Denis H. Tyras

Late Patency of the Internal Mammary Artery as a Coronary Bypass Conduit

From January, 1972, through August, 1977, 472 patients had internal mammary artery (IMA) coronary bypass, of which 100 were double-IMA bypasses. We selected those patients having a widely patent IMA one year postoperatively who then had a second catheterization 49 to 105 (mean, 64) months following operation. None of the 93 patients who met these criteria was specifically recalled for this study; they all had follow-up catheterizations for multiple other reasons. All of the 91 left IMA and 22 right IMA bypasses (total, 113) were patent at late catheterization, but 1 right IMA was diffusely narrowed. One left IMA had acute angulation with 50% stenosis proximal to the distal anastomosis, which was unchanged over the follow-up interval. There were 100 patent saphenous vein bypasses at one year and 87 at late catheterization. Late closure of coronary bypass grafts is secondary to progression of coronary disease, atherosclerosis of the bypass conduit, or intimal proliferation. Because we have not encountered the latter two causes of conduit closure, IMA grafts remain our graft of choice for nonemergent operations in patients under 60 years of age having revascularization of the left anterior descending coronary artery system.

Myocardial Revascularization in Women

During the period January, 1970, through June, 1977, 1,541 patients underwent coronary artery bypass grafting; 241 of them were women (15.6%). Operative mortality rates for the entire study were 2.4% in men and 3.7% in women, but they showed a marked decline in women during 1975 to mid-1977, with only 2 deaths in 140 patients (1.4%). Women comprised a larger percentage of patients (16.7%) in these later years. Women were slightly older, received fewer grafts, had better preservation of ventricular function on preoperative studies, and had more severe anginal symptoms than men. Patency rates were significantly lower in women at 1 month, 1 year, and 3 years. Five-year survival was not significantly different between women (88.3%) and men (93.5%). Many of these findings may be explained on the basis of women having smaller coronary arteries than men. These favorable results differ from earlier reports of higher mortality rates in women and indicate that myocardial revascularization should not be withheld from female patients.

Fastidious mycobacteria grown from porcine prosthetic-heart-valve cultures.

WE report here the contamination of eight of 16 porcine xenograft heart valves placed in 15 patients over a three-month period. The micro-organisms cultured from the xenografts were identified as M...

Operative Risk Factors in Patients with Left Main Coronary-Artery Disease

To identify the factors associated with operative mortality, we evaluated clinical, angiographic, and surgical variables in 1172 patients with left main coronary-artery stenoses of at least 50 per cent, who underwent coronary-bypass procedures in the Collaborative Study in Coronary Artery Surgery (CASS). The operative mortality was 4.2 per cent overall and was less than 3 per cent in seven of the 15 participating hospitals. Historical variables associated with an increase in operative mortality were age, female sex, and duration and severity of angina. Other variables associated most closely with poor survival were urgency of operation, left coronary-artery dominance, severity of left main coronary-artery stenosis, and impairment of left ventricular contraction. The results of this multicenter study show that aortocoronary bypass surgery in patients with left main coronary-artery disease can be performed with a low mortality and that patients at high risk can often be identified before surgery.

Long-term results of myocardial revascularization.

During 1970 to 1977, among 1,733 patients who underwent isolated coronary bypass grafting, the operative mortality was 2.5 percent. Actuarial 5 year survival is 88.1 percent. At an average follow-up of 46 months (range 13 to 108), 90 percent of patients remain angina-free or with symptomatic improvement. The 5 year survival rate of patients with single vessel coronary artery disease is 97.9 percent. In patients with multivessel disease, operative survival appears to be favorably influenced by the presence of normal preoperative ventricular function. Late survival is significantly better in patients with multivessel disease with normal preoperative ventricular function or with complete revascularization. Risk of perioperative myocardial infarction has been appreciably reduced by the introduction of cold potassium chloride cardioplegia. Late myocardial infarction has occurred at an average annual risk of 1.46 percent. These data show that long-term survival and a small incidence of late myocardial infarction after myocardial revascularization are more likely in patients who undergo complete revascularization before significant left ventricular myocardial damage has occurred.

Cold Blood as the Vehicle for Potassium Cardioplegia

Cold blood with potassium, 34 mEq/L, was compared with cold blood and with a cardioplegic solution. Three groups of 6 dogs had 2 hours of aortic cross-clamp while on total bypass at 28 degrees C with the left ventricle vented. An initial 5-minute coronary perfusion was followed by 2 minutes of perfusion every 15 minutes for the cardioplegic solution (8 degrees C) and every 30 minutes for 3 minutes with cold blood or cold blood with potassium (8 degrees C). Hearts receiving cold blood or cold blood with potassium had topical cardiac hypothermia with crushed ice. Peak systolic pressure, rate of rise of left ventricular pressure, maximum velocity of the contractile element, pressure volume curves, coronary flow, coronary flow distribution, and myocardial uptake of oxygen, lactate, and pyruvate were measured prior to ischemia and 30 minutes after restoration of coronary flow. Myocardial creatine phosphate (CP), adenosine triphosphate (ATP), and adenosine diphosphate (ADP) were determined at the end of ischemia and after recovery. Changes in coronary flow, coronary flow distribution, and myocardial uptake of oxygen and pyruvate were not significant. Peak systolic pressure and lactate uptake declined significantly for hearts perfused with cold blood but not those with cold blood with potassium. ATP and ADP were lowest in hearts perfused with cardioplegic solution, and CP and ATP did not return to control in any group. Heart water increased with the use of cold blood and cardioplegic solution. Myocardial protection with cold blood with potassium and topical hypothermia has some advantages over cold blood and cardioplegic solution.

Coronary Artery Stenosis Following Aortic Valve Replacement and Intermittent Intracoronary Cardioplegia

From July, 1977, to July, 1980, intermittent cold blood potassium cardioplegia was used in 208 patients undergoing aortic valve replacement. Aortic root injection of the cardioplegic solution at 10 degrees C was followed every 20 to 30 minutes by infusions of the solution through Silastic cannulas sutured in the coronary orifices or reinserted with each injection. Symptoms of myocardial ischemia developed in 6 patients 3 to 30 months postoperatively. Coronary angiography confirmed new stenoses of the left orifice (3 patients), left main trunk (1 patient), left anterior descending coronary artery (2 patients), circumflex coronary artery (1 patients), and right orifice (3 patients). Four patients underwent saphenous vein grafting procedures, with 2 deaths; 2 patients refused reoperation. A seventh patient with 80% stenosis of the circumflex coronary artery and a posterolateral myocardial infarction died 2 months after double-valve replacement. Intermittent cold blood potassium cardioplegia instead of continuous perfusion did not prevent coronary arterial injury. Injuries occurred in the distal coronary arteries as well as the orifices and were not prevented by withdrawal of the cannulas between injections. Tight-fitting cannulas and high-pressure injection should be avoided. A careful search for coronary arterial injury should be made in all symptomatic patients following aortic valve replacement.

Clinical Experience with Cold Blood as the Vehicle for Hypothermic Potassium Cardioplegia

Intermittent cold ischemic arrest was compared with hypothermic potassium cardioplegia using cold blood as the vehicle in two consecutive series of patients having isolated coronary bypass grafting. Between January 1, 1977, and June 30, 1977, 196 patients were operated on using cold ischemic arrest. The incidence of perioperative infarction was 14.3%, and mean total myocardial ischemia time was 42 +/- 1.2 minutes. From July 1, 1977, to June 30, 1978, there were 428 operations done using cold blood with potassium. The incidence of perioperative infarction was 5.6% (p less than 0.005), and the mean total myocardial ischemic time was 80 +/- 2.1 minutes. In the five years prior to this study, the incidence of perioperative infarction was constant at 13% while operative mortality was declining from 5 to 1% and the need for postoperative myocardial support was declining also. Use of cold blood potassium cardioplegia compared with cold ischemic arrest for myocardial protection during coronary artery operations has significantly reduced the incidence of perioperative infarction while doubling cross-clamp time.

Paraplegia Following Intraaortic Balloon Assistance

In a patient receiving intraaortic balloon counterpulsation following myocardial revascularization, paraplegia developed two days post-operatively. Postmortem examination demonstrated a dissecting hematoma of the thoracic aorta and spinal cord infarction. The neurological deficit is thought to be due to embarrassment of spinal cord blood supply, and mechanisms of injury are discussed.

Late Sequelae of Perioperative Myocardial Infarction

The late suquelae of myocardial injury occurring at the time of direct myocardial revascularization are unknown. Fifty of 500 consecutive patients undergoing aortocoronary bypass grafting developed both electrocardiographic and enzymatic evidence of myocardial injury. They were matched with 50 patients of similar age, sex, history of previous infarction, severity of angina, degree of coronary arteriosclerosis, and level of ventricular function as determined by preoperative angiographic studies. The conduct of the operation was identical in each group except for prolongation of total cross-clamp time in those patients with myocardial injury. The total number of vessels grafted, the conduit used, and the operative mean graft flow were similar. Results of treadmill stress testing at 24 to 36 months were not significantly different between groups. Angina status, long-term survival, graft patency, and ventricular function were not adversely affected by intraoperative myocardial injury. However, postoperative ventricular function and stress test performance were related to graft patency.