Influence of ionic and non-ionic radiographic contrast media on the vasomotor tone of epicardial coronary arteries

Contrast Medium-Induced Vasoconstrictions

Angiographic contrast media (CM) may cause both vasodilatation and vasoconstriction. This study evaluates a contrast medium-induced vasoconstriction that occurs when isolated arteries are exposed directly to a CM. Segments of rabbit coronary arteries were mounted in tissue baths containing buffer solution. During the experiments the buffer solution was exchanged with iohexol iso-osmolar with plasma, which caused a temporary vasoconstriction of the vessel segments. The constriction did not depend on the degree of oxygenation of iohexol. The endothelium was not involved in the vasoconstriction. Prazosin slightly decreased the vasoconstriction and a small part of the constriction might thus depend on liberation of norepinephrine by iohexol. The constriction was totally inhibited by the calcium antagonist nifedipine, while it was augmented by addition of low concentrations of KCl to ihoexol. It is concluded that the otherwise safe CM iohexol causes vasoconstriction in vitro by depolarizing the smooth muscle cells and the nerve terminals in the vessel wall.

Iodinated radiographic contrast media inhibit the capacitative calcium entry into smooth muscle cells of the swine renal artery

RATIONALE AND OBJECTIVES

To investigate whether nonionic, iodinated, radiographic contrast media (RCM) could modulate calcium release from or calcium entry into smooth muscle cells of the swine renal artery.

METHODS

Intracellular calcium concentrations of isolated myocytes loaded with the calcium-sensitive dye fluo-3 were analyzed using a fluorescence imaging system. Calcium signals were compared with isometric contractions of vascular segments in an organ bath. The effects of the triiodinated monomer iomeprol were compared with those of a mannitol solution.

RESULTS

Stimulation of alpha-receptors by phenylephrine caused a biphasic calcium signal. Transient liberation of calcium from intracellular stores triggered the sustained entry of extracellular calcium (capacitative entry). Iomeprol and mannitol slightly inhibited the initial transient spike to the same extent. The calcium influx was reversibly inhibited by RCM by about 50%. Up to a concentration of 40 mmol/L, the inhibition induced by iomeprol was significantly higher than that induced by mannitol (P < 0.05-0.01). In isolated arterial segments, relaxation of the contraction phase depending on the calcium influx was significantly higher with the RCM than with mannitol (P < 0.01).

CONCLUSIONS

Vasodilatation by CM is associated with a reduction in the capacitative entry of calcium. The mechanism of this effect is not clear, but it can be ruled out that it is mainly due to the high osmolarity of these compounds.

Nitroglycerin withdrawal increases endothelium-dependent vasomotor response to acetylcholine

OBJECTIVES

We sought to determine whether nitroglycerin (NTG) withdrawal contributes to worsening of endothelial dysfunction and development of the rebound phenomenon during intermittent transdermal NTG therapy.

BACKGROUND

Intermittent transdermal NTG therapy is recommended to avoid the development of tolerance. However, this regimen may precipitate worsening angina in the NTG-free interval.

METHODS

Twenty patients were randomized to intermittent transdermal NTG (0.6 mg/h; NTG group) or no treatment (control group) five days before angiography. The risk factors for endothelial dysfunction were similar in both groups. After diagnostic angiography, the patients underwent quantitative angiography before and after intracoronary acetylcholine (ACh), 10(-4) mol/liter. Immediately after the morning study, the patch was removed from the NTG group, and 3 h later, the ACh infusion was repeated in both groups. All patients had mild to moderate coronary artery disease (CAD).

RESULTS

The diameter of the left anterior descending coronary artery at baseline was 2.0 +/- 0.1 mm in the control group and 2.6 +/- 0.1 mm in the NTG group (p < 0.05). Acetylcholine caused mild vasoconstriction in the control group in the morning and afternoon (2.7 +/- 5.3% and 2.4 +/- 3.9%, respectively; p = NS). The NTG group demonstrated mild vasoconstriction to ACh in the morning (3.2 +/- 2.8%; p = NS vs. control group). After patch removal, there was a significant increase in the magnitude ofvasoconstriction in the NTG group (11.6 +/- 3.9%, p = 0.04 vs. morning constriction).

CONCLUSIONS

These results confirm that NTG withdrawal increases the coronary vasomotor response to ACh in patients with mild CAD and suggests that the rebound phenomena may be secondary to the development of endothelial dysfunction after discontinuation of NTG therapy.

The impact of coronary artery disease on the coronary vasomotor response to nonionic contrast media

BACKGROUND

Coronary artery disease (CAD) alters the vasomotor response to a variety of pharmacological agents. We tested the hypothesis that CAD also has an impact on the coronary vasomotor response to radiologic contrast media.

METHODS AND RESULTS

We performed quantitative coronary angiography in 42 patients without angiographic evidence of CAD and 38 patients with CAD in the left coronary artery. Angiographically smooth coronary segments (n=235) were analyzed for changes on luminal diameters and coronary venous oxygen saturation in response to 3 media: the nonionic dimer iodixanol, the nonionic monomer iopromide, and the ionic agent ioxaglate. In subjects without CAD, we assessed the effects of intracoronary administration of the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine and of the cyclooxygenase inhibitor indomethacin on such changes. Iodixanol induced coronary vasodilation in subjects without CAD (8.8+/-8.6%, P<0.001). Patients with CAD exhibited no significant diameter changes in segments >/=20 mm apart from a stenosis (4.7+/-9.4%, P=NS) and significant constriction in segments <20 mm from a stenosis (-3.8+/-4.6%, P<0. 05). Similar results were obtained with iopromide, but no changes were found with ioxaglate. All contrast media induced transient (<35 seconds) increases in coronary venous oxygen saturation in all subjects. Indomethacin, but not N(G)-monomethyl-L-arginine, blunted the vasodilating effect of iodixanol and iopromide (by 80% and 76%, respectively; P<0.001).

CONCLUSIONS

Nonionic contrast media induce a vasodilatory response in normal vessels not by a mechanism involving increased flow or endothelial nitric oxide synthesis, but rather by depending on preserved vascular cyclooxygenase activity. CAD changes normal epicardial vasodilatory response into vasoconstriction.

Influence of radiographic contrast agents on quantitative coronary angiography

PURPOSE

Quantitative angiographic studies on the vasomotility of epicardial coronary arteries are gaining increasing relevance. We investigated whether radiographic contrast agents might influence coronary vasomotor tone and thereby the results of such studies.

METHODS

Coronary angiograms were taken in 12 patients with coronary artery disease at intervals of 5, 3, 2, and 1 min with the low-osmolar, nonionic contrast agent iopamidol 300, and were repeated at identical intervals with the high-osmolar, ionic agent diatrizoate 76%.

RESULTS

Quantitative cine film analysis demonstrated no significant diameter changes in angiographically normal and stenotic coronary arteries with iopamidol. With diatrizoate, however, normal segments were dilated 2% +/- 2% (p < 0.01) after 2 min and 10% +/- 3% after the 1 min interval (p < 0.001). Stenoses showed no uniform responses to diatrizoate.

CONCLUSION

Low-osmolar, nonionic contrast agents should be preferred for quantitative angiographic studies on epicardial coronary vasomotility. When using ionic contrast agents, injection intervals of at least 3 min are required.

Comparative validation of quantitative coronary angiography systems. Results and implications from a multicenter study using a standardized approach

BACKGROUND

Computerized quantitative coronary angiography (QCA) has fundamentally altered our approach to the assessment of coronary interventional techniques and strategies aimed at the prevention of recurrence and progression of stenosis. It is essential, therefore, that the performance of QCA systems, upon which much of our scientific understanding has become integrally dependent, is evaluated in an objective and uniform manner.

METHODS AND RESULTS

We validated 10 QCA systems at core laboratories in North America and Europe. Cine films were made of phantom stenoses of known diameter (0.5 to 1.9 mm) under four experimental conditions: in vivo (coronary arteries of pigs) calibrated at the isocenter or by use of the catheter as a scaling device and in vitro with 50% contrast and 100% contrast. The cine films were analyzed by each automated QCA system without observer interaction. Accuracy and precision were taken as the mean and SD of the signed differences between the phantom stenoses, and the measured minimal luminal diameters and the correlation coefficient (r), the SEE, the y intercept, and the slope were derived by their linear regression. Performance of the 10 QCA systems ranged widely: accuracy, +0.07 to +0.31 mm; precision, +/- 0.14 to +/- 0.24 mm; correlation (r), .96 to .89; SEE, +/- 0.11 to +/- 0.16 mm; intercept, +0.08 to +0.31 mm; and slope, 0.86 to 0.64.

CONCLUSIONS

There is a marked variability in performance between systems when assessed over the range of 0.5 to 1.9 mm. The range of accuracy, intercept, and slope values of this report indicates that absolute measurements of luminal diameter from different multicenter angiographic trials may not be directly comparable and additionally suggests that such absolute measurements may not be directly applicable to clinical practice using an on-line QCA system with a different edge detection algorithm. Power calculations and study design of angiographic trials should be adjusted for the precision of the QCA system used to avoid the risk of failing to detect small differences in patient populations. This study may guide the fine-tuning of algorithms incorporated within each system and facilitate the maintenance of high standards of QCA for scientific studies.

Vasodilatative and vasoconstrictive effects of angiography contrast media

During angiography contrast media (CM) induces changes in vessel tone. The pathophysiological reasons for this are poorly understood. In this short review the anatomical structures and physiological factors involved in vessel tone are described, and previous and recent findings in vitro and in vivo concerning the effect of CM on vessel tone are discussed. Although multifactorial, the main effect seems to result from a direct action of the CM on the vessel wall. For a particular CM formulation, the effect is due to a combination of its osmolality, molecular properties as well as electrolyte content. In vitro experiments performed in iso-osmolar solutions of pure CM suggest the CM interfere with the cellular mechanisms controlling intracellular calcium. When injected intravascularly, CM may cause either vasodilatation and vasoconstriction. Vasodilatation is the most frequent effect when CM is injected into a vessel while vasoconstriction is relatively uncommon. Both vasodilatation and vasoconstriction can be caused by all types of CM.

Acute effect of cigarette smoking on the coronary circulation: constriction of epicardial and resistance vessels

OBJECTIVES

This study was performed to determine the acute effect of cigarette smoking on proximal and distal epicardial conduit and coronary resistance vessels.

BACKGROUND

Cigarette smoking causes constriction of epicardial arteries and a decrease in coronary blood flow in patients with coronary artery disease, despite an increase in myocardial oxygen demand. The role of changes in resistance vessel tone in the acute coronary hemodynamic effect of smoking has not been examined.

METHODS

Twenty-four long-term smokers were studied during cardiac catheterization after vasoactive medications had been discontinued. The effect of smoking one cigarette 10 to 15 mm long on proximal and distal conduit vessel segments was assessed before and immediately after smoking and at 5, 15 and 30 min after smoking (n = 8). To determine the effect of smoking on resistance vessels, coronary flow velocity was measured in a nonobstructed artery with a 3F intracoronary Doppler catheter before and for 5 min after smoking (n = 8). Eight patients were studied without smoking to control for spontaneous changes in conduit arterial diameter (n = 5) and resistance vessel tone (n = 3).

RESULTS

The average diameter of proximal coronary artery segments decreased from 2.56 +/- 0.12 mm (mean +/- SEM) before smoking to 2.41 +/- 0.09 mm 5 min after smoking (-5 +/- 2%, p < 0.05). Distal coronary diameter decreased from 1.51 +/- 0.07 to 1.39 +/- 0.06 mm (-8 +/- 2%, p < 0.01). Marked focal vasoconstriction after smoking was observed in two patients. Coronary diameter returned to baseline by 30 min after smoking. There was no change in vessel diameter in control patients. Despite a significant increase in the heart rate-mean arterial pressure product, coronary flow velocity decreased by 7 +/- 4% (p < 0.05) and coronary vascular resistance increased by 21 +/- 4% (p < 0.01) 5 min after smoking. There was no change in these variables in the control subjects.

CONCLUSIONS

Smoking causes immediate constriction of proximal and distal epicardial coronary arteries and an increase in coronary resistance vessel tone, despite an increase in myocardial oxygen demand. These acute coronary hemodynamic effects may contribute to the adverse cardiovascular consequences of cigarette smoking.

Progression of coronary artery disease is dependent on anatomic location and diameter. The INTACT investigators

OBJECTIVES

This study represents the first prospective, quantitative analysis of the association of progression of coronary atherosclerosis with anatomic site and diameter.

BACKGROUND

The progressive course of coronary artery disease has been documented in many angiographic follow-up trials.

METHODS

The data of 348 patients with coronary artery disease from the International Nifedipine Trial on Antiatherosclerotic Therapy (INTACT) were reviewed. Standardized coronary angiograms were taken 3 years apart and were analyzed quantitatively. The coronary tree was subdivided into 25 segments. The progression of 1,063 preexisting coronary stenoses and the appearance of 247 newly formed stenoses was assessed in relation to the mean diameter of segments (< 2 mm, 2 to 3 mm, > 3 mm) and to their position in the coronary tree (proximal, mid, distal) and in the three major coronary arteries.

RESULTS

Decreases in the minimal diameter of preexisting stenoses were largest in segments that were > 3 mm in diameter (mean +/- SD 0.23 +/- 0.5 mm vs. 0.10 +/- 0.4 mm and 0.02 +/- 0.3 mm, p < 0.001), in a proximal position (0.14 +/- 0.5 mm vs. 0.09 +/- 0.4 mm and 0.06 +/- 0.3 mm, p = 0.081) and in the right coronary artery (0.14 +/- 0.4 mm vs. 0.07 +/- 0.4 mm and 0.07 +/- 0.3 mm, p < 0.01). Changes in percent diameter stenosis of preexisting stenoses were lowest in segments that were < 2 mm in diameter and in a distal position (p = NS). The number of new stenoses/segment was lowest in segments that were < 2 mm in diameter (44 of 1,756 vs. 139 of 1,967 and 64 of 1,125, p < 0.001) and in a distal position (77 of 2,370 vs. 84 of 1,193 and 86 of 1,285, p < 0.001) and was highest in segments of the right coronary artery (100 of 1,546 vs. 66 of 1,496 and 72 of 1,492, p = 0.044).

CONCLUSIONS

Progression of coronary artery disease occurs most frequently in coronary segments that are > 2 mm in diameter, in a proximal or midartery position and in the right coronary artery.

Assessment of coronary conductance and resistance vessel reactivity in response to nitroglycerin, ergonovine and adenosine: in vivo studies with simultaneous intravascular two-dimensional and Doppler ultrasound

OBJECTIVES

The aim of this study was to determine the differential effects of nitroglycerin, ergonovine and adenosine on the resistance vessels in vivo by using a Doppler-tipped guide wire in combination with an ultrasound imaging catheter.

BACKGROUND

Catheter-based two-dimensional intravascular ultrasound yields images of the coronary arteries from which cross-sectional areas can be measured. Intravascular Doppler ultrasound techniques allow measurement of coronary blood flow velocity. The simultaneous use of the two techniques can yield anatomic and physiologic information on conductance and resistance vessels but has not been tried in the coronary arteries.

METHODS

In 15 dogs, we studied coronary flow and vascular reactivity in response to pharmacologic agents using two approaches: 1) a 30-MHz, 4.3F imaging catheter placed alongside a 0.018-in. (0.046 cm) Doppler wire in the circumflex or left anterior descending coronary artery (n = 5); 2) the ultrasound imaging catheter introduced directly over a 0.014-in. (0.036 cm) Doppler wire (n = 10). Vasodilator and vasoconstrictor responses were studied by using intracoronary nitroglycerin (50, 100 and 200 micrograms), ergonovine (200 micrograms) and adenosine (6 mg).

RESULTS

Nitroglycerin caused a dose-dependent increase in epicardial coronary artery cross-sectional area and, to a lesser extent, in average peak flow velocity, resulting in an increase in volumetric coronary blood flow of 39% and 50% at the doses of 100 and 200 micrograms, respectively. With these doses of nitroglycerin, the decrease in diastolic to systolic velocity ratio and the increased change in cross-sectional area from end-diastole to end-systole suggested an enhanced epicardial coronary artery compliance. With ergonovine, a 12% reduction in epicardial coronary artery cross-sectional area was seen, without a significant change in average peak velocity, resulting in a 15% decrease in volumetric coronary blood flow. Adenosine caused a 270% increase in average peak velocity but no change in epicardial coronary artery cross-sectional area, resulting in a 270% increase in volumetric blood flow.

CONCLUSIONS

This study demonstrates that nitroglycerin and ergonovine predominantly influence coronary conductance arteries whereas adenosine mainly dilates coronary resistance vessels. These findings also demonstrate that the combined use of a two-dimensional and a Doppler ultrasound transducer within one catheter assembly can provide information on the differential effects of vasoactive agents on the epicardial and microvascular coronary circulation.

Coronary vasomotor tone in large epicardial coronary arteries with special emphasis on beta-adrenergic vasomotion, effects of beta-blockade

Changes in coronary vasomotor tone of large epicardial coronary arteries today can be assessed quite accurately by exact measurements of coronary diameters applying computer assisted systems. The effect of various vasodilators (nitrates, calcium antagonists, EDRF-dependent compounds) was tested in this way. It appears that normal coronary artery segments reach a maximum of dilator reserve with an increase of luminal diameter of approximately 30-40%; different patterns of kinetics were, however, encountered. beta-Blocking agents, both non-selective (propranolol) and selective (atenolol), were found to lead to a gradual vasoconstriction, i.e., a decrease in diameter by approximately 20-25% over 20 min, an effect which is overcome by nitrates. New beta-blocking compounds with vasodilator properties, such as celiprolol, show no constriction. The vasoconstrictor effect of propranolol and atenolol may not only be due to the decrease of flow following the drop in myocardial oxygen consumption, but could also reflect an unopposed alpha-adrenergic tone. The clinical aspects of this observation are discussed.

Features of the angiographic evaluation of the INTACT study. International Nifedipine Trial on Antiatherosclerotic Therapy

INTACT (International Nifedipine Trial on Antiatherosclerotic Therapy) is a prospective, placebo-controlled, randomized, double-blind, multicenter trial analyzing the influence of 80 mg nifedipine/day on the angiographic progression of early stage coronary atherosclerosis. Coronary angiograms were taken in identical projections before and after a treatment period of 3 years. Quantitative analysis of the angiograms was performed with the computer-assisted contour detection system CAAS. For definition purposes, the coronary artery system was subdivided into 25 different segments, including all anatomic variants. Measurement parameters of segments were mean and minimal diameter, and of stenoses minimal diameter, percentage diameter reduction (at least 20%), length, and plaque area. The variable extent of the changes of these parameters in the different projections analyzed per patient in the two study angiograms was considered by separate computation of the maximal, mean, and minimal changes over these projections; the comparison of the parameter changes between the two treatment groups was performed separately according to these three modes. For all parameters, this comparison was performed on the basis of the individual 25 segments, as well as after aggregation of individual segments to arteries (RCA, LAD, and LCX), to groups of large and small segments, and to the entire coronary artery system. Assessment of changes of the coronary (patho)morphology by quantitative analysis of coronary angiograms is associated with a number of methodical limitations, which may lead to a certain variability of the results. However, due to the double-blind feature of INTACT, this variability should be comparable in the two groups of this study, allowing for a conclusive comparison.

Vasodilatory effects of nisoldipine on coronary arteries--correlation with plasma levels

Vasomotion of angiographically normal and stenotic epicardial coronary arteries was analyzed up to 15 minutes after the onset of an intravenous infusion (4 minutes) of 0.5 mg (13 patients, group A) or 1 mg nisoldipine (13 patients, group B). After both doses the maximal increase of the mean diameters of normal coronary segments was achieved not before the 15th minute, averaging 11 +/- 6% in group A (p less than 0.001) and 18 +/- 9% in group B (p less than 0.001). Eleven of 15 and 8 of 9 coronary stenoses in groups A and B dilated to 5-80% and 15-70%, respectively. The nisoldipine concentration reached maximal levels at the end of the infusion (fourth minute) with an average of 8 +/- 4 ng/ml and 17 +/- 7 ng/ml in groups A and B, respectively. A significant correlation between nisoldipine plasma levels and dilation of normal coronary segments was obtained only with the individual maxima of these parameters and only in group A (p less than 0.01). The hysteresis of the coronary dilation in relation to the drug plasma levels may be due to the high receptor affinity of nisoldipine. In either group nisoldipine provoked a persistent increase in coronary sinus oxygen saturation (p less than 0.01) and a substantial and prolonged drop in systolic and diastolic aortic pressure (p less than 0.001). Both doses of nisoldipine induced a rise in heart rate (p less than 0.01) and a slight drop in the rate-pressure product (p less than 0.05).