| Ventricular Dimensions by Coronary Cineangiography: Outer Contour, Wall Thickness, Valve Plane Displacement, Position of Ventricular Septum |
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The ventricular dimensions of the heart in situ in healthy adults were determined by echocardiography (EC). Such as outer contour, left ventricular posterior wall and ventricular septum thickness, valve plane displacement and the position of ventricular septum (VS) was studied.
Heart echocardiograms were obtained from nine healthy adults (of ages between 25 and 35 years) in four steps, using an ATL ultrasound scanner.
M-mode registrations and ECG-triggered mechanical sector scanning registrations were recorded by means of a dry silver recorder (Tektronix).
Measurements were made at midpoint of endocardial, and other lines.
The examinations were also video-recorded, in order to provide for more detailed analysis.
An ECG-lead was applied to the person lying on the left side.
A parasternal sector registration in the plane of the long heart axis was recorded.
A M-mode line was, with help of a sector image, positioned as exactly perpendicular as possible to the long heart axis. The line was penetrating at the point at which the cross-section of the left ventricular lumen is at its maximum (Fig 3-1 A, sector image of person No. 2).
A trace was recorded on paper in the optimally attainable position, at the end of exhalation Fig. 3-1B, M-mode of person No. 2).
The usual aim of such EC examinations is to study the variation of ventricular volumes [131], as well as the chanin thickness of ventricular walls. In the present case, however, the aim was primarily to study outer contour variation of the left ventricle during the cardiac cycle. This implies that the epicardium and pericardium, as well as the endothelial surface of VS in the right ventricle (RV), were studied.
It is often difficult to assess the variation of wall thickness of the RV in healthy adults. This is due to the right ventricular wall being thin, and to the various sources of error. It was therefore thought to be of no value to assign points of reference and monitor changes in the RV wall.
In instances where it nevertheless was possible to discern the right ventricular wall and its pericardium, no movement at the pericardial-epicardial interface was recorded.
For the sake of easier inter-individual comparison of ventricular interface movement over a full cardiac cycle, nine registrations were analysed. Maxima, minima and points of inflection was regarded (Fig. 3-1B).
The following EC events were defined by vertical lines a through k ("event lines", same symbols as for the corresponding events):
In addition to these events, some minor septal movements could be seen, that may be interpreted as equilibrating vibration phenomena. They were in most cases indistinct (they could only be identified in two of the volunteers), and have therefore not been given further consideration.
Cartesian coordinates for this M-mode registration were defined in the following way.
One event line a at its intersection with the epicardial - pericardial interface (base), is connected to the next such intersection. This connecting line defines the time axis (abscissa). Time zero is selected at the onset of the P-wave of a simultaneous ECG registration. Regarding events c through k, time zero is selected at the onset of the QRS-complex. P-Q time intervals are recorded individually.
The ordinata is directionally identical with the EC beam, with positive values in the direction of the probe.
Intersections were defined at lines a through k (in the beam direction), with the curves for:
( The curves are labeled {1},{2},{3} and {4} for the individual M-mode registrations. One of those curves are shown in Fig. 3-1C.)
Coordinates for the individual points of intersection were fed to a CAD-system, which reconstructed a M-mode for each of the original M-mode tracing. For one of them (M12), the reconstructed graph is shown in Fig. 3-1C.
The next step was the construction of a M-mode image containing the averaged information of individual registrations. This was done in the following way.
The time relation between events a through k was based on two independent points of reference i.e., atrial and ventricular contraction. The mean of PQ-intervals and RR-intervals was defined where event c and the point of repetition for the reconstituted cardiac cycle, respectively, were to be fixed. In other words, the mean of PQ-intervals was counted on the event c as reference.
Raw data given in Table I, show how often events at the left ventricular posterior wall (e, h or j) coincided with events at VS (d, f, g or i).
A standard LV dimension was obtained by averaging the distance defined by the base line and curve {3}, at event a, 59 mm. The total range at this point is 59 (-5,+3) mm and is indicated in Fig. 3-2 by a dotted line. The confidence intervals, at the other intersections of event lines, were calculated with a t-test on a 0.025 level and are marked with continuous lines.
The inner contour LV variation is given by curves 2 and 3.
Curve 2 was obtained by averaging the distance between the base line and intersections of event lines a, b, c, e, h, j and k with curve {2}, in the individual M-mode registrations (Table IIa).
Curve 3 was obtained by normalising the point of intersection of curve {3}, to a value of 59 mm at event a. The other points (b, c, d, f, g, i, k) were then normalised accordingly (Table IIb).
LV outer contour variation is given by curves 1 and 4.
Curve 1 was obtained as the distance mean between the base line and curve {1}, in the individual M-mode registrations at events a, b, c, e, h, j and k.
Curve 4 was obtained by adding to the normalised value of 59 mm, the average for the distance between points of intersection at events a, b, c, d, f , g, i and k, and curves {3} and {4}, respectively (Table IIIa, Table IIIb).
The effects of atrial systole and the early systolic ventricular phase (isovolumetric phase) on the ventricular septum and LV posterior wall, are shown in Table IV.
By means of sector scans along the major heart axis, positions were sought for allowing optimum recording of valve plane motion. M-mode registration was then performed in three positions: M2, M3 and M4.
The first position (M2) is given by the attachment of the posterior mitral valve leaf at the anulus fibrosus (Fig 3-3A, authentic sector image 22 from person no. 2).
The second position (M3) is given by the point of attachment of the anterior mitral valve leaf at the anulus fibrosus ( Fig 3-4A, authentic sector image 32).
The third (M4) is the point of attachment of the tricuspid valve at the medial part of the anulus fibrosus (Fig 3-5A , sector image 42).
The M-mode images obtained from the nine persons (cf.Fig 3-3B, Fig 3-4B, Fig 3-5B), M21 - M49, were reconstituted (Fig 3-3C, Fig 3-4C, Fig 3-5C). It is explained above in the case of M11 - M19, by definition of the following events:
A base line was drawn in M21 - M49 by connecting two intersections of event line b' with the valve plane (Fig 3-3B, Fig 3-4B, Fig 3-5B). This line forms the abscissa (time coordinate).
Time periods (in milliseconds) (Table Va, Table VIa and Table VIIa), were recorded for events a' through h' with reference to atrial events (starting with the onset of the P wave). Time periods were also recorded with reference to ventricular events (starting with the onset of the QRS complex).
Distances between base line and points of intersection of event lines a' through h' with valve plane, were measured by hand (Table Vb, Table VIb and Table VIIb). They were fed into a CAD-system, with reconstructed M-mode registration (Figures 3-3C, 3-4C, 3-5C).
Table VIII has values for the total displacement of the valve plane in M2-M4 (Table VIIIa), and its atrial contribution (Table VIIIb).
Because of possible interference with EC measurements, the complex morphology of the region between atria and ventricles was studied, for the purpose of exactly delimiting it.
That was done by dissection of a heart of a recently deceased adult. A triangular formation (in cross-section) of predominantly adipose and connective tissue with blood vessels was conspicuous. It was located in the zone between the posterior wall of LV and the posterior wall of the left atrium. It was in the same place from where the sector EC registrations for identification of valve plane motion were obtained (cf. Böhme [31]).
This composite tissue easily complies with elongation stress, and so adds some 10 to 15 mm to the extension of the AV-plane (Fig. 3-7A-B) (cf. [136], Fig. 3-9A-B, Fig. 3-9C).
No such region is observed in the corresponding zone between RA and RV. There is a groove though, just below the right auricle in which the right coronary artery is embedded (Fig. 3-8A-B).
It can also be seen how the chordae tendineae (with attached papillary muscles), are fixed at the anulus fibrosus. They are forming a bag-like connection, with the right ventricular muscle at the AV-plane. A similar (but less pronounced) form of attachment can also be noticed in LV.
The dimensional changes in anulus fibrosus, effected by atrial and ventricular systole, have been studied by Puff [134].
Analysis by "frozen image"-technique of LV outer contour in systole and in diastole, was attempted while simultaneously recording the position of the valve plane.
Sector EC images, triggered on the R-peak of the QRS-complex, were scanned in systole and diastole (Fig. 3-9A-B; authentic images from person no. 2).
Systolic and diastolic images for each subject were superimposed by using a digitizer tablet, a CAD-system and an x, y-plotter. This was made to visualise the differences with respect to LV and LA outer contour, and with respect to the motion of the valve plane. Fig. 3-9C is the differential image obtained for person no. 2.
Instrumentation allowed the freezing of only one image at a time, which had to be documented before the next could be obtained after repeated gating. This implies that between 10 and 20 seconds elapsed, between the recording of corresponding systolic and diastolic images. Factors such as changed positioning of probe and/or object, changed respiration period, defective gating etc., may influence the overall result, and necessitate the discarding of pairs of images. Those remaining are thus selected and the result may therefore be biased.
The image pairs were analysed by drawing lines L(s) and L(d) in the systolic and diastolic images respectively (Fig. 3-9C). The lines were drawn from the area adjacent to the ventricular septum where the aorta originates (or alternatively from where the aortic valve is seen). They were drawn to the attachment of the mitral anulus fibrosus at the posterior wall. This latter point is easily identified in systole by the configuration of the afore-mentioned adipose tissue wedge, although in diastole this is not the case.
It was high reflectivity of the posterior mitral valve leaflet, and the endocardium and pericardium had a curved form in diastole. Therefore it was necessary to assign that point of attachment to a special site. The site was placed, where the distance from the pericardium to the endocardial surface of the adipose wedge corresponds to the thickness of the myocardium in diastole.
In this way, opposite points of attachment were defined (M2' and M3'), comparable with points of attachment of the AV-plane, recorded in mode M2 and M3 (cf.Fig. 3-3A, 3-4A). Movement of the valve plane in M2' and M3' is presented in Table VIIIc under "frozen image".
Outer contour variation of LV was determined in two pairs of intersectional points, designated PI and PII, at VS and LV posterior wall, respectively ( Fig. 3-9C). They were defined as the intersection between the outer surface of LV and a line parallel with the EC-beam.
In systole, PIs is situated near the aortic valve and PIw at the posterior wall, where the adipose wedge meets LV muscular tissue.
The second pair, PIIs and PIIw, are positioned at VS and LV posterior wall as near to the apex as possible.
It was provided for, that the outer contour for the area surrounding it can be recorded in both systole and diastole1. The difference between the systolic and diastolic images is given in Table IXa, Table IXb, under "frozen image w" and "frozen image s", respectively.
1 That is, PIIs had
to be placed 1-2 cm below the valve plane in systole, which means a distance of 3-4 cm in
diastole.
PIIw had to be placed approximately 1 cm apically
from PIIs
Analysis by video replay is a repetition of the study described above, but with results analysed in a slightly different way.
Sector images of LV along the major axis of the heart were stored, and later replayed on a video screen. Images from the same respiratory phase representing extremes of ventricular and atrial systolic position of the valve plane were selected. The outer contour of LV and LA was delineated with a felt pen directly on the screen.
The part of the valve plane comprising aortic and mitral valves, was similarly delineated.
Images from a few cardiac cycles were replayed in slow motion, to check that the contours had been correctly traced. Felt pen traces were transferred to transparent sheets and images similar to that in Fig. 3-9C were obtained. Sometimes slight variations were noted despite proper control of respiration phase, probably due to minor movements of the EC probe. In this case several traces were drawn checked and transferred as described above. The images were analysed in a manner analogous to the procedure described earlier.
Results are given in Table VIIId under "video" and in Table IXa, Table IXb under "video w" and "video s", respectively.
There are several limitations to echocardiography, that should be kept in mind [143, 181].
Bony tissues and air give complete reflection, and thus form barriers from behind which no information can be gathered. In the present case, these barriers are the sternum, the anterior portions of the ribs and the lungs.
Areas that allow the heart to be explored by EC, are therefore rather limited and form "windows". This implies that it is not always possible to get ultrasound images of the heart in the particular projection which is desired. Skew projections have to be used, which may distort information in that muscles for instance will sometimes look much thicker than they actually are. Live registration will also be impaired.
The sonocardiographic images, displaying the intricate system of movement of the different parts of the heart, therefore often demand an interpretation that takes these limitations into account. If technical and operational sources of error are disregarded, three others remain:
Table VIIIa, Table VIIIb, Table VIIIc, Table VIIId shows the movement of the valve plane visualised by ultrasound. Mean values given under "M-mode", "frozen image" and "video" differ despite the subjects investigated being identical and the close proximity of M2 and M2', and M3 and M3' respectively. The reason for this disparity lies in their sources of error.
EC M-mode registration of the valve plane looks deceptively simple. The transducer cannot, however, be directed at the structural entities in the valve plane easiest to detect i.e., the valves themselves. That is because of their displacement, deviating from the movement of the valve plane itself. They vanish from the image when opening. It would be desirable to direct the beam at points of attachment of the mitral valve in M2, M3 and M4. For anatomic as well as for technical reasons and because of the movement of the valve plane in the direction of the major heart axis, the following happens. M-mode registration does not depict the movement in one point, but rather in a series of points over a curved area.
This implies that for points of definition M2 and M3, the movement recorded will be too small ( cf. Fig. 3-10). M4 at the attachment of the tricuspid valve medially at the anulus fibrosus has the proper prerequisites for correct reproduction. It may though nevertheless show a movement that is slightly exaggerated.
The contribution of atrial systole to the movement of the valve plane is approximately 25 % (Table VIIIb). From the movement of the valve plane in M2, M3 and M4 (Fig. 3-6A-E), we can see how the supposed isovolumetric presystolic phase b' through d' affects valve plane motion.
M-mode "frozen image" and "video" are two-dimensional images in the direction of the long heart axis. They allow a reduction of projection errors in the direction of valve plane movement. The figures of the "frozen image" series result from different heart beats, with rather long intervals between the maximum diastolic (atrial systolic) image and the minimum systolic image. Absolute maxima and minima of the valve plane in these images depend on how they are triggered. This differs from beat to beat, since the timing of sector images is restricted to 30 images per second. Furthermore this differs from beat to beat because diastolic triggering is carried out on the preceding (or actual) R-peak in the QRS-complex.
Therefore, "frozen image" values for valve plane motion would be too small. In addition to this, respiratory variation, changes in heart rate and instability in transducer attachment are to be considered.
In contrast to the "frozen image" technique, "video" recordings (where single beats can be analysed) do not show these deficiencies to the same extent. There is no triggering problem, but low updating frequency is still problematic. Delimitation of the valve plane in systole and diastole may constitute a source of error in both situations. The highest average values were obtained from "video". They should not, however, be exaggerated since the most common errors of the method (including projection errors) have tendency to reduce displacement values.
Considering the errors of the method, a realistic estimation of the displacement of the valve plane can be achieved. The best approximation to true values for valve plane movement at the side of the LV, is thus given by the displacement mean value recorded in M2 and M3. The result is 22 and 19 mm respectively, as shown under "Video" in Table VIIId.
The motion of the valve plane at the side of the RV could not be analysed by video-replayed sector scans. The mean from M4 in Table VIIIa under "M-mode"(24.9 mm) is probably slightly exaggerated.
It is uncertain whether the true movement of the valve plane is greater at its periphery, than at the site from which the aorta and pulmonary artery ascend. Experiments show on the whole a larger movement at the right side. This is especially true for M-mode studies, summarised in Fig. 3-6C, which illustrate the combined effect of ventricles and atria on the valve plane. They demonstrate that the movement of the latter ceases almost entirely after the "fast filling phase".
It is furthermore possible to form an opinion about the rest time between events g' and a', and how it is affected by increasing heart rate. It is obvious that g' and a' will coincide at a certain heart rate.
Fig. 3-6C demonstrates the divergence in time of events a' through g' between M2, M3 and M4. By variance analysis it was found that there is no statistically significant difference in event time between M2 and M3. Such a difference was found though, for M4 relative to M2 and M3 regarding events a', b', c' and g' , and relative to M2 alone for e' as well. Event times for d' and f' coincide for all of them. That indicates that the velocity (v) with which point M4 "moves" (in the direction of the apex), is lower at the onset of ventricular systole than at its end. This enables the valve plane to catch up with point M2 (thereby reaching a higher velocity than that by which M2 "moves" apically at the LV valve plane side). This difference in velocity, combined with a possibly greater blood mass above the right valve plane, indicates that generated kinetic energy differ on the right side during the end of systole. It is greater than on the left side. This would also explain the occurrence of event i i.e., the second systolic maximum of VS in the direction of the LV (Fig. 3-2).
Beam direction of M-mode scans should be as perpendicular as possible to the surfaces of interest. This is difficult, since the working-mode of the heart and its curved geometric form make various parts of the heart wall pass through the beam during the cardiac cycle. That resulting in a constantly changing reflection pattern. Variation of LV and VS outer contour between events a to b (atrial systole), b to h (ventricular systole) and h to a (ventricular diastole) may therefore be exaggerated.
Regarding LV posterior wall, the papillary muscle constitutes a barrier to precise positioning of the EC beam, when trying to avoid thickening artefacts in systole. Positioning the beam closer to the sharply curved posterior wall surface adjacent to the valve plane, will avoid interference of the papillary muscle. There will instead be a disadvantage, with a substantially exaggerated movement of the outer contour of the posterior wall (Fig. 3-9C).
Values for LV posterior wall motion are presented in Table IXc. They have been obtained by subtracting two distances. One is the distance between the base line and the point of intersection for event line h with curve 1. The other is the distance between the base line and the point of intersection for event lines a, b and e with curve 1 (Fig. 3-2).
The values for displacement of VS are shown in Table IXd. They have also been obtained by subtracting two distances; one is the distance between points of intersection formed by event lines a, b and d with the base line and with curve 4 respectively. The corresponding distance is obtained by intersection of event line f with the base line and curve 4 (Fig. 3-2).
Note that the displacement of VS between systole and diastole, provided that atrial contraction and the presystolic phase are disregarded, is close to zero. Neither is VS seen to be thinning from the onset of atrial systole and ventricular presystole.
The LV posterior wall though, is under ventricle systole making some displacement in the direction of VS. Furthermore, the LV posterior wall is seen to be thinning from the onset of atrial systole and ventricular presystole (cf. Table IVa, Table IVb and Fig. 3-2).
If the prevailing view (that the heart is pumping by squeezing motions) is true, the situation is rather peculiar; only one part of the LV is participating in this squeezing motion.
For a long time little interest has been shown [152] in ventricular outer contour variation. Most of it has been concerned with the nature and location of regional variation, as determined by kymographic methods [89]. Interpretation of such measurements usually stresses the importance of any contour variation observed and not the fact that total variation is small per se. In contrast to this, interest has been focused on inner contour variation. LV cine-angiography is now being a routine method for the evaluation of LV function. With this method, the problem is how to view the LV endocardial outline [26]. This, combined with the partial systolic cavity obliteration resulting in a virtual wall thickening near the apex, gives an essentially false idea of ventricular contraction and thus of cardiac pumping (cf. [35, 52, 105, 156, 162]).
As mentioned earlier, observation of a wall moving to the centre of the ventricle, does
not necessarily mean that the heart is working in a predominantly squeezing mode. It can
also be the result of the ultrasound reflection not occurring at the same site in systole
and diastole (Fig. 3-9C).
This consideration initiated the two-dimensional EC experiments, reported in Table IXa, Table IXb under "video"
and "frozen image". They differ only with respect to sources of error, which are
reduced in the "video" experiments.
Measurement of LV outer contour comprised, on one hand, the determination of posterior
wall displacement (in positions PIw and PIIw). On the other hand, it
comprised displacement of the RV endocardial interface of the VS (in positions PIs and PIIs). (PI = intersectional point one, close to the
AV-plane; PII = intersectional
point two, away from the AV-plane; w = posterior wall; s = septum, Fig.
3-9C).
Examination of sources of error for "video" and "frozen image" indicate that results from "video" are closest to true displacement values:
When "video" values are compared with those from M-mode registration in the short axis direction (reported in Table IXc and Table IXd), VS movement was found to correlate well (Table IXd). But M-mode registration is always preformed with a beam-position more close to the mitral valve, than in "video"-technique; therefore errors from "defective registration of lateral movements" (Fig. 3-10) will be larger for the M-mode registration.
The studies in persons no. 6 and 7 were excluded, because of pulmonary tissue and ribs hindering optimal positioning of the probe, resulting in exaggerated movement of VS. (In contrast, the same persons displayed a rather "normal" outer contour movement of the posterior wall (Table IXc), compared with movement in point PIw under "video w" (Table IXa)).
There is a difference between the movement of VS and the posterior wall in intersectional point pairs close to (PIS/PIw), and not so close to (PIIS/PIIw), anulus fibrosus. It is probably due to the following:
The pulmonary artery and ascending aorta are attached to the anterior part of the AV-plane, and are relative fix to the surroundings of the heart. Also the apex is relatively fix to the surroundings. Therefore, when the AV-plane moves in the direction of apex during systole, the posterior part of the AV-plane will move more easily than the anterior part. This creates a momentum that can be felt, which causing the apex to beat against the chest wall.
The "rocking heart" phenomenon seen in pericardial effusion, can be due to the same momentum. It can also be due to the redistribution of fluid around the heart, which is working within the boundaries set by the pericardium and surrounding tissues (constant outer form). A corresponding cyclic redistribution of fluid around the healthy heart is not possible.
By digitising left ventricular wall and septum displacements registered by M-mode in 9 healthy adults, it was possible to get an average of the posterior wall and septal outer contour movement during a heart cycle.
These findings were compared with outer contour variation. This was obtained by comparison of maximal diastolic ventricular sector image in the direction of the long axis (including atrial systole) with the minimum systolic sector image. It was made by frozen image and also by a video replay technique.
It was found that when projection and registration errors were taken into account, the mean value of the outer contour variation close to the AV plane was between 1-2 mm; at apex it was practically reduced to zero.
An analogous registration was performed to investigate the motion of the AV-plane. When the obtained values were compared, and projection and registration errors were taken into account, the motion of the AV-plane was about 21 mm on the left side; on the right side it was 25 mm.
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