Extensive Myocardial Blood Flow Distribution Through Individual Coronary Artery Bypass Grafts

Extensive Myocardial Blood Flow Distribution Through Individual Coronary Artery Bypass Grafts* Albert]. Kolibash, M.D.; 00 Richard P. Lewis, M.D.;f John S. Goodenow, M.D.;t Charles A. Bush, M.D.;§ and

MarcR. Tetalman,M.D.11

The regional myocardial perfusion distrlbntions of cor· onary artery bypass grafts were studied in 61 patients who received 162 grafts. Selective intragraft lnstilla· tlons of radioactive-labeled macroaggrepted albnmin particles were used to study perfusion. The extent of lndividnal graft perfusion was assessed in 100 patent grafts. Regional myocardial blood flow distn"bntion was similar to the blood flow distribution of the native vessel receiving the graft in 64 of 100 grafts and less than that expected of the native vessel in 12 grafts. However, 24 grafts demonstrated a blood flow distribution pattern which extended beyond the normal distribution ex-

pected of the native vessel receiving the graft. This extensive perfusion could be attributed to collateral vessels or retrograde flow. A high Incidence of both graft and native vessel occlusion was found in areas receiving blood from these distant grafts with extensive distributions (16/24), and left ventricular wall motion was preserved or siguiflcandy improved postoperatively in 28/31 segments in such areas. When comparing angiograpbic and sclntlgrapbic methods of evalnating myocardial perfusion, the angiopam underestimated the full extent of graft blood flow distribution in 13 of 24 in· stances (54 percent).

coronary artery bypass surgery has now become a widespread form of therapy in patients with coronary artery disease. 1-s The primary aim of a revascularization procedure is to provide sufficient blood flow to potentially ischemic or underperfused areas of myocardium. Therefore, graft patency, graft B.ow rate, and the amount of myocardial mass perfused by a graft should all contribute significantly toward the success of a revascularization procedure. Several investigators have emphasized that the graft B.ow rate is one of the most important factors influencing graft patency.4-7 Others have made the observation that the amount of myocardial mass perfused by grafts is variable. 8-11 The majority of these studies have been performed at the time of surgery or shortly thereafter; as such, there are few longterm studies of graft physiology other than angiographic assessment. Another question which remains unanswered is

whether or not a patent graft can provide blood B.ow, via collaterals, to ungrafted areas of the heart with severe native vessel disease or to areas of the heart where a graft is occluded. Since graft occlusion invariably occurs,3 the myocardial blood flow distribution pattern of remaining patent grafts might well assume greater significance. Recent developments of myocardial imaging techniques provide methods of assessing myocardial perfusion beyond the postoperative period. One such method is the instillation of radioactive-labeled macroaggregated albumin particles ( MAA) directly into the coronary circulation. 10-11 This technique enables the evaluation of myocardial blood flow distribution at the pre-capillary level. Although useful information concerning myocardial perfusion can also be derived from noninvasive imaging with the use of 201 thallium, l2-Ui the images obtained with thallium reflect perfusion of the entire heart. Thus, it is not possible to evaluate the perfusion distribution of a single graft. However, by selectively injecting radioactive MAA into a graft, the area of blood flow distribution of that graft may be qualitatively assessed. 15-18 The purpose of this investigation is to define resting myocardial blood flow distribution provided by coronary artery bypass grafts more precisely, thereby extending our knowledge of the physiologic capabilities of grafts.

•From the Divisions of Cardiology and Nuclear Medicine, The Ohio State University Hospitals, Columbus, Ohio. Supported in part by a grant from the Central Ohio Chapter of the American Heart Association. ••Assistant Professor of Medicine, Division of Cardiology. tProfessor of Medicine, Division of Cardiology. :tPostdoctoral Fellow, Division of Cardiology. §Associate Professor of Medicine, Division of Cardiology. I!Assistant Professor of Radiology, Division of Nuclear Medicine. Manuscript received March 15; revision accepted June 27.

CHEST, 77: l, JANUARY, 1980

EXTENSIVE MYOCARDIAL BLOOD FLOW DISTRIBUTION 17

METIIODS

Sixty-one patients who received 162 grafts underwent cardiac catheterization 1 to 36 months (average 7.9 months) following coronary artery bypass surgery. Although most patients at Ohio State University Hospital are encouraged to undergo a postoperative catheterization, this procedure is not performed routinely in all patients who have bad a myocardial revascularization procedure. Of these 61 patients, 27 were asymptomatic at the time of the postoperative catheterization, 29 bad improved symptomatology, and 6ve were unimproved. Ten patients received a single graft, 12 double grafts, 29 triple grafts, nine quadruple grafts, and one patient received 6ve grafts. The decision as to whether a patient received a saphenous vein graft ( SVG) or a left internal mammary anastomosis ( LIMA) to the left anterior descending artery (LAD) was made by the surgeon at the time of the procedure. If the LAD was a large vessel, a SVG was likely to be used. If the LAD was of moderate caliber, a LIMA was used providing it was of sufficient caliber and free of disease. All vessels grafted had at least 70 percent stenosis of their luminal diameters. Coronary angiography and selective angiography of the grafts were performed using the Judkins technique. Left ventriculograpby was performed in the 30° right anterior oblique (RAO) view, and segmental analysis of the ventriculogram was accomplished using the method of Leighton et al.11 This method provides quantitative analysis of wall motion along the anterior and inferior left ventricular wall. Since the perfusion distribution of the LAD includes the anterior left ventricular wall and that of the right coronary artery (RCA), the inferior heart border, the effects of perfusion through the LAD and RCA grafts upon left ventricular wall motion could be studied postoperatively. Following left ventricular angiography, selective angiography of the grafts and native coronary circulation was done. Myocardial perfusion was assessed with selective intracoronary and intragraft instillations of ee•tecbnetium and lllindium labeled MAA. A total of 200,000 to 300,000 particles were used in each patient. The particle size ranged from 10 to 40 microns. Instillation of radionuclides was performed slowly, in the resting state, 3 to 4 minutes following selective angiography. Catheter position was fluoroscopically verified prior to and during the instillations of the radionuclides. The ·same amount of isotope (approximately 0.5 mCi )was instilled into each graft in the same patient. There were no pressure changes, ischemic ECG changes, or complaints of angina during the instillations. As only two radionuclides were used, it was not always possible to study all patent grafts and both native vessels in every patient. Grafts to the LAD and RCA were

studied before other grafts or native vessels. If grafts to the LAD or RCA were occluded, or if these vessels were not grafted, patent grafts to other vessels and the native circulation were studied. Overall, it was possible to study the flow distribution patterns in 100 of 109 patent grafts. Myocardial perfusion imaging was performed within 20 to 30 minutes after angiography. A scintillation camera with a low-energy parallel hole collimator was used. An information density ( 1000 counts/ cm) was collected for all images in every case. Images were recorded on polaroid film in the anterior (ANT), 45° left anterior oblique (LAO) and left lateral (LAT) projections. The myocardial blood flow distributions of the 100 patent grafts were assessed on the basis of Figure 1. These schematic drawings represent views obtained at the time of scintigraphy. Although there is considerable variation of coronary anatomy from patient to patient, several discrete perfusion areas supplied by the individual coronary arteries remain constant and can be identified in each view. These areas have been defined on the basis of over 1,800 intracoronary studies in our laboratory as well as work by others. 18• 20 On the basis of these studies, a successful graft to the left anterior descending artery would be expected to supply all areas indicated by LAD, the circumflex, the areas indicated by Cx, and the right coronary artery areas indicated by RCA. Generally, there is minimal overlap of distributions in these speci6cally labeled areas. Since a normal perfusion .pattern for each coronary vessel can be defined by scintigraphic methods as described above, the area of myocardium perfused by each graft was compared to the perfusion pattern which would normally be expected to be provided by the native vessel which received that graft. The dominance of the vessel and the preoperative angiographic coronary anatomy pattern were taken into consideration when assessing blood flow distribution through grafts. Graft flow distribution was scored l+ if the graft perfused discernibly less area than normally supplied by the native vessel; "2+" if graft distribution was similar to the area supplied by the normal native vessel; and "3+" if a graft supplied areas of myocardium in addition to that normally supplied by the native vessel. Unprocessed images were independently interpreted and scored by two experienced observers who had no knowledge of clinical data. Major intraobserver and interobserver variations were 5 percent. Differences in interpretation and scoring were resolved by consensus of opinions. In order to compare angiographic and scintigraphic methods of assessing blood flow distribution patterns, the distribution pattern of each patent graft was evaluated angiographically witlwut knowledge of the scintigrams. A graft was angiographically scored 2+ if both antegrade flow and retrograde flow to the point of occlusion were present; l+ if less than one half of the native vessel was seen; and 3+ if other major vessels were visualized in addition to the vessel which received the graft. All angiograms were interpreted without Table I-Summary of Diatribution Scorea /or all Cra/ta

Graft

LAT LAO FIGURE 1. Regional blood flow distributions of major coronary arteries as seen in ANT, LAT, and LAO projections. Shaded areas indicate those areas of myocardium in which origin of blood supply varies depending upon dominance of coronary vessels.

18 KOLIBASH ET AL

No.

+1

LIMA

34

11

17

6

SVG LAn

15

0

8

7

SVG L Cx

25

0

24

SVGRCA Total

+2 +3

26

1

15

10

100

12

64

24

CHEST, 77: l, JANUARY, 1980

RC~:S ~ p

\

SVG TO LAD

AN

FIGURE 2. Scintigram shows extensive myocardial blood flow distribution through single SVG to LAD. Graft was scored 3+ as not only is the area of the LAD perfused, but activity is also seen in areas originally supplied by the RCA and left CX.

LAO

knowledge of the scintigrams by two observers with an interobserver variation of 8 percent with respect to scoring angiograms. A single observer scored the angiograms on two separate occasions with an intraobserver variation of 5 percent. Again, differences in scoring were resolved by consensus of opinion. Statistical analysis was performed with a computer-calculator ( Hewlitt-Packard 9600-B) using tests for paired data and chi-square analysis.

fu:suLTS Bl,ood Flow Characteristics of All Grafts A total of 109 grafts were found to be patent and 53 were occluded. Table 1 summarizes the myocardial blood flow distribution patterns of the 100 patent grafts which were selectively studied with the radioactive labeled particles. Seventy-six grafts had blood flow distribution patterns which were similar to or somewhat less than would be expected from the normal pattern of the native vessel receiving the graft ( 1 + and 2 + ). Twenty-four grafts provided blood flow distribution to areas of myocardium well beyond the normal distribution of the native vessel receiving the graft ( 3 + ). The majority of grafts scored 1 + were LIMA ( 11/ 12) and 23 of the 24 grafts assessed as 3 + involved either LAD or RCA. Figure 2 is a scintigram of a SVG to the LAD. This is an example of an

ANT

LAO SVG-RCA 3+

CHEST, 77: 1, JANUARY, 1980

extensive distribution pattern as the entire amount of activity seen on this scintigram is being supplied by a single vein graft. The blood flow distribution of this graft includes not only the interventricular septum (IVS) and apex (areas usually supplied by the LAD), but also the inferior left ventricular wall and part of the posterior wall, areas normally supplied by the RCA and Cx arteries respectively. Figure 3 is an example of extensive distribution from a graft to the RCA. In addition to supplying the right ventricle and inferior wall, the blood flow distribution of this graft includes over one half of the IVS and nearly the entire posterior and posterolateral wall, areas usually supplied by the LAD and Cx arteries respectively.

Native Vessel Patency, Graft Patency and Left Ventricular Wall Motion in Areas Receiving Blood from Distant Grafts (3+) Overall, 56 of 61 patients had at least one graft patent. The following information pertains to the patency of the native vessels and grafts in those 24 areas which received blood from the 24 grafts with 3+ distribution: occluded graft-negative vessel, 16 ( 67 percent); occluded graft-patent native vessel, 6; patent graft-occluded native vessel, 2; and

LAT

FIGURE 3. Images indicate extensive blood flow distribution to RCA which was scored 3+. Greater than one-hall of septum (arrowLAO) and nearly entire posterior (arrowLAT) and posterolateral walls are perfused from this graft.

EXTENSIVE MYOCARDIAL BLOOD FLOW DISTRIBUTION 19

Table 2--Compariaon o/ Percent Se.,,aental Slaortenin• Be/ore and A./ter a-.cularia:alion in A...lndireed:r Reeeilliq Blood From s+ Grafb•

1+,2+

3+

Normal Hypokinesis Normal Hypokinesis (20) (11) (16) (4) Preoperative

42 ±2

Postoperative

41 ±3

38±5

31±5

NS

P <0.005

P <0.05

S gnificance

13.6±2

43±5

15±5 23±7 . NS

*Numbers refer to mean values with standard error of mean.

patent graft-native vessel, 0. On the other hand, the combination of both an occluded graft and its native vessel occurred significantly less frequently with grafts graded 1 + or 2 +, occurring in only 10 of 76 instances ( P < 0.001). Stated in other words, there were 26 occasions in which both the native vessel and its graft were occluded in patients who had at least one other patent graft In 16 of these 26 cases (62 percent), perfusion was provided by a graft from another area of the heart. In order to define the physiologic significance of blood supply from distant grafts upon maintaining or improving left ventricular wall motion after surgery, segmental analysis of the left ventricular contractile pattern was performed in ten of these 16 areas where both graft and native vessel were occluded. The ten areas analyzed were in the distribution of either the LAD or RCA and included a total of 31 segments. The data are summarized in Table 2. Preoperatively, average shortening of each hemiaxis was 42 percent in 20 normal segments and 13.6 percent in 11 hypokinetic segments. Following revascularization, normal contraction of the ventricle was maintained in the 20 preoperative normal segments ( 41 percent) and improved to 38 percent in the 11 preoperative hypokinetic segments ( P < 0.005). Overall, following surgery, 28 segments were normal and 3 remained hypokinetic (P < 0.05). Segmental analysis of areas with occluded grafts and native vessels but without evidence of receiving blood from other distant grafts actually showed worsening of left ventricular wall motion postoperatively (Table 2). Again, the areas analyzed were in the distributions of the LAD or RCA and included 20 segments. In these cases, preoperative analysis of wall motion was 43 percent in 16 normal segments and 16 percent in 4 hypokinetic segments. Postoperative wall motion significantly worsened in the areas which were normal preoperatively ( 31 percent, P < 0.05). Although the four hypokinetic areas did show some improvement ( 24 percent), this was not statistically significant. Overall within this group of grafts, 13 segments remained normal whereas 7 were now hypokinetic.

20 KOUBASH ET AL

Thus, postoperatively, left ventricular wall motion in areas of myocardium associated with both an occluded graft and native vessel may be preserved or improved by blood supply from a graft in another area of the heart.

Comparison of Angiographic and Scintigraphic Methods in Evaluating Graft Blood Flow Distribution The angiographic estimation of graft blood flow distribution for the grafts with scintigraphic evidence of extensive ( 3 + ) blood flow distribution is shown in Table 3. Although the scintigrams indicated blood flow beyond the normal distribution of the vessel receiving the graft in 24 instances, angiographically, the full extent of flow distribution through the graft was appreciated in only 11 instances ( 46 percent). Thus, in 54 percent the scintigrams provide information which was not readily apparent on the angiogram. DISCUSSION

Several studies employing inert gases have indicated that coronary graft flow rates are extremely important in determining graft patency and providing an increased blood supply to an ischemic myocardium.21-24 Others using similar techniques have shown that, in addition to having different flow rates, grafts may perfuse variable amounts of myocardium. 8·9 Our results indicate that regional myocardial flow distribution through individual grafts is highly variable. While most grafts have distribution patterns similar to the native vessel receiving the graft, others may perfuse greater areas of myocardium than would be expected. Although our data are consistent with those reported by Kreulen et al8 and Greene et al, 9 several important aspects of our study need be considered when analyzing the significance of these results. First of all, the particulate technique of assessing graft flow differs considerably from that of the inert gases. Since the particles lodge in the coronary Table 3--Compariaon of Scinli1rraplaic and A.Rlfio1rraplaic Mealaoda o/ A.aae..iq Blood F'- Diatribudon Patterns

Grafts with 3+ perfusion (n-24) ~--------~.__·~------

Angio-2+

3+

LIMA (6)

3

3

SVG-LAD 7

3

4

SVG-Cx (1)

1

3

SVG-RCA Total (24)

13

11

CHEST, 77: l, JANUARY, 1980

microcirculation, this technique offers a unique opportunity to study regional myocardial blood flow distribution patterns at a time well beyond the operative period However, it should be emphasized that the radioactive particulate method is qualitative and actually delineates myocardial blood flow distribution. Therefore, it is not possible to comment on . absolute flow rates. Another aspect of this study which must be considered when interpreting the results is the high graft occlusion rate which can most likely be attributed to the method of selection of patients to be restudied. Most had severe disease preoperatively and many were restudied because of unexplained postoperative symptoms. Indeed, our results may have more significance in patients with occluded grafts, particularly with respect to those patent grafts with extensive distribution patterns. Additionally, despite the high occlusion rate and method of patient selection, 91 percent of the patients had less angina postoperatively, and nearly one-half were asymptomatic. Graft Flow Distribution, Graft and Native Vessel Patency, and Left Ventricular Function

.

The majority of grafts had blood flow distribution patterns similar to that of the native vessel receiving the grafts, and 12 actually had blood flow distributions less extensive than would have been expected of the vessel receiving the graft. It is interesting that 11 of 12 grafts scored 1 + were LIMA. This limited extent of LIMA blood flow distribution can likely be attributed to the method of selection of native vessels which received a LIMA. Generally, a LIMA was inserted only when the LAD was judged to be of insufficient caliber to receive a SVG. Thus, it is not surprising that blood flow distribution of LIMA was less than optimal in some instances. It should further be emphasized that because of the biased selection of LAD receiving LIMA, comments comparing LIMA to SVG cannot be made. Twenty-four percent of grafts had a blood flow distribution pattern which extended beyond the normal distribution of the native vessel receiving the graft. Twenty-three of these grafts were inserted into either the RCA or the LAD. This observation is consistent with previous studies reporting excellent flow rates through SVG to the LAD or RCA.22-24 A very high occlusion rate of both the native vessel and its graft was present ( 67 percent) in those areas which received blood from distant grafts ( 3+ ). In the entire group of patients with at least one patent graft, occlusion of both native vessel and graft occurred in 26 instances. In over one-half of these instances, perfusion was maintained in part

CHEST, 77: l, JANUARY, 1980

from a graft inserted in another area of the heart. Thus, bypass grafts have the capability of providing blood supply to extensive areas of myocardium, theoretically preventing or limiting myocardial necrosis in areas of the heart which have been deprived of blood supply because of occlusions of both the native vessel and graft. The most likely mechanism of a graft supplying blood flow to an area beyond the normal distribution of its native vessel is via collateral vessels, ie, LAD to RCA, or retrograde flow; ie, LAD to Cx artery. Another important observation concerning 3 + grafts was the postoperative improvement or preservation of left ventricular function (Table 2) in areas associated with both an occluded graft and native vessel. A significant improvement in segmental contractility ( P < 0.005) was noted in such areas, whereas areas with occluded grafts and native vessels but no evidence of receiving blood from other patent grafts showed a deterioration of left ventricular function. Similar findin~ have been previously reported in patients who have occlusion of their grafts and native vessels postoperatively.25-28 From this analysis, it can be concluded that occlusion of both graft and native vessel does not invariably result in worsening left ventricular function postoperatively as normal wall motion may be in part preserved by blood supply from a graft in another area of the heart. These results may offer another explanation for relief of angina in some patients with occluded grafts particularly since over 90 percent of our patients had less angina and nearly one-half were painfree. Several studies have reported improved symptomatolcgy and exercise tolerance in patients with occluded grafts. 29•30 Although these studies have dealt primarily with patients who have had all grafts occluded, a possible mechanism for relief of angina in patients with both occluded and patent grafts may be related to the fact that perfusion to areas of myocardium in the distribution of an occluded graft can be provided from a patent graft in another area of the ventricle. Angiographic and Scintigraphic Assessment of Blood Flow Distribution Patterns Our results agree with Hamilton et al1 6 as the scintigrams were able to provide additional information when compared to the angiogram (Table 3), particularly in the patients with 3 + grafts. The angiogram underestimated the extent of graft flow distribution in 13 of 23 grafts scored as 3 +. Since the particles are 10 to 40 microns in size, they are able to lodge in the microcirculation which cannot be visualized by the angiogram. Therefore, it is not

EXTENSIVE MYOCARDIAL BLOOD FLOW DISTRIBUTION 21

surprising that in some cases the angiogram may not detect the full extent of flow distribution. CoNCLUSIONS

In summary, this study shows that the myocardial blood fl.ow distribution of individual coronary bypass grafts is variable. As expected, patent grafts provide blood supply to an area comparable to that normally supplied by the native vessel in a large majority of instances. However, in nearly one-fourth of cases, the myocardial blood fl.ow distribution of a graft may be greater than that expected of the native vessel receiving the graft. This extensive fl.ow distribution by a graft to areas of myocardium beyond that normally supplied by the native vessel is most likely due to collateral formation or retrograde flow. Occlusion of both graft and native vessel does not invariably imply infarction of that particular area of myocardium nor deterioration of left ventricular function as perfusion may be provided by grafts in other areas of the myocardium. This latter observation may have important clinical implications in patients with multi-vessel disease who undergo coronary bypass surgery. In such instances, perfusion to areas of myocardium supplied by vessels unsuitable for grafts may be maintained from grafts in other areas of the myocardium via collateral vessels. ACKNOWLEDGMENT: The authors express sincere appreciation to the many Cardiology Fellows and technicians without whose time and help this work would not have been possible. Special thanks is extended to Dr. John Shue, Ms. Ladd Douglass Snyder and Mr. Jack McKinley for their technical aid, and to Mrs. Susan Kirsclmer for her secretarial assistance.

9

10

11

12 13 14

15

16

17 18

REFERENCES

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22 KOLIBASH ET Al

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22

23 24 25

bypass surgery: Assessment of revascularization by determination of blood ftow and myocardial mass. Am J Cardiol 34: 129-135, 1974 Greene DG, Klocke FJ, Schimert GL, et al: Evaluation of venous bypass grafts from aorto to coronary artery by inert gas desaturation and direct ftowmeter techniques. J Clin Invest 51:191-196, 1972 Ashburn WL, Braunwald E, Simon AL, et al: Myocardial perfusion imaging with radioactive-labeled particles injected directly into the coronary circulation of patients with coronary artery disease. Circulation 44:851-865, 1971 Hamilton GW, Ritchie JL, Allen D, et al: Myocardial perfusion imaging with 99 m Tc or usm In macroaggregated albumin: Correlation of the perfusion image with clinical, angiographic, surgical, and histologic findings. Am Heart J 89:708-715, 1975 Strauss HW, Harrison K, Langan JK, et al: Thallium-201 for myocardial imaging. Circulation 51:641-645, 1975 Bailey IK, Griffith LS, Rouleau J, et al: Thallium-201 myocardial perfusion imaging at rest and during exercise. Circulation 55:79-87, 1977 Ritchie JL, Narahara KA, Trobaugh GB, et al: Thallium201 myocardial imaging before and after coronary revascularization: Assessment of regional myocardial blood ftow and graft patency. Circulation 56:830-836, 1977 Kolibash AJ, Call TD, Lewis RP, et al: Myocardial perfusion as an indicator of graft patency following coronary artery bypass surgery, abstracted. Circulation 58:26, 1978 Hamilton GW, Murray JA, Lapin E, et al: Evaluation of myocardial perfusion by direct injection of radioactive particles following coronary bypass surgery. In, Norman JC( ed): Coronary Artery Medicine and Surgery: Concepts and Controversies. New York, Appleton-CenturyCrofts, 1975, p 860 Leighton RF, Wilt S, Lewis RP: Detection of hypokinesis by a quantitative analysis of left ventricular cineangiograms. Circulation 50:121-127, 1974 Ritchie JL, Hamilton GW, Williams DL, et al: Myocardial imaging with radionuclide-labeled particles: Analysis of the normal image, abnormal image, and technical considerations. Radiology 121: 131-138, 1976 Lenaers A, Block P, van Thiel E, et al: Segmental analysis of TI-201 stress myocardial scintigraphy. J Nucl Med 18:509-516, 1977 Bailey I, Burow R, Griffith L, et al: Localizing value of thallium-201 myocardial perfusion imaging in coronary artery disease, abstracted. Am J Cardiol 39:320, 1977 Grondin CM, Lepage G, Castonguay YR, et al: Aortocoronary bypass graft: Initial blood How through the graft, and early postoperative patency. Circulation 44:815-819, 1971 Lichtlen P, Moccetti T, Halter J, et al: Postoperative evaluation of myocardial blood fl.ow in aorta-to-coronary artery vein bypass grafts using the xenon-residue detection technic. Circulation 46:445-455, 1972 Korbuly DE, Formanek A, Gypser G, et al: Regional myocardial blood ftow measurements before and after coronary bypass surgery. Circulation 52:38-45, 1975 Goldberg AD, Crawley JCW, Raftery EB, et al: Myocardial blood ftow following saphenous vein bypass surgery. Circulation 51,52:1215-219, 1975 Kolibash AJ, Goodenow JS, Bush CA, et al: Improvement of myocardial perfusion and left ventricular function following coronary artery bypass grafting in patients with

CHEST, 77: l, JANUARY, 1980

unstable angina. Circulation 59:66-74, 1979 26 Gander MP, Jansen C, Wareham E: Internal mammary to anterior descending coronary anastomosis evaluated postoperatively with high resolution arteriography and myocardial perfusion scanning. Circulation 43:90, 1973 27 Rees G, Bristow JD. Kremkaw EL: Influence of aortocoronary bypass surgery on left ventricular performance. N Engl J Med 284:1116-1120, 1971 28 Steele P, Battock D, Pappas G, et al: Effect of parent

coronary arterial occlusion on left ventricular function after aortocoronary bypass surgery. Am J Cardiol 39:3949, 1977 29 Block TA, Murray JA, English MT: Improvement in exercise performance after unsuccessful myocardial revascularization. Am J Cardiol 40:673-680, 1977 30 Benchimol A, dos Santos A, Desser KB: Relief of angina pectoris in patients with occluded bypass grafts. Am J Med 60:339-343, 1976

Radiology Postgraduate Course The Department of Radiology, Duke University Medical Center, will present a postgraduate course in radiology at the Hyatt Regency Hotel, Waikiki Beach, Hawaii, March 11-15. For information, contact Dr. Robert McLelland, Radiology, Box 3808, Duke University Medical Center, Durham 27710.

Workshop in Echocardiography The Workshop in Echocardiography will be held March 27-30 at the Don Cesar Beach Resort Hotel, St. Petersburg Beach, under the sponsorship of Tampa Tracings. For information, contact Ms. Billie N. Chiles, Tampa Tracings, PO Box 1245, Tarpon Springs, Florida 33589.

Basic Cardiology for the Practicing Physician A course on Basic Cardiology for the Practicing Physician will be held at the Ahwahnee

in Yosemite National Park, California, March 16-19. The course is sponsored by the

Department of Medicine, Division of Cardiology, and Extended Programs in Medical Education, University of California School of Medicine, San Francisco. For information, please contact: Extended Programs in Medical Education, Room 569-U, University of California, Third and Parnassus, San Francisco 94143.

CHEST, 77: 1, JANUARY, 1980

EXTENSIVE MYOCARDIAL BLOOD FLOW DlmlBUTION 23