Selective revascularization of the myocardium by internal-mammary-artery implant

Vineberg's procedure modified technique: flow analysis, immediate postoperative results and angiographic evaluation

BACKGROUND

The purpose of this study was to evaluate angiographic results of patients subjected to a technique variation of Vineberg's procedure, as well as their morbidity and mortality in immediate postoperative period, and to analyze the flow of grafted left internal thoracic artery (LITA) at rest and under stress.

METHODS

Between September 1999 and April 2002 eight patients were operated upon, with implant of the internal thoracic artery (ITA) in the intimal layer of the left ventricle (LV) muscle. After 6 months, they underwent angiographic and Doppler evaluation. According to Doppler study of LITA, the sample was divided in two groups: "Vineberg group," formed by eight patients; and "control group" consisting of 20 patients whose LITA directly revascularize the anterior interventricular artery (AIV). Angiography showed patency of all grafts in both groups. Blood flow and flow velocity in grafts were measured by Doppler echocardiography. T-test for paired and unpaired samples were used for statistical analysis.

RESULTS

There were no deaths or complications in immediate postoperative period. Angiography showed 100% patency. The total flow (TF) of Vineberg group was 55% of the flow in the control group. In both groups, the TF increased with the stress.

CONCLUSIONS

This Vineberg's technique modification can be successfully used in patients who cannot undergo traditional direct revascularization due to its low rates of morbidity and mortality and a high rate of patency, providing a significant blood flow both at rest and under stress.

Transmyocardial and percutaneous myocardial revascularization: current and future role in the treatment of coronary artery disease

Transmyocardial revascularization (TMR) is a new treatment modality under evaluation in patients with severely symptomatic, diffuse coronary artery disease, in whom the potential for medical or interventional management has been exhausted. Preliminary clinical trials show improved ischemic symptoms within the first 3 months in about 70% of TMR-treated patients. The original proposed mechanism of surgical or catheter-based TMR (percutaneous myocardial revascularization [PMR]) was that channels mediate direct blood flow between the left ventricular cavity and ischemic myocardium. However, several alternative explanations for the clinical success of TMR have recently been suggested, including improved perfusion by angiogenesis, an anesthetic effect by nerve destruction, and a potential placebo effect. This article reviews the clinical role of TMR/PMR, its possible pathophysiologic mechanisms, and its controversies. It provides an overview of the actual scientific and clinical status of TMR and details future directions.

Blood flow capacity via direct acute myocardial revascularization

The concept of direct myocardial revascularization, achieving myocardial perfusion through means other than the normal coronary vasculature, has a long history with the most widely investigated technique being the Vineberg procedure; current interest centers around the encouraging preliminary clinical results obtained with transmyocardial laser revascularization. Despite significant previous research, the acute blood flow potential through the direct myocardial route remains unknown. Nontransmural laser channels were made in the distal LAD territory from the epicardial surface of 5 mongrel dogs to which an internal mammary artery was connected. A flow probe was placed on the distal most portion of the artery and an intercostal branch was cannulated for infusion of colored microspheres. Measurements were taken under baseline conditions and following LAD and epicardial collateral ligation. Under all conditions, blood flow pattern was of a to-and-fro nature. At baseline, there was an average 0.60 +/- 0.24 ml/min net flow into the myocardium which was all contained within 0.5 cm of the central channel with a final myocardial perfusion of 0.011 +/- 0.016 ml/min/g. Following induction of ischemia average flow increased to 1.41 +/- 0.51 ml/min which extended as far as 1 cm from the channel with a final myocardial perfusion of 0.22 +/- 0.19 ml/min/g. In conclusion, a limited amount of acute myocardial perfusion can be achieved by the present technique of direct myocardial revascularization and the amount of flow is highly dependent upon the amount of flow through the native circulation.

The phantom of "myocardial sinusoids": a historical reappraisal

The concept of myocardial sinusoids has been described in the literature during the past 60 years. They have been the basis of several revascularization procedures, such as the "Vineberg" procedure and more recently transmural laser revascularization. This article will review the historical evolution as well as the validity of the concept of "myocardial sinusoid."

The Vineberg procedure: the immediate forerunner of coronary artery bypass grafting

Promulgated by the Canadian surgeon Arthur Vineberg, internal mammary artery implantation received fairly widespread clinical application during the 1960s, only to be abandoned upon the introduction of coronary artery bypass grafting toward the end of the decade. By 1978, Hurst and Logue's The Heart (4th ed. New York: McGraw-Hill, page 1291) mentioned the procedure only to relate that "indirect myocardial revascularization using the internal thoracic artery is now seldom used." Between the introduction of the operation in 1945 and the mid-1960s, a remarkably hard-fought debate raged over the value of internal mammary artery implantation. Despite the fact that coronary arteriography ultimately demonstrated the viability of Vineberg's concept, for a variety of reasons the operation could not compete with coronary artery bypass grafting, and therefore rapidly fell into disuse. The central role the Vineberg procedure has played in the evolution of coronary revascularization surgery highlights the importance of reviewing the history of its development, application, and eventual abandonment. The Vineberg procedure was, after all, the first intervention documented to increase myocardial perfusion. Recent reports of long-term graft patency and clear patient benefit with internal mammary artery implants reinforce the belief that Vineberg should be given more credit for his work than he has generally received, and that internal mammary artery implantation should not be relegated to the status of a historical curiosity.

Creation of anastomoses between an extracardiac artery and the coronary circulation. Proof that myocardial angiogenesis occurs and can provide nutritional blood flow to the myocardium

The purpose of this investigation was to determine whether blood vessels could develop de novo between an extracardiac artery and a collateral-dependent zone of the heart and to quantify the nutritive blood flow afforded by the new vessels. We also adapted the preparation so that angiogenically active agents could be chronically administered directly to the site of neovascularization in subsequent studies. To induce neovascularization between a systemic artery and the coronary circulation, the left internal mammary artery (IMA) was implanted in an intramyocardial tunnel in proximity to the left anterior descending coronary artery (LAD). A tube situated in the distal IMA connected to an implanted pump provided for continuous intra-arterial infusion at the site of angiogenesis. During the same procedure, an ameroid constrictor was placed on the proximal LAD, rendering its perfusion territory collateral dependent during a 2-3 week period. After 8 weeks, the functional capacity of the anastomoses established between the implanted IMA and the LAD territory was assessed by determining regional myocardial blood flow under basal conditions, during adenosine-induced vasodilatation, and during differential occlusions of the IMA and left circumflex coronary artery (LCCA). For all dogs, IMA occlusion decreased maximal LAD territory flow from 1.31 +/- 0.11 to 1.16 +/- 0.10 ml/min/g (p less than 0.005). Occlusion of the LCCA decreased LAD zone flow to 0.73 +/- 0.12 ml/min/g, whereas occlusion of the IMA in addition to the LCCA further decreased LAD zone flow to 0.42 +/- 0.11 ml/min/g (p less than 0.02). The IMA provided measurable nutritive blood flow in seven of 12 dogs, and in these dogs, the artery provided 30.0 +/- 2.5% of total LAD zone collateral conductance under conditions of maximal vasodilatation (range, 23-42%). We conclude that angiogenesis can occur between an implanted internal mammary artery and the native coronary circulation in dogs, providing modest nutritive blood flow to a collateral-dependent region. Further studies will be necessary to determine whether direct, local infusion of angiogenically active factors can enhance neovascularization and whether sufficient flow can be reliably supplied to make some variant of this approach clinically applicable.

Clinical utility of exercise, pacing, and pharmacologic stress testing for the noninvasive determination of myocardial contractility and reserve

The ability of the left ventricle to modulate its performance is an important and integral component in the cardiovascular system's adaptive response to increased workload. Abnormalities in ventricular contractility can blunt this response and thus significantly limit the patient's functional capacity. The accurate determination and quantitation of cardiac contractility and reserve is a difficult task in the symmetrically contracting ventricle and more so when regional contraction abnormalities are present. Moreover, derangements in other physiologic variables, such as ventricular loading conditions, heart rate, systemic vascular tone, cardiac autonomic function, and pulmonary gas exchange, can diminish cardiopulmonary reserve. This report relates the determinants of myocardial oxygen demand and efficiency to the currently available forms of exercise, pacing, and pharmacologic stress testing. Within this framework, commonly used as well as newer approaches to the noninvasive assessment of stress-induced changes in left ventricular performance and contractility are addressed. In addition, several examples are presented in which noninvasive techniques for assessing intracardiac structures, pressures, and flows (eg, echo/Doppler, radionuclide angiography, rapid acquisition computed tomography, and magnetic resonance imaging) are combined with various cardiovascular stress tests to achieve more reliable measures of myocardial contractility and reserve.

[Value and limitations of coronary blood flow measurement in man (author's transl)]

Attempts to measure coronary blood flow in man have made considerable progress during the last 25 years. The major techniques are based on the direct or indirect Fick principle; coronary flow is calculated from the arterio-coronary venous difference of inert gases or from the precordial recorded disappearance curve of radioactive gases or substances. The accuracy of the techniques depends upon the properties or the indicators used and the precision of their determination. All techniques applied hitherto are intricate and unsuitable for general use. -A lot of information is obtained about coronary circulation in health and disease by coronary flow measurements in man. Further studies in this field may influence pathophysiological and clinical concepts especially concerning coronary heart disease.

Effects of surgery on angina (pre- and postinfarction) and myocardical function (failure)

With the advent of direct bypass surgery, the dramatic clinical responses in some patients has been followed by enormous enthusiasm in many centers. Surgical technics have advanced to such a point that nearly all patients with obstructive coronary disease could have the obstructions bypassed to one or many areas. Criteria for evaluating surgery include mortality, operative infarction rate, patency of grafts, clinical response, and stress testing. Many reports fail to correlate results with angiographic studies of vein function and with completeness of revascularization. When cine studies are performed, a good correlation exists between patent veins and relief of angina and improved stress response. Different patterns of response to stress, sometimes independent of relief of angina, are obtained depending on the completeness of revascularization. Predictable relief of angina is found if revascularization is complete. At times dramatic, but much less predictable, relief of failure (improved ventricular function) follows revascularization. Angina is a valuable aid in selecting some patients for surgery. Stress testing (bicycle ergometry) can now define general groups of patients who are likely, and who are not likely, to show improved myocardial response to stress after surgery. These studies also demonstrate the need for the surgeon to provide complete revascularization whenever possible. The criteria for selection for surgery of patients with symptoms of gross heart failure remain unclear. While revascularization technics could be technically applied to nearly all coronary patients, present methods are unable accurately to define who really needs the surgery and, equally important, which hearts will respond once revascularization is completed.

Postoperative evaluation of myocardial blood flow in aorta-to-coronary artery vein bypass grafts using the xenon-residue detection technic

By the use of the xenon-residue detection technic, myocardial blood flow (MBF) was assessed 3-17 months after surgery in nine patients with an aorta-to-left anterior descending bypass (LAD-BP), in nine patients with an aorta-to-right coronary artery bypass (RCA-BP), and in two patients with both LAD-and RCA-BP. In addition, MBF was registered in the corresponding main coronary artery. In each case coronary angiography revealed a patent vein graft. LAD-BP flow averaged 58 ml/min/100 g, this being slightly lower than the average flow value recorded after injection into the main left coronary artery of these patients (64 ml/min/100 g). LAD-BP flow did not differ from the value recorded in 20 normal subjects (63.9 ml/min/100 g). In contrast, average RCA-BP flow amounted to 47.1 ml/min/100 g and was significantly higher than the values recorded in the obstructed main RCA of these patients (22.1 ml/min/100 g) ( P < 0.0025) or those observed in 20 patients with severe disease of the right coronary artery (34.9 ml/min/100 g) ( P < 0.025); no difference was seen between RCA-BP flow and the average of 20 normal subjects (46.1 ml/min/100 g). In six patients a two-to threefold increase of BP flow was found during exercise (50-100 w). Total coronary vascular resistance showed a similar behavior to MBF, not differing in the bypass area from the values obtained in the normal control groups. It is concluded that the venous bypass procedure substantially increases perfusion at rest and during exercise and that a good correlation exists between MBF and postoperative angiography.

Left ventricular hemodynamics before and 1 year after internal mammary artery implantation in patients with coronary artery disease and angina pectoris

Left ventricular hemodynamics at rest and during supine exercise were studied before and 1 year after internal mammary artery implantation in 24 patients with severe coronary artery disease and angina pectoris and in five similar patients before and after 1 year of medical treatment. In the surgical group, 14 had evidence of one or more implants providing collaterals to coronary arteries, and 10 had no evidence of collaterals from the implant. Only two patients, both with functioning implants, showed a return to normal of left ventricular end-diastolic pressure at rest and during exercise. There was no correlation between clinical improvement and hemodynamics at the time of the postoperative study. It is concluded that left ventricular hemodynamics may return to normal after internal mammary artery implantation but this was uncommon in the present study.

The effects of internal mammary artery implantation on cardiac function and survival following acute coronary artery occlusion

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Stress electrocardiography in the evaluation of surgical revascularization of the heart

Electrocardiography was carried out during hypoxemia and graded exercise tests before and at intervals between 2 and 20 months after attempts to revascularize the heart by internal mammary artery implantation in 44 patients with angiographically documented coronary disease and angina pectoris. Eleven patients had single vessel disease; the right coronary was involved in seven of these patients. Thirteen patients had single vessel implants, employing the left internal mammary artery in 11 patients and a saphenous vein graft from the aorta in two. Thirty-one patients had double internal mammary artery implantation accompanied by gastroepiploic arterial implantation in four.

Fifty per cent of the patients were symptomatically improved after surgery, the best results occurring in two patients with isolated anterior descending coronary disease. Of the 34 patients having postoperative coronary and mammary arteriography, 15% showed improvement which could be ascribed to mammary revascularization; 24% had limited myocardial revascularization and no symptomatic improvement; 29% had patent implants without development of collateral vessels, and the implanted vessels were occluded in 32%. Eleven of the 34 (32%) had fair or good symptomatic improvement in the absence of revascularization.

The results of postoperative stress electrocardiography correlated closely with the findings on postoperative coronary and mammary angiography. The stress tests were persistently positive after operation in 83% of the patients having angiographically confirmed implant occlusion or nonrevascularization. The stress ECG response was reversed, becoming negative postoperatively, in five cases of angiographically proved significant revascularization. Thus, stress electrocardiography provided objective evidence of improvement in a small number of patients with limited coronary disease who developed good collateral circulation and correlated with the lack of revascularization in the majority even in those subjectively improved.

Visual assessment of regional myocardial perfusion utilizing radioactive xenon and scintillation photography

A method was devised to visualize the areas of left ventricle supplied by various coronary arterial branches utilizing scintillation photography and an inert radioactive gas which distributes instantaneously between coronary blood and perfused myocardial cells. From 1 to 5 millicuries of 133 Xe dissolved in saline solution was injected through a catheter into the anterior descending or posterior circumflex branch of the left coronary artery of 15 dogs. Scintillation images produced during arrival and washout of 133 Xe in the various regions of the heart were recorded by an image intensifier scintillation camera and high speed television monitor and were reproduced on Polaroid film during replay of the videotape on an oscilloscope. The resulting scintiphotographs defined the region of the left ventricle supplied by the coronary arterial branch. In nine of the dogs acute myocardial infarctions were produced by occluding one or the other branch of the left coronary artery. When 133 Xe was injected again into the coronary artery proximal to the occlusion, that area of the left ventricle that was deprived of nutrient blood flow was no longer visualized on the gamma-ray scintiphotograph. The results indicate that regional myocardial perfusion may be dynamically visualized in the intact animal.

The effect of myocardial ischemia on internal mammary artery implant patency: a controlled experimental cineangiographic study

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Left ventricular performance during mild supine leg exercise in coronary artery disease

Left ventricular (LV) performance was studied during mild exercise (100 kg-m/min for 3 minutes) in 19 cases of coronary artery disease (CAD). Each patient suffered from a severe anginal syndrome. None had ventricular aneurysm, cardiomegaly, or clinical heart failure. Mean resting values follow: LV end-diastolic pressure (LVEDP), 19 ± 7 mm Hg; LV systolic pressure (LVSP), 150 ± 16 mm Hg; stroke volume index (SVI), 48 ± 10 ml/beat/m 2 ; and LV stroke work index (LVSWI), 81 ± 19 g-m/m 2 . During exercise LVEDP rose to 30 ± 8 mm Hg ( P ≤0.001) and LVS to 160 ± 20 (not significant [NS]); SVI diminished to 46 ± 11 (NS) and LVSWI, to 76 ± 24 (NS). Patients with decreased or asynchronous areas of LV myocardium identified on cine left ventriculograms had higher mean LVEDPs during exercise than did those with normal ventriculograms (34 ± 10 versus 26 ± 4 mm Hg; P ≤0.05). The difference between responses to exercise of patients who experienced angina during the study and of those who did not was NS. Administration of nitroglycerin reduced the increase in LVEDP during exercise. An abnormality in LV performance-a significant rise in LVEDP without a significant increase in SVI or LVSWI-was observed in 13 of 19 cases of CAD.