Does visual interpretation of the coronary arteriogram predict the physiologic importance of a coronary stenosis?

Intraoperative two-dimensional echocardiography: new application of an old technique

Intraoperative two-dimensional echocardiography is a new diagnostic and monitoring technique that provides immediate information, unavailable from routine hemodynamic measurements, on both myocardial and valvular function. The presence and severity of valvular regurgitation can be assessed from the visualized flow pattern of microbubbles generated by an injection of saline solution: reflux flow into the retrograde chamber represents valvular insufficiency. The extent of valvular regurgitation can be determined immediately after conservative valve repair (annuloplasty or commissurotomy) or replacement to avoid the patient's leaving the operating suite with significant but undetected valvular insufficiency. Additionally, intraoperative echocardiography permits rapid evaluation of left ventricular systolic and diastolic volumes and myocardial contractility, thereby facilitating therapeutic interventions in the operating room. It also permits assessment of congenital heart defects and the competency of their repair. Pulsed, continuous and color-flow real time Doppler imaging methods allow further intraoperative definition of stenotic and regurgitant lesions.

Alterations in myocardial metabolism and function at rest in stable angina pectoris: relations with the amount of exercise-induced thallium-201 perfusion defect

The relation between the amount of exercise-induced ischemia and alterations in left ventricular (LV) function and metabolism at rest was studied in 18 coronary patients with stable angina pectoris. An ischemic defect area score was computed from quantitative exercise thallium-201 (Tl-201) scintigraphy; this estimation of the amount of ischemic myocardium was used to classify the patients in group I (n = 8; score less than 15%, mean 6.7 +/- 2.5%) and II (n = 10; score greater than 15%; mean 27.2 +/- 8.9%). Hemodynamics and metabolism were studied in basal state. No patient had anginal pain during the study, and the extent of angiographic coronary artery disease (CAD) was comparable in the two groups. Heart rate, aortic pressure, coronary blood flow, and myocardial oxygen uptake were also similar in both groups. However, ejection fraction was reduced in group II (51 +/- 13 vs 63 +/- 5%; p less than 0.01) and LV relaxation was impaired as shown by the increase in time-constant of isovolumic pressure fall (55 +/- 16 vs 44 +/- 6 ms in group I; p less than 0.05); the LV end-diastolic pressure was also increased in group II (19 +/- 8 vs 10 +/- 4 mmHg in group l; p less than 0.05). Furthermore, in group II, myocardial lactate uptake was reduced (4 +/- 19 vs 30 +/- 29 mumole/min in group I; p less than 0.01) and the productions of alanine and glutamine were augmented (-7.5 +/- 4.4 vs -4.6 +/- 1.6 mumole/min in group I; p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of coronary stenoses by myocardial perfusion imaging during pharmacologic coronary vasodilation. VII. Validation of coronary flow reserve as a single integrated functional measure of stenosis severity reflecting all its geometric dimensions

The purpose of this study was to determine whether coronary flow reserve measured by flow meter correlated with or could be predicted by quantitative coronary arteriography accounting for all dimensions of a coronary artery stenosis. Five dogs were chronically instrumented with an inflatable stenosing cuff, a Doppler flow velocity meter, proximal and distal coronary artery catheters and aortic and pulmonary artery catheters. For 18 stenoses over a wide range of severity, orthogonal coronary arteriograms were analyzed quantitatively at rest to predict coronary flow reserve based on fluid dynamic equations. The X-ray-predicted coronary flow reserve correlated closely with that measured directly by implanted flowmeter with an r value of 0.91, a regression equation of X-ray-predicted coronary flow reserve = 1.08 (measured coronary flow reserve) - 0.08 and 95% confidence limits (+/- 2 SD) of 0.66. Neither percent diameter narrowing alone nor absolute stenosis diameter alone correlated well with measured coronary flow reserve. Results confirm that coronary flow reserve is a single integrated measure of coronary stenosis severity reflecting all its geometric dimensions. Flow reserve correlated closely with and was accurately predicted by quantitative coronary arteriography taking into account all stenosis dimensions. This study establishes the theoretical and experimental basis for using coronary flow reserve as a single, integrated functional measure of stenosis severity reflecting all of its geometric characteristics.

Papaverine: the ideal coronary vasodilator for investigating coronary flow reserve? A study of timing, magnitude, reproducibility, and safety of the coronary hyperemic response after intracoronary papaverine

A potent, short-acting vasodilator that induces a maximal hyperemic response of the coronary vascular bed is needed to determine coronary flow reserve. In 12 patients, we measured coronary sinus blood flow by thermodilution over a period of 2 min during which a bolus of 10 mg papaverine was given into the left main coronary artery. This was repeated after 5 min to assess the reproducibility of the changes. The maximal hyperemic response lasted from 24 until 37 sec after papaverine administration. There was no significant difference between the two consecutive hyperemic responses (Student's t-test for paired observations). The mean difference between first and second hyperemic responses at 30 sec was 7.0% (SD +/- 6.2%). In conclusion, 10 mg of intracoronary papaverine is a short-lasting and reproducible means of inducing a maximal hyperemic response in the coronary vascular bed and therefore appears to be the ideal agent for investigating coronary flow reserve.

Digital subtraction angiographic assessment of the coronary arteries and coronary flow reserve

Although intravenous digital subtraction angiography was originally intended as a means of performing less invasive peripheral angiography, this less invasive approach has not proven feasible for coronary artery studies. Digital imaging has, however, proven helpful for the immediate replay, enhancement and quantification of coronary arteriography and enables the performance of regional blood flow (coronary flow reserve) analysis. Flow analysis is clinically helpful in determining the hemodynamic significance of individual coronary stenoses, which cannot always be assessed even using quantitative stenosis measurements. One method of assessing flow reserve by digital means uses parametric images to display the timing (color coded) and density (intensity coded) of the contrast bolus as it transverses the regional myocardial circulation. Analysis of baseline and hyperemic condition parametric images provides quantitative regional flow reserve information.

Abnormal coronary flow reserve and abnormal radionuclide exercise test results in patients with normal coronary angiograms

Coronary flow reserve, exercise thallium-201 scintigraphy and exercise radionuclide ventriculography were compared in 18 patients with chest pain and angiographically normal coronary arteries. Regional exercise thallium-201 perfusion was abnormal in three patients, regional exercise wall motion was abnormal in three other patients and results of both tests were abnormal in one additional patient. Left ventricular ejection fraction responses were abnormal in five of these seven patients. The coronary flow reserve of arterial distributions with abnormal perfusion or regional dysfunction was significantly lower than that of distributions associated with normal radionuclide results (1.42 +/- 0.23 versus 2.58 +/- 0.83, p less than 0.001). All patients with abnormal scintigraphic results had low coronary flow reserve (less than 1.95) in at least one distribution. Perfusion abnormalities appeared to be more localized in the arterial distributions with the lowest flow reserve. Only two patients had low flow reserve (less than 1.95) with normal scintigraphic results; both were hypertensive. These data suggest that abnormal exercise scintigraphic findings in patients with angiographically normal coronary arteries and chest pain are indicative of true blood flow or perfusion abnormalities.

Exercise testing in suspected coronary artery disease

The interpretation and selection of exercise tests depends on the pretest probability of CAD. Imperfect tests (like exercise tests) provide probability estimates, not definite statements (such as "the patient has CAD" or "the patient does not have CAD"). In patients with a low pretest probability of CAD (asymptomatic persons or men and women with nonanginal chest pain), abnormal exercise test results provide probability estimates that are much too low to conclude that the patient has CAD. In patients with anginal pain and normal exercise tests, the probability of CAD is too high to conclude that the patient has a normal coronary circulation. Exercise tests are not useful for trying to rule out CAD in patients with anginal pain. In patients with an intermediate pretest probability of CAD (men and women with atypical angina and women with typical angina), abnormal exercise tests (particularly the myocardial scintiscan) provide probability estimates that are high enough to justify starting treatment for CAD. Exercise tests are most useful in this group, a conclusion that has been reached by other methods of analysis. The myocardial scintiscan is much more useful than the exercise ECG in women. When CAD is strongly suspected, exercise tests have relatively little diagnostic value but may be useful for prognosis. However, clinical evidence of poor ventricular function may alone suffice to select patients with angina pectoris for coronary arteriography. Conversely, when clinical indicators of congestive heart failure are absent, the prognosis in chronic stable angina is so favorable that any further testing may be unnecessary. Screening asymptomatic persons for CAD is a very low yield practice. Patients who have no cardiac risk factors (hypercholesterolemia, family history of CAD, cigarette smoking, and hypertension) are at especially low risk of a primary cardiac event. Older men with stable typical angina are particularly likely to have left main coronary artery stenosis or three-vessel disease with poor ventricular function. The exercise ECG can identify groups of older men with a relatively high risk of having left main coronary artery stenosis. Physicians should be cautious when applying these recommendations to a primary care practice. The foregoing analysis is based on data obtained from patients who had been selected for coronary arteriography. There are two principal effects of biased selection of study patients: The pretest probability of CAD in clinical subgroups is probably lower than as shown here.(ABSTRACT TRUNCATED AT 400 WORDS)

Noninvasive Doppler flowmetry for measuring regional blood flow

Ultrasonic Doppler flowmetry should assume an increasingly important role in the serial evaluation of human cardiovascular physiology. The principal advantages of this method are that it (1) is noninvasive, (2) is nontraumatic, (3) provides anatomic and physiologic data, and (4) provides dynamic measurements. Nevertheless, the equally important limitations of the technique are that it (1) is difficult to apply in some subjects (ie, those who are obese or have anatomic variations), (2) requires operator skill and a thorough knowledge of human anatomy and cardiovascular dynamics, (3) has a finite spatial resolution that may compromise the measurement of small (1 mm) vessel diameters, and (4) has a finite velocity-measuring capability that will affect measurements of blood velocities outside the range of approximately 2 to 200 cm/sec. Full appreciation of the capabilities and limitations of noninvasive ultrasonic Doppler flowmetry makes possible a better understanding of the dynamic interplay of anatomy, pressure, flow, and resistance in the normal and abnormal intact human cardiovascular system.

Comparative long-term effects of coronary artery bypass graft surgery and percutaneous transluminal coronary angioplasty on regional coronary flow reserve

To evaluate the relative long-term improvement in coronary artery hemodynamics after revascularization by coronary artery bypass graft surgery (CABG) or percutaneous transluminal coronary angioplasty (PTCA), regional coronary flow reserve (CFR) was measured, by digital computer analysis of 35 mm cine film, in 50 men undergoing cardiac catheterization. CFR (mean +/- SEM) in 12 atherosclerotic arteries before revascularization was 1.02 +/- 0.05. Mean CFR in 29 normal arteries of men with normal coronary arteriograms was significantly higher (2.59 +/- 0.11) than that in 16 atherosclerotic arteries of patients revascularized by CABG (2.02 +/- 0.17, p less than .01) or in 14 atherosclerotic arteries of those revascularized by PTCA (1.97 +/- 0.12, p less than .01). No difference in CFR between the CABG and PTCA groups was found and variables known to influence CFR were similar between groups. Equivalent and significant long-term improvement in coronary artery hemodynamics is provided by CABG or PTCA. We postulate that the difference in CFR in the men with normal arteries and those who underwent revascularization was related to the effects of the general atherosclerotic process, which remain despite successful treatment by these techniques.

Dipyridamole-echocardiography test in effort angina pectoris

This study assesses the clinical feasibility and usefulness of dipyridamole infusion for the detection of coronary artery disease (CAD) by using 2-dimensional echocardiography (2-D echo) and 12-lead electrocardiographic monitoring. Dipyridamole infusion (0.14 mg/kg/min for 4 minutes) was performed in 66 consecutive patients with effort chest pain and in 9 control subjects. Among the 28 patients with positive dipyridamole-echocardiography test responses, 18 had diagnostic electrocardiographic changes (ST-segment depression on anterolateral leads), but these changes were unrelated to the site of asynergy. The dipyridamole-echocardiography test had an overall sensitivity of 56% and specificity of 100% for the presence of CAD. Exercise stress testing (EST) had an overall sensitivity of 62% and a specificity of 80%. Thus, the dipyridamole-echocardiography test, which is feasible in essentially all patients with good basal echocardiograms, has a lower overall sensitivity in detecting CAD than EST but a higher specificity, detects the site of apparent ischemia as identified by regional asynergy more precisely than EST, and can unmask electrocardiographically silent effort ischemia.

Strategy for the detection and management of coronary artery disease. "Physiology before anatomy"

A strategy for the diagnosis of ischemic heart disease should be based on knowledge of the prevalence of the disease in population subgroups. Asymptomatic patients should not be routinely screened. Asymptomatic patients or patients with nonanginal chest pain should have both a positive exercise electrocardiogram and stress nuclear scan before a diagnosis of ischemic heart disease is justified or arteriography is recommended. Patients with atypical angina should be evaluated with exercise radionuclide ventriculography. Coronary arteriography is rarely needed for diagnosis and is most properly used as a preoperative evaluation of a patient who has symptoms uncontrolled by medical management, or in whom a significant amount of myocardium is at risk as determined by physiologic testing with exercise electrocardiography or stress nuclear techniques.

Characterization of the functional significance of subcritical coronary stenoses with H(2)15O and positron-emission tomography

We have previously developed a method employing cardiac positron-emission tomography (PET) with 15O (half-life 2.1 min)-labeled water (H2(15)O) and blood pool subtraction with C15O for assessment of myocardial perfusion. This study was performed to determine whether the method developed permits detection of the differences in blood flow, induced by vasodilator stress, indicative of functionally significant subcritical coronary stenosis despite normal perfusion at rest. Coronary stenoses were induced with a small Teflon cylinder placed in the left anterior descending coronary artery of the closed-chest dog. Regional myocardial blood flow was assessed tomographically with H(2)15O given intravenously and C15O given inhalation. Blood flow distal to the stenoses was normal under conditions of rest. However, significant reductions in the hyperemic response to dipyridamole were detected consistently in regions distal to 50% to 70% diameter stenoses. Flow distal to stenoses more than doubled in absolute terms in response to dipyridamole but was only 43 +/- 9% of the increased flow in normal regions in the same dogs or in corresponding anterior regions in normal dogs. Relative myocardial blood flow measured noninvasively with PET correlated closely with the distribution of radiolabeled microspheres measured in vitro (r = .88). Thus, assessment of myocardial blood flow with H(2)15O and PET in dogs at rest and during vasodilator-induced stress permits detection of physiologically significant coronary stenoses. The procedure should therefore prove useful diagnostically for the detection of coronary insufficiency in patients as well as for the assessment of clinical interventions designed to augment regional perfusion.

Decreased coronary reserve in primary scleroderma myocardial disease

We assessed coronary reserve, by measuring the increase in coronary sinus blood flow (CSBF) after intravenous administration of dipyridamole (0.14 mg/kg/minute for 4 minutes), in 7 patients with primary scleroderma myocardial disease (PSMD) and in 7 control subjects. Coronary reserve was greatly impaired in PSMD: before administration of dipyridamole, CSBF was similar in patients with PSMD (89 +/- 32 ml/minute/100 gm, mean +/- SD) and in controls (100 +/- 15 ml/minute/100 gm); after dipyridamole infusion, CSBF was significantly lower in patients with PSMD (191 +/- 45 ml/minute/100 gm) than in controls (399 +/- 58 ml/minute/100 gm) (P less than 0.01). Six of the 7 patients with PSMD had angiographically normal epicardial coronary arteries and normal left ventricular function. Decreased coronary reserve may be an important contributor to the pathogenesis of primary scleroderma myocardial disease.

Myocardial perfusion after aortocoronary bypass surgery: measurements at rest and after administration of isoproterenol

This study examined quantitative regional myocardial perfusion (RMP) measured by the washout of 133Xe at rest and after an isoproterenol challenge in 50 patients (group I) studied 8 to 14 days after they underwent saphenous vein bypass grafting to the left coronary artery, and compared this with RMP measured in the native left coronary artery in 14 patients (group II) with significant coronary artery disease and in 12 normal subjects (group III). The double product of the heart rate and aortic systolic pressure was used as an indicator of demand. The statistical significance of group comparisons was analyzed with Dunn's multiple comparisons among means test. Analysis of the data showed no significant difference among the groups with respect to aortic systolic pressure. In subjects at rest, heart rate was lower in groups II and III than in group I, and double product was lower in group II than in group I. After isoproterenol, both heart rate and double product were lower in group II compared with groups I and III, but there was no significant difference between groups I and III with respect to heart rate or double product. Mean resting RMP in group II was lower than in group I; however, results of other group comparisons were insignificant for resting parameters. After isoproterenol, mean flow (ml/100 g/min) in group I was similar to flow in group III (130 +/- 24 vs 139 +/- 26). In contrast, the average flow response after isoproterenol was significantly less in group II when compared with that in group I (105 +/- 20 vs 130 +/- 24) and with that in group III (105 +/- 20 vs 139 +/- 26). Because of differences in levels of demand with isoproterenol, the change in flow was normalized to the percent increase in double product. These data showed results similar to those above, i.e., normalized RMP in patients with coronary artery disease was significantly lower than that in normal subjects (82 +/- 41 vs 119 +/- 57) and in revascularized patients (82 +/- 41 vs 105 +/- 54). However, there was no significant difference between normal subjects and patients who had undergone surgery. To further evaluate the relationship of flow response to demand parameters, we plotted RMP/double product vs resistance. The data revealed a significant correlation between these variables in all groups both in subjects at rest and after isoproterenol.(ABSTRACT TRUNCATED AT 400 WORDS)

Usefulness of transstenotic coronary pressure gradient measurements during diagnostic catheterization

A difficult problem in coronary arteriography is the assessment of the hemodynamic significance of stenoses that appear angiographically to be of only moderate severity (25 to 75% diameter narrowing). This is particularly important in patients who may be candidates for invasive therapy, such as percutaneous transluminal coronary angioplasty (PTCA) or coronary bypass surgery. To determine the significance of such lesions, we measured transstenotic coronary pressure gradients in 15 patients with angiographically moderate stenoses. For comparison, similar measurements were made in 17 patients with severe stenoses (more than 75% diameter narrowing) being considered for PTCA. The transstenotic pressure gradients were measured with a 2.0Fr polyvinyl chloride catheter cleared of microbubbles of air by flushing with carbon dioxide and degassed saline solution and attached to a low-volume displacement transducer for optimal frequency response. Mean transstenotic pressure gradients greater than 10 mm Hg at rest or more than 20 mm Hg under conditions of high coronary blood flow, as induced by Renografin 76, appeared to be associated with objective evidence of myocardial ischemia and symptomatic relief from PTCA. Smaller pressure gradients occurred in patients whose symptoms probably were not ischemic in nature. Transstenotic pressure gradient determination performed at the time of diagnostic catheterization may provide assistance in clinical decision-making in selected patients with angiographically moderate stenoses.

Relation of coronary blood flow and reactive hyperemia to regional dysfunction induced by dopamine infusion in dogs: limitations in detecting subcritical coronary stenoses

Sympathomimetic agents have been used clinically to elicit regional dysfunction or heterogeneity of coronary blood flow to detect coronary artery lesions. However, the usefulness of this procedure in detecting mild to moderate coronary stenoses has not been defined previously. This was investigated in 10 open chest anesthetized dogs using subendocardial ultrasonic crystals to measure segment lengths. An electromagnetic flow probe was placed on the proximal left anterior descending artery, and graded coronary stenoses were created using a cuff occluder. In the first phase of the study, subcritical coronary stenoses were created which impaired maximal postocclusion reactive hyperemia, but not coronary blood flow at rest. A constant infusion of dopamine (average 15 micrograms/kg per min) was then administered. Regional dysfunction during dopamine infusion was not consistently observed despite production of coronary stenoses resulting in total loss of reactive hyperemia at rest. Regional function during dopamine treatment was, however, critically related to the actual changes in coronary blood flow during the infusion. In the second phase of the study, regional function during dopamine challenge was investigated during progressive impairments of coronary blood flow. Regional function was maintained until coronary blood flow during the infusion was reduced to near rest levels below which regional function deteriorated rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of hemodynamic significance of isolated stenoses of the left anterior descending coronary artery using thallium-201 myocardial scintigraphy

This study tests the hypothesis that the results of stress thallium-201 myocardial perfusion scans (TI-201) are related to the mean transstenotic pressure gradient of coronary stenoses independent of the percent luminal diameter narrowing seen at angiography. The 22 study patients (20 men, 2 women, mean age 47 years, range 30 to 62) had no previous myocardial infarction. Each underwent a symptom-limited, erect bicycle TI-201 test off antianginal therapy, shortly before percutaneous transluminal coronary angioplasty for isolated left anterior descending coronary artery stenosis. The percent narrowing, mean gradient at percutaneous transluminal coronary angioplasty and presence of a visually apparent TI-201 defect were independently evaluated and results compared. All 4 patients with 90% or greater diameter narrowing had positive TI-201 responses, and the mean gradient was 72 +/- 11 mm Hg. Among the 18 patients with less than 90% diameter narrowing, the mean gradient was higher (p less than 0.001) in the 11 with a positive TI-201 (63 +/- 15 mm Hg) than in the 7 with a negative TI-201 (33 +/- 20 mm Hg), but their percent narrowing did not differ significantly (72 +/- 14% vs 66 +/- 19%). Multiple regression analysis showed that the presence of a TI-201 defect was a strong (p = 0.003) and percent narrowing (p = 0.048) a weak independent predictor for gradient. When the mean gradient was normalized for the prestenotic pressure, both percent narrowing (p = 0.003) and TI-201 defects (p = 0.006) were significant independent predictors.(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid ultrasonography--the new "gold standard". Surgical and angiographic correlation

Atherosclerotic plaques and high grade stenosis in the carotid circulation are responsible for symptoms of cerebral and retinal ischemia. Identification of these lesions by angiography has been the "gold standard" for which the decision of endarterectomy depended. The recent introduction of high resolution carotid ultrasonography has allowed us to compare thirty-seven surgical specimens with the results of preoperative screening with angiography. UCI had a 97% correlation whereas angiography was accurate only 70%. More importantly there were ten negative angiograms in patients with clinically active ulcerative plaque disease. If surgery were based solely on the angiographic appearance of ulcerative plaques or high grade stenosis, then less than half of the patients have received the correct treatment. UCI deserves to be considered the new reference standard.

Positive exercise thallium-201 test responses in patients with less than 50% maximal coronary stenosis: angiographic and clinical predictors

The incidence and causes of abnormal thallium-201 (TI-201) myocardial perfusion studies in the absence of significant coronary artery disease were examined. The study group consisted of 100 consecutive patients undergoing exercise TI-201 testing and coronary angiography who were found to have maximal coronary artery diameter narrowing of less than 50%. Maximal coronary stenosis ranged from 0 to 40%. The independent and relative influences of patient clinical, exercise and angiographic data were assessed by logistic regression analysis. Significant predictors of a positive stress TI-201 test result were: (1) percent maximal coronary stenosis (p less than 0.0005), (2) propranolol use (p less than 0.01), (3) interaction of propranolol use and percent maximal stenosis (p less than 0.005), and (4) stress-induced chest pain (p = 0.05). No other patient variable had a significant influence. Positive TI-201 test results were more common in patients with 21 to 40% maximal stenosis (59%) than in patients with 0 to 20% maximal stenosis (27%) (p less than 0.01). Among patients with 21 to 40% stenosis, a positive test response was more common when 85% of maximal predicted heart rate was achieved (75%) than when it was not (40%) (p less than 0.05). Of 16 nonapical perfusion defects seen in patients with 21 to 40% maximal stenosis, 14 were in the territory that corresponded with such a coronary stenosis. Patients taking propranolol were more likely to have a positive TI-201 test result (45%) than patients not taking propranolol (22%) (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Accelerated progression of atherosclerosis in coronary vessels with minimal lesions that are bypassed

Accelerated progression of atherosclerosis is known to occur in surgically bypassed coronary arteries in which the preoperative stenosis was greater than 50 per cent. To assess the effect of coronary bypass on vessels with lesser degrees of stenosis, we studied 85 men who had undergone coronary bypass surgery. In this group we identified bypass grafts placed in 37 arteries with minimal atherosclerosis, which was defined as less than 50 per cent stenosis of the vessel diameter. In the same 85 men there were 93 coronary vessels with minimal atherosclerosis for which a bypass graft had not been placed. Progression of atherosclerosis, defined as further loss of at least 25 per cent of the lumen, during an average follow-up period of 37 months was more than 10 times as frequent (38 per cent vs. 3 per cent) in bypassed arteries with minimal atherosclerosis as in comparable arteries that were not bypassed. These findings support the view that minimally diseased coronary arteries should not be bypassed.