- Email: [email protected]
Quantitative assessment of infarct size reduction by coronary venous retroperfusion in baboons
Quantitative Assessment of Infarct Size Reduction by Coronary Venous Retroperfusion in Baboons GRAYSON G. GEARY, MB, FRACP, GREGORY T. SMITH, PhD, GLEN T. SUEHIRO, CHARLES ZEMAN, BENJAMIN SIU, and J. JUDSON McNAMARA, MD
Initial favorable reports in which coronary venous retroperfusion was begun after acute coronary artery occlusion have demonstrated a reversal of ischemic injury and improved left ventricular function. However, little information has been generated to document the extent to which retroperfusion may decrease ultimate histologically determined infarct size . The objective of the present study was to evaluate the effectiveness of retroperfusion in reducing infarct size by using an accurate quantitative method in which infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk for infarction) . In an experimental group of 5 baboons, the left anterior descending coronary artery was occluded and coronary venous retroperfusion started 1 hour after occlusion . After a 4-hour period of occlusion, retroperfusion was discontinued and anterograde perfusion was si-
multaneously restored. A control group of 5 baboons underwent an identical procedure without retroperfusion . Twenty-four hours after occlusion, hearts were excised and the previously occluded left anterior descending coronary artery as well as the adjacent arteries were injected with microvascular dye to delineate the perfusion bed of the occluded artery . Planimetry of serial cross-sections of the left ventricle enabled the size of the perfusion bed of the occluded artery and size of the infarct to be determined . The mean percentage of the perfusion bed infarcted in the control group was 94 .110 .9 (mean ± standard error) and in the retroperfused group was 57 .4 f 3 .5 (p <0 .001) . Hence, the results demonstrated that when retroperfusion was initiated after 1 hour of coronary occlusion, the mean percentage of the perfusion bed salvaged was increased by 36 .7% .
Several investigators have shown that selective synchronized coronary venous retroperfusion, when started after acute coronary artery occlusion, may result in partial reversal of ischemic injury1 3 and improved left ventricular function . 1,2,1 Despite these favorable reports, little information has been available as to whether retroperfusion reduces infarct size as histologically assessed . In our previous study in the baboon, we demonstrated that retroperfusion begun 15 minutes after coronary artery occlusion combined with later anterograde reperfusion substantially reduced the percentage of the left ventricle ultimately infarcted . 5 Because
retroperfusion was initiated early at a time when the entire ischemic region has been shown to remain viable, 6 the optimal effectiveness of the retroperfusion system was demonstrated . The results of the initial study demonstrated the capability of the retroperfusion system to maintain the viability of ischemic myocardium . Because of these results, the next step was to examine the effectiveness when it was delayed for a period consistent with its clinical use . Therefore, the objective of the present study was to examine the effectiveness of coronary venous retroperfusion in reducing infarct size when retroperfusion was delayed for 1 hour after coronary occlusion . Additionally, a more accurate methodologic approach was employed to determine the degree of myocardial salvage achieved by retroperfusion . Infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk for infarction) . This technique eliminated the variability in infarct size which may occur due to inherent variability in the size of the anatomic perfusion bed of an occluded artery . Thus, a
From the Cardiovascular Research Laboratory, Department of Surgery, John A . Burns School of Medicine, Queen's Medical Center, Honolulu, Hawaii . This study was supported by Grant 5 R01 HL 14571-09 from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, and by a grant from the George F . Straub Trust, Honolulu, Hawaii . Manuscript received January 25, 1982 ; revised manuscript received June 22, 1982, accepted June 25, 1982 . Address for reprints : J . Judson McNamara, MD, Department of Surgery, Queen's Medical Center, 1301 Punchbowl Street, Honolulu, Hawaii 96813 .
1424
December 1982 The American Journal of CARDIOLOGY
Volume 50
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
infusion of heparinized saline solution was maintained through the catheter to ensure patency until retroperfusion was initiated . Two rows of 6 unipolar atraumatic epicardial electrodes spaced at 5 mm intervals were placed across the anticipated region of ischemia parallel to the minor axis of the left ventricle . Recordings from the electrode rows were used to assess directional changes in S-T segment elevation during periods of occlusion, retroperfusion, and anterograde reperfusion . Coronary venous retroperfusion system : The coronary venous retroperfusion system is schematically illustrated in Figure 1 . It is similar to our previously described systeme except that a commercially available pulsatile pump and pumping chamber were employed . The right femoral artery served as the source of arterial blood which flowed through an occlusive roller pump calibrated to accurately deliver the small required blood flow rates .'1'he roller pump provided a continuous blood flow of 40 to 50 ml/min into a bladder contained within a pediatric pulsatile bypass chamber (Kontron Cardiovascular, Everett, Massachusetts) . The chamber contains 2 bladders ; I is connected to the roller pump and the other is connected to a pulsatile bypass pump (Model 20, Kontron Cardiovascular) which provides active compression and decompression of the blood-filled bladder . Arterialized blood from the bladder was pumped in a pulsatile manner through the retroperfusion catheter positioned in the great cardiac vein . A Statham P23 Db pressure transducer was connected between the pumping chamber and the retroperfusion catheter to assist in monitoring venous perfusion pressures . These pressures directly reflect the pressures in the coronary veins. An elevation in pressure may occur due either to wedging of the catheter in the coronary veins or inadequate drainage due to the flow rate being set too high . If the flow was set at >50 ml/min, the retroperfusion pump was usually not able to deliver the required volume during the diastolic compression phase . Consequently flow would continue into the coronary veins during systole, resulting in inadequate drainage and an elevation in pressure . We previously showed
more accurate quantitative assessment of myocardial salvage by retroperfusion may be determined .
Methods Surgical preparation: Ten baboons (Papio anubis), 20 to 26 kg, were initially sedated with ketamine hydrochloride (10 mg/kg intramuscularly) . Anesthesia was induced and maintained with intravenous infusions of sodium thiopental (2 mg/kg) . A standard lead H electrocardiogram was monitored . Baboons were intubated with a cuffed endotracheal tube and ventilated with a Harvard volume respirator maintaining an arterial pH of 7 .40 f 0.05 . Supplemental oxygen was administered as necessary to maintain an arterial oxygen saturation of at least 95% . Arterial pressure was monitored by an 8Fr stiff-walled catheter advanced through the left femoral artery . Intravenous fluids were administered via a catheter through the left femoral vein . A 9Fr cannula was inserted into the right femoral artery and served as the source of arterialized blood for the coronary venous retroperfusion system . A mid-sternal thoracotomy was performed and the heart suspended in a pericardial cradle . The left anterior descending coronary artery was dissected free from the anterior interventricular vein distal to the first diagonal branch . A 3-0 Mersilene® snare was placed around the dissected left anterior descending coronary artery for subsequent ligation . An electromagnetic flow catheter (Millar instruments, Houston, Texas) was inserted into the pulmonary artery by means of a purse-string suture for measurement of cardiac output . Left ventricular pressure, the rate of rise of left ventricular pressure, and left ventricular end-diastolic pressure were monitored with use of a micromanometer tip catheter (Millar) which was inserted through a 12-gauge cannula into the left ventricle . A 6Fr thin-walled preshaped polyethylene retroperfusion catheter was inserted into the right atrium through a purse-string suture in the atrial appendage . The catheter was then advanced through the coronary sinus to position its tip at the junction of the great cardiac vein and the anterior interventricular vein . A slow
Pressure Transducer
I _
Great Cardiac Vein
Left Marginal Vein
Anterior Interventricular Vein
I
Middle Cardiac Vein
Coronary Sinus
Pulsatile Balloon Pump Arterial Blood Supply tow
FIGURE 1 . Diagram of the retroperfusion system . See text for detailed description .
December 1982
The American Journal of CARDIOLOGY Volume 50
1 42 5
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
that a flow rate of 40 to 50 ml/min produced adequate rearterialization 5 We did not simultaneously record the pressures in the coronary veins as this would have required insertion of a separate line for pressure recording. However, in preliminary experiments, we monitored pressure in the anterior interventricular vein during retroperfusion with flows up to 60 ml/min and found the pressure <50 mm Hg . The pulsatile pump system was adjusted so that forward pulsed perfusion occurred only in diastole and perfusion was interrupted during systole so that normal coronary venous drainage was allowed . This was accomplished by simultaneously displaying the left ventricular pressure and the retroperfusion pressure tracings so the retroperfusion pulse could be adjusted to occur during the diastolic interval . Anticoagulation was maintained during the period of retroperfusion by initial heparinization (5 mg/kg intravenously), with supplemental intravenous heparin administered to maintain the activated clotting time at 350 to 500 seconds to prevent blood clotting in the retroperfusion system. Study protocol : An experimental group of 5 baboons underwent coronary venous retroperfusion . Control baseline hemodynamic recordings and epicardial electrograms were monitored for 30 minutes before coronary occlusion . The left anterior descending coronary artery was then occluded, and hemodynamic and electrocardiographic recordings were obtained every 15 minutes throughout the experiment . Coronary venous retroperfusion was initiated after 1 hour of occlusion and maintained through a 4-hour period of coronary artery occlusion . When retroperfusion was ended, anterograde perfusion was simultaneously restored by release of the occluding snare . The retroperfusion catheter was then removed, and protamine sulfate was administered to return the activated clotting time to the control level . After a 1-hour reperfusion monitoring period, the epicardial electrodes as well as the cardiac output and left ventricular pressure catheters were removed . The chest was closed while monitoring arterial pressure and the electrocardiogram. The remaining indwelling lines were then removed and the baboons returned to their cages . At 24 hours after occlusion the baboons were killed by rapid infusion of a saturated solution of potassium chloride and their hearts were excised for histologic analysis . A control group of 5 baboons underwent an identical protocol to that utilized in the experimental group including placement of the coronary venous retroperfusion catheter and heparinization . In this group, however, no retroperfusion was initiated . Anterograde reperfusion was restored after 4 hours of coronary occlusion.
Perfusion bed delineation and histologic assessment : Cannulas (0 .58 mm internal diameter) were placed into (1) the left anterior descending coronary artery at the site of previous occlusion, (2) the proximal left anterior descending artery, (3) the proximal left circumflex artery, and (4) the proximal right. coronary artery. These arteries were then injected simultaneously and at equal flow rates with colored silicone rubber microvascular dyes (Microfil, Canton BioMedical Products, Boulder, Colorado) which readily pass through the capillary beds? We previously showed that this dye injection technique allows accurate delineation of the perfusion bed subserved by an occluded coronary artery .8 After fixation of the hearts in 10% formalin for 3 days, serial cross-sections of the left ventricle were made at 3 mm intervals parallel to the minor axis . A microscopic slide was made from each cross-section and stained with hematoxylin and eosin . The perfusion bed of the occluded artery was clearly visualized on the paraffin tissue block of the left ventricular cross-section and was marked on the corresponding histologic slide by superimposing the slide on the tissue block . Microscopic examination of each histologic slide allowed the area of infarction to be also marked on the slide . The areas of the perfusion bed and the areas of infarction were determined by planimetry. These areas were multiplied by the thickness of each cross-section to give the respective volumes for each section . Summation of the volumes of each tissue section yielded the total volume of the perfusion bed and the total volume of infarction for each heart. These values were multiplied by the tissue density to yield the mass of the perfusion bed and the mass of infarct . Statistical analysis : The significance of hemodynamic and histologic changes between control and retroperfused baboons was examined using Student's t test . All values are given as mean ± standard error of the mean.
Results After occlusion of the left anterior descending coronary artery in all 10 baboons, a discrete area of the anterior left ventricular wall appeared visibly cyanotic . In the retroperfused baboons, with the initiation of coronary venous retroperfusion, the anterior interventricular vein was visibly arterialized, and resolution of the area of ventricular cyanosis occurred . With release of the occluding snare 4 hours after ; occlusion, rearterialization occurred promptly in the previously occluded coronary artery in all baboons .
FIGURE 2. The progression of electrocardiographic
BASELINE
I HR POST OCCLUSION
Iq HR POST OCCLUSION
4 HR POST OCCLUSION
I HR POST REPERFUSION
LI CONTROL
=r ∎®® OMEN
®!n not ∎ Min Elk
RETROPERFUSED
r
®N
ME ∎∎ Big
OL
1426
December 1982
The American Journal of CARDIOLOGY Volume 50
changes during the periods of occlusion and reperfusion are shown for a representative control baboon and a retroperfused baboon . No significant S-T segment elevation was present before occlusion in either baboon . One hour after occlusion there were markedly elevated S-T segments in both the control and retroperfused baboons . At 1 a/4 hours after occlusion (15 minutes after the initiation of retroperfusion), there was a significant reduction in S-T segment elevation in the retroperfused baboon with no significant change in S-T segment elevation in the control nonretroperfused baboon . Four hours after occlusion, immediately before reperfusion, the S-T segment in the control baboon remained elevated while the S-T segment in the retroperfused baboon was near baseline. One hour after reperfusion, the control baboon had lost most of its R-wave amplitude and developed a Q wave while the retroperfused baboon retained significant R-wave amplitude and did not develop a 0 wave .
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
FIGURE 3 . Representative cross-section of the heart from a control baboon with a 4-hour occlusion of the left anterior descending coronary artery followed by reperfusion . The perfusion bed of the previously occluded artery was injected with yellow microvascular dye and the adjacent perfusion beds with red dye . The perfusion bed of the occluded artery is readily delineated and contains a large hemorrhagic region which occupies virtually the entire perfusion bed .
Epicardial electrocardiographic recordings : The progression of electrocardiographic changes during the periods of occlusion and reperfusion for a representative control and retroperfused baboon are shown in Figure 2 . There was no significant S-T segment elevation in any of the epicardial leads in either group immediately before occlusion . S-T segment elevation occurred in epi-
FIGURE 4 . Representative cross-section of the heart from a retroperfused baboon . Retroperfusion was mutated 1 hour after occlusion of the left anterior descending coronary artery and maintained for a 4-hour period of occlusion followed by reperfusion . The perfusion bed of the occluded artery is readily delineated by the yellow dye and contains patchy areas of hemorrhage in the subendocardial and mld-wall regions .
cardial leads in the area of ventricular cyanosis within minutes after occlusion of the left anterior descending coronary artery . In the retroperfused baboons, S-T segment elevation decreased rapidly to near control values after the initiation of coronary venous retroperfusion . In the control group, S-T segments remained elevated throughout the 4-hour period of occlusion . In both groups, the remaining S-T segment . elevation steadily decreased during the 1-hour period of anterograde reperfusion, although S-T segments sometimes remained slightly elevated in the control baboons . Delineation of the perfusion bed of the occluded coronary artery : Cross-sections of the left ventricle in both control and retroperfused baboons showed the perfusion bed of the occluded coronary artery to be readily delineated by the microvascular dye . A representative cross-section of the heart from a control baboon, shown in Figure 3, demonstrates the distinct demarcation of perfusion bed boundaries as well as the extensive hemorrhage which occupied virtually the entire perfusion bed of the Occluded artery . Figure 4 shows a representative cross-sect ion of the heart from a retroperfused baboon and again illustrates the distinct demarcation of the perfusion bed boundaries . In contrast to the control group of baboons, however, hemorrhage was confined to the subendocardial and mid-wall regions of the perfusion bed . Comparison of histologic changes in control and retroperfused baboons : Microscopic examination of hematoxylin and eosin-stained left ventricular crosssections in control baboons showed extensive coagulation necrosis which essentially occupied the entire perfusion bed of the occluded artery . The area of infarction was completely contained within the perfusion bed . Necrotic myocardial cells exhibited the characteristic changes of pyknosis, karyolysis, and loss of cross-striations . There was extensive hemorrhage within the inf'arctcd region . Microscopic examination of left ventricular crosssections in the retroperfused baboons showed that the area of infarction was also completely contained within the perfusion bed of the occluded artery . Infarcts characteristically consisted of a central confluent zone of infarction surrounded by a peripheral zone of small foci of patchy infarction . The infarcts showed coagulation necrosis and involved the suhendocardial and mid-wall regions of the perfusion bed, while myocardial preservation was observed in the suhepicardial and lateral regions . Hemorrhage was evident within the central area of infarction ; however, no hemorrhage was observed outside the infarcted region . In the retroperfused baboons, minimal venous hemorrhage was often evident close to veins at the epicardial surface and particularly those close to the retroperfusion catheter . This hemorrhage did not extend below the epicardial surface . There was no gross evidence of damage to the coronary veins in either group of baboons . Comparison of the percentage of the perfusion bed infarcted in control and retroperfused baboons: Table I shows the mass of the perfusion bed, the mass of the infarct, and the mass of hemorrhage for individual
December 1982
The American Journal of CARDIOLOGY Volume 50
1 427
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
TABLE I
Comparison of Data on the Control and Retroperfused Baboons Perfusion Bed Mass (g)
Baboon
Infarct Mass (g)
% of Perfusion Bed Infarcted
Hemorrhagic Mass (g)
% of Perfusion Bed Hemorrhagic
18 .2 8 .7 8 .5 14 .6 8 .4 11 .732 .0
71 .9 57 .6 59 .2 75 .4 54 .2 63 .7+4 .2
8 .6 0 .1 0 .0 2 .6 1 .1 2 .531 .6'
21 .0 1 .0 0 .0 15 .7 11 .3 9 .8+4 .1'
Control 25 .3 15 .1 14 .3 19 .3 15 .4 17 .9 ± 2 .0
23 .7 13 .8 13 .7 18 .7 14 .3 16 .8 ± 2 .0
40 .7 4 .7 11 .7 16 .8 9 .9 16 .8+6 .3
20 .3 2 .8 6 .4 11 .1 5 .5 9 .2+3 .1
93 .6 91 .9 95 .5 96 .5 92 .8 94 .1 3 0 .9 Retroperfused
1 2 3 4 5
49 .9 58 .1 52 .8 70 .1 55 .9 57 .4+3 .5'
* Significant difference (p <0 .001) between control and retroperfused groups .
baboons in both groups . A substantial reduction was observed in the percentage of the anatomic perfusion bed infarcted in the retroperfused baboons when compared to that in the control nonretroperfused baboons . The mean perfusion bed mass was 17 .9 f 2 .0 g in the control baboons and 16 .8 ± 6 .3 g in the retroperfused baboons . These values are not statistically different (p >0.1) . In the control group, the mean percentage of the perfusion bed infarcted was 94 .1 ± 0.9 . In the retroperfused group, the mean percentage of the perfusion bed infarcted was 57 .4 ± 3 .5 . This difference was highly significant (p <0.001) . Hence, with retroperfusion begun after 1 hour of coronary occlusion, the area of the perfusion bed undergoing ultimate infarction was reduced by a mean of 36 .7% when comparing the control and retroperfused groups. Hemorrhage was always contained within the infarct region and the mean percentage of the perfusion bed that was hemorrhagic was significantly lower than the mean percentage of the perfusion bed infarcted in both control and retroperfused groups (p <0 .001) . In the control group, the mean percentage of the perfusion bed
TABLE II
that was hemorrhagic was 63 .7 ± 4 .2 ; in the retroperfused group the mean percentage of the perfusion bed that was hemorrhagic was 9 .8 t 4 .1 . This difference was also highly significant (p <0 .001) . Hemodynamic changes : Table II summarizes the hemodynamic values in the control and retroperfused baboons for the preocclusion, 15-minute postocclusion, 4-hour postocclusion (before ending retroperfusion), and 1-hour postreperfusion recording periods . At the preocclusion recording period, there was no significant differences in any of the hemodynamic values in control and retroperfusion baboons . There were no significant changes from the preocclusion recording period in any of the hemodynamic values in the control or retroperfused groups at any of the recording periods . Discussion The coronary veins have been utilized as a means of rearterialization of a region of myocardial ischemia since the initial experimental and clinical observations of Beck et a19'10 and others.' L12 The concept of selective rather than global coronary venous retroperfusion, to-
Hemodynamic Values Before and After Occlusion and After Reperfuslon for the Control and Retroperfuslon Baboons After Occlusion
HR _(beats/min) AP (mm Hg) LVEDP (mm Hg) CO (ml/min) Peak dP/dt (mm Hg/s
Control Retroperfused Control Retroperfused Control Retroperfused Control Retroperfused Control Retroperfused
Before Occlusion
15 Minutes
4 Hours
1 Hour After Reperfusion
124 + 4 110 ± 3 117+4 108+4 5 .3 ± 1 .0 4 .4 ± 0 .9 1,831 ± 215 1,700 ± 265 2,180 ± 156 1,888 ± 254
128 + 6 112 + 4 12337 107 ± 3 8 .0 ± 3 .3 4 .0 ± 1 .4 1,950 f 180 1,710 ± 105 1,848 ± 221 1,436 ± 192
125 + 4 107 ± 6 114+3 100 ± 6 4 .6 ± 1 .0 4 .8 ± 1 .9 1,860 1 262 1,450 ± 180 1,880 ± 153 1,748 ± 297
124 + 5 106 3 7 112+6 106 + 6 5 .410 .8 5 .0 ± 1 .0 1,770 f 378 1,550 ± 132 1,840 ± 172 1,896 ± 262
AP = mean arterial pressure ; CO = cardiac output ; HR = heart rate : LVEDP = left ventricular end-diastolic pressure ; peak dP/dt = peak value of rate of rise of left ventricular pressure .
1 42 8
December 1982
The American Journal of CARDIOLOGY
Volume 50
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
gether with the identification of a group of patients with severe chronic arterial disease not amenable to coronary bypass grafting, led to surgical procedures aimed at selective arterialization of the coronary venous system.'2 i- Subsequently, several investigators modified this concept and employed retroperfusion by selective catheterization of the coronary venous system to reverse ischemia following acute coronary artery occlusion .1 ,18 These systems have employed pulsatile venous retroperfusion which is synchronized with the cardiac cycle, so that the retrograde arterial pulse is programmed to occur during diastole and is discontinued during systole to allow for adequate venous drainage . These studies have demonstrated that after the initiation of retroperfusion, there is (1) a reduction in epicardial S-T segment elevation,' 3,4 .IS (2) improved myocardial oxygen tension in the ischemic segment, 3. 4 (3) improved function in the ischemic segment,2' 4 and (4) an increase in global left ventricular function. 1,2 However, despite these favorable reports, little information has been generated to document the extent to which retroperfusion may decrease ultimate histologically determined infarct size . Therefore, the present study evaluated the effectiveness of retroperfusion in reducing infarct size when begun 1 hour after occlusion and maintained throughout a total 4-hour period of coronary occlusion . Additionally, infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk to infarction) for a more accurate assessment of the effects of retroperfusion on infarct size . Quantitative method of determining myocardial salvage due to coronary venous retroperfusion : It has been shown considerable variability exists in infarct size resulting from coronary artery occlusion at any given anatomic site . 19 ' 20 This variability results from differences in the region at risk to infarction due to inherent differences in the size of the anatomic perfusion bed subserved by an occluded artery . We have previously demonstrated in the baboon that : the microvascular dye technique employed in this study accurately delineates the anatomic perfusion bed of the occluded artery .' By comparing the percentage of the perfusion bed of the occluded artery which undergoes infarction in control and retroperfused baboons, an accurate quantitative assessment of the degree of myocardial salvage achieved by retroperfusion may be determined . Effectiveness of coronary venous retroperfusion in reducing infarct size : We previously demonstrated in the baboon that retroperfusion started at 15 minutes after coronary occlusion and maintained for a total 4hour period of occlusion resulted in an 84% mean reduction in infarct size .' Because retroperfusion was initiated early, before the onset of necrosis within the ischemic region, the optimal effectiveness of retroperfusion was demonstrated in the study . In the present study, retroperfusion was begun 1 hour after occlusion and resulted in a 36 .7% mean reduction in infarct size . Thus, the delay from the onset of coronary occlusion to the initiation of retroperfusion is a critical determinant of the degree of myocardial salvage .
Comparison of anterograde arterial reperfusion versus coronary venous retroperfusion in reducing infarct size : The degree of myocardial salvage with anterograde arterial reperfusion depends on the time reperfusion is begun . The degree of myocardial salvage with retroperfusion depends not only on the time retroperfusion is begun, but also on how effectively the retroperfusion system is capable of delivering arterial blood to the ischemic region . Thus, it is interesting to examine how closely coronary venous retroperfusion approaches the effectiveness of arterial reperfusion in reducing infarct size. In order for coronary venous retroperfusion to be effective, it must deliver sufficient arterial blood to all levels of the myocardial wall within the ischemic region to satisfy the oxygen demands of this region . A number of studies using injection of various contrast agents have indirectly suggested that retroperfused blood is effectively delivered to the ischemic region . 2 t ,22 The studies of Hochberg et a116,23 using radioactive microspheres demonstrated that retrograde arterial blood flow is distributed to all levels of an acutely ischemic region and not significantly shunted by thebesian or veno-venous channels . More recently, Berdeaux et al," also using microspheres, demonstrated that retroperfusion initiated at 1 hour after coronary occlusion returned transmural flow in the ischemic region to 45% of the normal control flow which existed before coronary occlusion . The results of this study of Berdeaux et al 18 bear directly on the question of whether this degree of restoration of flow is sufficient to substantially prolong myocardial viability . This question may be clarified by directly comparing the degree of infaret salvage achieved by anterograde reperfusion with the degree of inf'arctsalvage achieved by retroperfusion instituted at comparable times after acute coronary occlusion . We have shown in the baboon that with anterograde reperfusion 2 hours after coronary occlusion, a mean of 50 .1% of the perfusion bed of the occluded artery was infarcted .L4 With retroperfusion 1 hour after coronary occlusion in the present study, a mean of 57 .4% of the perfusion bed of the occluded artery was infarcted . It is interesting that with retroperfusion 1 hour after coronary occlusion, the percentage of the perfusion bed infarcted was approximately the same as that found with anterograde reperfusion 2 hours after occlusion . This finding is consistent with the observation by Berdeaux et al's that retroperfusion initiated 1 hour after coronary occlusion was capable of restoring blood flow to only 45% of the normal control flow . Hemorrhage associated with retroperfusion : Is hemorrhage associated with retroperfusion deleterious to ischemic myocardium? Although the infarcts in the retroperfused baboons were hemorrhagic, the hemorrhage was confined within the infarcted region and did not appear to extend the infarct . This observation is similar to that noted with anterograde reperfusion ; several investigators have demonstrated that hemorrhage after reperfusion does not extend infarct size . 25 28 Some hemorrhage was noted around superficial veins,
December 1982
The American Journal of CARDIOLOGY Volume 50
1 42 9
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
but it did not extend below the epicardial surface and there was no gross damage to the coronary veins . Clinical application of coronary venous retroperfusion : Experimental animal studies suggest that anterograde reperfusion must be undertaken within the first few hours after coronary occlusion for significant salvage of ischemic myocardium to occur .24 .25,29 The time interval in the clinical setting in which restoration of perfusion salvages significant myocardium remains unclear but may be longer than experimental animal studies suggest . Hence, retroperfusion may be useful clinically as a simple and prompt method to temporarily rearterialize an acutely ischemic region until such time as more definitive revascularization may be undertaken . It is also noted that coronary venous retroperfusion may be useful by providing a potential avenue for the introduction of pharmacologic agents directly into the ischemic region . References 1 . Markov AK, Lehan PH, Hellems HK . Reversal of acute myocardial ischemia in closed chest animals by retrograde perfusion of the coronary sinus with arterial blood . Acts Cardiol 1976 ;31 :185-199 . 2 . Farcol JC, Meerbaum S, Lang T, Kaplan L, Corday E . Synchronized retroperfusion of coronary veins for circulatory support of jeopardized ischemic myocardium . Am J Cardiol 1978 ;21 :1191-1201 . 3 . Feola M, Weiner L . A method of coronary retroperfusion for the treatment of acute myocardial ischemia . Cardiovasc Dis 1978 ;5 :235-243 . 4 . Meerbaum S, Lang T, Osher JV, Hashlmoto K, Lewis OW, Feldstein C, Corday E. Diastolic retroperfusion of acutely ischemic myocardium . Am J Cardiol 1976 ;37 :588-598 . 5 . Smith GT, Geary GG, Blanchard W, McNamara JJ . Reduction in infarct size by synchronized selective coronary venous retroperfusion of arterialized blood . Am J Cardiol 198 1 ;48:1064-1070 . 6 . Jennings RB, Sommers HM, Smyth GA, Flack HA, Linn H . Myocardial necrosis induced by temporary occlusion of a coronary artery in the dog . AMA Arch Pethol 1960 ;70 :68-78 . 7 . Grayson J, Davidson JW, Fitzgerald-Finch A, Scott C . The functional morphology of the coronary microcirculation in the dog . Microvasc Pies 1974 ;8 :20-43 . 8 . Geary GG, Smith GT, McNamara JJ . Defining the anatomic perfusion bed of an occluded coronary artery and the region at risk to infarction . A comparative study in the baboon, pig and dog. Am J Cardiol 1981 ;47 :12401247 . 9. Beck CS, Stanton E, Balluchok W, Leiter E . Revascularization of the heart by graft of systemic artery into coronary sinus . JAMA 1948 ;137:436442 . 10 . Beck CS, Leighnlnger DS . Operations for coronary artery disease . JAMA 1954;13:1226-1233 .
1 43 0
December 1982
The American Journal of CARDIOLOGY
11 . Eckstein RW, Horberger C, Sara T . Acute effects of elevation of coronary sinus pressure . Circulation 1953 ;7:422-436 . 12. Baket AA, Coslas-Durleux J, Goldberg H, Bailey CP . Protection of the heart by arterialization of the coronary sinus . II . Coronary flow in dogs with aortico-coronary sinus anastomosis . J Thorac Cardiovasc Surg 1954 :27: 442-454 . 13 . Andreadis P, Natsikas N, Arealis E, Lazarides OP . The aortocoronary venous anastomosis in experimental acute myocardial ischemia . Vasc Stag 1974;8:45-52 . 14 . Bheyana JN, Olson DB, Bryne JP, Koift WJ. Reversal of myocardial ischernia by arterialization of the coronary vein . J Thorac Cardiovasc Stag 1974; 67 :125-132. 15 . Benedict JS, Buhl TL, Henney RP . Cardiac vein myocardial revascularization . An experimental study and report of 3 clinical cases . Ann Thorac Surg 1975 ;20 :550-555 . 16 . Hochberg MS. Hemodynamic evaluation of selective arterialization of the coronary venous system : an experimental study of myocardial perfusion using radioactive microspheres. J Thorac Cardiovasc Sug 1977 ;74 : 774-783 . 17 . Chiu CJ, Mulder DS. Selective arterialization of coronary veins for diffuse coronary occlusion: an experimental evaluation . J Thorac Cardlovasc Surg 1975 ;70 :177-182 . 18 . Bordeaux A, Farcol J, Boundaries J, Barry M, Bardet J, Gualcelll J . Effects of diastolic synchronized retropertusion on regional coronary blood flow in experimental myocardial ischemia . Am J Cardiol 1981 :47 :10331040 . 19 . Lowe JE, Relmer KA, Jennings RB. Experimental infarct size as a function of the amount of myocardium at risk . Am J Pathol 1978 ;90:363-377 . 20 . Baughman KL, Maroko RP, Vatner SF . Effects of coronary artery reperfusion on myocardial infarct size and suvival in conscious dogs . Circulation 1981 ;63 :317-323 . 21 . Bishop SP, White FC, Beer CM . Regional myocardial blood flow during acute myocardial infarction in the conscious dog . Circulation 1976 ;38 : 429-438 . 22 . Solorzano J, Taitelbaum G, Chiu CJ . Retrograde coronary sinus perfusion for myocardial protection during cardiopulmonary bypass . Ann Thorne Sung 1978 ;25 :201-208 . 23 . Hochberg MS, Roberts WC, Morrow AG, Auslen WG . Selective arterialization of the coronary venous system . Encouaging long term flow evaluation utilizing radioactive microspheres . J Thorac ardiovasc Surg 1979 ; 77:1-12 . 24 . Geary GG, Smith GT, McNamara JJ . Extent of myocardial salvage by early coronary artery reperfusion in the absence of significant collaterals in baboons (abstr) . Circulation 1981 ;64: Suppl IV :IV-98 . 25. Reimer KA, Lowe JE, Rasmussen MM, Jennings RS . The wavefront phenomenon of ischemic cell death . I . Myocardial infarct size vs duration of coronary occlusion in dogs . Circulation 1977 ;56 :786-794 . 26. Geary GG, Smith GT, McNamara JJ . Quantitative effect of early coronary artery reperfusion in baboons . Extent of salvage of the perfusion bed of an occluded artery . Circulation 1982;66:391-396 . 27 . Kloner RA, Rude RE, Carlson N, Maroko PR, DeBoer LW, Braunwald E . Ullrastructural evidence of mlcrovascular damage and myocardial cell injuy after coronary artery occlusion : which comes first? Circulation 1960 ;62 : 945--952. 28 . Fishbeln MC, V-Rlt J, Lando U, Kanamatsuse K, Mercier JC, Ganz W . The relationship of vascular injury and myocardial hemorrhage to necrosis after reperfusion . Circulation 1980 ;62 :1274-1279 . 29 . Smith GT, Sorrier JR, Haston HH, McNamara JJ . Coronary reperfusion in primates . Serial electrocardiographic and histological assessment . J Clin Invest 1974 ;54 :1420 1427 .
Volume 50
Initial favorable reports in which coronary venous retroperfusion was begun after acute coronary artery occlusion have demonstrated a reversal of ischemic injury and improved left ventricular function. However, little information has been generated to document the extent to which retroperfusion may decrease ultimate histologically determined infarct size . The objective of the present study was to evaluate the effectiveness of retroperfusion in reducing infarct size by using an accurate quantitative method in which infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk for infarction) . In an experimental group of 5 baboons, the left anterior descending coronary artery was occluded and coronary venous retroperfusion started 1 hour after occlusion . After a 4-hour period of occlusion, retroperfusion was discontinued and anterograde perfusion was si-
multaneously restored. A control group of 5 baboons underwent an identical procedure without retroperfusion . Twenty-four hours after occlusion, hearts were excised and the previously occluded left anterior descending coronary artery as well as the adjacent arteries were injected with microvascular dye to delineate the perfusion bed of the occluded artery . Planimetry of serial cross-sections of the left ventricle enabled the size of the perfusion bed of the occluded artery and size of the infarct to be determined . The mean percentage of the perfusion bed infarcted in the control group was 94 .110 .9 (mean ± standard error) and in the retroperfused group was 57 .4 f 3 .5 (p <0 .001) . Hence, the results demonstrated that when retroperfusion was initiated after 1 hour of coronary occlusion, the mean percentage of the perfusion bed salvaged was increased by 36 .7% .
Several investigators have shown that selective synchronized coronary venous retroperfusion, when started after acute coronary artery occlusion, may result in partial reversal of ischemic injury1 3 and improved left ventricular function . 1,2,1 Despite these favorable reports, little information has been available as to whether retroperfusion reduces infarct size as histologically assessed . In our previous study in the baboon, we demonstrated that retroperfusion begun 15 minutes after coronary artery occlusion combined with later anterograde reperfusion substantially reduced the percentage of the left ventricle ultimately infarcted . 5 Because
retroperfusion was initiated early at a time when the entire ischemic region has been shown to remain viable, 6 the optimal effectiveness of the retroperfusion system was demonstrated . The results of the initial study demonstrated the capability of the retroperfusion system to maintain the viability of ischemic myocardium . Because of these results, the next step was to examine the effectiveness when it was delayed for a period consistent with its clinical use . Therefore, the objective of the present study was to examine the effectiveness of coronary venous retroperfusion in reducing infarct size when retroperfusion was delayed for 1 hour after coronary occlusion . Additionally, a more accurate methodologic approach was employed to determine the degree of myocardial salvage achieved by retroperfusion . Infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk for infarction) . This technique eliminated the variability in infarct size which may occur due to inherent variability in the size of the anatomic perfusion bed of an occluded artery . Thus, a
From the Cardiovascular Research Laboratory, Department of Surgery, John A . Burns School of Medicine, Queen's Medical Center, Honolulu, Hawaii . This study was supported by Grant 5 R01 HL 14571-09 from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, and by a grant from the George F . Straub Trust, Honolulu, Hawaii . Manuscript received January 25, 1982 ; revised manuscript received June 22, 1982, accepted June 25, 1982 . Address for reprints : J . Judson McNamara, MD, Department of Surgery, Queen's Medical Center, 1301 Punchbowl Street, Honolulu, Hawaii 96813 .
1424
December 1982 The American Journal of CARDIOLOGY
Volume 50
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
infusion of heparinized saline solution was maintained through the catheter to ensure patency until retroperfusion was initiated . Two rows of 6 unipolar atraumatic epicardial electrodes spaced at 5 mm intervals were placed across the anticipated region of ischemia parallel to the minor axis of the left ventricle . Recordings from the electrode rows were used to assess directional changes in S-T segment elevation during periods of occlusion, retroperfusion, and anterograde reperfusion . Coronary venous retroperfusion system : The coronary venous retroperfusion system is schematically illustrated in Figure 1 . It is similar to our previously described systeme except that a commercially available pulsatile pump and pumping chamber were employed . The right femoral artery served as the source of arterial blood which flowed through an occlusive roller pump calibrated to accurately deliver the small required blood flow rates .'1'he roller pump provided a continuous blood flow of 40 to 50 ml/min into a bladder contained within a pediatric pulsatile bypass chamber (Kontron Cardiovascular, Everett, Massachusetts) . The chamber contains 2 bladders ; I is connected to the roller pump and the other is connected to a pulsatile bypass pump (Model 20, Kontron Cardiovascular) which provides active compression and decompression of the blood-filled bladder . Arterialized blood from the bladder was pumped in a pulsatile manner through the retroperfusion catheter positioned in the great cardiac vein . A Statham P23 Db pressure transducer was connected between the pumping chamber and the retroperfusion catheter to assist in monitoring venous perfusion pressures . These pressures directly reflect the pressures in the coronary veins. An elevation in pressure may occur due either to wedging of the catheter in the coronary veins or inadequate drainage due to the flow rate being set too high . If the flow was set at >50 ml/min, the retroperfusion pump was usually not able to deliver the required volume during the diastolic compression phase . Consequently flow would continue into the coronary veins during systole, resulting in inadequate drainage and an elevation in pressure . We previously showed
more accurate quantitative assessment of myocardial salvage by retroperfusion may be determined .
Methods Surgical preparation: Ten baboons (Papio anubis), 20 to 26 kg, were initially sedated with ketamine hydrochloride (10 mg/kg intramuscularly) . Anesthesia was induced and maintained with intravenous infusions of sodium thiopental (2 mg/kg) . A standard lead H electrocardiogram was monitored . Baboons were intubated with a cuffed endotracheal tube and ventilated with a Harvard volume respirator maintaining an arterial pH of 7 .40 f 0.05 . Supplemental oxygen was administered as necessary to maintain an arterial oxygen saturation of at least 95% . Arterial pressure was monitored by an 8Fr stiff-walled catheter advanced through the left femoral artery . Intravenous fluids were administered via a catheter through the left femoral vein . A 9Fr cannula was inserted into the right femoral artery and served as the source of arterialized blood for the coronary venous retroperfusion system . A mid-sternal thoracotomy was performed and the heart suspended in a pericardial cradle . The left anterior descending coronary artery was dissected free from the anterior interventricular vein distal to the first diagonal branch . A 3-0 Mersilene® snare was placed around the dissected left anterior descending coronary artery for subsequent ligation . An electromagnetic flow catheter (Millar instruments, Houston, Texas) was inserted into the pulmonary artery by means of a purse-string suture for measurement of cardiac output . Left ventricular pressure, the rate of rise of left ventricular pressure, and left ventricular end-diastolic pressure were monitored with use of a micromanometer tip catheter (Millar) which was inserted through a 12-gauge cannula into the left ventricle . A 6Fr thin-walled preshaped polyethylene retroperfusion catheter was inserted into the right atrium through a purse-string suture in the atrial appendage . The catheter was then advanced through the coronary sinus to position its tip at the junction of the great cardiac vein and the anterior interventricular vein . A slow
Pressure Transducer
I _
Great Cardiac Vein
Left Marginal Vein
Anterior Interventricular Vein
I
Middle Cardiac Vein
Coronary Sinus
Pulsatile Balloon Pump Arterial Blood Supply tow
FIGURE 1 . Diagram of the retroperfusion system . See text for detailed description .
December 1982
The American Journal of CARDIOLOGY Volume 50
1 42 5
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
that a flow rate of 40 to 50 ml/min produced adequate rearterialization 5 We did not simultaneously record the pressures in the coronary veins as this would have required insertion of a separate line for pressure recording. However, in preliminary experiments, we monitored pressure in the anterior interventricular vein during retroperfusion with flows up to 60 ml/min and found the pressure <50 mm Hg . The pulsatile pump system was adjusted so that forward pulsed perfusion occurred only in diastole and perfusion was interrupted during systole so that normal coronary venous drainage was allowed . This was accomplished by simultaneously displaying the left ventricular pressure and the retroperfusion pressure tracings so the retroperfusion pulse could be adjusted to occur during the diastolic interval . Anticoagulation was maintained during the period of retroperfusion by initial heparinization (5 mg/kg intravenously), with supplemental intravenous heparin administered to maintain the activated clotting time at 350 to 500 seconds to prevent blood clotting in the retroperfusion system. Study protocol : An experimental group of 5 baboons underwent coronary venous retroperfusion . Control baseline hemodynamic recordings and epicardial electrograms were monitored for 30 minutes before coronary occlusion . The left anterior descending coronary artery was then occluded, and hemodynamic and electrocardiographic recordings were obtained every 15 minutes throughout the experiment . Coronary venous retroperfusion was initiated after 1 hour of occlusion and maintained through a 4-hour period of coronary artery occlusion . When retroperfusion was ended, anterograde perfusion was simultaneously restored by release of the occluding snare . The retroperfusion catheter was then removed, and protamine sulfate was administered to return the activated clotting time to the control level . After a 1-hour reperfusion monitoring period, the epicardial electrodes as well as the cardiac output and left ventricular pressure catheters were removed . The chest was closed while monitoring arterial pressure and the electrocardiogram. The remaining indwelling lines were then removed and the baboons returned to their cages . At 24 hours after occlusion the baboons were killed by rapid infusion of a saturated solution of potassium chloride and their hearts were excised for histologic analysis . A control group of 5 baboons underwent an identical protocol to that utilized in the experimental group including placement of the coronary venous retroperfusion catheter and heparinization . In this group, however, no retroperfusion was initiated . Anterograde reperfusion was restored after 4 hours of coronary occlusion.
Perfusion bed delineation and histologic assessment : Cannulas (0 .58 mm internal diameter) were placed into (1) the left anterior descending coronary artery at the site of previous occlusion, (2) the proximal left anterior descending artery, (3) the proximal left circumflex artery, and (4) the proximal right. coronary artery. These arteries were then injected simultaneously and at equal flow rates with colored silicone rubber microvascular dyes (Microfil, Canton BioMedical Products, Boulder, Colorado) which readily pass through the capillary beds? We previously showed that this dye injection technique allows accurate delineation of the perfusion bed subserved by an occluded coronary artery .8 After fixation of the hearts in 10% formalin for 3 days, serial cross-sections of the left ventricle were made at 3 mm intervals parallel to the minor axis . A microscopic slide was made from each cross-section and stained with hematoxylin and eosin . The perfusion bed of the occluded artery was clearly visualized on the paraffin tissue block of the left ventricular cross-section and was marked on the corresponding histologic slide by superimposing the slide on the tissue block . Microscopic examination of each histologic slide allowed the area of infarction to be also marked on the slide . The areas of the perfusion bed and the areas of infarction were determined by planimetry. These areas were multiplied by the thickness of each cross-section to give the respective volumes for each section . Summation of the volumes of each tissue section yielded the total volume of the perfusion bed and the total volume of infarction for each heart. These values were multiplied by the tissue density to yield the mass of the perfusion bed and the mass of infarct . Statistical analysis : The significance of hemodynamic and histologic changes between control and retroperfused baboons was examined using Student's t test . All values are given as mean ± standard error of the mean.
Results After occlusion of the left anterior descending coronary artery in all 10 baboons, a discrete area of the anterior left ventricular wall appeared visibly cyanotic . In the retroperfused baboons, with the initiation of coronary venous retroperfusion, the anterior interventricular vein was visibly arterialized, and resolution of the area of ventricular cyanosis occurred . With release of the occluding snare 4 hours after ; occlusion, rearterialization occurred promptly in the previously occluded coronary artery in all baboons .
FIGURE 2. The progression of electrocardiographic
BASELINE
I HR POST OCCLUSION
Iq HR POST OCCLUSION
4 HR POST OCCLUSION
I HR POST REPERFUSION
LI CONTROL
=r ∎®® OMEN
®!n not ∎ Min Elk
RETROPERFUSED
r
®N
ME ∎∎ Big
OL
1426
December 1982
The American Journal of CARDIOLOGY Volume 50
changes during the periods of occlusion and reperfusion are shown for a representative control baboon and a retroperfused baboon . No significant S-T segment elevation was present before occlusion in either baboon . One hour after occlusion there were markedly elevated S-T segments in both the control and retroperfused baboons . At 1 a/4 hours after occlusion (15 minutes after the initiation of retroperfusion), there was a significant reduction in S-T segment elevation in the retroperfused baboon with no significant change in S-T segment elevation in the control nonretroperfused baboon . Four hours after occlusion, immediately before reperfusion, the S-T segment in the control baboon remained elevated while the S-T segment in the retroperfused baboon was near baseline. One hour after reperfusion, the control baboon had lost most of its R-wave amplitude and developed a Q wave while the retroperfused baboon retained significant R-wave amplitude and did not develop a 0 wave .
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
FIGURE 3 . Representative cross-section of the heart from a control baboon with a 4-hour occlusion of the left anterior descending coronary artery followed by reperfusion . The perfusion bed of the previously occluded artery was injected with yellow microvascular dye and the adjacent perfusion beds with red dye . The perfusion bed of the occluded artery is readily delineated and contains a large hemorrhagic region which occupies virtually the entire perfusion bed .
Epicardial electrocardiographic recordings : The progression of electrocardiographic changes during the periods of occlusion and reperfusion for a representative control and retroperfused baboon are shown in Figure 2 . There was no significant S-T segment elevation in any of the epicardial leads in either group immediately before occlusion . S-T segment elevation occurred in epi-
FIGURE 4 . Representative cross-section of the heart from a retroperfused baboon . Retroperfusion was mutated 1 hour after occlusion of the left anterior descending coronary artery and maintained for a 4-hour period of occlusion followed by reperfusion . The perfusion bed of the occluded artery is readily delineated by the yellow dye and contains patchy areas of hemorrhage in the subendocardial and mld-wall regions .
cardial leads in the area of ventricular cyanosis within minutes after occlusion of the left anterior descending coronary artery . In the retroperfused baboons, S-T segment elevation decreased rapidly to near control values after the initiation of coronary venous retroperfusion . In the control group, S-T segments remained elevated throughout the 4-hour period of occlusion . In both groups, the remaining S-T segment . elevation steadily decreased during the 1-hour period of anterograde reperfusion, although S-T segments sometimes remained slightly elevated in the control baboons . Delineation of the perfusion bed of the occluded coronary artery : Cross-sections of the left ventricle in both control and retroperfused baboons showed the perfusion bed of the occluded coronary artery to be readily delineated by the microvascular dye . A representative cross-section of the heart from a control baboon, shown in Figure 3, demonstrates the distinct demarcation of perfusion bed boundaries as well as the extensive hemorrhage which occupied virtually the entire perfusion bed of the Occluded artery . Figure 4 shows a representative cross-sect ion of the heart from a retroperfused baboon and again illustrates the distinct demarcation of the perfusion bed boundaries . In contrast to the control group of baboons, however, hemorrhage was confined to the subendocardial and mid-wall regions of the perfusion bed . Comparison of histologic changes in control and retroperfused baboons : Microscopic examination of hematoxylin and eosin-stained left ventricular crosssections in control baboons showed extensive coagulation necrosis which essentially occupied the entire perfusion bed of the occluded artery . The area of infarction was completely contained within the perfusion bed . Necrotic myocardial cells exhibited the characteristic changes of pyknosis, karyolysis, and loss of cross-striations . There was extensive hemorrhage within the inf'arctcd region . Microscopic examination of left ventricular crosssections in the retroperfused baboons showed that the area of infarction was also completely contained within the perfusion bed of the occluded artery . Infarcts characteristically consisted of a central confluent zone of infarction surrounded by a peripheral zone of small foci of patchy infarction . The infarcts showed coagulation necrosis and involved the suhendocardial and mid-wall regions of the perfusion bed, while myocardial preservation was observed in the suhepicardial and lateral regions . Hemorrhage was evident within the central area of infarction ; however, no hemorrhage was observed outside the infarcted region . In the retroperfused baboons, minimal venous hemorrhage was often evident close to veins at the epicardial surface and particularly those close to the retroperfusion catheter . This hemorrhage did not extend below the epicardial surface . There was no gross evidence of damage to the coronary veins in either group of baboons . Comparison of the percentage of the perfusion bed infarcted in control and retroperfused baboons: Table I shows the mass of the perfusion bed, the mass of the infarct, and the mass of hemorrhage for individual
December 1982
The American Journal of CARDIOLOGY Volume 50
1 427
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
TABLE I
Comparison of Data on the Control and Retroperfused Baboons Perfusion Bed Mass (g)
Baboon
Infarct Mass (g)
% of Perfusion Bed Infarcted
Hemorrhagic Mass (g)
% of Perfusion Bed Hemorrhagic
18 .2 8 .7 8 .5 14 .6 8 .4 11 .732 .0
71 .9 57 .6 59 .2 75 .4 54 .2 63 .7+4 .2
8 .6 0 .1 0 .0 2 .6 1 .1 2 .531 .6'
21 .0 1 .0 0 .0 15 .7 11 .3 9 .8+4 .1'
Control 25 .3 15 .1 14 .3 19 .3 15 .4 17 .9 ± 2 .0
23 .7 13 .8 13 .7 18 .7 14 .3 16 .8 ± 2 .0
40 .7 4 .7 11 .7 16 .8 9 .9 16 .8+6 .3
20 .3 2 .8 6 .4 11 .1 5 .5 9 .2+3 .1
93 .6 91 .9 95 .5 96 .5 92 .8 94 .1 3 0 .9 Retroperfused
1 2 3 4 5
49 .9 58 .1 52 .8 70 .1 55 .9 57 .4+3 .5'
* Significant difference (p <0 .001) between control and retroperfused groups .
baboons in both groups . A substantial reduction was observed in the percentage of the anatomic perfusion bed infarcted in the retroperfused baboons when compared to that in the control nonretroperfused baboons . The mean perfusion bed mass was 17 .9 f 2 .0 g in the control baboons and 16 .8 ± 6 .3 g in the retroperfused baboons . These values are not statistically different (p >0.1) . In the control group, the mean percentage of the perfusion bed infarcted was 94 .1 ± 0.9 . In the retroperfused group, the mean percentage of the perfusion bed infarcted was 57 .4 ± 3 .5 . This difference was highly significant (p <0.001) . Hence, with retroperfusion begun after 1 hour of coronary occlusion, the area of the perfusion bed undergoing ultimate infarction was reduced by a mean of 36 .7% when comparing the control and retroperfused groups. Hemorrhage was always contained within the infarct region and the mean percentage of the perfusion bed that was hemorrhagic was significantly lower than the mean percentage of the perfusion bed infarcted in both control and retroperfused groups (p <0 .001) . In the control group, the mean percentage of the perfusion bed
TABLE II
that was hemorrhagic was 63 .7 ± 4 .2 ; in the retroperfused group the mean percentage of the perfusion bed that was hemorrhagic was 9 .8 t 4 .1 . This difference was also highly significant (p <0 .001) . Hemodynamic changes : Table II summarizes the hemodynamic values in the control and retroperfused baboons for the preocclusion, 15-minute postocclusion, 4-hour postocclusion (before ending retroperfusion), and 1-hour postreperfusion recording periods . At the preocclusion recording period, there was no significant differences in any of the hemodynamic values in control and retroperfusion baboons . There were no significant changes from the preocclusion recording period in any of the hemodynamic values in the control or retroperfused groups at any of the recording periods . Discussion The coronary veins have been utilized as a means of rearterialization of a region of myocardial ischemia since the initial experimental and clinical observations of Beck et a19'10 and others.' L12 The concept of selective rather than global coronary venous retroperfusion, to-
Hemodynamic Values Before and After Occlusion and After Reperfuslon for the Control and Retroperfuslon Baboons After Occlusion
HR _(beats/min) AP (mm Hg) LVEDP (mm Hg) CO (ml/min) Peak dP/dt (mm Hg/s
Control Retroperfused Control Retroperfused Control Retroperfused Control Retroperfused Control Retroperfused
Before Occlusion
15 Minutes
4 Hours
1 Hour After Reperfusion
124 + 4 110 ± 3 117+4 108+4 5 .3 ± 1 .0 4 .4 ± 0 .9 1,831 ± 215 1,700 ± 265 2,180 ± 156 1,888 ± 254
128 + 6 112 + 4 12337 107 ± 3 8 .0 ± 3 .3 4 .0 ± 1 .4 1,950 f 180 1,710 ± 105 1,848 ± 221 1,436 ± 192
125 + 4 107 ± 6 114+3 100 ± 6 4 .6 ± 1 .0 4 .8 ± 1 .9 1,860 1 262 1,450 ± 180 1,880 ± 153 1,748 ± 297
124 + 5 106 3 7 112+6 106 + 6 5 .410 .8 5 .0 ± 1 .0 1,770 f 378 1,550 ± 132 1,840 ± 172 1,896 ± 262
AP = mean arterial pressure ; CO = cardiac output ; HR = heart rate : LVEDP = left ventricular end-diastolic pressure ; peak dP/dt = peak value of rate of rise of left ventricular pressure .
1 42 8
December 1982
The American Journal of CARDIOLOGY
Volume 50
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
gether with the identification of a group of patients with severe chronic arterial disease not amenable to coronary bypass grafting, led to surgical procedures aimed at selective arterialization of the coronary venous system.'2 i- Subsequently, several investigators modified this concept and employed retroperfusion by selective catheterization of the coronary venous system to reverse ischemia following acute coronary artery occlusion .1 ,18 These systems have employed pulsatile venous retroperfusion which is synchronized with the cardiac cycle, so that the retrograde arterial pulse is programmed to occur during diastole and is discontinued during systole to allow for adequate venous drainage . These studies have demonstrated that after the initiation of retroperfusion, there is (1) a reduction in epicardial S-T segment elevation,' 3,4 .IS (2) improved myocardial oxygen tension in the ischemic segment, 3. 4 (3) improved function in the ischemic segment,2' 4 and (4) an increase in global left ventricular function. 1,2 However, despite these favorable reports, little information has been generated to document the extent to which retroperfusion may decrease ultimate histologically determined infarct size . Therefore, the present study evaluated the effectiveness of retroperfusion in reducing infarct size when begun 1 hour after occlusion and maintained throughout a total 4-hour period of coronary occlusion . Additionally, infarct size was related to the size of the anatomic perfusion bed of the occluded artery (region at risk to infarction) for a more accurate assessment of the effects of retroperfusion on infarct size . Quantitative method of determining myocardial salvage due to coronary venous retroperfusion : It has been shown considerable variability exists in infarct size resulting from coronary artery occlusion at any given anatomic site . 19 ' 20 This variability results from differences in the region at risk to infarction due to inherent differences in the size of the anatomic perfusion bed subserved by an occluded artery . We have previously demonstrated in the baboon that : the microvascular dye technique employed in this study accurately delineates the anatomic perfusion bed of the occluded artery .' By comparing the percentage of the perfusion bed of the occluded artery which undergoes infarction in control and retroperfused baboons, an accurate quantitative assessment of the degree of myocardial salvage achieved by retroperfusion may be determined . Effectiveness of coronary venous retroperfusion in reducing infarct size : We previously demonstrated in the baboon that retroperfusion started at 15 minutes after coronary occlusion and maintained for a total 4hour period of occlusion resulted in an 84% mean reduction in infarct size .' Because retroperfusion was initiated early, before the onset of necrosis within the ischemic region, the optimal effectiveness of retroperfusion was demonstrated in the study . In the present study, retroperfusion was begun 1 hour after occlusion and resulted in a 36 .7% mean reduction in infarct size . Thus, the delay from the onset of coronary occlusion to the initiation of retroperfusion is a critical determinant of the degree of myocardial salvage .
Comparison of anterograde arterial reperfusion versus coronary venous retroperfusion in reducing infarct size : The degree of myocardial salvage with anterograde arterial reperfusion depends on the time reperfusion is begun . The degree of myocardial salvage with retroperfusion depends not only on the time retroperfusion is begun, but also on how effectively the retroperfusion system is capable of delivering arterial blood to the ischemic region . Thus, it is interesting to examine how closely coronary venous retroperfusion approaches the effectiveness of arterial reperfusion in reducing infarct size. In order for coronary venous retroperfusion to be effective, it must deliver sufficient arterial blood to all levels of the myocardial wall within the ischemic region to satisfy the oxygen demands of this region . A number of studies using injection of various contrast agents have indirectly suggested that retroperfused blood is effectively delivered to the ischemic region . 2 t ,22 The studies of Hochberg et a116,23 using radioactive microspheres demonstrated that retrograde arterial blood flow is distributed to all levels of an acutely ischemic region and not significantly shunted by thebesian or veno-venous channels . More recently, Berdeaux et al," also using microspheres, demonstrated that retroperfusion initiated at 1 hour after coronary occlusion returned transmural flow in the ischemic region to 45% of the normal control flow which existed before coronary occlusion . The results of this study of Berdeaux et al 18 bear directly on the question of whether this degree of restoration of flow is sufficient to substantially prolong myocardial viability . This question may be clarified by directly comparing the degree of infaret salvage achieved by anterograde reperfusion with the degree of inf'arctsalvage achieved by retroperfusion instituted at comparable times after acute coronary occlusion . We have shown in the baboon that with anterograde reperfusion 2 hours after coronary occlusion, a mean of 50 .1% of the perfusion bed of the occluded artery was infarcted .L4 With retroperfusion 1 hour after coronary occlusion in the present study, a mean of 57 .4% of the perfusion bed of the occluded artery was infarcted . It is interesting that with retroperfusion 1 hour after coronary occlusion, the percentage of the perfusion bed infarcted was approximately the same as that found with anterograde reperfusion 2 hours after occlusion . This finding is consistent with the observation by Berdeaux et al's that retroperfusion initiated 1 hour after coronary occlusion was capable of restoring blood flow to only 45% of the normal control flow . Hemorrhage associated with retroperfusion : Is hemorrhage associated with retroperfusion deleterious to ischemic myocardium? Although the infarcts in the retroperfused baboons were hemorrhagic, the hemorrhage was confined within the infarcted region and did not appear to extend the infarct . This observation is similar to that noted with anterograde reperfusion ; several investigators have demonstrated that hemorrhage after reperfusion does not extend infarct size . 25 28 Some hemorrhage was noted around superficial veins,
December 1982
The American Journal of CARDIOLOGY Volume 50
1 42 9
CORONARY VENOUS RETROPERFUSION-GEARY ET AL
but it did not extend below the epicardial surface and there was no gross damage to the coronary veins . Clinical application of coronary venous retroperfusion : Experimental animal studies suggest that anterograde reperfusion must be undertaken within the first few hours after coronary occlusion for significant salvage of ischemic myocardium to occur .24 .25,29 The time interval in the clinical setting in which restoration of perfusion salvages significant myocardium remains unclear but may be longer than experimental animal studies suggest . Hence, retroperfusion may be useful clinically as a simple and prompt method to temporarily rearterialize an acutely ischemic region until such time as more definitive revascularization may be undertaken . It is also noted that coronary venous retroperfusion may be useful by providing a potential avenue for the introduction of pharmacologic agents directly into the ischemic region . References 1 . Markov AK, Lehan PH, Hellems HK . Reversal of acute myocardial ischemia in closed chest animals by retrograde perfusion of the coronary sinus with arterial blood . Acts Cardiol 1976 ;31 :185-199 . 2 . Farcol JC, Meerbaum S, Lang T, Kaplan L, Corday E . Synchronized retroperfusion of coronary veins for circulatory support of jeopardized ischemic myocardium . Am J Cardiol 1978 ;21 :1191-1201 . 3 . Feola M, Weiner L . A method of coronary retroperfusion for the treatment of acute myocardial ischemia . Cardiovasc Dis 1978 ;5 :235-243 . 4 . Meerbaum S, Lang T, Osher JV, Hashlmoto K, Lewis OW, Feldstein C, Corday E. Diastolic retroperfusion of acutely ischemic myocardium . Am J Cardiol 1976 ;37 :588-598 . 5 . Smith GT, Geary GG, Blanchard W, McNamara JJ . Reduction in infarct size by synchronized selective coronary venous retroperfusion of arterialized blood . Am J Cardiol 198 1 ;48:1064-1070 . 6 . Jennings RB, Sommers HM, Smyth GA, Flack HA, Linn H . Myocardial necrosis induced by temporary occlusion of a coronary artery in the dog . AMA Arch Pethol 1960 ;70 :68-78 . 7 . Grayson J, Davidson JW, Fitzgerald-Finch A, Scott C . The functional morphology of the coronary microcirculation in the dog . Microvasc Pies 1974 ;8 :20-43 . 8 . Geary GG, Smith GT, McNamara JJ . Defining the anatomic perfusion bed of an occluded coronary artery and the region at risk to infarction . A comparative study in the baboon, pig and dog. Am J Cardiol 1981 ;47 :12401247 . 9. Beck CS, Stanton E, Balluchok W, Leiter E . Revascularization of the heart by graft of systemic artery into coronary sinus . JAMA 1948 ;137:436442 . 10 . Beck CS, Leighnlnger DS . Operations for coronary artery disease . JAMA 1954;13:1226-1233 .
1 43 0
December 1982
The American Journal of CARDIOLOGY
11 . Eckstein RW, Horberger C, Sara T . Acute effects of elevation of coronary sinus pressure . Circulation 1953 ;7:422-436 . 12. Baket AA, Coslas-Durleux J, Goldberg H, Bailey CP . Protection of the heart by arterialization of the coronary sinus . II . Coronary flow in dogs with aortico-coronary sinus anastomosis . J Thorac Cardiovasc Surg 1954 :27: 442-454 . 13 . Andreadis P, Natsikas N, Arealis E, Lazarides OP . The aortocoronary venous anastomosis in experimental acute myocardial ischemia . Vasc Stag 1974;8:45-52 . 14 . Bheyana JN, Olson DB, Bryne JP, Koift WJ. Reversal of myocardial ischernia by arterialization of the coronary vein . J Thorac Cardiovasc Stag 1974; 67 :125-132. 15 . Benedict JS, Buhl TL, Henney RP . Cardiac vein myocardial revascularization . An experimental study and report of 3 clinical cases . Ann Thorac Surg 1975 ;20 :550-555 . 16 . Hochberg MS. Hemodynamic evaluation of selective arterialization of the coronary venous system : an experimental study of myocardial perfusion using radioactive microspheres. J Thorac Cardiovasc Sug 1977 ;74 : 774-783 . 17 . Chiu CJ, Mulder DS. Selective arterialization of coronary veins for diffuse coronary occlusion: an experimental evaluation . J Thorac Cardlovasc Surg 1975 ;70 :177-182 . 18 . Bordeaux A, Farcol J, Boundaries J, Barry M, Bardet J, Gualcelll J . Effects of diastolic synchronized retropertusion on regional coronary blood flow in experimental myocardial ischemia . Am J Cardiol 1981 :47 :10331040 . 19 . Lowe JE, Relmer KA, Jennings RB. Experimental infarct size as a function of the amount of myocardium at risk . Am J Pathol 1978 ;90:363-377 . 20 . Baughman KL, Maroko RP, Vatner SF . Effects of coronary artery reperfusion on myocardial infarct size and suvival in conscious dogs . Circulation 1981 ;63 :317-323 . 21 . Bishop SP, White FC, Beer CM . Regional myocardial blood flow during acute myocardial infarction in the conscious dog . Circulation 1976 ;38 : 429-438 . 22 . Solorzano J, Taitelbaum G, Chiu CJ . Retrograde coronary sinus perfusion for myocardial protection during cardiopulmonary bypass . Ann Thorne Sung 1978 ;25 :201-208 . 23 . Hochberg MS, Roberts WC, Morrow AG, Auslen WG . Selective arterialization of the coronary venous system . Encouaging long term flow evaluation utilizing radioactive microspheres . J Thorac ardiovasc Surg 1979 ; 77:1-12 . 24 . Geary GG, Smith GT, McNamara JJ . Extent of myocardial salvage by early coronary artery reperfusion in the absence of significant collaterals in baboons (abstr) . Circulation 1981 ;64: Suppl IV :IV-98 . 25. Reimer KA, Lowe JE, Rasmussen MM, Jennings RS . The wavefront phenomenon of ischemic cell death . I . Myocardial infarct size vs duration of coronary occlusion in dogs . Circulation 1977 ;56 :786-794 . 26. Geary GG, Smith GT, McNamara JJ . Quantitative effect of early coronary artery reperfusion in baboons . Extent of salvage of the perfusion bed of an occluded artery . Circulation 1982;66:391-396 . 27 . Kloner RA, Rude RE, Carlson N, Maroko PR, DeBoer LW, Braunwald E . Ullrastructural evidence of mlcrovascular damage and myocardial cell injuy after coronary artery occlusion : which comes first? Circulation 1960 ;62 : 945--952. 28 . Fishbeln MC, V-Rlt J, Lando U, Kanamatsuse K, Mercier JC, Ganz W . The relationship of vascular injury and myocardial hemorrhage to necrosis after reperfusion . Circulation 1980 ;62 :1274-1279 . 29 . Smith GT, Sorrier JR, Haston HH, McNamara JJ . Coronary reperfusion in primates . Serial electrocardiographic and histological assessment . J Clin Invest 1974 ;54 :1420 1427 .
Volume 50