrode the wire from the left arm terminal of the galvanometer were attached. *From tThe or fourth

the Department of Medicine, expression “precordial” lead or anteroposterior lead.

Cornell is used

in

University this paper

Medical College. synonym~msly

with

ch%qt

5i2

THE

AMERIC’AN

HEART

.JOURNAT>

The P-wave was inverted ; the a.mplitude averaged -0.7 mm. The average duration of the P-wave was 0.06 second. The limits are given in Table I where the measurements are summarized. At first glance, the P-wave (Fig. 1) appeared diphasic, for the interval bekveen the P-wave and the QRS group was always slightly above the isoelectric level. This was due to the end deflect.ion of the auricular contrac-

Fig.

1.--A,

B,

C,

Three

normal

individuals at’ fonl~th

with Lea~ls 1 1cn:l.

I,

II,

III

an<1

precordial

(chest

tion, the “T-wave of the P-wave, ” so to speak. In the standard electrocardiogram this end deflection of the P-wave is usually eviclent but is not so large as in the precordial lead. The a~~l.iculoventricular conduction time, that is, the P-Q interval, measured 0.15 second, but the range was from 0.10 t,o 0.18 second. It attained 0.20 second once. The QR group is perhaps a better term than the QRS group, for in the precordial lead there mere only two waves visible. In the ordinary standard electrocarcliogram three waves are common, and one

534

THE

AMERICAN

HEART

.TOUR.NAI>

wave alone is not uncommon. In our series, the first wave of the QR group was always a downward deflection, or Q-wave. The absence of a Q-wave, therefore, is abnormal. The average size was -5.3 mm., but the amplitude ranged from -1.5 t.o -1.4.0 mm. Not one Q-wave measured less than -1.5 mm. The next wave, the R-wave, was upright. Its average height was +10.7 mm., ranging usually from t2.0 to t17.0 mm., but attaining +19.0 mm., +23.0 mm., and t26.0 mm., each, once. The Q-wave was usually smaller t,han t,he R-wave, but to this there were eleven exceptions. The absence of an R-wave or one whose size is less than -t2.0 mm. is abnormal. The duration of the QR.8 was 0.09 second. In fact, the variation shown in this group was apparently much less than that in the standnrd electrocardiogram. It ranged, nevertheless, from 0.06 second to 0.12 second, each of these limits being attained only once, so that one is safe in stating that the upper limit of normal is 0.10 second. Notching or slurring was never present in the precordial chest lead of the normal individual. On the other hand, this is not uncommon in Lead III of the standard tracing. The R-T transition of the precordial electrocardiogram differed from the RS-T transition of the standard record. The T-wave was angularly inverted almost immediately after the R-wave, with hardly a semblance of isoelectric level (Fig. 1). The average of the R-T transition was 0.08 second. The R-T interval, measured from the end of the downstroke of the R.-wave to the end of the T-wave, was 0.26 second, but the range was from 0.20 to 0.32 second. The R-T transition usually was I mm. below the isoelectric level; it was isoelectric on eight occasions, but never once above the isoelectric line. The T-wave was invert,ecl. The negativity ranged in amplitude from -1.0 mm. to -6.0 mm. Onc,e indeed it measured -7.5 mm. Any T-wave greater than -6.0 mm. is probably abnormal. The average duration of the T-wave was 0.19 second, but there were wide variations, i.e., from 0.08 second t,o 0.26 second. There were a few exceptions to the foregoing descriptions. The P-wave was positive in 2 instances out, of the 104 examinations. This occurred in subjects of forty-eight, and thirty years of age, respectively. These individuals were considered normal in every respect, but t,hep had long, narrow hearts. It may be that an unusual rotation of the heart was responsible for these variations from t,lle predominant findings. The T-wave was barely positive once, about +0.5 mm. This was present in a woma.n forty-four years old in whom history, physical examination, teleroentgenogram of the heart and laboratory examinations were normal. Her electrocardiogram revealed a normal sinus rhythm with a left ventricular preponderance. The only doubtful

MASTER:

PRECORDIAL

IlEAD

IN

NOKMAL

ADULTS

515

finding was an inverted cove plane T-wave in Lead III. The patient was reexamined in January, 1934. All examinations including fluoroscopy of the heart and lung were negative, but, the precordial lead now revealed not only a positive T-wave of -to.5 mm., but a notchecl QR and an R preceding the Q-wave, an observation which is considered definitely abnormal and which was never found in any of the first 104 records. For these reasons it is my opinion t,hat the inverted T-wave in Lead III was an abnormal finding, and that the patient did not possess a normal heart,. Moreover, the fact that the slightly positive T-wave of the precordial lead was the only exception in the 104 cases proves that it may be discarded from a statistical point of view. In other words, a positive T-wave in the precordial lead should always be considered abnormal. It appears from the foregoing t,hat, the precordial lead may help to decide when an inverted T-wave in the third lead of the clectrocardiogram is of significance: Left ventricular preponderance on the electrocardiogram occurred 44 times. The precordial tracings in these cases showed nothing different from those observed in the remaining cases.

Many types of electrodes were experimented with in taking chest. One of the simplest of these was an ordinary glass funnel, wit.11 leads. outside diameter of about from 1.5 to 2 inches. lnside the funnel, as near the periphery as possible, were wound a few coils of thick copper wire which emerged through t,he narrow end. The funnel was stuffed with a wad of absorbent cotton moistened with warm salt water. The cotton was bulky so that it formed the area of contact with the chest wall. The glass, held in the hand, served as an insulator. Another such elect,rode was held in place posteriorly. I am now substituting the posterior chest electrode with the left leg elecAs Wilson” has shown, the lead over the heart is the import.ant trode. one, and the other lead ma.y be placed at a greater distance from thcs heart without significant changes in the electrocardiogram. I have confirmed this observation in at least 30 patients, and hence use the funnel electrode over the precordium, and the left leg as the indifferent electrode. The precordial lead is then taken as one ordinarily derives the standard Lead II. This method is simpler than utilizing both the anterior and posterior chest electrodes. It was usually found unnecessary to rub the skin at the site upon which the funnel was placed, unless the chest was hairy. The best means of reducing resistance was by making two or three very superficial scratches with a hypodermic needle. It was never necessary to draw blood.

516

THE

AMER.ICAK

HEAR1’

JOTJRKAI.

It will be observed that the I?- and T-waves were inverted, and on this account many writers have suggested that t,he chest leads should be reversed. The P-wave would then be upright, the first wave of the QRS group would be upright, the second inverted, and the T-wave would be positive. In the standard electrocardiogram the waves usually occur in this form ; hence the advantage of reversing the leads. The measurements given in Table T would still 11old except. that their signs woulcl change. SUMMARY

For the precordial lead the right arm electrode is placed on t,he anterior chest, just to the left. of thr sternum about the level of the apex, and the second electrode is on the left. leg. The record is then taken as onr usually derives Lead Tl of the stanclard electrocardiogra.m. This met,hocl is simpler than that of placing one electrode on the front and the ot,her on t,hr back of t,he chest,. A simple glass electrocle is describetl for obt,aining precordial leads. It is suggested that the rlec+rodes of the precordial lead be reversed so t,hat P, R and T will be positive and only S inverted, just as thtxy are in the standard electrocardiogram of normal adults. The precordial chest, lead in 104 normal individuals is summarized. Iu this series the P-wavtl is shown to be negative. is not more’ than -1.5 mm. and is usually followecl by an end deflection above the isoelectric level. The P-Q interval averages 0.15 second. The QRS group is always diphasic, and never notched or slurred. Ttx duration is 0.09 second. The absence of the Q-wave or of the R,-wave is definitely abThe Q-wave averages -5.3 mm. in size and the R-wave, 110.17 normal. mm. No Q-wave less than -1.5 mm. and no R-wave less tfhan ~2.5 mm. in size was ever observed. The R-T transition is below the isoeleebric ,2 positive R-T transition or one level, occasionally just, isoelectric. that is more than 2 mm. below the isoelectric is clefinitely abnormal. The T-waves are always invert(Ld ant1 ltsually are Irhss t,ha.n -6.0 mm. in size. The precordial lead may l~ove of srrvice in ii~terpretii~g which T-wave inversions of the t,hird lead are abnorn1a.l. Left ventricular preponderance in the standard clectrocarcliogralll of normal adults does not change the form of the precorclial leacl. &l3- thanks

are due to Dr.

TIamld

E. R. I’ardee

for

his

umny

helpful

suggestions.

REFEREIVCES

1. K&Z,

of I,cad IV. Its Appearance Normally, L. K., and Kiusin, $1.: A Study in Myocardial Disease, rind in l