Chatelain, P.

Doriot, P. A.

Melchior, J. P.

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Usef ulness of realignement and "phase analysis" in the assessment of thesynchronism of regional lefl ventricular contraction and relaxationMelchior, J. P. (Geneva); Doriot, P. A.; Chatelain, P.Cardiology Center, University Hospital, CH-1211 Geneva 4IntroductionA great variety of models have been proposed forthe quantification of the left ventricular regionalcontraction from angiographic sequences. Most ofthem involve an enddiastolic/endsystolic image paironly, but could be extended without additional con-ceptual difficulties to all silhouettes of a selec-ted cardiac cycle. Comparisons of the differentexisting models have been perfonned by variousgroups on large samples of control subjects andpatients, but consensus on the best approach isstill not obtained.The aim of the present study was not to demonstratethe superiority of our model (described in the fol-lowing). Nevertheless, we believe that it does notpresent certain (in our judgement) unsatisfying as-pects of some chordal, radial or "center-line" de-rived models.Our main goal was rather to investigate followingpoint which, in our opinion, should be clarified inpriority and conclusively:Should the silhouettes be repositioned relativelyto the enddiastolic Silhouette (for instance) pre-viously to any quantification, in order to elimi-nate äs well äs possible translation and rotationcomponents of the heart motion during the cardiaccycle, relatively to the x-ray imaging System ?The results obtained in our patient studies mayconstitute a valuable answer to this Key question.A Criterion for the Usefulness of RealignementFrom a physical point of view, it is obvious thattranslation and rotation of the left ventricularcavity in the image during the cardiac cycle shouldbe compensated, äs one would eliminate such motioncomponents to study the oscillatory deformation ofa kicked, flying rugby ball. This is equivalent tosay that the contraction pattern of the left ven-tricle (LV) should be considered äs shape modifica-tion of the Silhouette rather than äs apparent"wall motion". Putting the weight onto the shapeleads to design a model in which the shape specifi-city of the LV Silhouette plays a dominant role.This in turne leads to let a caracteristic point ofthe valvular region and the apex govern the reali-gnement of each Silhouette, äs would the 2 poles ofthe rugby ball define the orientation ofquate coordinates System.the ade-However, even evidences must be supported by expe-rimental results in agreement with a well acceptedpostulate. Such a postulate fortunately exists: itstates that left ventricles of control subjectscontract and relax essentially in a synchrone fa-shion (when refered for instance to the mid-aorticpoint). The "phase analysis" technique is an idealtool for the investigation of contraction/relaxa-tion synchronism since its basic criterion is pre-cisely the degree of synchronism of the LV contrac-tion/relaxation. Superiority of realignement compa-red to non-realignement can thus be assessed byshowing that i t yields higher synchronism of thecontraction/relaxation in control subjects.Our contraction/relaxation model includes thereforepreliminar realignement of the silhouettes (rightanterior oblique 30 projection) by use of mid-aortic point and Silhouette long axis, and "phaseanalysis" of a complete cardiac cycle.The MethodBeginning with the enddiastolic Silhouette, thecontours of all silhouettes of the selected cardiaccycle are drawn on mask subtracted images (25 i/s)and stored in a VAX-11/750 Computer (Enddiastole isdefined by the R peak of the ECG). These nativecontours are then realigned by super i mposi tion ofthe mid-aortic points and of the "long axisM of thesilhouettes. The "long axis" of each Silhouette isdefined by the mid-aortic point and an apical pointdetermined in following way (Fig. 1): First theusual long-axis of the Silhouette through the mid-aortic point and the farthest contour point is de-termined; then a line perpendicular to this firstaxis is drawn at 19/20ths of its length (measuredfrom the mid-aortic point). This auxillary line de-fines a small apical area, whose center of gravityis the second point of our new "long-Axis" (Thisreduces the variability of apex determination).The first (enddiastolic) contour is then divided by2x64 equidistant points: 64 before and 64 after theapex (anterior, respectively inferior region of theLV). Linking these 128 points to the correspondingpoints of all following contours creates 128 shor-BIOMEDIZINISCHE TECHNIK · BAND 31 · ERGÄNZUNGSBAND - 1986 SEPTEMBER-161-Figure 1: Principle of Silhouette realignement.Figure 2: Enddiastolic/endsystolic Silhouette pair,before and after realignement.tening segments (Fig. 2). "Phase analysis" is per-fonned on the selected cardiac cycle äs follows:For each segroent a contraction-relaxation time-curve is obtained by a 2-harmonics Fourier fit ofits measured lengths in the course of cardiac cycle(Cardiac cycle duration is nonnalized to 360 ). Thephase (Pha) of the first hanaonic is the first pa-rameter obtained. Two other parameters, the "timeof peak contraction" (TPC) and the "time of peakrelaxation" (TPR), are defined äs the times of themaximum respectively of the minimum value of thefirst derivative of the fitted curve. Thus, 3 pa-rameters expressed in degrees are assigned to eachsegment, each one reflecting an aspect of the tirae-evolution of the segment during the cardiac cycle.The tegments are coloc1 coded according to the valueof the considered paramoter and displayed at thei rrespective location in the enddiastolic/endeystollcsilhouettes pair. This yields 3 parametric Images.The histogram of each parameter is also computed,with mean and Standard deviation (SD).Study on Control SubjectsWe have first studied 13 control subjects (C)without and with contour realignement. In our expe-rience the means of the 3 histograms are not use-ful. But the 3 SD, which reflect the degree of syn-chronism of the contraction or relaxation, showclearly (p<0.02)) that the postulated synchronismof left ventricular contraction and relaxation incontrol subjects is better reflected if realigne-ment is performed:C (13) SD of Pha SD Of TPC SD of TPRNot realigned9.2 + 4 . 0 1 5 . 1 + 10.814.9 + 9.9Realigned 5 .8*2 .3 6 . 5 + 2.0 6 .5+2 .1SD: mean Standard deviationsThe Standard deviations of the SD are also lowerafter realignement, which is a further. finding. quite in agreement with the postulate of high syn-chronism in control subjects. · .·.Study on Patients .Sixteen patients with a proven myocardial infarc-tion (MI) were studied next. As can be seen in thetable below, all 3 SD appear to be sensitive indi-cators of pathological States when compared to theSD of normal subjects:MI (16) SD of Pha SD of TPC SB of TPRNot realigned 23.3 + 16.226.8 + 16.133.4 + 14.4Realigned 13.9+ 7.9 13.2+ 7.5 23.8 + 12.9SD: mean Standard deviations ~~ ~The SD in this group of MI patients are also redu-ced by realignement, but, unlike to the case of• control subjects, this is not relevant. However, afurther interesting result consists in the decreaseof the Standard deviations of the §D in the sensethat it reflects less overlap of the individual SDvaluejbetween the MI and C groups. Realignement al-lows thus for a better differentiation of MI pa-tients from normal subjects, whereby the parameterTPR appears to be more sensitive than the 2 others.Regional amplitude of contraction was also studiedin these 16 patients. After realignement hypokine-sia was detected, in the 16 infarcted territoriescorresponding to the occluded coronary artery.Without realignement hypokinesia was not detectedin one patient and localized in a wrong territory(unrelated with the occluded vessel and the ECG Q-waves) in 2 patients. . 'ConclusionRealignement of contours provides in control sub-jects a higher homogeneity of each 3 parameters,in agreement with the, basic postulate that leftventricles of normal subjects contract and relax ina synchrone fashion. Realignement results also inroore sensitivity in detection and localization ofasynchronism, and reduces erroneous localization ofhypokinesia. The parameter TPR appears to be moresensitive than the 2 others for the detection ofisehende states.BIOMEDIZINISCHE TECHNIK · BAND 31 · ERGÄNZUNGSBAND ·" 1986 SEPTEMBER-162-

Usefulness of realignement and "phase analysis" in the assessment of the synchronism of regional left ventricular contraction and relaxation

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