THE CANADIAN MEDICAL

LSJOURNAL 2JH IDECAILfE

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N VE IBER 26, 1960 * VOL. 83, NO. 22.-...I

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CLINICAL SPATIALVECTORCARDIOGRAPHY*

HARRY ABRANISON, MI.D. and C. R. BURTON,MI.D., M.R.C.P., F.R.C.P.[C], Toronto

THERE IS NO DOUBT that the electrocardiogram hasbecome firmly established in clinical medicine.Spatial vectorcardiography, on the other hand, isstill in its infancy. Both deal with vectors. Avector is a mathematical symbol to denote a force.Such a force is represented by a straight line in theform of an arrow. The length of the arrow repre-

sents the magnitude of the force, while the positioinof the arrow in space indicates the direction ofthe force. Positivity and negativity are defined byan axis of reference.

Mathematically, a multitude of instantaneousvectors may be represented by a single resultantvector. Thus, in the heart, the sum total of theelectrical activity at any particular instant may berepresented by a single resultant vector. This re-

sultant vector changes from moment to momentduring the electrical cycle of the heart, so thatalthough ventricular depolarization is completedwithin a finite time period, it may be representedby an infinite number of resultant vectors. A linewhich joins the tips of these resultant vectors isknown as a vector loop. Since such a loop is a

record of the time-course of the infinite number ofresultant vectors occurring during depolarizationof the ventricles, it is known as the QRS loop.Similarly, that defining repolarization of theventricles is known as the T loop. The P loopdescribes depolarization of the atria.

Fig. 1 is a vector representation of the spread of

depolarization throughout the ventricles of theheart. Each arrow shown represents one of theinfinite number of electrical resultant vectors oc-

curring during the process. The resultant vector isconstantly changing in direction and magnitude.The dotted line outlining the ends of these result-ant vectors is the vector loop. This loop has beeninscribed in a clockwise direction. This meaiis

that the initial forces of ventricular depolarizationare directed superiorly to the patient's left. As the

*From the Departmen-t of Medicinie, University of Toronto,and the Cardiovascular Unit, Toronto General Hospital.This work was supported by the Ontario Heart Foundationand the National Health Grants Administration, Canada.

INTSTNJTANEOUS--TELECTRICAL

RESULTANT

I- VECTOR LOOP\I

Fig. 1. A v-ector representation of ventricular depolariza-tion.

process continues, these forces increase in magni-tude and become directed inferiorly. The terminalforces are directed inferiorly and to the right. Ifthis loop were inscribed in a counterclockwisedirection, the initial forces would be directed in-feriorly to the right and the terminal ones

superiorly to the patient's left.The QRS, T and P loops are spatial and do not

lie in the same plane. The usual method of studyingthem consists in visualizing these loops from thefront, top and side of the patient's body; hence thefrontal, horizontal and sagittal plane projections ofthe spatial loops. These three plane projectionscomprise the vectorcardiogram (VCG).Over the years, there has been a great contro-

versy concerning the relative merit of the differentsystems of electrode placement used to record theVCG. The tetrahedral system of Wilson and thecube system of Grishman have enjoyed considerablepopularity. In 1956, Ernest Frank of the Universityof Pennsylvania described a precordial lead systemwhich he showed experimentally to be superior toothers.1 2 We have adopted the Frank system in our

laboratory, and the following briefly describes thetechnique involved.

Basically, any system of electrode placement invectorcardiography seeks to achieve one aim, i.e.to determine all the electrical activity arising inthe heart and to divide this into three differentcomponents acting at right angles to one another.Commonly, these are referred to as the X com-

ponent acting transversely in a horizontal direction,

1131

ASSOCIATION

VAOSOCRAIrnON

1132 ABRAMSON AND BuRrON: SPATIAL VECTORCARDIOGRAPHY CanaO.M.6 . 83

R the plates. The beam deflection may be representedby a vector. The length of this vector will vary

ANATOMICdirectly with the magnitude of the potential dif-

SPACEMIC M ference. Similarly, the electron beam is deflected+ in a vertical direction if a potential difference acts

across the vertical plates. This deflection may be/THORAX, \represented by another vector. If both potentials

1A act simultaneously, then the electron beam is de-flected not horizontally or vertically but diagonally.

2 The vector representing this third deflection is the450 trigonometric resultant of the horizontal and verti-

cal vectors. Thus the beam is under the influencec4.59R of electromotive forces acting at right angles to

l . one another.Fig. 2

ANATOMIC. SPPCEthe Y component acting vertically, and the Z com- Rponent acting in an anteroposterior direction. TheFrank system of electrode placement determinesX, Y and Z by means of seven electrodes, one on Vthe back of the neck in the midline, one on the 8left leg, and five on the chest. The right leg is +grounded. All chest electrodes are placed at the 2.9ORlevel of the fifth interspace in the midsternal line. / . ,Figs. 2, 3 and 4 describe the electrode placement vvAand the circuitry used to determine X, Y and Z. I _ - -Electrodes are placed in the midstemal line (E), inthe middle of the back (M) and in the left andright midaxillary lines (A and I respectively). A E Cfifth electrode (C) is placed on the left precordiumso that a line joining (C) to the centre of thethorax (0) exactly bisects the 900 angle formedby lines OA and OE. The position of C is de-termined by means of a protractor, for electrodeplacement must be accurate if this system is to bevalid.A cathode ray oscilloscope is used to obtain a

vector loop. If a potential difference acts acrossthe horizontal plates of an oscilloscope, then thebeam of electrons is influenced by these plates onlyand is deflected towards or away from them, de-pending on the relative positivity or negativity of F

ANATOMIC +I

Fig. 4HIORAX \\^,

This principle is utilized in obtaining the frontal,. \4S 1 sAx horizontal and sagittal plane projections of the

\ 45S/ / vectorcardiogram. In order to obtain the frontal45\ \ /plane projection or view of the vector loops ob-

c)ZC tained from the front of the patient's body, Vx, thepotential acting in a horizontal direction, is thrown

oeM of iacross the horizontal plates of a cathode ray oscil-

CY . i N ' tloscope. Simultaneously, Vy, acting vertically, is{n̂ te thrown across the vertical plates. These potentialspI Xi m

I vary throughout the heart cycle but, at any par-Fig. 3 ticular instant, the beam of electrons is influenced

ABRAMSON AND BURTON: SPATIAL VECTORCARDIOGRAPHY 1133

by both Vx and V,. to produce a resultant deflectionwhich as it changes from moment to moment out-lines the frontal plane projection of the vector-cardiogram. By using different combinations ofVx, VY and V, across the opposing plates of theoscilloscope, one obtains the horizontal and sagittalprojections as well. Vx and V7, give the horizontal

projections; V7 and V! the sagittal. Permanentrecords are obtained by photographing the loops.The Einthoven triangle, a fundamental concept

of electrocardiography, is based on the assumptionthat the heart is at the geometric centre of an

equilateral triangle formed by the right and leftshoulders and left leg. It describes the directiontaken by the axes of the standard and unipolarlimb leads and defines, as well, arbitrary positivityand negativity. This information may be simplifiedby transposing it to the multiaxial scale depictedin Fig. 5. This shows more clearly than does theEinthoven triangle the actual direction taken bythe axes of the various leads of standard electro-cardiography. It may be seen that the positive lead1 axis acts in a horizontal direction to the patient'sleft, lead aVF acts vertically and inferiorly. Leads2 and 3 each act 300 to the vertical, lead aVL 300superiorly to lead 1 and lead aVR 300 superiorlyto the horizontal direction but to the patient's right.

Superimposed on this system of lead axes inFig. 5 is a single vector R, acting +40° to thehorizontal. The sole purpose of this system of leadsis to determine R as accurately as possible. Un-fortunately all six leads cannot do so to the same

extent. The electrical force represented by R willcause maximal deflections only in those leadswhose axes are roughly parallel to the direction ofR and minimal deflections in those leads whoseaxes lie at right angles to R. An arbitrary principleof electrocardiography is that an electrical forcewill be registered as an upright or positive de-flection if the force is directed towards the exploringelectrode in a unipolar lead or towards the positiveelectrode in a bipolar lead. Thus, in the examplecited, the force represented by vector R willregister maximally in leads 2 and aVR and mini-mally in leads aVL and 3. The deflection in lead 2will be positive and that in lead aVR negative.The galvanometer deflections of the standard

electrocardiogram (ECG) are obtained by super-

imposing the system of lead axes shown in Fig. 5upon the frontal plane projection of the spatialvectorcardiogram (VCG). Thus the relationshipbetween the ECG and the VCG is a very closeone, for the ECG is indeed derived from the VCG.Fig. 6 demonstrates this relationship. It is thefrontal plane projection of the VCG of a patientwith an atrial septal defect. The lead axes of thestandard ECG have been superimposed. There isa time interval of 0.004 second between each dew-drop-shaped dot in the QRS loop of the VCG. Sinceeach dot thins out in the direction of loop inscrip-tion, one can tell that the QRS loop has been in-

scribed in a clockwise direction. The smaller P and

LEAD aVR a

300 _,o °30 LEAD 1

R30'0 300

LEAD 3 LEAD 2

LEAD aVF

Fig. 5. Simplifled Einthoven triangle.

T loops are superimposed one upon the other. Thesignificance of the various positive and negative de-flections in the ECG now becomes apparent. LeadaVR shows a deep Q or negative deflection and a

small R or positive deflection because most of theelectrical forces in the heart are directed awayfrom the direction of lead aVR. Only the terminalforces as described by the terminal portion of theQRS loop are directed towards aVR, hence thelate positive deflection. The initial forces as de-scribed by the initial portion of the QRS loop are

directed away from the lead 3 axis, hence an

initial negative deflection or Q wave; and as theforces change direction, become directed towardslead 3 and increase in magnitude, this change ismanifested by a tall positive deflection or R wave

following the Q wave. Similarly leads 1 and aVLshow initial positive R waves and secondary nega-tive S waves. The initial Q wave in lead aVF isgreater than that in lead 2 and the Q wave in lead3 is greater than the one in lead aVF, for the initialpart of the loop is heading approximately 1800away from lead 3 whereas it is only 1200 away

from the axis of lead 2. Since the terminal part of

Fig. 6.-Frontal plane projection wvith corresponding ECG.

Canad. M. A. J.Nov. 26, 1960, vol. 83

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1134 ABRAMSON AND BURTON: SPATIAL VECTORCARDIOGRAPHY

the QRS loop is heading away from lead 2, thislead shows a secondary negative deflection or Swave which is barely perceptible in lead aVF andabsent in lead 3. The most upright P and T wavesare present in lead 2, for the P and T loops of theVCG are directed along the axis of this lead. LeadaVR has an inverted P and T wave, for this leadaxis is directed 1500 away from the axes of thesetwo loops. Thus the six standard and unipolar limbleads may be derived from the frontal plane pro-jection of the VCG, and similarly a rough frontalplane projection of the P, QRS and T loop may besketched from these leads.The vectorcardiogram shown in Fig. 7 a, b and c

is that of a 27-year-old subject with a normal heart.In each plane projection one may see a small Ploop, larger QRS loop and intermediate-sized Tloop. In the frontal plane the QRS loop has beeninscribed in a clockwise direction. It is directedinferiorly and to the patient's left. Normally in thisplane, the QRS loop may be inscribed either clock-wise or counterclockwise. It may even have afigure-of-eight configuration. The normal QRS looptends to assume the shape of a flat disc, lying moreor less in the plane of the interventricular septum.Thus we view it almost on edge when studying itfrom the front of the patient. The P and T loopsare both directed inferiorly and to the left.

In the horizontal plane projection the QRS loopis always inscribed in a counterclockwise direction.The loop is directed first anteriorly and thenposteriorly because of early septal depolarizationand subsequent depolarization of the free wall ofthe left ventricle. Lead V1 of the electrocardiogramshows a small initial R wave because the QRS loopinitially is directed towards this electrode. Thedeep late S wave is due to most of the QRS loopheading away from the V1 electrode. Left lateralprecordial leads usually show an initial Q wave forthe same reason. The QRS loop at first is headingaway from the V,-6 position. As the terminal part ofthe loop heads towards these electrodes, a tall Rdeflection results. The T loop is directed anteriorlyand to the left. The P loop is also directed to theleft; it may be anterior, but never posterior.The left sagittal plane projection always shows

counterclockwise inscription of the QRS loop in thenormal heart. As in the horizontal plane, the QRSloop is directed first anteriorly and then posteriorly.The anterior position of the T loop is typical. TheP loop is directed inferiorly.

Toscano-Barbosa, Brandenburg and Burchell3 ofthe Mayo Clinic first pointed out in 1956 thatvectorcardiography assists in the differentiation ofdifferent types of atrial septal defects.The ostium secundum defect is usually centrally

situated and may be corrected under hypothermiaalone. The ostium primum defect, whether singleor associated with a complete atrioventriculariscommunis defect, is situated in relation to the A-Vvalves and requires the use of a pump-oxygenatorfor correction. Thus preoperative differentiation of

Canad. M. A. J.Nov. 26, 1960, vol. 83

Fig. 7 a, b, c.-Normal vectorcardiogram.

these two types of defects is important for propermanagement. The QRS loop in the secundum de-fect is situated inferiorly, whereas that in theostium primum defect is situated superiorly. Thisdifference is especially apparent in the frontalplane projection.

Fig. 8.-(a^) Ostium secundum defect, frontal plane. (b)Ostium primum defect, frontal plane.

Fig. 8a shows the frontal plane projection of theVCG of a patient with surgically proved ostiumsecundum defect. The QRS loop is situated belowthe isoelectric point and is inscribed in a clockwisefashion. The QRS loop shown in Fig. 8b is that ofa patient with surgically proved ostium primumdefect. It is situated above the isoelectric pointand is inscribed in a counterclockwise direction.The primum defect somehow has lifted the loop.It is generally felt that this specific loop configura-tion is due to a disturbance in conduction resultingfrom the very low position of the defect.

Different abnormalities of right ventricular de-polarization may produce practically identicalECG's and yet distinctly different VCG's. Figs. 9and 10 show the precordial leads of two electro-cardiograms. In each the QRS duration is 0.10

Canad. M. A. J. ABRANISON AND BURTON: SPATIAL, VECTOR{:ARDIOGRAPHY 1135Nov. 26, 1960, vol. 83

: . V2 - VW2e4 V3+ 8

Fig. 9

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V1 .2Vh..4Fig. 10

seoond. Because of the presence of an RSR patternin lead V1 and a wide slurred S in VG;, most cardi-ologists would interpret this pattern as that ofincomplete right bundle branch block. On viewingthe horizontal plane projection of the VCG in eachinstance, one can immediately see that althoughthe precordial leads are almost identical, these

Fig. 11.-(a) Incomrplete right bundle branch block, hori-zontal pla.ne. (b) Right ventricular di.stolic overload,horizontal plane.

leads have been derived from two quite dissimilarQRS loops. In Fig. lla the QRS loop shows normalcounterclockwise inscription with a marked termi-nal delay. The initial one-inch segment of loop hasbeen inscribed in 0.024 second, the terminal one-inch segment in 0.032 second. Such a pattern isindicative of delayed right ventricular depolariza-tion. Fig. llb shows a horizontal plane projectionin which the QRS loop is inscribed in a clockwisefashion as in right ventricular hypertrophy. There isno terminal delay. Both initial and terminal one-inch segments of the QRS loop have been inscribedin 0.020 second. Although the electrocardiogramappears to be that of incomplete right bundlebranch block, these vector studies show clearlythat this electrocardiogram is really a manifestationof right ventricular diastolic overload and not ofdelayed right ventricular depolarization. Thus these

two abnormalities involving the right side of thelheart can be differentiated immediately by meansof the vectorcardiogram.

It is not yet clear whether the vectoreardiogramcan diagnose myocardial infarction not apparentin the standard electrocardiogram. Milnor feelsthat the vectorcardiogram is of help in cases of oldinfarction showing a small Q wave in lead t3 ordiminished R waves in the precordial leads.4 Itmutst be remembered that the abnormal Q wave,so important in the electrocardiographic diagnosisof infarction, is a manifestation of the initial seg-ment of the QRS loop. Abnormalities of the termi-natl segment of the QRS loop result in barelyperceptible electrocardiographic changes. It maywvell be that the VCG is superior to the ECG indiagnosing myocardial infarction. Certainly morework remains to be done in this important field.

SUNINIARYSome of the basic priniciples of spatial vectorcardi-

ography have been reviewed aand the fact that thestacndard electrocardiogram is derived from this morebasic study has been emphasized. Both, in turn, aremianifestations of the same electrical phenomena arisingwithin the heart. Although it is too early as yet toassess its ultimate value as a diagnostic aid, there cainbe nio doubt thalt spatial vectorcardiography has adefinite place in clinical medicine.

Figs. 2, 3 and 4 are reproduced from Circulation, 13:737, 1956, by kind permission of the American Heart Associ-ation, Inc., and the auithor, Dr. Ernest Frank.

REFERE N CES

1. FRANK, E.: Circulation, 13: 737, 1956.2. Idem: Ibid., 10: 101, 1954.3. TOSCANO-BARBOSA, _., BRANDENBURG, R. 0. AND BURCIIELL,

H. B.: Proc. Staff Meet. Mla lio Clinu., 31: 513, 1956.4. MILNOR, W. R.: Proyr) Cardiorase. Dis., 1: 175, 1958.

DEATH WATCH

Psychic trauma has cropped up again as a medico-legalentity . . . in the recently raised question: Is a fatal heartattack caused by psychic trauma "accidental"? Yes, says theTexas Supreme Court, basing its opinion on expert medicaltestimony to the effect that a cerebral arteriothroimbosismight be precipitated by emotional stress and strain.The decision resulted in payment of double indemnity

by two insuLrance companies to the beneficiaries of a 44-year-old accountant who died of cerebral thrombosis morethan aimonth after witnessing a serious fire in his office.Although the arteriosclerosis found in his brain at autopsywas insufficient to have caused the thrombosis, the expertssaid hisi nervousness and excitement on seeing the firecould have produced damage to cell tissue not only in thebrain but in. other organs, too.The court, therefore, saw no difference between this case

and one of drowning or asphyxiation, where the "externaland violenft" force enters through the nose or mouth ratherthan the eyes, and causes dealth by injuring other organs.-MHedical News, September 28, 1960.