Asynergy of right ventricular wall motion in man

J

THoRAc CARDIOVASC SURG

1989;97:104-9

Asynergy of right ventricular wall motion in man Canine studies have shown a correlation betweenimtantaneous segmentallengtm in the right ventricular free wall and chamber volume, pressure, and stroke work. To determinewhether such correlations exist in intact man, we studied the temporal relationshipsbetweenchord dynamics in various regions of the right ventriclein 21 heart transplant recipients with apparently normal right ventricular ftmctioo. Patients were examined by biplane radiography while performing various maneuvers (e.g., Valsalva maneuver~ Computer-aided analysis of biplane radiograms of five surgically inserted radiopaque tantalum right ventricular myocardial markers was used to calculate interpoint chord Iengtm at 33 msec sampling intervals. Two patterns of right ventricular chord asynergy were defined: (1) An akinetic chord had an amplitude of less than 2.0 mm during the course of at least one beat; (2)an out-of-phase chord was more than a quarter periodout of phase from the averagecurve(derived from all concurrentlymeasured marker pairs during each maneuver) for at least one beat COlL'iidering all chords (n = 978),60 chords (6.1%) were akinetic and nine chords (0.9%) were out of phase. Excluding the ootftow tract markers (n = 581), 33 chords (5.7%) were akinetic and five chords (0.9%) showed out-of-phase movement During some maneuver, at least one akinetic chord occurred in 57% of patients and out-of-phase chords in 33% of patients. Most right ventricular regions were implicated in asynergic motion, including the right ventricularfree wall, acute margin,and ootftow tract The frequency and distribution of asynergy in right ventricular chord dynamics observed in this study suggests that changes in a single right ventricular dimension may not accurately reflect global right ventricular events.

Kenley W. Chin, BS,. George T. Daughters, MS,. Palo Alto, Calif., Edwin L. Alderman, MD,b and D. Craig Miller, MD,c Stanford. Calif.

Studying the right ventricle has been difficult because of its complicated geometry, contraction pattern, and mechanical interaction with the left ventricle." Right ventricular (RV) systole has been characterized as a sequential, peristalsis-like contraction pattern with contraction beginning at the inflow tract, extending across the sinus portion, and terminating at the conal region.v' or a sequential contraction pattern starting at the apex and ending at the conus." The RV outflow tract or infundibulum, derived from the embryonic bulbus corFrom the Department of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation,' Palo Alto, Calif., and the Division of Cardiology," Department of Cardiovascular Surgery," Stanford University Medical Center, Stanford, Calif. Supported by the David Krupp Memorial Fellowship and National Heart, Lung, and Blood Institute Grant HL29589. Received for publication Feb. 19, 1988. Accepted for publication July 25, 1988. Address for reprints: Kenley W. Chin, BS, Department of Cardiovascular Physiology and Biophysics, Research Institute of the Palo Alto Medical Foundation, 860 Bryant St., Palo Alto, CA 94301.

104

dis,7,8 is an anatomically and physiologically distinct region that contracts later and longer than the inflow

tract.v'

Recent studies in canine subjects reported that a single RV chord dimension, perpendicular to the RV long axis, correlates in a linear fashion with directly measured RV flow, volume, and stroke work." 10 Dimensional change of this chord was measured with epicardial ultrasonic transducers. Earlier studies investigating the nature and uniformity of RV and left ventricular (LV) systole in dogs, and LV function in intact man, used radiopaque myocardial markers to measure two-dimensional motion of a planar projection of the three-dimensional changes of ventricular geometry. 2, II We used the tantalum marker technique I I to study the dynamics of individual RV chords in various regions of the right ventricle in intact human subjects. We compared the three-dimensional instantaneous interpoint distances between markers over two to six consecutive beats as patients performed various physiologic maneuvers. The dynamic motion of RV chords (range 3 to 15 chords, average 9.3, standard deviation 2.7) during

Volume 97 Number 1

Asynergy of RVwall motion in man 105

January 1989

MARKER PAIR

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3-5 4-5

a total of 80 physiologic maneuvers was calculated. Asynergic chords were defined in each patient with reference to other chords and the timing of the electrocardiographic R wave as being normal, akinetic, or out of phase. The observed asynergic chord dynamics suggests caution in the use of single RV chord dimension changes as a reliable means of estimating global RV function in man.

Methods Patient selection. Informed consent was obtained from 21 patients undergoing cardiac transplantation for the implantation of LV and RV intramyocardial markers and subsequent radiographic studies in accordance with the requirements of the Committee on the Use of Human Subjects in Research at the Stanford University Medical Center. There were no complications resulting from the implantation of markers or the follow-up studies. Placement of intramyocardial RV markers. At the time of operation, LV intramyocardial tantalum markers were placed as described previously. II In addition, up to six radiopaque markers were placed in the RV myocardium (average 4.9, standard deviation 0.6) in a subepicardial position in specific regions of the right ventricle. One marker was placed in the RV outflow tract, one at the apex (near the left anterior descending coronary artery), one in the free wall of the sinus portion, one or two in the interventricular septum, and one along the acute margin near the atrioventricular groove (Fig. 1). The exact placement of the markers varied from patient to

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Fig. 2. Chord length versus time in a patient performing a Valsalva maneuver: Note that the chord between marker 2 and marker 3 appears subjectively to be out of phase with the others. patient (Table I), as no markers were inserted within 5 mm of any visible coronary arterial branch or through epicardial fat that obscured the myocardial surface. Data acquisition. During physiologic maneuvers with the patient in the supine position, the markers were imaged cinefluoroscopically at 30 frames per second. Sequential biplane recordings were made in the 3D-degree right anterior oblique and 60-degree left anterior oblique projections. Physiologic maneuvers performed included the Valsalva maneuver, inspiration, expiration, and, in selected patients, leg raising. Images were recorded on an Ampex DRlOA analog video disc recorder (Ampex Corp., Redwood City, Calif.). The electrocardiographic R-wave amplitude was also recorded on the video image. After each fluoroscopic study, (x, y) coordinates of the marker images in each view (along with the R-wave timing) were digitized frame-by-frame with a Tektronix light pen (Tektronix, Inc., Beaverton, Ore.) coupled to a HewlettPackard 2115A minicomputer (Hewlett-Packard Company,

The Journal of Thoracic and Cardiovascular

Chin et al.

10 6

Surgery

Table I. Marker distribution by patient No. and position of RV intramyocardial markers Patient

Outflow tract

Acute margin

I

2 3 4

5

6 7 8 9 10 II

12 13

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Total"

5

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4 I I

0

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16 18 3 10 16 17

6

80

Akinetic

9 2 22

1

0 3

"Total column is the number of maneuvers of each type observed.

Andover, Mass.). Marker coordinates were corrected for magnification and distortion and then transferred to an IBM System/Sri computer. I I Data reduction and analysis, Software was developed to calculate the degree to which the periodic change in each three-dimensional R V intermarker chord dimension coincided with the amplitude and phase of an average dimension curve, which measured the sum of all intermarker distances during a given maneuver. First, the two separate right and left anterior oblique data files were merged, each marker position being defined in three-dimensional space ([x, y, z]; external laboratory coordinates). A phantom planar matrix of radiopaque markers was used to determine that the standard deviation for a given two-dimensional interpoint length was 0.4 mm, II and the reproducibility of a given three-dimensional interpoint length in this study was 0.7 mm. Next, instantaneous (i.e., every 33.3 msec) values of all

Apex

Total

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5

1

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4 4 5

5 5 5 5 5

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2 2 2 2 3 3

6

2

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6

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16 17 18 19 20 21

Totals

Free wall

2

14 15

Normal inspiration Normal mid expiration Normal end expiration Feet raised Early Valsalva ("squeeze") Valsalva release

Septum

possible intermarker chord dimensions were calculated for each beat (referenced in time to the onset of the R wave). The data were then smoothed by means of a moving average. A small number of points on the chord dimension curves, which appeared as sharp spikes more than 2.0 mm from both adjacent values, were judged to be due to digitizing error and the value of the point was replaced by the average of the two adjacent points. An average dimension versus time curve was calculated simply as the sum of all individual chord dimensions at each sampling instant, divided by the number of chords. The average curve and each chord's curve were plotted with an HP2647A graphics terminal coupled to an HP9872T plotter (Fig. 2). Two patterns of asynergic chord motion were arbitrarily defined: (I) An akinetic chord had a dimension change amplitude of less than 2 mm during one or more beats; (2) an out-of-phase chord had a nadir (i.e., a minimum for each beat), which occurred either before or after the nadir of the corresponding average curve by more than 25% of the R-R interval. The period of a cardiac cycle (t RR ) was defined as the R-R interval. The phase of each chord for each beat (in each individual, for each maneuver) was calculated as the difference between the time (referenced to the peak of the R wave) of the chord's minimum (t m ) and the time of the minimum of the average curve (T m), expressed as a fraction of the period. t., - Tm Phase = - - t RR

See Fig. 3 for an example of an out of phase chord. Because the RV outflow tract is sometimes considered to be a distinct anatomic region, two categories of asynergic chords were examined: (I) asynergic chords involving all marker

Volume 97 Number 1

Asynergy of RV wall motion in man

January 1989

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TIME (seconds) Fig. 3. Definition of an out-of-phase chord: The change in chord length versus time for the average chord (see text) and an individualchord suspected of being out of phase are plotted. The time difference between the minimum (for a given beat) of the average curve (T m) and the minimum (for the same beat)of the suspect chord (t m ) is calculated as a fraction of the R-R interval (t RR) . If this fraction is greater than 0.25, the chord in question is defined as out-of-phase with other chords in the right ventricle.

CD

AM

5/11 (45%)

Apex

RVOT

pairs, and (2) asynergic chords excluding the outflow tract markers.

Results Seven of 21 patients (33%) had at least one out of phase RV chord, and 12 patients (57%) had at least one akinetic chord during some physiologic maneuver. Considering all marker pairs and all maneuvers (n = 978), nine chords were found to be out of phase (0.9%), and 60 chords (6.1 %) were akinetic. Excluding outflow tract markers (n = 581), five chords were out of phase (0.9%) and 33 chords (5.7%) were akinetic during some maneuver (Table 11). Regional distribution of abnormal marker motion. Chords from all patients were examined for the frequency of regional akinetic and out-of-phase chords. Chords most consistently implicated in asynergic motion were between markers in the free wall and either the outflow tract or acute margin, as shown in Fig. 4. Conversely, chords least likely to show asynergy, that is, to be representative of the average curve, were between markers in the septum and either the free wall or apex. Physiologic maneuvers involved in abnormal chord motion. Specific maneuvers resulting in at least one abnormal chord between any two regions are listed in Table II. Note that normal inspiration, the respiratory

AM

0/11

Apex

(0"10)

Fig. 4. Schematic representation of the regional distribution of asynergic RV chords: The first number between the two marker sites defining a chord represents the frequency of asynergy in that chord. The second number is the total number of chords examined between the two markers. The percentage of asynergic chords is also given for comparison purposes. RVOT. Right ventricular outflow tract; AM, acute margin. A, Akinetic chords. B, Out-of-phase chords

phase most commonly used for right and left ventriculography, was associated with five akinetic chords and one out-of-phase chord. The early ("squeeze") phase of the Valsalva maneuver was most commonly associated with asynergic chords, and other physiologic maneuvers also resulted in some asynergic chords. Discussion Our results concur with earlier studies reporting the irregular nature of the motion of the R V outflow tract

The Journal 01

1 0 8 Chin et al.

(conus region)3.s,7,8 and RV free wall contraction in different regions. I, 4-6 Pouleur and associates I found no consistent relationship between dynamic RV chord dimensions and chamber events during the cardiac cycle in dogs; under normal conditions, the tension-velocitylength relations of the RV free wall were comparable to those of the left ventricle only during early ejection, and RV ejection was load dependent. Morris and associates," however, reported that the relationship between a single RV chord dimension and global RV events changed only minimally over a wide range of preload, afterload, and stroke volume in dogs. Our results demonstrate that, in the human right. ventricle with apparently normal function, chords will become asynergic occasionally during a variety of physiologic maneuvers that are expected to change loading conditions: For example, asynergic. chord movement occurred in patients during the early phases of the Valsalva maneuver when venous return to the right ventricle is decreased. Although a linear correlation between the dynamics of a particular RV chord dimension and global RV measurements, for example, rate of RV pressure development and pulmonary artery flow (which have been used to derive R V stroke volume and RV stroke work), may well be. present in a homogeneous group of anesthetized dogs," our present observations reveal that asynergic R V chord dimension changes can occur in conscious patients after transplantation. A previous study placed ultrasonic transducers 10 inm apart on the RV free wall, defining a single chord perpendicular to the RV long axis, within an area of approximately 2 to 3 square centimeters," In contrast, the myocardial markers in these transplanted hearts were placed farther apart and in several different RV regions. A limitation of the present study is that it was conducted in the transplanted human heart. It is conceivable that trauma during procurement and preservation of the donor heart, the denervated state of the orthotopically transplanted heart, and the absence of an intact pericardium all could cause deviations from normal RV dynamics. It has been .found, however, that LV systolic function is apparently normal in these hearts,12,13 as are right atrial and pulmonary artery

pressures.": 14 In the present study, measurement of absolute dimensions was relatively unimportant, because these results are based mainly on the phasic relationships of various intermarker (relative) dimensional dynamics. All chords were judged for their abnormality with reference to the other chords in a given maneuver and the R-wave peak. The 0.7 mm system reproducibility for interpoint dimen-

Thoracic and Cardiovasculal

Surg811

sions arose from the combined effects of the resolution of the light pen system, parallax, and operator variabil ity in positioning the light pen. I I Estimating LV chamber (or global) events from a single LV chord dimension IS gave impetus for use of a single RV dimension as a technique to measure global RV events.v" Measurement of global R V events has historically been difficult because of the greater geometric complexity of the right ventricule (compared to the left ventricle), 1-6 which does not lend itself to simple geometric models to calculate RV chamber volume, for example. The present study demonstrates that akinetic RV chords occur in 57% and out-of-phase RV chords in 33% of transplanted hearts with apparently normal RV function, with the R V free wall site being involved in 30% of the out-of-phase chords observed and in 24% of the akinetic chords. Therefore, we urge caution in assuming correlation between the dimensional changeof a single RV chord and global R V chamber dynamics in the human heart. 1.

2.

3.

4.

5.

6.

7. 8.

9.

10.

REFERENCES Pouleur H, Lefevre J, Van Mechelen H, Charlier AA Free wall shortening and relaxation during ejection in the ~nine right ventricle. Am J Physiol 1980;239:H60l-13. Rushmer RF, Crystal OK, Wagner e. The functional anatomy of ventricular contraction. Circ Res 1953;1:162· 70, Armous JA, Pace JB, Randall We. Interrelationship of architecture and function of the right ventricle. Am J PhysioI1970;218:174-9, Raines RA, LeWinter MM, Covell JM. Regional shortening patterns in canine right ventricle. Am J Physiol 1976;231:1395-1400, Santamore WP, Meier GO, Bove AA. Effects of hemodynamic alterations on wall motion in the canine right ventricle. Am J Physiol 1979;236:H254-62. Meier GO, Bove AA, Santamore WP, Lynch P. Contractile function in the canine right ventricle. Am J Physiol 1980;239:H794-804. Keith A. Fate of the bulbis cordis in the human heart. Lancet 1924;2:1267-73. March HW, Ross JK, Lower RR. Observations on the behavior of the right ventricular outflow tract, with reference to its developmental origins. Am J Med 1962; 32:835-45. Morris J, Pellom GL, Hamm OP, Everson CT, Wechsler AS. Dynamic right ventricular dimension: relation to chamber volume during the cardiac cycle. J THORAe CARDIOVASC SURG 1986;91:879-87. Hamm OP, Everson CT, Freedman BM, Pellom GL, Christian C, Wechsler AS. The passive right ventricular volume-dimension relationship in the isolated canine heart. Surg Forum 1984;35:266-8.

Volume 97 Number 1 January 1989

II. Ingels NB, Daughters GT, Stinson EB, Alderman EL. Measurement of midwall myocardial dynamics in intact man by radiography of surgically implanted markers. Circulation 1975;52:859-67. 12. Borow KM, Neumann A, Arensman FW, Yacoub MH. Left ventricular contractility and contractile reserve in humans after cardiac transplantation. Circulation 1985; 71:866-72. 13. First WE, Stinson EB, Oyer PE, Baldwin rc, Shumway NE. Long-term hemodynamic results after cardiac trans-

Asynergy of RV wall motion in man

1 09

plantation. 1 THORAC CARDIOVASC SURG 1987;94:68593. 14. Young 18, Leon CA, Short HD, et al. Evolution of hemodynamics after orthotopic heart and heart-lung transplantation: early restrictive patterns persisting in occult fashion. 1 Heart Transplant 1987;6:34-43. 15. Van Trigt P, Spray T, Pasque M, Christian C, Fagraeus L, Wechsler AS. Comparative effects of dopamine vs. dobutamine on venrricular contractile mechanics. Circulation 1983;68(Pt 2):I1I152.

Bound volumes available to subscribers Bound volumes of THE JOURNAL OFTHORACIC AND CARDIOVASCULAR SURGERY are available to subscribers (only) for the 1989 issues from the Publisher, at a cost of $55.00 ($72.00 international) for Vol. 97 (January-June) and Vol. 98 (July-December). Shipping charges are included. Each bound volume contains a subject and author index and aU advertising is removed. Copies are shipped within 60 days after publication of the last issue of the volume. The binding is durable buckram with the JOURNAL name, volume number, and year stamped in gold on the spine. Payment must accompany all orders. Contact The C.V. Mosby Company, Circulation Department, 11830 Westline Industrial Drive, St. Louis, Missouri 63146-3318, USA; phone (800) 325-4177, ext. 351. Subscriptions must be in force to qualify. Bound volumes are not available in place of a regular JOURNAL subscription.