Festschrift for Sir John McMichael

The spatial vectorcardiogram in diagnosis

D. EMSLIE-SMITH K. G. LOWEDepartment of Medicine, University of Dundee

THE spatial vectorcardiogram is an approximatemodel of the moment-to-moment changes indirection and magnitude of the unbalanced elec-trical activity of the heart in three dimensions.In practice it is recorded from the surface ofthe human thorax through specially placed elec-trodes, so the information it records is essentiallysimilar to that recorded by scalar (surface) elec-trocardiography. Although the basic electrical in-formation may be similar, it is, however, dis-played in a different manner by the two differentmethods. Each method of display can emphasizeparticular features of cardiac excitation.

In a survey of 500 records and 10 years' ex-perience of clinical and experimental vector-cardiography we have found there are at leasttwo aspects of the cardiac electrical activity thatare better demonstrated in the QRS loop of thevectorcardiogram (VCG) than in the QRS com-plex of the scalar electrocardiogram (ECG). Thefirst involves directional properties that are theequivalent of inconspicuous phase-relationshipsbetween simultaneously recorded complexes inscalar leads (Fig. 1). The superiority of the spatial

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FIG. 1. The upstrokes of the R waves in the orthogonalscalar leads X and Y start simultaneously but areinscribed at different rates. In (a) the peak ofR in lead Xprecedes that in lead Y so the vector loop is inscribedclockwise; in (b) the peak of R in lead Y precedes thatin lead X so the loop is anticlockwise.

VCG in demonstrating this aspect is graduallybeing appreciated by electrocardiographers. Thesecond aspect, which does not seem to be sowell appreciated, concerns the speed of inscrip-tion of various parts of the scalar QRS complexor the QRS vector loop.

Scalar records are often made by direct-writ-ing machines that tend to slur the complexes andare greatly influenced by factors such as theheat of the stylus. Even in good photographicrecords the speed of inscription of different partsof the complex may be very hard to estimate.The simple VCG, being a plot of voltage againstvoltage, does not by itself allow an appreciationof time. In most modern vectorcardiographs,however, timing is introduced by an interruptionof the tracing by a regular blanking-pulse. Thiscan only be seen while the cathode beam ismoving, but during the inscription of the QRSloop changes in the rate of inscription are veryreadily appreciated. When the beam moves slowlythe blanking-pulses are close together; when itmoves fast they are wide apart. The speed ofinscription can only be accurately assessed fromconsideration of the three-dimensional spatialVCG and not from the QRS loop projected on asingle plane, for example the frontal, alone.We present here some examples of the help

afforded in diagnosis by the spatial VCG throughits ability to demonstrate properties of speedand direction during the electrical excitation ofthe ventricles.

Abnormal direction of inscriptionNormally the vectors resulting from the initial

forces of ventricular excitation are directed for-ward, downward and to the right and then in-scribe an anticlockwise loop in the horizontalprojection. If, however, the unbalanced electricalactivity during the first few milliseconds is al-tered by a loss of excitable myocardium antero-laterally the initial crochet of the QRS loop inthe horizontal plane may be inscribed clockwise.This very important clue to antero-lateral myo-cardial damage may not be apparent in scalarleads.

Figure 2 shows the scalar ECG and frontal

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FIG. 2. Antero-lateral myocardial infarction. There has been a lossof electrical forces anteriorly and to the left with resulting clockwiseinscription of the QRS loop in the horizontal plane. 0 = origin, QRS= QRS loop, T = T loop, arrows indicate the direction of inscription.

FIG. 3. Infarction of the left side of the interventricularseptum with left bundle-branch block. The initial crochetis directed to the right and the whole QRS loop isinscribed clockwise in the horizontal plane. In otherrespects the loop is that of left bundle-branch block.

and horizontal plane VCGs of a man of 44years with acute pulmonary oedema. Apart

from a rather abnormal low voltage complex inlead V3 the scalar ECG is unhelpful. On theother hand, the horizontal VCG shows the wholeQRS loop inscribed in an abnormal clockwisedirection, the initial crochet being directed for-wards and to the right. This suggests lack ofearly electrical activity antero-laterally and iscompatible with antero-lateral infarction or otherdamage.

Figure 3 shows the scalar and vector recordsof a woman of 53 years who presented withcongestive cardiac failure and a history of 2years' chest pain and breathlessness on exertion.The scalar ECG shows the pattern of completeleft bundle-branch block, the only unusual fea-ture being the complex in lead V5. Again, how-ever, the horizontal QRS loop is inscribed en-tirely in a clockwise direction with an initialcrochet directed forwards and to the right. Thisvectorcardiographic pattern is characteristic ofleft bundle-branch block complicating a leftseptal infarction (Scott, 1965).

Abnonnal speed of inscriptionIn normal ventricular excitation the spatial

vectorcardiogram is usually more slowly in-scribed during the first and last 15 msec thanduring the intervening part of the loop. Certainabnormalities of ventricular excitation are char-acterized by abnormally slow initial or terminal

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FIG. 4. Type A (left) ventricular pre-excitation. There is a veryslow conduction velocity of the initial forces (delta vector)directed anteriorly. Asterisks denote the delta vector.

crochets, notably ventricular pre-excitation, rightbundle-branch block and post-infarction conduc-tion disturbances.

Ventricular pre-excitation gives rise to thedelta wave in scalar records. In the spatial VCGthis is represented by an abnormally slow in-scription of the initial part of the loop. Fig. 4shows the scalar and vector records from apatient with Type A (left) ventricular pre-excitation. The abnormal speed of inscriptionand direction of the first part of the loop areeasily seen and can be contrasted with the equi-valent part of the loop in Fig. 5. The slurredupstroke of R in right precordial leads inpatients with right ventricular hypertrophy maysuperficially resemble the delta wave of Type Apre-excitation, especially when the PR intervalis at the lower limit of normal, but inspection ofthe VCGs readily differentiates the two patterns(Figs. 4 and 5).An abnormally slow inscription of the ter-

minal part of the QRS loop is seen in rightbundle-branch block. Fig. 6 shows the recordsfrom a patient with Type B (right) ventricular

pre-excitation and right bundle-branch block.This unusual combination of abnormalities isresponsible for the abnormal slowing of boththe initial and terminal parts of the QRS loop(Robertson et al., 1963). The full diagnosis wouldbe difficult from an inspection of scalar recordsalone.

Intraventricular conduction defects, other thanclassical bundle-branch block, may be due tomyocardial infarction or cardiomyopathy. Thecommonest is post-infarction block, either intra-infarction block, characterized by delay in theinitial ventricular forces, or peri-infarction block,characterized by terminal delay (Castellanos &Lemberg, 1966). These are much more clearlydemonstrated by vector than by scalar methods.Fig. 7 shows an example of peri-infarctionblock in an elderly woman with ischaemic heartdisease. The VCG in the frontal and sagittalplanes shows a loss of the normal inferior forcesand strongly suggests a diaphragmatic infarctiondespite the presence of small r waves in leadsII, III and aVF. As is characteristic of peri-infarction block the very slow terminal part of

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FIG. 5. Right ventricular hypertrophy with the PR interval atthe lower limit of normal (0-12 sec) and a slurred upstroke ofR inright chest leads. The VCG shows normal conduction velocities.

FIG. 6. Type B (right) ventricular pre-excitation and right bundle-branch block. Asterisks mark the slow conduction at the beginning(delta vector) and end (R.BBB) of the QRS loop.

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FIG. 7. Inferior (diaphragmatic) infarction with peri-infarctionblock. The large asterisk indicates the absence of inferior forces andthe small asterisks mark the slow inscription of the terminal partof the QRS loop.

the QRS loop lies in the quadrant opposite theinfarcted area.

Vectorial interpretationThe spatial VCG is determined by the spread

of electrical activity through the myocardium.Its interpretation must similarly be made in termsof altered spread of excitation.

Abnormalities of speed of inscription give in-formation about altered conduction velocities.Abnormal directions of inscription reflect ab-normalities in the balance of forces in theventricles. Thus both addition of forces, as inhypertrophy, and subtraction of forces, as ininfarction, can alter the balance.

This kind of interpretation can be applied tothe solution of clinical problems. For example,the interpretation of an RSR' pattern in scalarrecords from right chest-leads is sometimes diffi-cult, but the spatial VCG can help.

Figure 8 shows records from a man of 21

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FIG. 8. Right bundle-branch block. The terminalpart of the QRS loop is displaced anteriorly and to theright with a slow terminal conduction velocity (asterisk).

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II III aVR ahV VF Mounting electrocardiograms for vectorialanalysis

In Britain it is customary to mount the twelve-*_ lead records of the scalar ECG around the

Einthoven triangle. For vectorial analysis it seemsmore logical to mount the records along thelead axes of a corrected twelve-lead spatial refer-

ys 96 ~ence system based on Burger's scalene triangle(Fig. 11). This method of display emphasizesthe correlation between the vector and scalarforces and aids the vectorial interpretation ofthe scalar records.

FIG. 9. Right ventricular hypertrophy. Normal con-duction velocities. Apart from the initial crochet thewhole QRS loop is displaced forward and to the right.

years with an atrial septal defect. The spatialVCG shows that late unbalanced electrical forcessituated anteriorly and to the right have dis-placed the terminal part of the loop in thatdirection and a slow conduction velocity hascaused a slow 'run in' from the right. This loopis characteristic of right bundle-branch block.

Figure 9 shows records from a boy of 11years with congenital heart disease. The hori-zontal plane VCG shows that apart from theinitial crochet the whole QRS loop is displacedforward and to the right because of unbalancedelectrical activity in that direction. While hereagain there is a 'run in' from the right, theconduction velocity is not abnormally slow andthe pattern is that of right ventricular hyper-trophy.

Figure 10 shows tracings from a boy of 15years. The scalar records again show an RSR'pattern from right chest-leads, but the spatialVCG shows that the late R is associated with anormal terminal crochet in the vectorcardiogram.The long axis of the QRS loop is oriented alittle further backward than usual, so the ter-minal crochet produces a conspicuous R wavein lead V1. There is no abnormality of con-duction velocity or of balance of forces. It is anormal record.

FIG. 10. A normal QRS loop whose long axis is rotatedrather far backward, bringing the terminal crochet (tc)into the axis of right chest leads.

ConclusionBecause the QRS loop of the spatial vector-

cardiogram represents the unbalanced electricalactivity of the ventricles it gives informationabout the spread of excitation through the ven-tricular muscle. Its importance in electro-cardiographic theory, in research and in teach-ing is now accepted. It can also help in theelucidation of ambiguous scalar ECGs in clin-ical cardiological practice.

AcknowledgmentsWe gratefully acknowledge the assistance of the Scottish

Hospitals Endowment Research Trust and a research grantfrom the British Heart Foundation.

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Festschrift for Sir John McMichael 45

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FIG. 11. Scalar records mounted along the lead axes of a corrected twelve-leadspatial reference system based on Burger's scalene triangle.

ReferencesCASTELLANOS, A., JR & LEMBERG, L. (1966) Post-infarction

conduction disturbances, Vectorcardiography-1965 (Ed.by I. Hoffman and R. C. Taymor), p. 219. North-Holland,Amsterdam.

ROBERTSON, P.G.C., EMSLIE-SMITH, D., LOWE, K.G. &WATSON, H. (1963) The association of type B ventricularpre-excitation and right bundle-branch block. Brit. Heart J.25, 755.

SCOTT, R.C. (1965) Left bundle-branch block-A clinicalassessment. Amer. Heart J. 70, 691.

Renal disease in pregnancy

K. F. FAIRLEYRoyal Women's Hospital,

Melbourne

PRISCILLA KINCAID-SMITHQueen Victoria Hospital,

Melbourne

SURPRISINGLY, little data is available about thematernal and foetal prognosis when pregnancy iscomplicated by renal disease.Over the past 8 years we have studied various

aspects of renal disease in pregnancy and ourfindings are summarized below.

Renal infection in pregnancyThis is certainly the commonest form of renal

disease in pregnancy. Frank pyelonephritis ofpregnancy occurs in about 1% of women andin over 30% of women who show over 100,000organisms/ml in a urine specimen collected at

their first antenatal visit (Kincaid-Smith, 1965;Kincaid-Smith & Bullen, 1965). About two-thirdsof all cases of pyelonephritis of pregnancy canbe prevented by treatment of asymptomatic bac-teriuria (Kincaid-Smith & Bullen, 1965).The incidence of asymptomatic bacteriuria

varies from 4 to 15% in various parts of theworld (Kass, 1960; Kincaid-Smith & Bullen,1965; Le Blanc & McGanity, 1965; Stuart, Cum-mins & Chin, 1965; Little, 1967). The compli-cations of pregnancy bacteriuria also vary indifferent series. We related the high incidence ofprematurity, foetal loss and pre-eclamptic toxae-

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