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Myocardial scintigraphy
Myocardial scintigraphy Post- Vineberg study In order to assess myocardial perfusion of Vineberg implants, tracer particles (99 m Tc and 1.I11-MAA) were injected into the internal mammary implants of 7 patients (6 years after the operation) after selective contrast visualization. The myocardial perfusion images were correlated with the internal mammary arteriographic findings. Of those patients with patent implants with communication, the myocardial scintigrams demonstrated even distribution of radioactive particles reflecting myocardial perfusion at the capillary or precapillary bed.
F. R. Begg (by invitation), M. H. Adatepe (by invitation), M. I. Salvoza (by invitation), and G. J. Magovern, Pittsburgh, Pa.
Internal mammary artery implantation to augment myocardial perfusion was reported by Vineberg' in 1946. During the ensuing years extensive laboratory investigation demonstrated that the internal mammary artery implanted into the myocardium was capable of establishing collateral communications to the patient's own coronary arterial tree. Selective contrast visualization of the implanted internal mammary artery was routinely employed in the postoperative evaluation of such patients. Although internal mammary arteriography provides a highly accurate morphologic assessment of the implant, it does not visualize regional myocardial perfusion at the capillary or precapillary level. Physiological and metabolic studies demonstrating added myocardial perfusion from implants have been performed." However, these indirect studies did not assess regional myocardial perfusion. Successful experience in identifying abnormal regional pulmonary perfusion patterns with radioactive particles led to the albumin microsphere technique of myocardial perfusion imaging. Myocardial perfusion imagFrom Allegheny General Hospital, 320 East North Avenue, Pittsburgh, Pa. 15212. Read at the Fifty-fifth Annual Meeting of The American Association for Thoracic Surgery, New York, N. Y., April 14, 15, and 16, 1975.
398
ing has been found to be satisfactory for investigating the coronary arteriolar-capillary bed." The clinical experience of Grames and associates' has shown that the albumin microsphere technique can be used safely in the study of the myocardial microcirculation. In the present study myocardial scintigraphy was performed by direct injection of tracer microspheres into internal mammary artery implants to assess the integrity of the coronary arteriolar-capillary bed and the regional perfusion patterns. Method
Seven patients undergoing internal mammary arteriography had myocardial perfusion scintigraphy. The Vineberg implant(s) were performed in 1968 with an average follow-up of 6 years. The patients were men whose ages ranged from 36 to 58 years at the time of the postoperative study. Internal mammary arteriography was performed by direct injection during the course of selective coronary arteriography by the Judkins technique. The injections were recorded in the left anterior oblique and right anterior oblique projections on 35 mm. Double X film. Left ventriculography was performed routinely in the right anterior oblique projection.
Volume 70
Myocardial scintigraphy
Number 3 September, 1975
The results of internal mammary arteriography were classified as follows: ( 1) patent internal mammary artery and communication with coronary arteries; (2) patent internal mammary artery without communication with coronary arteries; and (3) occluded internal mammary artery implant. In the arteriographic evaluation of the Vineberg implants, attention was given to the size of the internal mammary artery, velocity of flow of the contrast media, and its rate of clearance through the implant. The extent of myocardial staining and the number, size, and location of the coronary arteries opacified were determined. Contraction of the left ventricle was classified as normal, hypokinetic, and akinetic. The radioactive particles were injected into the internal mammary arteries when the contrast study was completed. 99mTc_ labeled microspheres were injected into the internal mammary artery supplying the anterior wall of the left ventricle. The particle size ranged from 10 to 40 JL with the average being 30 JL. The number of particles per dose ranged from 10,000 to 30,000 with 0.1 to 0.3 mg. of albumin. The 131J_ macro aggregated albumin (131I-MAA) particles were injected into the internal mammary artery supplying the posterior wall of the left ventricle. The partical size ranged from 10 to 60 JL with the average being 30 JL. The number of particles per dose averaged 100,000 with 0.1 to 0.2 mg. of albumin. In evaluating the perfusion patterns of the implants, we injected particles directly into the internal mammary artery. The position of the catheter tip before and after the injection of particles was confirmed by injecting a small quantity of contrast material through the catheter. In order to achieve better mixing of particles a slow rate of injection was used. The particles were injected manually through the coronary catheter at a rate of 2 ml. per second. The patient's condition during injection of the particles was monitored by continuous electrocardiographic and pressure recordings.
399
Table I. Postoperative arteriographic results in 7 patients receiving 10 internal mammary implants Condition ofimplant Patent with communication Patent without communication Occluded
4 3 3
40 30 30
Table II. Internal mammary arteriography, left ventriculography, and myocardial scanning
Scintigram Anterior Anterior Posterior Posterolateral Anterior (apex) Anterior (apex) Chest wall
Internal mammary arteriogram: Coronary artery LAD LAD RCA Cx 0 0
0
Left ventriculogram Hypokinetic apex Normal Normal Normal Normal Hypokinetic (anterior) Hypokinetic
Legend: LAD, Left anterior descending coronary artery. RCA, Right coronary artery. Cx, Circumflex.
After the particles had been injected and the catheter removed the patient was transferred to the nuclear medicine department for myocardial imaging. With the biological half life of macrospheres being 5 hours and that of microspheres of 9 hours, there was sufficient time for delayed imaging. Images of myocardial perfusion were acquired with a Searle HP model camera with a 4,000 (high sensitivity) parallel-hole collimater used for single injections of 99mTc-Iabeled microspheres. For 131I-MAA injections, a 1,500 parallel-hole collimater (medium energy) was used. Images were photographed on Polaroid and standard xray film. Multiple views were obtained; these included the anterior, left lateral, left anterior oblique, and right anterior oblique projections. Careful analysis of all views was absolutely necessary. Underperfused regions were identified by focal areas of reduced or
The Journol 01
400
Begg et at.
Thoro cic ond Cord iovoscu lor Surgery
Fig. 1. Left, Left intern al mammary arteriogram, right anterior oblique projection. The implant communicates with the left anterior descending and diagonal branches. Right, Myocardial perfusion images. Radioactivity corresponding to left anterior descending distribution.
Fig. 2, Left, Right internal mammary arteriogram, right anterior oblique projection, Implant communicates with the left anterior descending coronary artery. Right, Myocardial perfusion images . Radioactivity corresponding to the left anterior descending distribution.
uneven accumulation of particles, while even accumulation was identified as normal perfusion distribution. Results Seven patients had technically satisfactory internal mammary arteriograms, cine left ventriculograms, and myocardial scintigrams. Table I presents the results of internal mammary arteriography. Table II correlates the internal mammary arteriographic findings with cine left ventriculography and myocardial imaging. Myocardial perfusion anatomy correlates
with normal coronary arteries. In the left anterior oblique view, which provides the best determination, the left anterior descending coronary arterial distribution is visualized anteriorly, the circumflex distribution posterolaterally, and the right coronary artery inferiorly. Myocardial perfusion scintigrams were taken after the Vineberg procedure: The anterior implants correspond with the left anterior descending distribution , and posterior implants are visualized inferiorly (right coronary artery distribution) or posterolaterally (circumflex distribution).
Volume 70
Myocardial scintigraphy
Number 3 September, 1975
40 1
Fig. 3. Left, Left internal mammary arteriogram, right anterior oblique projection. Implant communicates with the posterior descending artery. Right, Myocardial perfusion images. Intense radioactivity interiorly in the distribution of the posterior descending artery.
Fig. 4. Left, Left internal mammary arteriogram, right anterior oblique projection. The implant communicates with the circumflex artery. Right, Myocardial perfusion images. Radioactivity corresponding to the circumflex distribution.
On the basis of the internal mammary arteriograms , patients were divided into three categories as follows: 1. Patent implants with communication. Two patients had uniform perfusion of the anterior wall of the left ventricle (left anterior descending distribution) via the anterior wall implant (Figs. 1 and 2). One patient had intense radioactivity of the inferior wall via a posterior implant (right coronary artery distribution) (Fig. 3). A posterolateral implant demonstrated activity along the circumflex distribution (Fig. 4). 2. Patent implants without communica-
tion. Figs. 5 and 6 show the myocardial scintigrams of patients with patent Vineberg implants, proved by myocardial staining arteriographically, but no communication with the pre-existing coronary arteries. 3. Closed implants. Fig. 7 demonstrates myocardial scintigraphy in a patient with occluded bilateral Vineberg implants. Discussion In a 1969 review article on circulation study with radioactive microspheres, Wagner and associates" outlined the historical development of the technique and cover
The Journal of
402
Begg et at.
Thoracic and Cardiovascular Surgery
Fig. 5. Left, Right internal mammary arteriogram, right anterior oblique projection. Patent implant with myocardial staining but no communication. Right, Myocardial perfusion images. Radioactivity along the course of the internal mammary artery with uniform distribution area of myocardial staining.
Fig. 6. Myocardial perfusion images of a patient with a patent implant to the anterior wall of the left ventricle without communication.
in depth the theoretical basis and validation of the method. There seems little doubt that the distribution of radioactive microspheres accurately reflects blood flow distribution. Myocardial perfusion imaging by the albumin microsphere technique reflects the condition of the myocardial capillary bed, permits visualization of regional blood flow distribution, and determines the extent and location of segments of myocardium irreversibly scarred from viable myocardium. At present, the technique has been useful in the following situations: ascertaining the
Fig. 7. Myocardial perfusion Vineberg implants----closed. A, responding to distribution of (chest wall) of left internal B, Radioactivity corresponding right internal mammary artery
images-bilateral Radioactivity corproximal segment mammary artery. to distribution of (chest wall).
hemodynamic importance of a stenosis of questionable significance by arteriography and distinguishing between reversible and irreversible myocardial dysfunction in patients undergoing bypass graft surgery. 6 Postoperative myocardial perfusion scintigraphy performed by Jansen and associates' demonstrated normal myocardial perfusion in patients with patent saphenous vein grafts. Two patients who had Vineberg procedures with radioactive MAA injected into
Volume 70
Myocardial scintigraphy
Number 3
403
September, 1975
the internal mammary artery showed no myocardial perfusion. In this study myocardial perfusion imaging was a useful adjunct in the assessment of the Vineberg implant. The scintigrams demonstrated segmental perfusion to the area of the myocardium supplied by the arterial implant. Uniform distribution of the radioactive particles established the integrity of the capillary bed with viable myocardium secondary to improved myocardial perfusion. Correlation with cine left ventriculography demonstrates normal segmental contraction of the perfused area. In the Vineberg phenomena three separate events have been distinguished by contrast study: patency of the arterial implant, development of collateral flow, and communication between the implant and the coronary arteries. The albumin microsphere technique defines a fourth event by demonstrating regional myocardial perfusion at the capillary or precapillary level. REFERENCES
2 3
4
5
6
7
Vineberg, A. M.: Development of Anastomosis Between Coronary Vessels and Transplanted Internal Mammary Artery, Can. Med. Assoc. J. 55: 117, 1946. Godin, R., and Taylor, W. J.: Selective Revascularization by Internal Mammary Artery Implant. N. Engl. J. Med. 275: 283, 1968. Quinn, J. L., Serratto, M., and Kezdi, P.: Coronary Artery Bed Photoscanning Using Radio-iodine Albumin Macroaggregates (RAMA), J. Nucl. Med. 7: 107, 1966. Grames, G. M., Jansen, C., Gander, M. P., Wieland, B. S., and Judkins, M. P.: The Safety of the Direct Coronary Injection of Radiolabeled Particles in 800 Patients Undergoing Coronary Angiography, J. Nucl. Med. 15: 2, 1974. Wagner, H. N., Jr., Rhodes, B., Lasaki, Y., and Ryan, J.: Studies of the Circulation With Radioactive Microspheres, Invest. Radiol. 4: 374, 1969. Kay, E. B., Naraghipour, H., Beg, R. A., et al.: Limitation of Coronary Angiography as a Criterion to Bypass Surgery (Abstr.). Am. J. Cardiol. 33: 147, 1947. Jansen, C., Judkins, M. P., Grames, G. M., Gander, M. P., and Adams, R.: Myocardial Perfusion Color Scintigraphy With MAA, Radiology 109: 369, 1973.
Discussion DR. ARTHUR M. VINEBERG Montreal, Quebec, Canada
I would like 'to congratulate Dr. Begg and his associates on their beautiful demonstration by modern technique of how left ventricular-internal mammary artery implants supply blood in a wide distribution to precapillary vessels, that is, myocardial arterioles. At this point, for the benefit of the younger men, I should like to describe our present concept of the microcirculation through which oxygenated blood supplied by the implanted internal mammary artery is distributed. This is a diagram of the microcirculation made by our medical artist under my direction. It is based upon the careful studies of Dr. 1. T. Wearn published in 1933. Dr. J. T. Wearn showed that surface coronary arteries sent out three different types of branches into the left ventricular muscle: (1) those which join the intramyocardial arteriolar networks, (2) those which go directly into the left ventricular lumen (arterial luminal), and (3 ) those which join the myocardial sinusoidal spaces (arterial sinusoidal). The myocardial sinusoids are thin-wallel spaces measuring 400 by 50 p. in size and lie between muscle bundles. They in turn communicate with the capillaries on one side and the ventricular lumen on the other. They are definitely on the arterial side. They represent the remnants of the ventricular circulation in primitive hearts. This is present in the crayfish and consists of loosely arranged ventricular fibers. Between these fibers there are spaces which communicate directly with the left ventricular lumen. Ventricular contraction squeezes nutrient fluids into its walls providing a circulation by ebb and flow. In the sturgeon, the inner two thirds of the left ventricular wall is nourished through such spaces from the left ventricular cavity. The outer one third, consisting of compact muscle, is vascularized by an artery from the gills. These spaces persist in the human heart as myocardial sinusoids. They are present most frequently in the walls of the right ventricle and in the inner one third of the left ventricular wall. A tunnel made in the ventricular wall opens these spaces and thus provides a runoff for the bleeding branches of the internal mammary artery after it has been pulled into the tunnel. In the right ventricle an implanted internal mammary artery supplies oxygenated blood to right and left ventricular walls due to the continuity of myocardial sinusoidal spaces. In the left ventricle, fresh oxygenated blood is supplied locally, immediately, for the same reason. The internal mammary artery pulled into ventricular tunnels thus remains open and in time branches. The branches join the surrounding myocardial arteriolar networks.
The Journol of
404
Begg et al.
Thorocic and Cardiovascular Surgery
In certain positions in the left ventricle, some of the branches of all coronary arteries terminate in definite arteriolar zones according to G. Baroldi. At the apex this occurs in 72 per cent of human hearts. In the anterolateral left ventricular wall it occurs in 72 per cent of human hearts. In the posterior wall of the left ventricle there is an area where the arteries terminate in 85 per cent of the human hearts. Thus an internal mammary artery implanted into the apical or anterolateral triarteriolar zones of the left ventricle, when it branches, has a 72 per cent chance of revascularizing the myocardial arteriolar zones of all three coronary arteries. The same is true in the antero-
lateral left ventricular implant and of the right gastroepiploic implant placed in the posterior wall of the left ventricle. However, in this case it is 85 per cent. In all three positions an arterial implant may revascularize the entire heart if the branches form anastomoses with the terminal arteriolar branches of all three coronary arteries. This is probably what happened in the cases that I described in my paper (page 381). Once again, I would like to congratulate the authors who so very beautifully helped to explain the mechanism of how the Vineberg implants revascularize through the microcirculation of the left ventricle.
F. R. Begg (by invitation), M. H. Adatepe (by invitation), M. I. Salvoza (by invitation), and G. J. Magovern, Pittsburgh, Pa.
Internal mammary artery implantation to augment myocardial perfusion was reported by Vineberg' in 1946. During the ensuing years extensive laboratory investigation demonstrated that the internal mammary artery implanted into the myocardium was capable of establishing collateral communications to the patient's own coronary arterial tree. Selective contrast visualization of the implanted internal mammary artery was routinely employed in the postoperative evaluation of such patients. Although internal mammary arteriography provides a highly accurate morphologic assessment of the implant, it does not visualize regional myocardial perfusion at the capillary or precapillary level. Physiological and metabolic studies demonstrating added myocardial perfusion from implants have been performed." However, these indirect studies did not assess regional myocardial perfusion. Successful experience in identifying abnormal regional pulmonary perfusion patterns with radioactive particles led to the albumin microsphere technique of myocardial perfusion imaging. Myocardial perfusion imagFrom Allegheny General Hospital, 320 East North Avenue, Pittsburgh, Pa. 15212. Read at the Fifty-fifth Annual Meeting of The American Association for Thoracic Surgery, New York, N. Y., April 14, 15, and 16, 1975.
398
ing has been found to be satisfactory for investigating the coronary arteriolar-capillary bed." The clinical experience of Grames and associates' has shown that the albumin microsphere technique can be used safely in the study of the myocardial microcirculation. In the present study myocardial scintigraphy was performed by direct injection of tracer microspheres into internal mammary artery implants to assess the integrity of the coronary arteriolar-capillary bed and the regional perfusion patterns. Method
Seven patients undergoing internal mammary arteriography had myocardial perfusion scintigraphy. The Vineberg implant(s) were performed in 1968 with an average follow-up of 6 years. The patients were men whose ages ranged from 36 to 58 years at the time of the postoperative study. Internal mammary arteriography was performed by direct injection during the course of selective coronary arteriography by the Judkins technique. The injections were recorded in the left anterior oblique and right anterior oblique projections on 35 mm. Double X film. Left ventriculography was performed routinely in the right anterior oblique projection.
Volume 70
Myocardial scintigraphy
Number 3 September, 1975
The results of internal mammary arteriography were classified as follows: ( 1) patent internal mammary artery and communication with coronary arteries; (2) patent internal mammary artery without communication with coronary arteries; and (3) occluded internal mammary artery implant. In the arteriographic evaluation of the Vineberg implants, attention was given to the size of the internal mammary artery, velocity of flow of the contrast media, and its rate of clearance through the implant. The extent of myocardial staining and the number, size, and location of the coronary arteries opacified were determined. Contraction of the left ventricle was classified as normal, hypokinetic, and akinetic. The radioactive particles were injected into the internal mammary arteries when the contrast study was completed. 99mTc_ labeled microspheres were injected into the internal mammary artery supplying the anterior wall of the left ventricle. The particle size ranged from 10 to 40 JL with the average being 30 JL. The number of particles per dose ranged from 10,000 to 30,000 with 0.1 to 0.3 mg. of albumin. The 131J_ macro aggregated albumin (131I-MAA) particles were injected into the internal mammary artery supplying the posterior wall of the left ventricle. The partical size ranged from 10 to 60 JL with the average being 30 JL. The number of particles per dose averaged 100,000 with 0.1 to 0.2 mg. of albumin. In evaluating the perfusion patterns of the implants, we injected particles directly into the internal mammary artery. The position of the catheter tip before and after the injection of particles was confirmed by injecting a small quantity of contrast material through the catheter. In order to achieve better mixing of particles a slow rate of injection was used. The particles were injected manually through the coronary catheter at a rate of 2 ml. per second. The patient's condition during injection of the particles was monitored by continuous electrocardiographic and pressure recordings.
399
Table I. Postoperative arteriographic results in 7 patients receiving 10 internal mammary implants Condition ofimplant Patent with communication Patent without communication Occluded
4 3 3
40 30 30
Table II. Internal mammary arteriography, left ventriculography, and myocardial scanning
Scintigram Anterior Anterior Posterior Posterolateral Anterior (apex) Anterior (apex) Chest wall
Internal mammary arteriogram: Coronary artery LAD LAD RCA Cx 0 0
0
Left ventriculogram Hypokinetic apex Normal Normal Normal Normal Hypokinetic (anterior) Hypokinetic
Legend: LAD, Left anterior descending coronary artery. RCA, Right coronary artery. Cx, Circumflex.
After the particles had been injected and the catheter removed the patient was transferred to the nuclear medicine department for myocardial imaging. With the biological half life of macrospheres being 5 hours and that of microspheres of 9 hours, there was sufficient time for delayed imaging. Images of myocardial perfusion were acquired with a Searle HP model camera with a 4,000 (high sensitivity) parallel-hole collimater used for single injections of 99mTc-Iabeled microspheres. For 131I-MAA injections, a 1,500 parallel-hole collimater (medium energy) was used. Images were photographed on Polaroid and standard xray film. Multiple views were obtained; these included the anterior, left lateral, left anterior oblique, and right anterior oblique projections. Careful analysis of all views was absolutely necessary. Underperfused regions were identified by focal areas of reduced or
The Journol 01
400
Begg et at.
Thoro cic ond Cord iovoscu lor Surgery
Fig. 1. Left, Left intern al mammary arteriogram, right anterior oblique projection. The implant communicates with the left anterior descending and diagonal branches. Right, Myocardial perfusion images. Radioactivity corresponding to left anterior descending distribution.
Fig. 2, Left, Right internal mammary arteriogram, right anterior oblique projection, Implant communicates with the left anterior descending coronary artery. Right, Myocardial perfusion images . Radioactivity corresponding to the left anterior descending distribution.
uneven accumulation of particles, while even accumulation was identified as normal perfusion distribution. Results Seven patients had technically satisfactory internal mammary arteriograms, cine left ventriculograms, and myocardial scintigrams. Table I presents the results of internal mammary arteriography. Table II correlates the internal mammary arteriographic findings with cine left ventriculography and myocardial imaging. Myocardial perfusion anatomy correlates
with normal coronary arteries. In the left anterior oblique view, which provides the best determination, the left anterior descending coronary arterial distribution is visualized anteriorly, the circumflex distribution posterolaterally, and the right coronary artery inferiorly. Myocardial perfusion scintigrams were taken after the Vineberg procedure: The anterior implants correspond with the left anterior descending distribution , and posterior implants are visualized inferiorly (right coronary artery distribution) or posterolaterally (circumflex distribution).
Volume 70
Myocardial scintigraphy
Number 3 September, 1975
40 1
Fig. 3. Left, Left internal mammary arteriogram, right anterior oblique projection. Implant communicates with the posterior descending artery. Right, Myocardial perfusion images. Intense radioactivity interiorly in the distribution of the posterior descending artery.
Fig. 4. Left, Left internal mammary arteriogram, right anterior oblique projection. The implant communicates with the circumflex artery. Right, Myocardial perfusion images. Radioactivity corresponding to the circumflex distribution.
On the basis of the internal mammary arteriograms , patients were divided into three categories as follows: 1. Patent implants with communication. Two patients had uniform perfusion of the anterior wall of the left ventricle (left anterior descending distribution) via the anterior wall implant (Figs. 1 and 2). One patient had intense radioactivity of the inferior wall via a posterior implant (right coronary artery distribution) (Fig. 3). A posterolateral implant demonstrated activity along the circumflex distribution (Fig. 4). 2. Patent implants without communica-
tion. Figs. 5 and 6 show the myocardial scintigrams of patients with patent Vineberg implants, proved by myocardial staining arteriographically, but no communication with the pre-existing coronary arteries. 3. Closed implants. Fig. 7 demonstrates myocardial scintigraphy in a patient with occluded bilateral Vineberg implants. Discussion In a 1969 review article on circulation study with radioactive microspheres, Wagner and associates" outlined the historical development of the technique and cover
The Journal of
402
Begg et at.
Thoracic and Cardiovascular Surgery
Fig. 5. Left, Right internal mammary arteriogram, right anterior oblique projection. Patent implant with myocardial staining but no communication. Right, Myocardial perfusion images. Radioactivity along the course of the internal mammary artery with uniform distribution area of myocardial staining.
Fig. 6. Myocardial perfusion images of a patient with a patent implant to the anterior wall of the left ventricle without communication.
in depth the theoretical basis and validation of the method. There seems little doubt that the distribution of radioactive microspheres accurately reflects blood flow distribution. Myocardial perfusion imaging by the albumin microsphere technique reflects the condition of the myocardial capillary bed, permits visualization of regional blood flow distribution, and determines the extent and location of segments of myocardium irreversibly scarred from viable myocardium. At present, the technique has been useful in the following situations: ascertaining the
Fig. 7. Myocardial perfusion Vineberg implants----closed. A, responding to distribution of (chest wall) of left internal B, Radioactivity corresponding right internal mammary artery
images-bilateral Radioactivity corproximal segment mammary artery. to distribution of (chest wall).
hemodynamic importance of a stenosis of questionable significance by arteriography and distinguishing between reversible and irreversible myocardial dysfunction in patients undergoing bypass graft surgery. 6 Postoperative myocardial perfusion scintigraphy performed by Jansen and associates' demonstrated normal myocardial perfusion in patients with patent saphenous vein grafts. Two patients who had Vineberg procedures with radioactive MAA injected into
Volume 70
Myocardial scintigraphy
Number 3
403
September, 1975
the internal mammary artery showed no myocardial perfusion. In this study myocardial perfusion imaging was a useful adjunct in the assessment of the Vineberg implant. The scintigrams demonstrated segmental perfusion to the area of the myocardium supplied by the arterial implant. Uniform distribution of the radioactive particles established the integrity of the capillary bed with viable myocardium secondary to improved myocardial perfusion. Correlation with cine left ventriculography demonstrates normal segmental contraction of the perfused area. In the Vineberg phenomena three separate events have been distinguished by contrast study: patency of the arterial implant, development of collateral flow, and communication between the implant and the coronary arteries. The albumin microsphere technique defines a fourth event by demonstrating regional myocardial perfusion at the capillary or precapillary level. REFERENCES
2 3
4
5
6
7
Vineberg, A. M.: Development of Anastomosis Between Coronary Vessels and Transplanted Internal Mammary Artery, Can. Med. Assoc. J. 55: 117, 1946. Godin, R., and Taylor, W. J.: Selective Revascularization by Internal Mammary Artery Implant. N. Engl. J. Med. 275: 283, 1968. Quinn, J. L., Serratto, M., and Kezdi, P.: Coronary Artery Bed Photoscanning Using Radio-iodine Albumin Macroaggregates (RAMA), J. Nucl. Med. 7: 107, 1966. Grames, G. M., Jansen, C., Gander, M. P., Wieland, B. S., and Judkins, M. P.: The Safety of the Direct Coronary Injection of Radiolabeled Particles in 800 Patients Undergoing Coronary Angiography, J. Nucl. Med. 15: 2, 1974. Wagner, H. N., Jr., Rhodes, B., Lasaki, Y., and Ryan, J.: Studies of the Circulation With Radioactive Microspheres, Invest. Radiol. 4: 374, 1969. Kay, E. B., Naraghipour, H., Beg, R. A., et al.: Limitation of Coronary Angiography as a Criterion to Bypass Surgery (Abstr.). Am. J. Cardiol. 33: 147, 1947. Jansen, C., Judkins, M. P., Grames, G. M., Gander, M. P., and Adams, R.: Myocardial Perfusion Color Scintigraphy With MAA, Radiology 109: 369, 1973.
Discussion DR. ARTHUR M. VINEBERG Montreal, Quebec, Canada
I would like 'to congratulate Dr. Begg and his associates on their beautiful demonstration by modern technique of how left ventricular-internal mammary artery implants supply blood in a wide distribution to precapillary vessels, that is, myocardial arterioles. At this point, for the benefit of the younger men, I should like to describe our present concept of the microcirculation through which oxygenated blood supplied by the implanted internal mammary artery is distributed. This is a diagram of the microcirculation made by our medical artist under my direction. It is based upon the careful studies of Dr. 1. T. Wearn published in 1933. Dr. J. T. Wearn showed that surface coronary arteries sent out three different types of branches into the left ventricular muscle: (1) those which join the intramyocardial arteriolar networks, (2) those which go directly into the left ventricular lumen (arterial luminal), and (3 ) those which join the myocardial sinusoidal spaces (arterial sinusoidal). The myocardial sinusoids are thin-wallel spaces measuring 400 by 50 p. in size and lie between muscle bundles. They in turn communicate with the capillaries on one side and the ventricular lumen on the other. They are definitely on the arterial side. They represent the remnants of the ventricular circulation in primitive hearts. This is present in the crayfish and consists of loosely arranged ventricular fibers. Between these fibers there are spaces which communicate directly with the left ventricular lumen. Ventricular contraction squeezes nutrient fluids into its walls providing a circulation by ebb and flow. In the sturgeon, the inner two thirds of the left ventricular wall is nourished through such spaces from the left ventricular cavity. The outer one third, consisting of compact muscle, is vascularized by an artery from the gills. These spaces persist in the human heart as myocardial sinusoids. They are present most frequently in the walls of the right ventricle and in the inner one third of the left ventricular wall. A tunnel made in the ventricular wall opens these spaces and thus provides a runoff for the bleeding branches of the internal mammary artery after it has been pulled into the tunnel. In the right ventricle an implanted internal mammary artery supplies oxygenated blood to right and left ventricular walls due to the continuity of myocardial sinusoidal spaces. In the left ventricle, fresh oxygenated blood is supplied locally, immediately, for the same reason. The internal mammary artery pulled into ventricular tunnels thus remains open and in time branches. The branches join the surrounding myocardial arteriolar networks.
The Journol of
404
Begg et al.
Thorocic and Cardiovascular Surgery
In certain positions in the left ventricle, some of the branches of all coronary arteries terminate in definite arteriolar zones according to G. Baroldi. At the apex this occurs in 72 per cent of human hearts. In the anterolateral left ventricular wall it occurs in 72 per cent of human hearts. In the posterior wall of the left ventricle there is an area where the arteries terminate in 85 per cent of the human hearts. Thus an internal mammary artery implanted into the apical or anterolateral triarteriolar zones of the left ventricle, when it branches, has a 72 per cent chance of revascularizing the myocardial arteriolar zones of all three coronary arteries. The same is true in the antero-
lateral left ventricular implant and of the right gastroepiploic implant placed in the posterior wall of the left ventricle. However, in this case it is 85 per cent. In all three positions an arterial implant may revascularize the entire heart if the branches form anastomoses with the terminal arteriolar branches of all three coronary arteries. This is probably what happened in the cases that I described in my paper (page 381). Once again, I would like to congratulate the authors who so very beautifully helped to explain the mechanism of how the Vineberg implants revascularize through the microcirculation of the left ventricle.