Altered coronary flow responses to vasoactive drugs in the presence of coronary arterial stenosis in the dog

Coronary physiology revisited : practical insights from the cardiac catheterization laboratory

Various coronary physiological measurements can be made in the cardiac catheterization laboratory using sensor-tipped guidewires; they include the measurement of poststenotic absolute coronary flow reserve, the relative coronary flow reserve, and the pressure-derived fractional flow reserve of the myocardium. Ambiguity regarding abnormal microcirculation has been reduced or eliminated with measurements of relative coronary flow reserve and fractional flow reserve. The role of microvascular flow impairment can be separately determined with coronary flow velocity reserve measurements. In addition to lesion assessment before and after intervention, emerging applications of coronary physiology include the determination of physiological responses to new pharmacological agents, such as glycoprotein IIb/IIIa blockers, in patients with acute myocardial infarction. Measurements of coronary physiology in the catheterization laboratory provide objective data that complement angiography for clinical decision-making.

Linear hydraulic pressure-pulse actuator (LHPA): a versatile instrument that produces a simulated blood pressure pulse wave for small sized vessels

An instrument is presented which produces a simulated circulatory pulsatile pressure wave for small sized vessels. The linear hydraulic pressure-pulse actuator (LHPA) is designed to be extremely versatile, that is, a blood pressure wave source of any shape, amplitude, offset and frequency can be simulated. In addition, the LHPA can reproduce accurately a real pulse pressure wave by simply imputting an actual data record of a circulatory pressure pulse. The design is accomplished by incorporating the use of a linear force solenoid driven with a voltage-to-current source power amplifier. Testing of the device is presented here, as well as pressure pulse results from a recorded pulsatile pressure input to the LHPA. The device is simple to implement in that its response is linear, for volume changes upto +/- 5 mL, without the need for feedback compensation.

Transdermal nitroglycerin patch therapy reduces the extent of exercise-induced myocardial ischemia: results of a double-blind, placebo-controlled trial using quantitative thallium-201 tomography

OBJECTIVES

This study prospectively evaluated whether transdermal nitroglycerin patches could limit the extent of exercise-induced left ventricular ischemia as assessed by quantitative thallium-201 tomography.

BACKGROUND

Although antianginal medications are effective at reducing chest pain symptoms in patients with coronary artery disease, there is limited evidence that these agents can also reduce myocardial ischemia.

METHODS

This was a randomized, double-blind, parallel, placebo-controlled trial evaluating nitroglycerin patch therapy in patients in stable condition with angiographic coronary artery disease and no previous myocardial infarction. All patients were weaned from antianginal agents and had a baseline symptom-limited treadmill test followed by thallium-201 tomography. Forty patients with perfusion defects involving > or = 5% of the left ventricle were randomized to receive either intermittent (12 h on/off) active nitroglycerin patch therapy (0.4 mg/h) or placebo. Exercise tomography was repeated a mean (+/- SD) of 6.1 +/- 1.8 days after randomization.

RESULTS

Patients randomized to receive active patch therapy had a significant reduction in their total perfusion defect size (-8.9 +/- 11.1%) compared with placebo-treated patients (-1.8 +/- 6.1%, p = 0.04), which was most apparent in those with the largest (> or = 20%) baseline perfusion defects (-11.4 +/- 13.4% vs. 1.0 +/- 3.6%, respectively, p < 0.02). Furthermore, 7 (33%) of 21 patients receiving active therapy had a > or = 10% decrease in their perfusion defects compared with only 1 (5%) of 19 patients randomized to receive placebo (p = 0.002). Nitrate therapy did not significantly reduce heart rate, blood pressure or double product, indicating benefit through enhancement of coronary blood flow.

CONCLUSIONS

Short-term, intermittent nitroglycerin patch therapy significantly reduces myocardial ischemia, particularly in patients with large ischemic perfusion defects. Thallium-201 tomography can be used to assess sequential changes in the extent of exercise-induced left ventricular ischemia.

In vivo validation of a transit-time ultrasonic volume flow meter

The objective of this investigation was to validate a transit-time ultrasound blood flow metering system in vivo. Implanted chronically and acutely on the ascending aorta of the dog, the transit-time flow probe determined varying flow rates simultaneously with measurements made by the electromagnetic flow metering method. The transit-time technique was also compared to two methods in which blood was collected volumetrically by either graduated cylinder (ascending aorta/dog) or pump withdrawal (abdominal aorta/cat). Statistical analysis of the results provided evidence that the transit-time ultrasound method measured in vivo blood flow rate no differently than the electromagnetic or pump withdrawal techniques, however, transit-time determinations of blood volume were 10% below that indicated by graduated cylinder collection. With transit time represented on the y-axis, three linear regressions of all paired blood flow measurements were calculated yielding the following slopes (delta y/delta x) and regression coefficients (r), respectively: electromagnetic (1.00, 0.98), graduated cylinder (0.85, 0.93), and pump withdrawal (0.93, 1.00). The results validate the transit-time ultrasound system used in the present investigation as an accurate method capable of measuring blood flow in both acutely and chronically instrumented animal preparations.

Does thrombolysis in myocardial infarction (TIMI) perfusion grade 2 represent a mostly patent artery or a mostly occluded artery? Enzymatic and electrocardiographic evidence from the TEAM-2 study. Second Multicenter Thrombolysis Trial of Eminase in Acute Myocardial Infarction

One measure of the success of thrombolysis is the early patency status of the infarct-related coronary artery. The Thrombolysis in Myocardial Infarction (TIMI) study group designated patency grades 0 (occluded) or 1 (minimal perfusion) as thrombolysis failure and grade 2 (partial perfusion) or 3 (complete perfusion) as success. To evaluate their true functional significance, perfusion grades were compared with enzymatic and electrocardiographic (ECG) indexes of myocardial infarction in 359 patients treated within 4 h with anistreplase (APSAC) or streptokinase. Serum enzymes and ECGs were assessed serially. Patency was determined at 90 to 240 min (median 2.1 h) and graded by an observer who had no knowledge of patient data. Results for the two drug arms were similar and combined. Distribution of patency was grade 0 = 20%, n = 72; grade 1 = 8% n = 27; grade 2 = 16%, n = 58 and grade 3 = 56%, n = 202. Interventions were performed after angiography but within 24 h in 51% (n = 37), 70% (n = 19), 41% (n = 24) and 14% (n = 28) of patients with grades 0, 1, 2 and 3, respectively. Outcomes were compared among the four patency groups by the orthogonal contrast method. Patients with perfusion grade 2 did not differ significantly from those with grade 0 or 1 in enzymatic peaks, time to peak activity and evolution of summed ST segments, Q waves and R waves (contrast 2). Conversely, comparisons of patients with grade 3 perfusion with those with grades 0 to 2 yielded significant differences for enzymatic peaks and time to peak activity for three of the four enzymes (p = 0.02 to 0.0001) and ECG indexes of myocardial infarction (p = 0.02 to 0.0001) (contrast 3). Thus, patients with grade 2 flow have indexes of myocardial infarction similar to those in patients with an occluded artery (grades 0 and 1 flow). Only early grade 3 flow results in a significantly better outcome than that of the other grades. Because early achievement of grade 2 flow does not appear to lead to optimal myocardial salvage, the frequency of achieving grade 3 perfusion alone may best measure the reperfusion success of thrombolytic therapy.

Reactivity of proximal and distal angiographically normal and stenotic coronary segments in chronic stable angina pectoris

To assess whether vasoreactivity of significant coronary stenosis (greater than 50% intraluminal diameter reduction) and that of angiographically normal coronary segments differs in proximal and distal locations, 53 patients (40 men, 13 women, mean +/- standard deviation age 55 +/- 11 years) with chronic stable angina and angiographically documented coronary artery disease were studied. While abstaining from antianginal therapy, all 53 patients underwent coronary arteriography before and after 1 mg of intracoronary isosorbide dinitrate and 21 of the 53 also before and after 20 to 30 micrograms intracoronary ergonovine. Computerized quantitative angiography was used to assess changes in the intraluminal diameter of 126 normal coronary segments (63 proximal, 63 distal) and 43 significant coronary stenoses. Nitrates dilated proximal normal coronary segments by 7.4 +/- 1.2% and distal normal coronary segments by 15 +/- 1.7% (p less than 0.01). Significant proximal coronary stenoses dilated by 11 +/- 2.5% and distal stenoses by 23 +/- 2.8% (p less than 0.01) after nitrates. Ergonovine reduced the diameter of proximal normal coronary segments by 9.3 +/- 1.7% and that of normal distal segments by 15.5 +/- 1.4% (p less than 0.01). Proximal stenoses constricted by 11 +/- 2.2% and distal stenoses by 18.4 +/- 2.8% (p = 0.06). Analysis of segments showed that nitrates dilated 19 of 63 (30%) proximal normal segments by (greater than or equal to 10%), 31 of 63 (49%) distal (p less than 0.05) and 21 of 43 (49%) stenoses.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of hypertension from unilateral renal artery stenosis in conscious dogs

The renal and systemic changes after stenosis of the left renal artery (n = 5) or sham stenosis (n = 6) in conscious dogs were studied sequentially over 25 days. Stenosis produced a prompt rise in arterial pressure, which was at all times due to reduced peripheral vascular conductance, with no increase in cardiac output despite initial evidence of mild fluid retention. The decrease in peripheral conductance was attributable to 1) the stenotic kidney (25% of the total and due to the mechanical effect of the stenosis itself), 2) the nonstenotic kidney (about 15% of the total and not caused by angiotensin II), and 3) the nonrenal vasculature (60%). The decrease in conductance in the nonrenal vasculature was due partly to angiotensin II, but there was also a gradually developing non-angiotensin II component. Acute administration of captopril caused significantly greater changes in arterial pressure and peripheral conductance throughout the period of stenosis than before stenosis (and greater than in sham-stenosis dogs), indicating that angiotensin II was constricting the peripheral vasculature even when plasma renin levels were no longer elevated. In the stenotic kidneys, captopril produced a fall in renal vascular resistance, but renal blood flow did not rise because there was an approximately equal rise in the resistance of the stenosis. There was no evidence for a role for the autonomic nervous system in the hypertension, as ganglion blockade (pentolinium) had similar hemodynamic effects before and after stenosis. Thus, the hypertension was due at all times to reduced peripheral conductance, with the two kidneys responsible for 40% of this reduced conductance.

Endothelium-dependent vasodilating effect of substance P during flow-reducing coronary stenosis in the dog

The effects of substance P, a putative central and peripheral neurotransmitter, on coronary vasculature and its mechanisms were studied in 31 anesthetized open chest dogs. Without coronary stenosis, intracoronary infusion of substance P (0.001 to 1 pmol/kg per min) for 40 s increased coronary blood flow up to 173 +/- 10.7% in dose-dependent fashion. Application of coronary stenosis created by an inflated intraluminal microballoon that preserved active vasomotion of the stenosed segment produced a pressure gradient of 34 +/- 2 mm Hg, a decrease in rest coronary blood flow of 21 +/- 1.6% and significant depression of the rate of rise in left ventricular pressure (dP/dt). During coronary stenosis, substance P increased coronary blood flow up to 150 +/- 9.4%, lowered mean distal coronary pressure and decreased stenosis resistance in dose-dependent fashion. After endothelial denudation of the proximal part of the coronary artery, the substance P-induced increments in coronary blood flow during coronary stenosis were abolished. In vitro measurements of isometric tension from both intact and denuded portions of coronary arteries confirmed a marked inhibition of substance P-induced relaxation in the denuded segments. These results show the obligatory role of the endothelium in substance P-induced coronary artery dilation. Furthermore, intracoronary infusion of substance P (1 pmol/kg per min) from the site distal to coronary stenosis that precluded the responsiveness of the large coronary artery decreased coronary blood flow by 24 +/- 4%, lowered mean distal coronary pressure by 15 +/- 1.9 mm Hg and intensified stenosis resistance by 77 +/- 7.2%. Thus, substance P exerts a direct potent dilating effect on both large and small coronary arteries. However, because of its strict endothelium-dependency, this peptide may play a detrimental role in the regulation of coronary blood flow when an atherosclerotic stenotic lesion with endothelial damage or dysfunction is present in the proximal part of the coronary artery.

Paradoxical narrowing of atherosclerotic coronary arteries induced by increases in heart rate

Vasodilation in normal and vasoconstriction in atherosclerotic coronary arteries have been observed in response to complex stimuli such as exercise and the cold pressor test. To study a single parameter that changes during these activities, and to better understand the pathophysiology of ischemia associated with increases in heart rate, we studied coronary vasomotion and blood flow response to increasing heart rate alone, produced by atrial pacing, with quantitative angiographic and Doppler flow-velocity measurements in 15 patients. In five patients with angiographically smooth coronary arteries (group 1), tachycardia produced progressive dilation of the epicardial artery with increases in cross-sectional area (CSA) of +15.5 +/- 3.4%, +22.4 +/- 2.1%, +28.5 +/- 3.3%, and +30.6 +/- 2.2% at 90, 110, 130, and 150 beats/min, respectively. In contrast, in five patients with mild angiographic narrowings (group 2), coronary segments failed to dilate with progressive tachycardia (-6.3 +/- 2.0%, -8.3 +/- 2.0%, -12.5 +/- 2.0%, and -11.4% at 90, 110, 130, and 150 beats/min, respectively), and progressive loss of luminal area was observed in five patients with severe angiographic narrowings (group 3) (-34.4 +/- 3.4%, -49.6 +/- 2.2%, -59.2%, and -72.8% at 90, 110, 130, and 150 beats/min, respectively). Coronary blood flow increased significantly with tachycardia in group 1 (+44.5 +/- 10.2%, +86.0 +/- 24.6%, +105.8 +/- 29.3%, and +137.5 +/- 46.0%), increased slightly in group 2 (+7.8 +/- 3.2%, +9.4 +/- 4.4%, +8.4 +/- 3.9%, and +10.0%), and decreased significantly in group 3 (-31.8 +/- 6%, -42.6 +/- 10.7%, -61.0%, and -70.0%). We conclude that an isolated increase in heart rate in patients with normal coronary arteries results in a modest increase in flow and vasodilation. In early atherosclerosis, the flow increase is blunted and dilation is replaced with paradoxical loss in luminal size. In patients with stenoses, further loss in luminal size occurs accompanied by a decrease in coronary blood flow. Thus, increasing heart rate alone in the setting of coronary stenoses could produce myocardial ischemia by a reduction in coronary supply, as well as by an increase in oxygen demand.

Coronary artery spasm during cardiac angiography

Unexpected occurrence of coronary artery spasm is sometimes observed during cardiac catheterization. We report here two cases of coronary artery spasm with hypotension and urticaria subsequent to administration of contrast material. The etiology of coronary artery spasm is discussed.

Effect of stenosis on wall motion. A possible mechanism of stroke and transient ischemic attack

The mechanism by which atherosclerotic plaque causes stroke and transient ischemic attack is not fully understood. One possibility is that the plaque stenosis may set up hemodynamic conditions causing local arterial wall collapse. Arterial wall collapse may, in turn, affect the integrity of the plaque. This study was designed to define the effects of stenosis on the production of arterial wall collapse using a latex tube model. Stenoses ranging up to 81% by diameter were tested in a Starling resistor chamber under pulsatile pressure conditions upstream of the tube. Increasing the degree of stenosis progressively decreased the external pressure necessary to produce collapse, from 37 mm Hg with the 0% stenosis to 24 mm Hg for the 81% stenosis. The stenoses greater than 70% produced a new phenomenon of "systolic wall collapse" just distal to the stenosis. The maximum diameter decrease was 2.83 mm from the baseline diameter of 6.41 mm. Cyclic wall motion just downstream of the stenosis increased with the increased degree of stenosis from 0.34 mm at 0% stenosis to -1.28 mm at 75% stenosis. The phenomena are discussed in terms of simplified Bernoulli pressure drops. We conclude that local arterial stenosis can produce conditions favorable for wall collapse and increased wall motion at physiologic pressure and flow. This collapse may be important in the development of atherosclerotic plaque fracture and subsequent thrombosis or distal embolization.

Constriction of a large coronary artery contributes to serotonin-induced myocardial ischemia in the dog with pliable coronary stenosis

To clarify the role of serotonin in eliciting myocardial ischemia, the effects of serotonin on coronary vasculature and cardiac performance were examined in anesthetized open chest dogs. Without coronary stenosis, intracoronary infusion of serotonin (0.001 to 1.0 micrograms/kg per min) for 40 s caused dose-dependent increases in coronary blood flow up to 175 +/- 8.3%. During fixed coronary stenosis produced by a metal constrictor that restricted active vasomotion of the stenosed segment, only the highest dose of serotonin increased coronary blood flow by 23 +/- 5.7% and decreased distal coronary pressure without any changes in stenosis resistance and systemic hemodynamic variables. During dynamic coronary stenosis created by inflation of an intraluminal microballoon that preserved active vasomotion of the stenosed segment, intracoronary serotonin (0.1 and 1.0 micrograms/kg per min) evoked marked decreases in coronary blood flow and distal coronary pressure and an increase in stenosis resistance, resulting in an elevation of left ventricular end-diastolic pressure and worsening of left ventricular dP/dt. These deleterious effects were reversed by additive intracoronary infusion of nitroglycerin (10 micrograms/min). The detrimental effects of serotonin were not attenuated by pretreatment with aspirin (10 mg/kg, intravenously), which suppressed adenosine disphosphate- and arachidonic acid-induced platelet aggregation in vitro. Furthermore, intracoronary infusion of serotonin (0.1 and 1.0 micrograms/kg per min) from the site distal to coronary stenosis failed to decrease coronary blood flow during dynamic coronary stenosis. Therefore, these detrimental effects of serotonin during dynamic coronary stenosis could be caused by constriction of a large coronary artery but not by platelet aggregation. Vascular effects of serotonin without coronary stenosis and with dynamic coronary stenosis were inhibited by pretreatment with methysergide (0.3 mg/kg, intravenously), but not with ketanserin (0.5 mg/kg, intravenously) which inhibited serotonin-induced platelet aggregation in vitro. Thus, serotonin produced opposing effects on coronary vasculature, that is, small coronary artery dilation and large coronary artery constriction. Both vascular effects were mediated by non-S2-serotonergic receptor activation of the coronary artery. The data obtained in this study suggest that serotonin-elicited constriction of a large coronary artery may play a crucial role in the pathogenesis of myocardial ischemia during pliable coronary stenosis.

Superior efficacy of propranolol versus nifedipine in double-component angina, as related to different influences on coronary vasomotility

PURPOSE

In 24 patients with stable spontaneous and effort-related angina, ischemic episodes at rest were not preceded by changes in circulatory variables (heart rate, systemic and pulmonary arterial pressures) that may raise the myocardial oxygen consumption. We interpreted these episodes as caused by critical and reversible coronary flow reduction at the site of a stenotic lesion, and evaluated the clinical efficacy of nifedipine and propranolol in the treatment of this condition.

PATIENTS AND METHODS

The study was randomized, placebo-controlled, and crossover in design. Nineteen of the 24 subjects were men (mean group age, 59 years; range, 47 to 65 years). The study consisted of four four-day periods. The first and the fourth periods, during which patients received placebo, were single-blind. The treatment consisted of 80 mg of propranolol or 20 mg of nifedipine administered four times daily. The second and the third periods, during which patients received propranolol or nifedipine crossing over to the alternative drug in the next period, were double-blind and separated by a 24-hour interval.

RESULTS

Propranolol fully abolished or reduced the number of spontaneous ischemic episodes in a significantly larger proportion of patients than did nifedipine; it was also effective in several cases in which nifedipine had failed or had even caused a paradoxic effect. Quantitative angiographic evaluation of the influences of nifedipine (Group 1, 12 patients, 10 mg sublingually) and propranolol (Group 2, 12 patients, 0.1 mg/kg intravenously) on the residual lumen diameter of one significant coronary stenosis in each patient showed that (1) after nifedipine, the lumen was unchanged in one, augmented in seven, and reduced in four cases; (2) variations ranged between +1.59 and -1.2 mm, and their direction correlated closely with the influence of oral nifedipine on the episodes of spontaneous ischemia; and (3) in no case did treatment with propranolol vary the stenosis lumen by more than 0.3 mm.

CONCLUSION

In this form of angina, a number of lesions seem to offer a compliant substrate for vasomotion and, possibly, for critical changes in flow. The vasomotor influences of nifedipine on these lesions are variable as well as the efficacy of the drug on the manifestations of ischemia at rest. Propranolol produces no important variations of the coronary stenotic lesions, causes a decrease of heart rate that facilitates coronary flow in diastole, and reduces the baseline metabolic demand of the heart so that the threshold of ischemia during critical reduction of coronary flow may become elevated.

Mechanisms of regional ischemia and antianginal drug action during exercise

Several mechanisms involved in the production of regional exercise-induced ischemia are described. Each offers the potential for modification using different types of antianginal drugs operating to alter regional O2 demands, improve regional perfusion, or both, leading to reduced ischemia and increased contractile function in the ischemic zone. Evidence is presented for matching of regional subendocardial myocardial blood flow and flow per beat with regional myocardial contraction at various levels of ischemia at rest, during steady-state exercise, and after antianginal drugs, signifying a particularly important role for heart rate control. In addition to reducing myocardial O2 demand per minute, beta-blockers and bradycardic drugs cause improvement of absolute subendocardial blood flow and particularly flow per beat by producing vasoconstriction in the epicardial region of the ischemic zone, with improvement of transmural blood flow distribution. Vasodilator drugs can act at several locations to increase regional blood flow and also to decrease O2 demands. A recruitable vasodilator reserve has been shown to exist during exercise-induced ischemia either in native resistance vessels, collateral channels, or both, which appears to be due at least in part to reduction of increased alpha-adrenergic constrictor tone to the coronary vessels during exercise, even in the presence of severe ischemia. The potential for additive effects using combinations of bradycardic and vasodilating agents are described within a framework relating regional subendocardial blood flow to regional systolic contraction. The experimental findings described suggest some potential new directions for antianginal therapy and, along with recent clinical observations, support the use of combinations of antianginal agents that act by different mechanisms.

Paradoxical elevation of threshold to angina pectoris by cold pressor test in men with significant coronary artery disease

Patients with coronary artery disease (CAD) have angina pectoris at varying levels of myocardial oxygen demand. Fluctuations in coronary blood supply due to dynamic changes in coronary vasomotor tone are believed to be responsible for this variation in angina threshold. Cutaneous cold application produces an inappropriate increase in coronary vascular resistance in patients with CAD. To assess the effect of a coronary vasoconstrictor stimulus during exercise (when there are competitive stimuli for coronary dilatation), 16 men with documented CAD and angina underwent 2 exercise tolerance tests, 1 performed for control purposes and the other during cold application (hand and forearm immersed in ice). The cold pressor test elicited an increase in systolic blood pressure at rest (134 vs 159 mm Hg, p less than 0.02) at the end of stage I (145 vs 165 mm Hg, p less than 0.02) and at peak exercise (154 vs 166 mm Hg, p less than 0.05). The diastolic pressure was similarly increased during cold pressor exercise test, but the heart rate showed little or no change. Most patients (11 of 16) tolerated equal or greater double products (heart rate X systolic pressure X 10(-3) at angina (17 vs 20, p less than 0.02), 1-mm ST-segment depression (16 vs 18, p less than 0.05) and peak exercise (18 vs 20, p less than 0.08) during cold pressor exercise test as compared with the baseline exercise test, without a reduction in exercise capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Different coronary vasomotor effects of nifedipine and therapeutic correlates in angina with spontaneous and effort components versus Prinzmetal angina

Flow impedance, probably of vasomotor origin, superimposed on severe coronary stenosis has been considered a trigger for the spontaneous component of angina occurring both on effort and at rest. To investigate more thoroughly this pathophysiologic aspect we evaluated (by means of quantitative coronary angiography) the acute vasomotor reaction to nifedipine (10 mg sublingually) of significant (greater than 50%) stenotic lesions in 22 patients with double-component angina. We also correlated this reaction with the clinical response (daily number of ischemic episodes evaluated by means of 48-hour Holter ambulatory monitoring) to treatment with nifedipine (20 mg four times a day); calcium channel blockade, in fact, is considered a specific remedy in cases of altered coronary vasomotility. Patients with Prinzmetal angina, who were known to have homogeneous coronary vasodilating reactions and favorable clinical responses to nifedipine, were studied by means of the same methods and served as the control group (14 patients). In double-component angina the residual lumen diameter of significant lesions was unchanged in two patients, enhanced in 10, and reduced in 10 after sublingual nifedipine; lumen variations from baseline values ranged from +1.29 to -1.56 mm. Acute changes in stenosis correlated closely with results obtained with oral treatment. In the group with Prinzmetal angina, coronary stenoses invariably responded with dilatation (the residual coronary lumen increased by an average of 69% of baseline); 100% of the patients in this group responded favorably to treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Different vasomotor action of nifedipine on dynamic coronary obstructions and therapeutic response in effort and prinzmetal angina

Variations induced by nifedipine (10 mg sublingually) in the residual lumen diameter of significant (greater than 50%) coronary lesions were assessed angiographically in 58 patients with effort angina (group 1) and in 19 patients with Prinzmetal angina (group 2). A relationship was sought between these acute variations of the stenotic lumen and the clinical response to treatment with the same drug (20 mg four times daily). Treatment efficacy was evaluated with exercise testing in group 1 and Holter monitoring in group 2. In group 1 the residual segment of stenotic diameter showed an increase, decrease, or no change with the calcium antagonist. Nifedipine failed to improve 40% of the cases (21% unchanged and 19% worsened) in group 1. In the same group of patients, the responses to exercise tests were dissociated from the acute vasomotor pattern. Changes in the pressure-rate product also did not explain the clinical results. In group 2 the majority of lesions had compliant portions, which invariably reacted to nifedipine with dilatation. All patients with the Prinzmetal form had relief of the anginal episodes with treatment. These data suggest that the therapeutic efficacy of nifedipine in classic effort angina probably is the net result of influences on the myocardial oxygen consumption and supply, and the acute coronary vasomotor pattern does not allow to predict the clinical response. Stenotic lesions in the Prinzmetal form possess a distinct sensitivity to the relaxant action of calcium channel blockade, which reasonably explains the highly positive response to treatment.

Coronary vasomotor and clinical effects of nifedipine in effort, mixed and Prinzmental angina

Changes induced by nifedipine (10 mg s.l.) in the residual lumen diameter of significant (greater than 50%) coronary lesions were assessed angiographically in 69 patients with effort angina (Group 1), in 22 patients with mixed angina (Group 2), and in 14 patients with Prinzmental angina (Group 3). These changes were related to the clinical response to treatment with the same drug (diary records, exercise testing, Holter monitoring). In Groups 1 and 2 segments of stenotic vessels showed either increase, decrease or no change in diameter with the calcium antagonist; in Group 3 the majority of the vessels showed compliant portions which invariably responded with dilatation. Nifedipine failed to improve cases with exertional (21% unchanged, 19% worsened) and mixed (41% exacerbated) forms; all patients with the Prinzmental form had relief of the anginal episodes. In Group 1, the response to exercise tests were dissociated from the acute vasomotor pattern and the pressure-rate product failed to explain the clinical results. Fifty-two percent of the patients in Group 2 showed significant acute widening of critical stenoses as well as obvious improvement; patients in this group who did worse with treatment had reacted to nifedipine with narrowing of their critical stenoses. These data suggest that: the response to nifedipine of classic effort angina is probably the net result of an interaction of changes in myocardial oxygen consumption and supply; coronary vasomotion has a role in mixed angina and influences of nifedipine may be either favorable or unfavorable; stenotic lesions in the Prinzmental form are quite sensitive to the relaxant action of calcium blockade and this probably represents a background to the highly positive clinical response to treatment.

Nifedipine and angina pectoris. Short-term changes in quantitative coronary angiography with nifedipine and clinical response to treatment in effort-induced, mixed, and spontaneous angina pectoris

Changes induced by nifedipine (10 mg sublingually) in the residual luminal diameter of significant (greater than 50 percent) coronary lesions were assessed angiographically in 69 patients with effort-induced angina (group 1), in 22 patients with mixed angina (group 2), and in 14 patients with Prinzmetal's angina (group 3). These changes were related to the clinical response to treatment with the same drug, as evaluated through diary records and Holter monitoring in the mixed (spontaneous component) and Prinzmetal forms and through exercise testing in effort-induced and mixed (effort-associated component) angina. In groups 1 and 2, segments of stenotic vessels showed either an increase or decrease or no change in diameter with the calcium antagonist; in group 3, the majority of the lesions had compliant portions which invariably responded with dilatation. Nifedipine failed to improve cases with exertional (20 percent [14/69] unchanged; 19 percent [13/69] worsened) and mixed (41 percent [9/22] exacerbated) forms; 100 percent of the 14 patients with the Prinzmetal form had relief of the anginal episodes. In group 1, the response to exercise tests was dissociated from the short-term vasomotor pattern, and the pressure-rate product failed to explain the clinical results. Forty-five percent (ten) of the patients in group 2 showed significant short-term widening of critical stenoses, as well as obvious improvement; patients who did worse with treatment in this group had reacted to nifedipine with narrowing of critical stenoses. These data suggest that the response to nifedipine of classic effort-induced angina is probably the net result of an interaction of changes in myocardial oxygen consumption and supply; coronary vasomotion has a role in mixed angina, and influences of nifedipine may be either favorable or unfavorable; stenotic lesions in the Prinzmetal form are quite sensitive to the relaxant action of calcium blockade, and this probably represents a background to the highly positive clinical response to treatment.

Role of nitrates in silent myocardial ischemia

Assessment of systemic and coronary hemodynamics, myocardial metabolic and mechanical function and scintigraphic and electrocardiographic studies has provided ample evidence for the existence of asymptomatic silent myocardial ischemia in both acute and chronic coronary artery syndromes. There is growing evidence to suggest that a primary decrease in coronary blood flow, resulting from increased coronary arterial resistance, is the principal cause for spontaneous symptomatic and asymptomatic myocardial ischemia in these patients. The precise mechanism for increased coronary arterial resistance has not been clarified, and it is likely to be different in different angina syndromes but similar for both symptomatic and asymptomatic myocardial ischemia. Since nitroglycerin and nitrates can decrease coronary arterial tone and coronary artery resistance, as well as myocardial oxygen requirements, these agents have the potential to relieve episodes of silent myocardial ischemia in patients with coronary artery syndromes.

Relation between graded, subcritical impairments of coronary flow reserve and regional myocardial dysfunction induced by isoproterenol infusion in dogs

Isoproterenol has been used experimentally and clinically to elicit ischemia. The usefulness of this approach, however, in eliciting regional dysfunction in the presence of mild to moderate single-vessel coronary disease quantitated on the basis of coronary flow reserve measurements has not been previously defined. Open-chest, anesthetized dogs were instrumented with an electromagnetic flow probe, high-fidelity micromanometers, and subendocardial ultrasonic crystals. A rigid, screw occluder was used to produce five subcritical coronary stenoses in each dog associated with varying impairment of postocclusion reactive hyperemia at rest but no impairment of resting coronary blood flow. Regional function at rest and in response to the isoproterenol challenge (0.25 micrograms/kg/min) in nonstenotic and stenotic conditions was assessed. Relative regional function was maintained during the infusion until nearly total loss of coronary flow reserve. With this near-critical stenosis, function was lower than in the nonstenotic state but remained greater than resting control values. Moderate impairments of coronary flow reserve were not associated with isoproterenol-induced deterioration of regional function. In conclusion, detection of impaired coronary flow reserve at rest is a more sensitive index of the severity of a coronary stenosis than is detection of regional dysfunction during isoproterenol challenge. Failure to maintain the expected isoproterenol-induced increase in regional function is manifested only when stenoses are associated with nearly total loss of resting coronary flow reserve. This suggests that the clinical use of isoproterenol challenge is not effective in eliciting regional dysfunction when mild coronary disease is present.

Louis F. Bishop lecture. Role of coronary artery spasm in symptomatic and silent myocardial ischemia

The revival of the concept of coronary spasm has stimulated research into coronary artery disease. Observations in patients with variant angina have substantially contributed to the appreciation of painless myocardial ischemia. However, the presence or absence of pain during ischemic episodes is not related to the cause of ischemia, because painless ischemia can be observed in variant angina (caused by spasm), in effort-induced angina (caused by increased myocardial demand) and in myocardial infarction (caused by thrombosis). Continuous monitoring initially of patients with variant angina and subsequently of patients with unstable and stable angina proved that often painful and painless ischemic episodes are caused by a transient impairment of regional coronary blood flow rather than by an excessive increase of myocardial demand. The transient impairment of coronary flow appears to be caused by dynamic stenosis of epicardial coronary arteries. This most often occurs at the site of atherosclerotic plaques encroaching on the lumen to a variable extent. Dynamic stenosis can be caused by 1) "physiologic" increase of coronary tone, as in stable angina, 2) spasm, as in variant angina, and 3) thrombosis, usually in combination with "physiologic" changes in tone or with spasm, or both, as in unstable angina. The mechanisms of spasm, as typically observed in variant angina, are different from those of "physiologic" increase of tone; they appear to be related to a local alteration that makes a segment of coronary artery hyperreactive to a variety of constrictor stimuli causing only minor degrees of constriction in other coronary arteries. The nature of this abnormality, which may remain stable for months and years, is yet unknown.

Comparative effects of intracoronary vasodilators on restoring coronary perfusion during flow-reducing coronary stenosis in the dog

The effects of intracoronary injection of nitroglycerin, adenosine, nifedipine and prostacyclin on restoring coronary perfusion during flow-reducing partial coronary obstruction in anesthetized dogs were studied. Coronary obstruction was obtained by inflation of an intraluminal balloon to decrease coronary blood flow and rate of rise in left ventricular pressure (dP/dt) by approximately 30 to 40 and 10%, respectively. Nitroglycerin (0.01 to 10 micrograms/kg per min) increased coronary blood flow and distal coronary pressure and decreased stenosis resistance associated with improved left ventricular dP/dt depending on its dose. In contrast, adenosine (0.3 to 1.0 micrograms/kg per min) decreased coronary blood flow and distal coronary pressure and intensified stenosis resistance associated with depression of left ventricular dP/dt. Nifedipine and prostacyclin caused divergent effects on the coronary circulation related to each dose. Nifedipine (0.01 and 0.1 micrograms/kg per min) and prostacyclin (0.01 micrograms/kg per min) increased coronary blood flow and distal coronary pressure and reduced stenosis resistance. Nifedipine (1.0 micrograms/kg per min) and prostacyclin (0.3 micrograms/kg per min) did not increase coronary blood flow, but reduced distal coronary pressure and intensified stenosis resistance. Thus, the vasodilators produced different effects on restoration of coronary perfusion during pliable severe coronary stenosis. Nitroglycerin and lower doses of nifedipine and prostacyclin improved coronary perfusion due to selective or preferential dilation of large coronary arteries. Adenosine and higher doses of nifedipine and prostacyclin had deleterious effects on the coronary circulation due to potent arteriolar vasodilation.

Dynamic variations in resistance of coronary arterial narrowings in angina pectoris at rest

The coronary hemodynamic events in 4 patients with frequent episodes of spontaneous rest angina were investigated. The basal coronary transstenotic pressure gradients showed more severe stenosis than that seen on coronary arteriography, suggesting that angiography in this setting may underestimate the true extent of coronary atherosclerosis. Episodes of angina were triggered by marked, sudden increases in the transstenotic coronary pressure gradient and a decrease in coronary blood flow without alterations in systemic arterial pressure or heart rate. These changes in coronary hemodynamics were promptly reversed by the intracoronary administration of nitroglycerin. No such spontaneous variations in transstenotic coronary pressure gradients were observed in 37 patients with a history of classic exertional angina but no rest angina. These unique data represent direct hemodynamic evidence that an increase in resistance at the site of a coronary stenosis, most likely the result of an increase in arterial tone, can be a cause of transient myocardial ischemia in patients with angina at rest.

Use of two-dimensional ultrasonic imaging to measure pharmacologically induced vasomotion in rabbit aorta

We have developed a novel method combining two-dimensional ultrasonic imaging and computerized edge detection to study the vasomotor responses of isolated arterial vessels to various pharmacological agents. Using this in vitro system, we studied the contraction and relaxation of rabbit aorta, respectively, to phenylephrine and acetylcholine. Quantification of these drug-induced changes in vessel wall diameter was achieved by computerized edge detection processing of the two-dimensional ultrasonic vessel wall images. Resolution of this imaging system was determined to be +/- 0.27 mm. Dose-response curves obtained via this new method showed a high degree of correlation with data obtained by classical tissue bath techniques using ring segments. Two-dimensional ultrasonic imaging combined with computerized edge detection is a new and sensitive method to study vasoreactivity of whole, isolated arterial vessels to pharmacological agents.

Local coronary supersensitivity to diverse vasoconstrictive stimuli in patients with variant angina

It has been shown in different groups of patients with variant angina that coronary spasm can be reproduced by physiologic maneuvers and pharmacologic agents. It is not known, however, to what extent different stimuli can induce spasm in the same patient. To investigate whether coronary arterial spasm results from specific abnormal agonist-receptor interactions or from a local nonspecific coronary supersensitivity to different stimuli, 28 patients with vasospastic angina were submitted to a series of diverse vasoconstrictive stimuli known to provoke coronary spasm. Ergonovine, hyperventilation, handgrip, cold pressor, and exercise-tests, were carried out in all 28 patients. In the last 15 patients histamine was also administered. Spasm was provoked by ergonovine in 96% of patients, by hyperventilation in 54%, by histamine in 47%, by exercise in 46%, and by the cold pressor and handgrip tests in 11% and 7%, respectively. No significant differences were found in the responses to provocative tests of patients with normal coronary arteries or nonsignificant stenoses and those with significant lesions. In the same individual, spasm was induced by at least two vasoconstrictive stimuli, although with a different mechanism of action, in 82% of patients and spasm was induced by three or more stimuli in 39%. Tests were repeated in at least 23 patients and short-term reproducibility paralleled sensitivity. These results suggest that in patients with variant angina, a local nonspecific supersensitivity rather than an abnormal specific agonist-receptor interaction plays a major role in the genesis of coronary arterial spasm.

Cardiovascular effects of a single high dose of dilazep by oral route

The acute hemodynamic effects on the coronary and systemic arteries of a single high dose of dilazep given orally (200-400 mg; 3-5 mg/kg) were studied in 25 anginal patients who, for diagnostic reasons, underwent cardiac catheterization and coronary angiography. From 20 to 30 min after drug administration, systemic vascular resistance (1666 +/- 348 to 1367 +/- 312 dyn X sec X cm-5, P less than 0.05) and left ventricular end-diastolic pressure (16.5 +/- 5 to 12 +/- 4.4 mm Hg, P less than 0.01) decreased significantly. The heart rate rose from 74 +/- 10 to 84 +/- 12 beats/min (P less than 0.05), while the cardiac index, dp/dt max and pulmonary arteriolar resistance did not change significantly. Concomitantly, coronary blood flow significantly increased, coronary resistance was reduced by 42% (P less than 0.01) while myocardial oxygen consumption was unchanged. The increase in mean coronary arterial diameter was by 22-25%. It is concluded that dilazep has a prompt and potent vasodilating action even after oral administration. The drug is therefore useful in the chronic treatment of ischemic heart disease.

Vasoconstriction of stenotic coronary arteries during dynamic exercise in patients with classic angina pectoris: reversibility by nitroglycerin

To study the vasomotility of normal and diseased coronary arteries during dynamic exercise, symptom-limited supine bicycle exercise during cardiac catheterization was performed by 18 patients with classic angina pectoris. The cardiovascular response was assessed by hemodynamic measurements and computer-assisted determination of normal and stenotic coronary artery luminal areas from biplane coronary angiograms made before, during, and after exercise. After baseline measurements were recorded, 12 patients (group 1) performed bicycle exercise for 3.4 min (mean), reaching a maximum workload of 81 W (mean); at the end of exercise they received 1.6 mg sublingual nitroglycerin. After measurements at rest in six other patients (group 2), 0.1 mg intracoronary nitroglycerin was given, followed by exercise (3.8 min, 96 W; NS) and sublingual nitroglycerin as in group 1. During exercise in group 1, luminal area of the coronary stenosis decreased to 71% of resting levels (p less than .001), while area of the normal coronary artery increased to 123% of control (p less than .001). After sublingual nitroglycerin at the end of exercise, area of the normal vessel further increased to 140% of control (p less than .001), while luminal area of the stenosis dilated to 112% of resting levels (p less than .001 vs exercise, NS vs rest). Pretreatment with intracoronary nitroglycerin increased both normal (121%; p less than .05) and stenotic (122%; p less than .05) luminal areas, while preventing the previously observed narrowing of stenosis during exercise (114%; NS). Exercise resulted in a similar heart rate-systolic pressure product and caused angina pectoris in two-thirds of the patients in each group. However, patients pretreated with intracoronary nitroglycerin (group 2) had a lower mean pulmonary arterial pressure during maximum exercise (35 mm Hg) than those patients (group 1) not receiving pretreatment (47 mm Hg; p less than .001). Group 2 patients reached a percentage of their predicted work capacity (65%) that was about the same as that during previous upright bicycle exercise (71%; NS), while group 1 patients had a significantly lower work capacity (51% of predicted) than that before catheterization (82%; p less than .001). Hence, narrowing of coronary artery stenosis during dynamic exercise is attributable to active vasoconstriction due to its reversibility by preexercise intracoronary nitroglycerin. Patients who did not experience narrowing of stenosis during exercise (group 2) had less evidence of myocardial ischemia (lower mean pulmonary arterial pressure) and maintained their work capacity.(ABSTRACT TRUNCATED AT 400 WORDS)

Response of normal and diseased epicardial coronary arteries to vasoactive drugs: quantitative arteriographic studies

Coronary vasodilators known to be effective in effort and vasospastic angina were studied in 93 patients undergoing catheterization for evaluation of chest pain. The ischemia-provoking stresses were isometric handgrip (25% of maximum for 4 to 5 minutes) or ergonovine maleate (0.2 mg intravenously). Hemodynamic changes and changes in angiographic diameter of epicardial coronary arteries were measured during these stresses, with and without drug administration. Drugs included intravenous diltiazem (0.25 mg/kg load + 0.003 mg/kg/min), intravenous verapamil (0.14 mg/kg load + 0.0075 mg/kg/min) and intracoronary (0.012 mg/min X 4 minutes) and sublingual (0.4 mg) nitroglycerin. From these studies, the following statistically valid conclusions were reached. First, nitroglycerin is a potent dilator of epicardial coronary arteries, increasing normal luminal area an average of 28% and luminal area in significantly stenotic segments by 29%. Second, verapamil and diltiazem are nonsignificant epicardial coronary dilators (9% and 4% luminal area increase, respectively). Similarly, diltiazem does not dilate significant coronary stenoses. Third, sustained isometric handgrip increases systemic blood pressure and heart rate by reflex activation of the sympathetic nervous system. By this means, handgrip also constricts luminal area in normal and diseased coronary segments by 20% and 22%, respectively. One result of these changes is a handgrip-induced, ischemic 56% rise in pulmonary wedge pressure in patients with significant stenosis. Fourth, intracoronary nitroglycerin, in very small doses, does not block the systemic hemodynamic response to handgrip, but prevents handgrip-induced coronary constriction and the associated ischemic left ventricular dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic principles in the control of coronary blood flow

The effects of atherosclerotic epicardial stenoses on coronary vascular resistance can be understood in terms of basic principles of fluid mechanics. Resistance is directly related to the pressure drop across the stenosis and inversely related to flow. Even with a fixed anatomic stenosis, however, resistance is not fixed; it increases as flow across the stenosis increases. This exacerbates the pressure drop across the stenosis that develops as a result of flow; at high flows, large pressure drops can occur. This characteristic of flow through stenotic lesions can contribute to a "steal" phenomenon between either epicardial or intramural coronary arteries. Studies have also shown the clinical importance and influence of dynamic alterations in coronary resistance, occurring either at the large or small vessel level. In addition, compressive forces exerted by the myocardium or by elevated intraventricular pressures can increase coronary vascular resistance, and thus interfere with myocardial perfusion. All of these factors must be considered in order to obtain a comprehensive understanding of the mechanisms leading to myocardial ischemia and, therefore, to the clinical syndrome of angina pectoris.

Influence of the chosen model of stenosis on pressure-flow relationships in isolated perfused arteries

Passive changes in luminal diameter caused by a fall in the intravascular distending pressure at the site of a severe coronary artery stenosis were recently proposed as a possible cause of transient myocardial ischaemia. We tested this hypothesis in 5 dog carotid arteries perfused with blood at a constant inflow (100 mm Hg) and variable outflow pressures (40-0 mm Hg). Similar degrees of stenosis were induced either with an external circumferential snare or with an intravascular fluid-filled balloon catheter. In 39 experiments outflow pressure was progressively decreased from 40 to 0 mm Hg. This was done first in the absence of stenosis, secondly with an external stenosis (snare) and finally with an internal stenosis of comparable severity (fluid-filled balloon). When stenosis was absent or intraluminal, flow increased progressively from 109.1 +/- 39 to 136 +/- 55 ml/min (P less than 0.06) and from 23 +/- 16 to 34.2 +/- 16 ml/min (P less than 0.001), respectively. Resistance also rose because flow increased proportionally less than the pressure gradient. Conversely, when stenosis was produced by a snare, flow decreased progressively, from 23.9 +/- 17 to 10.7 +/- 15 ml/min (P less than 0.001). Assuming the reduction of flow was caused by the external stenosis compressing the wall into the lumen (against the intravascular pressure) we prepared an artificial vessel with a foam rubber wall inside a silastic tubing. In this artificial vessel (but not in a glass model) a snare stenosis caused reduction in flow when outflow pressure was lowered. Passive changes in caliber due to a reduced distending pressure do not therefore appear to be a cause of flow reduction.

Hemodynamics of human arterial stenoses

We assessed the hemodynamic and geometric changes in compliant, human arterial stenoses in response to manipulation of vascular tone, perfusion pressure and distal resistance. Coronary and popliteal arteries were harvested from human cadavers shortly after death. Following incubation for several hours to permit recovery of physiologic energy stores and ion gradients, the vessels were attached to a perfusion apparatus and perfusion pressure (PP), distal pressure (DP), and flow (F) were recorded as perfusion pressure and distal resistance (DR) were varied. The experiments were then repeated in the presence of a vasoconstrictor (100 mM KCl). Orthogonal arteriograms were performed at maximums of vasoconstriction and vasodilation. Stenotic resistance (SR) was calculated as (PP-DP)F. Minimum cross-sectional area was determined by computer assisted analysis of the arteriograms. Stenosed vessels with normal wall segments at the stenosis responded to vasoconstriction with a large stenotic resistance increase (111 +/- 15%; P less than 0.05) and a flow decrease averaging 39.3 +/- 6.2% (P less than 0.05). In addition, decreased perfusion pressure also increased stenotic resistance significantly (P less than 0.05). Stenotic resistance changes were of sufficient magnitude to be both statistically significant and clinically important. These results confirm the existence of dynamic arterial stenoses in humans and further support the assertion that dynamic stenotic severity changes elicited by manipulation of proximal and distal vascular tone and pressure are of sufficient magnitude to create acute ischemia. This information may apply to clinical situations in which compliant stenoses and acute ischemia coexist.

Hemodynamic and coronary effects of molsidomine at basal state, during atrial pacing, and during cold pressor test in patients with stable angina pectoris

Heart rate (HR), cardiac output (CO), coronary sinus blood flow (CSF), left ventricular systolic pressure (LVSP), left ventricular end-diastolic pressure (LVEDP), mean arterial (MAP), and coronary arteriovenous difference for oxygen (AVDcO2) were measured in patients with stable angina pectoris without cardiac failure before and 40 to 60 minutes after administration of 2 or 3 mg of molsidomine. In 20 patients these measurements were made in basal state during spontaneous rhythm. In eight of these patients (including three receiving beta blockers) the measurements were made during atrial pacing. In eight other patients, all receiving long-term beta-blocker therapy, the measurements were made during cold pressor test. At the basal state in spontaneous rhythm, a gradual reduction in the LVSP to 70% or less of its initial value was observed in four patients receiving 3 mg of molsidomine (two of whom received beta-blocker treatment). The LVSP was immediately restored by vascular filling. In the 16 other patients molsidomine decreased LVSP, LVEDP, MAP, CO, and double product (DP = LVSP X HR). The AVDcO2 was unchanged. CSF and myocardial oxygen uptake index (MVO2 = CSF X AVDcO2) were decreased. During atrial pacing, hemodynamic and coronary effects were similar to those seen in the basal state. During the cold pressor test, the increases in LVSP, MAP, and LVEDP were significantly reduced by molsidomine. The variations in CSF and coronary resistance (MAP/CSF) were also significantly different after administration of molsidomine, with better metabolic regulation of the coronary circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary hemodynamic and metabolic effects of nifedipine in patients with coronary artery disease treated with beta-blocking drugs

In humans, reflex sympathetic nerve activation modulates the direct cardiac action of nifedipine after systemic administration and results in a positive chronotropic and inotropic response. The coronary hemodynamic and metabolic effects of nifedipine were evaluated after propranolol-induced acute beta-receptor blockade in 12 patients with angiographically documented coronary artery disease. The intravenous injection of propranolol led to a decrease in heart rate, coronary blood flow and myocardial oxygen consumption and an increase in coronary vascular resistance and the coronary arteriovenous oxygen difference. Mean aortic pressure did not change. The subsequent intravenous administration of nifedipine resulted in a transient increase in coronary blood flow and a reduction in coronary vascular resistance and the coronary arteriovenous oxygen difference and a sustained decrease in mean aortic pressure and myocardial oxygen consumption without significant changes in heart rate. Thus, in the presence of beta-receptor blockade, the positive chronotropic response to nifedipine is attenuated and nifedipine reduces myocardial oxygen consumption significantly. The vasodilatory effect of nifedipine is maintained and a potential propranolol-related inappropriate vasoconstriction may be reversed. The combination of nifedipine and beta-receptor blocking agents may be useful in the treatment of patients with both effort-induced angina and angina related to changes in coronary vasomotor tone.

A canine model of transient myocardial dysfunction regional shortening in the presence of critical stenosis and cardiac stimulation

An experimental model of exercise-induced angina pectoris was developed in anesthetized dogs. Two i.v. bolus injections of isoproterenol (ISO, 0.25 microgram/kg; time interval: 10 min) were administered, followed by constriction of the circumflex coronary artery (LCX; critical stenosis). Further i.v. bolus injections of ISO were administered before and after i.v. infusion of 0.9% NaCl (control infusion). Stenosis of the LCX did not modify regional function at rest as assessed with ultrasonic crystals implanted subendocardially both in the distribution areas of the circumflex coronary artery and of the left anterior descending coronary artery (LAD). In the presence of critical stenosis, ISO induced a reproducible, transient decrease in systolic shortening and percent systolic shortening in the area supplied by the LCX and a marked increase in systolic shortening and percent systolic shortening in the area supplied by the LAD. During a 60-min observation period following control infusion, no further substantial changes in regional dimensions were observed. The ISO-induced hemodynamic changes were reproducible during this period. The experimental model of exercise-induced angina pectoris presented in this study can be assumed to provide a reliable basis for evaluating the efficacy of various therapeutical interventions.

Coronary angiography during exercise-induced angina with ECG changes

Coronary angiography was performed at rest and during bicycle exercise immediately after the onset of angina and significant ST segment elevation or depression in the ECG. Of 11 patients, six showed significant reduction of coronary lumen diameter at the site of organic stenosis; mean values of stenosis (range) before and during exercise were 55% (25% to 88%) and 98% (89% to 100%), respectively. Five patients did not have any diameter change of the organic lesion; mean values of stenosis (range) before and during exercise were 84% (74% to 89%) and 84% (73% to 92%), respectively. Excluding the areas of these stenoses, diameters of left main coronary artery, proximal, middle, and distal left anterior descending, circumflex, and right coronary artery segments were measured before and during exercise. Diameter in each coronary artery segment during exercise was not significantly changed from that before exercise, both in the groups with and without diameter reduction. Exercise provoked a localized worsening of coronary artery stenosis without changing the diameter in the remaining artery. These findings suggest that the worsening of stenosis might be caused by a regional abnormality of the coronary artery that is not necessarily related to the degree of organic stenosis.

Reflex constriction of significant coronary stenosis as a mechanism contributing to ischemic left ventricular dysfunction during isometric exercise

To study the mechanisms of myocardial ischemia during isometric exercise, handgrip was sustained, for 4.5 min at 25% of maximum by 11 patients with at least one significant coronary stenosis each, during cardiac catheterization. After recovery, the handgrip that was repeated with simultaneous infusion of nitroglycerin (50 micrograms over 4 min) directly into the diseased vessel. The cardiovascular response was assessed by hemodynamic and by computer-assisted measurements of stenosis. During the first handgrip test pulmonary capillary wedge pressure rose 56% (15 to 23 mm Hg; p less than .001), the heart rate-systolic pressure product rose 33% (p less than .01), and the diseased epicardial arteries constricted. Luminal area in the stenotic segment was reduced by 35% (p less than .01), resulting in a 243% increase in estimated stenotic flow resistance (30 to 103 mm Hg/ml/sec; p less than .001). During handgrip with intracoronary nitroglycerin, the pressure-rate product again increased 33%, but relative to resting control, capillary wedge pressure fell 4 mm Hg in association with a 32% increase in luminal area of the stenosis and a 28% reduction in flow resistance (all significantly different from the response to handgrip alone: p less than .001, .01, and .005, respectively). Thus, coronary vasoconstriction, not increased pressure-rate product, is the dominant mechanism for ischemic left ventricular dysfunction during isometric exercise in patients with significant coronary stenoses.

Rethrombosis after reperfusion with streptokinase: importance of geometry of residual lesions

We tested the hypothesis that lesion rethrombosis after streptokinase reperfusion is related to luminal size of the residual stenosis. Two independent techniques of analyzing coronary angiograms, quantitative coronary angiography and computer-based videodensitometry, were used to estimate the size of the residual lumen immediately after discontinuation of streptokinase. These techniques were selected because they provide independent estimates of cross-sectional area of a lesion with high degrees of reproducibility and minimal observer variability. Twenty-four patients who had undergone successful reperfusion with streptokinase were studied. Seven patients had lesion rethrombosis documented either on a repeat angiogram, at autopsy, or, in one case, by the fact that the patient had an acute transmural infarction resulting in death. Vessel patency was documented by repeat coronary angiography 8 to 14 days after initial streptokinase reperfusion in the other 17 patients. As assessed by quantitative coronary angiography, seven of 13 patients (54%) with minimal luminal cross-sectional areas of less than 0.4 mm2 had rethrombosis. None of the 11 patients with lumens greater than 0.4 mm2 had rethrombosis. In the 17 patients with vessels that remained patent the size of the residual lesion at repeat catheterization was compared with its size immediately after reperfusion with streptokinase. Over the intervening 8 to 14 day interval, an average percentage increase in minimal cross-sectional area of 116 +/- 34% was observed. In seven patients minimal luminal cross-sectional area more than doubled. Integrated optical density, an index of the severity of coronary stenosis derived from computer-based videodensitometry, was also useful in identifying a subgroup of patients at high risk for rethrombosis of lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

Determinants of transstenotic gradients observed during angioplasty: an experimental model

Pressure gradient measurement across a stenosis is used during angioplasty to aid catheter positioning and estimate dilatation efficacy. The angioplasty catheter itself, however, further reduces lumen size, and therefore augments the transstenotic gradient. To more precisely define the catheter influence on gradient, we derived a theoretical expression relating the measured gradient with the angioplasty catheter in situ to the "true" gradient; that is, the gradient in the absence of the angioplasty catheter. We then tested this theoretical construct in a canine femoral artery angioplasty model. Fifty-four measurements were performed using 23 separate, 3-mm-long, 40 to 70% stenoses. As predicted by the theoretic model, "true" gradient is compounded by the angioplasty catheter principally as a function of the angioplasty catheter diameter (Dc) and the stenosis diameter (Ds). The best-fit curve of data points relating "true" and compounded gradients to various Dc and Ds combinations can be expressed as: Measured gradient = K X true gradient, where K = 0.25 (e)4.47 (Dc divided by Ds) and e = 2.718. Thus, the transstenotic gradient measured at angioplasty overestimates "true" resting gradient in a predictable manner, which is dependent on the ratio of Dc to Ds.

Reduced myocardial blood flow resulting from dynamic changes in coronary artery stenosis

To evaluate the interaction of coronary vasomotor tone and stenosis, we studied the effects of ergonovine and adenosine on partially obstructed coronary arteries in 6 closed chest dogs. Coronary stenosis was created by partially inflating a balloon catheter with a distal lumen in the left anterior descending or circumflex coronary artery. Stenotic resistance was calculated as the mean pressure gradient across the stenosis divided by the mean blood flow measured with 15 micron radioactive microspheres. Coronary artery vasoconstriction, induced by ergonovine (0.6 mg i.v.), caused a small, but nonsignificant, increase in stenotic resistance (1.42 +/- 0.25 to 2.68 +/- 0.64 mm Hg/ml per min) and had no effect on myocardial blood flow. Coronary arteriolar dilation induced by adenosine increased stenotic resistance (1.52 +/- 0.25 to 9.01 +/- 2.49 mm Hg/ml per min, P less than 0.05) and the pressure gradient across the stenosis (18.8 +/- 3.0 to 41.3 +/- 7.5 mm Hg, P less than 0.05). Adenosine increased myocardial blood flow from 0.52 +/- 0.05 ml/min per g to 1.43 +/- 0.20 ml/min per g (P less than 0.05) in the regions supplied by unstenosed arteries, while in the region perfused by the stenosed artery blood flow fell from 0.51 +/- 0.06 to 0.29 +/- 0.13 ml/min per g (P less than 0.05), with the endocardium most severely affected (0.55 +/- 0.04 ml/min per g to 0.26 +/- 0.09 ml/min per g, P less than 0.05). Thus changes in severity of stenosis produced by altered coronary pressure and flow can influence blood flow to the myocardium. Such dynamic changes in coronary artery stenosis may be important in the pathogenesis of angina and myocardial infarction.