Controlled delivery of a tyrphostin inhibits intimal hyperplasia in a rat carotid artery injury model

We examined the inhibitory effect of AG-17, a potent inhibitor of protein tyrosine kinase activity on injury-induced vascular SMC proliferation by polymeric-based, periadventitial controlled release implant in the balloon catheter carotid injury model in rats. The AG-17 delivery system was formulated from ethylenevinyl acetate copolymer and the release kinetics as well as drug stability were determined. Polymeric matrices containing 2 or 10% AG-17 were implanted perivascularly in rats following balloon catheter injury. Western blot analysis of explanted arterial segments revealed enhanced tyrosine phosphorylation in injured arteries that was essentially reduced to normal levels in treated arteries. The mean neointima to media ratios were significantly reduced in both 2% (0.79 +/- 0.17, n = 9, P < 0.02) and 10% AG-17 (0.59 +/- 0.09, n = 12, P < 0.001) groups in comparison to the control group (1.38 +/- 0.18, n = 16). The mean areas of the media in the control and the 2% AG-17 group did not differ significantly but a significant reduction of the mean area of the media was observed in 10% AG-17 group. Embedding of the unstable tyrphostin compound, AG-17, in a hydrophobic matrix stabilizes the drug both in vitro and in vivo, and allows delivery-rate modulation as well as protracted site-specific therapy. Perivascular controlled release delivery of the tyrphostin AG-17 inhibits neointimal formation in the rat carotid injury model.

Geometric remodeling is not the principal pathogenetic process in restenosis after balloon angioplasty. Evidence from correlative angiographic-histomorphometric studies of atherosclerotic arteries in rabbits

BACKGROUND

Restenosis after balloon angioplasty of coronary arteries is thought to be a proliferative response of the arterial wall to injury. Recently, it has been suggested that geometric remodeling of the arterial wall, rather than intimal fibromuscular hyperplasia, may be the major pathophysiological mechanism underlying restenosis. In this study, we evaluated the relative contribution of a geometric decrease in arterial size versus neointimal growth to luminal narrowing associated with restenosis after balloon angioplasty of atherosclerotic femoral arteries in rabbits.

METHODS AND RESULTS

Focal femoral atherosclerosis was induced by endothelial desiccation injury followed by a 2% cholesterol diet. After 1 month on the high cholesterol diet, the animals were subjected to one of four strategies: (1) balloon angioplasty, (2) balloon angioplasty followed by treatment with the factor Xa inhibitor antistasin, (3) combined laser and balloon angioplasty, or (4) no angioplasty. Animals were killed 2 hours or 28 days after angioplasty, and excised femoral artery segments were prepared for histomorphometric analysis. Angiography was performed serially before and immediately after angioplasty and before the animals were killed. An initial postprocedural gain in luminal diameter at sites of angioplasty was followed by a significant reduction in diameter by angiography and a significant increase in luminal cross-sectional area narrowing by plaque by histomorphometry 28 days after angioplasty compared to adjacent nonangioplastied segments of the same arteries, to nonangioplastied control arteries, or to angioplastied segments of animals treated with the factor Xa inhibitor antistasin. By contrast, the overall arterial size (cross-sectional area bounded by the external elastic lamina) at sites of restenosis was not significantly different from adjacent nonangioplastied segments in the majority of arteries excised at 28 days, and the mean overall arterial size at sites of restenosis was not significantly different from corresponding segments of nonangioplastied control arteries or from angioplastied segments of animals treated with antistasin. In the minority of angioplastied arteries in which the arterial size did change, most got larger.

CONCLUSIONS

Geometric remodeling resulting in a decrease in overall cross-sectional arterial size does not appear to be the principal pathogenetic mechanism for restenosis after balloon angioplasty with or without laser in this experimental model.

Neointimal proliferation in canine coronary arteries. A model of restenosis permitting local and continuous drug delivery

BACKGROUND

A number of experimental preparations have been used to elucidate the pathophysiology of restenosis after percutaneous transluminal coronary angioplasty; however, few models have been advanced that address restenosis in coronary arteries, and none provides an effective means of continuous local drug delivery. In this report, we describe a model of restenosis in coronary arteries with the provision for local, continuous delivery of cytotoxic and/or anti-proliferative agents.

EXPERIMENTAL DESIGN

An ameroid constrictor was placed on the left circumflex coronary artery of 17 normocholesterolemic dogs. One month later, after substantial collateral development had ensued, a segment of the left circumflex coronary artery distal to the ameroid was mechanically compressed using surgical forceps for 10 (N = 4), 15 (N = 4), 20 (N = 2), or 30 minutes (N = 5). In two dogs, an indwelling left circumflex catheter and implanted pump maintained a continuous infusion of saline at the injury site. In addition, the pump side port provided transcutaneous access for serial, selective coronary arteriography. The animals were maintained on a normal diet, without cholesterol or fat supplementation.

RESULTS

Three weeks after vascular injury, significant neointimal proliferation was observed in all dogs that was morphologically similar to the proliferation seen after percutaneous transluminal coronary angioplasty in human coronary arteries. The extent of neointimal formation was linearly related to the duration of injury: neointimal/medial area ratios were 0.35 +/- 0.10, 0.46 +/- 0.10, 0.58 +/- 0.03, and 1.16 +/- 0.26 (mean +/- SE) after 10, 15, 20, and 30 minutes of mechanical compression injury, respectively.

CONCLUSIONS

This model produces striking neointimal proliferation in the coronary arteries of normocholesterolemic dogs, morphologically similar to that seen in human coronary restenosis specimens. The model appears suitable to test the efficacy of agents with the potential to inhibit neointimal formation, providing continuous intracoronary drug delivery, as well as transcutaneous access for serial, selective arteriography.

Upregulation of vascular endothelial growth factor expression induced by myocardial ischaemia: implications for coronary angiogenesis

OBJECTIVE

The process of coronary collateral development is poorly understood. It is assumed that particular angiogenic factors are upregulated during episodes of myocardial ischaemia and act as a trigger for neovascularisation. However, the identity of these factors is unknown. The angiogenic factor vascular endothelial growth factor (VEGF) has been shown to be hypoxia inducible, so this factor may mediate ischaemia induced angiogenesis in the heart. The aim of this study was to examine hypoxia inducibility of VEGF in cultured myocardial cells as well as in normally perfused and ischaemic porcine myocardium.

METHODS

(1) In vitro experiment: cultured rat myocardial cells were subjected to hypoxia, and steady state levels of VEGF mRNA were measured after 2 and 4 h of hypoxia. (2) In vivo experiment: myocardial ischaemia in pigs hearts was induced by repeated 2-10 min left anterior descending coronary artery occlusions, separated by 20 min of reperfusion. Hearts were retrieved after 6 h of intermittent ischaemia. Total RNA was extracted from normal and ischaemic zones of the heart and processed for RNA blot hybridisation analysis.

RESULTS

In vitro experiment: as soon as 2-4 h after exposure of cultures to hypoxia, VEGF mRNA levels were significantly raised (6-10-fold). In vivo experiment: VEGF expression was significantly augmented in the ischaemic territory of the myocardium (three- to fivefold induction). Furthermore, polymerase chain reaction amplification of the reverse transcribed mRNA showed increased production of multiple forms of differentially spliced VEGF mRNA in the ischaemic myocardium.

CONCLUSIONS

VEGF production in the myocardium is significantly upregulated by hypoxia in vitro and by ischaemia in vivo. These results suggest that VEGF is a likely mediator in the natural process of ischaemia induced myocardial neovascularisation.

Angiogenic-induced enhancement of collateral blood flow to ischemic myocardium by vascular endothelial growth factor in dogs

BACKGROUND

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen that is angiogenic in vitro and in vivo. It has been hypothesized that VEGF plays a role in myocardial collateral formation; however, the effects of VEGF on collateral flow to ischemic myocardium are unknown.

METHODS AND RESULTS

We studied the effect of VEGF on collateral blood flow in dogs subjected to gradual occlusion of the left circumflex coronary artery (LCx). Beginning 10 days after placement of an LCx-constricting device, VEGF 45 micrograms (n = 9) or saline (n = 12) was administered daily via an indwelling catheter in the distal LCx, at a point just beyond the occlusion. Treatment was maintained for 28 days. Collateral blood flow was determined with microspheres 7 days before treatment, immediately before treatment (day 0), and 7, 14, 21, and 28 days into the treatment period. Collateral blood flow was quantified during chromonar-induced maximal vasodilation and expressed as a collateral zone/normal zone (CZ/NZ) ratio. Treatment with VEGF was associated with a 40% increase in collateral blood flow (final CZ/NZ blood flow ratios of 0.49 +/- 0.06 and 0.35 +/- 0.02 in the VEGF-treated and control groups, respectively, P = .0037) as well as an 89% increase in the numerical density of intramyocardial distribution vessels (> 20 microns diameter) in the CZ (6.6 +/- 1.4 versus 3.5 +/- 0.7 vessels/mm2 in VEGF-treated and control dogs, respectively, P < .05).

CONCLUSIONS

We conclude that intracoronary VEGF enhances the development of small coronary arteries supplying ischemic myocardium, resulting in marked augmentation of maximal collateral blood flow delivery. These results demonstrate the feasibility of pharmacological enhancement of collateral growth and suggest a new therapeutic approach for the treatment of myocardial ischemia.

Basic fibroblast growth factor enhances myocardial collateral flow in a canine model

Basic fibroblast growth factor (FGF) is a multifunctional peptide that may play an integral role in angiogenesis associated with coronary collateral formation and myocardial infarct healing. We sought to determine the effects of exogenously administered basic FGF on collateral blood flow to ischemic myocardium. Ameroid constrictors were used to cause gradual occlusion of the left circumflex coronary artery in dogs. Basic FGF (110 micrograms, n = 9) or saline (n = 12) was given as a daily bolus injection directly into the collateral-dependent zone, beginning 10 days after placement of the Ameroid and continuing for 28 days. Collateral flow was assessed weekly as the ratio of collateral to normal zone (CZ/NZ) blood flow during maximal pharmacologically induced coronary vasodilation. The CZ/NZ increased in both treated and control dogs as a function of time; however, transmural collateral flow in basic FGF-treated dogs significantly exceeded that of control dogs by the second week of treatment. Final CZ/NZ blood flow ratios were 0.49 +/- 0.05 and 0.35 +/- 0.02 in the treated and control groups, respectively (means +/- SE, P = 0.0002). Treatment with basic FGF was also associated with significant increases in the numerical density of distribution vessels and endothelial cell DNA synthesis within the CZ. We also found that basic FGF had acute effects as a coronary vasodilator. Thus exogenous administration of basic FGF enhances maximal collateral blood flow in dogs with myocardial ischemia secondary to single-vessel coronary occlusion, an effect that is likely mediated through the direct angiogenic effects of the peptide, although its acute vasodilatory effects may also play a role.

A model to assess interventions to improve collateral blood flow: continuous administration of agents into the left coronary artery in dogs

OBJECTIVE

The aim was to develop an experimental model in which angiogenic growth factor(s) could be targeted locally to enhance myocardial collateral formation. A preparation was developed in which agents could be infused selectively into the left main coronary artery on a chronic basis to assess the potential of acidic fibroblast growth factor (FGF) to improve collateral blood flow.

METHODS

Ameroid constrictors were placed on the left circumflex coronary artery of mixed hounds. Five weeks after ameroid placement, the artery was ligated and transected at the point of ameroid occlusion; a catheter was inserted and passed retrogradely into the left main coronary artery. The catheter was connected to an implantable infusion pump that provided continuous intracoronary drug infusion for 4 weeks. Dogs were randomised to receive acidic FGF with heparin (30 micrograms.h-1 and 30 IU.h-1, respectively, n = 16) or heparin alone (30 IU.h-1, n = 14). Regional myocardial blood flow was determined in the conscious state at the beginning and end of treatment.

RESULTS

There were no deaths or important surgical complications related to the establishment of the coronary artery infusions. During the treatment interval (5-9 weeks after ameroid placement) the ratio of maximum ischaemic zone/normal zone blood flow increased from 0.39(SD 0.10) to 0.50(0.11) (p < 0.01) in dogs treated with acidic FGF plus heparin; however, similar improvement was noted in dogs treated with heparin alone. Ischaemic zone and normal zone vascular density was also equivalent in the two groups.

CONCLUSIONS

This preparation makes possible the chronic intracoronary administration of agents which may promote myocardial angiogenesis, and allows assessment of collateral blood flow before and after treatment. As given in this investigation, acidic FGF had no demonstrable effect on collateral blood flow; however, this model may facilitate the identification of agents that do enhance myocardial collateral formation.

Drug therapy for torsade de pointes

Torsade de pointes is an uncommon and unique type of ventricular tachycardia. It differs from other forms of ventricular tachycardia by its morphological features, underlying mechanism, and modes of therapy. Recognizing torsade de pointes is of major clinical importance, as standard antiarrhythmic regimens might not only be ineffective in abolishing this life-threatening arrhythmia but may aggravate it. Torsade de pointes is most commonly precipitated by QT prolonging drugs, mainly type IA antiarrhythmic therapy such as quinidine and disopyramide, and other antiarrhythmic agents are reported to cause torsade de pointes as well. Predisposing factors known to increase the likelihood of developing torsade de pointes are: electrolyte imbalance (hypokalemia, hypomagnesemia, or both) and slow heart rate induced either by sinus bradycardia or heart block. Treatment of torsade de pointes is aimed at shortening the QT interval. By acceleration of the heart rate, the QT interval is shortened, thus preventing the recurrence of the arrhythmia. Treatment of torsade de pointes includes: isoproterenol infusion, cardiac pacing, and intravenous atropine. Intravenous magnesium sulfate, a relatively new mode of therapy for torsade de pointes, was proven to be extremely effective and is now regarded as the treatment of choice for this arrhythmia.

Circadian variations in ischemic threshold and their relation to the occurrence of ischemic episodes

BACKGROUND

The occurrence of ischemic episodes during daily activity has been reported to exhibit a bimodal circadian distribution, yet its relation to the ischemic threshold (heart rate at 1-mm ST segment depression) has not been explored.

METHODS AND RESULTS

To determine whether the ischemic threshold during daily activity exhibits a circadian pattern that might relate to the frequency of occurrence of ischemic episodes, we studied the time of occurrence and the heart rate at onset of ischemia in 1,371 ischemic episodes recorded in 41 patients with stable coronary disease, positive exercise testing, and repeated ischemic episodes during ambulatory ECG monitoring (AEM). All patients had 7 days of AEM; 23 were off any anti-ischemic therapy, while 18 were on low dose of beta-blockers. The occurrence of ischemic episodes exhibited the typical bimodal circadian distribution with a prominent peak between 7:00 and 11:00 AM and a second less prominent peak between 6:00 and 9:00 PM. The threshold of myocardial ischemia exhibited a different single-peaked circadian distribution; it was lowest between 1:00 and 3:00 AM and highest between 10 AM and 1 PM. Time series analyses indicated a strong hour-by-hour trend of each of the two circadian distributions, whereas the two series cross-correlated maximally at a lag of zero hours (p < 0.01), indicating a complex interplay between myocardial oxygen demand and supply in determining the occurrence of ischemic episodes during daily activity. The morning increase in the frequency of ischemic episodes could not be attributed to a reduced threshold but rather to an increase in demand. The low threshold at night-time might probably indicate that the mechanism of ischemia during these hours is reduced coronary flow due to increased coronary tone. Secondary analyses for several predefined patients' subsets gave similar results. Patients who received low-dose beta-blockers maintained the bimodal circadian distribution of the occurrence of ischemic episodes, whereas the ischemic threshold exhibited a constant pattern with no circadian changes.

CONCLUSIONS

Our results demonstrate that myocardial oxygen demand is a major determinant of daily ischemia, yet changes in the ischemic threshold that probably reflect dynamic changes in coronary tone play also an important role. The relative contribution of increased demand and decreased threshold to the genesis of ischemic episodes during daily activity can be assessed by AEM and may help to optimize medical therapy.

Dose-dependent smooth muscle cell proliferation induced by thermal injury with pulsed infrared lasers

BACKGROUND

Recently, laser-heated and radio frequency-heated balloon angioplasty techniques have been proposed as a means to treat or minimize dissection and elastic recoil but have been associated with a high rate of clinical restenosis. Similarly, pulsed laser angioplasty techniques proposed to minimize thermal injury while ablating obstructing atheroma have failed to reduce clinical restenosis. Because "hot balloon" and pulsed laser angioplasty create both mechanical and thermal injury, it has been difficult to discern the cause of the smooth muscle cell (SMC) proliferation resulting in restenosis and whether such magnitude of proliferation is predictable and dose related. This study was undertaken to explore these issues.

METHODS AND RESULTS

Localized thermal lesions accompanying efficient ablation were created with a pulsed Tm:YAG laser in nine rabbit aortas, which consistently led to a focal proliferation of SMC that filled the ablated region by 4 weeks. Transcutaneous Ho:YAG pulsed laser irradiation at multiple independent sites of 24 central rabbit ear arteries without ablation led to brief approximately 30 degrees C thermal transients and thermal damage to the artery wall resulting in significant neointimal proliferation by 3 weeks and a mean cross-sectional narrowing of 59 +/- 17% at a dose of 390 mJ/mm2. Acute and chronic responses to varying total energy deposition were studied by histology after the rabbits were killed at 2 hours to 4 weeks. Arterial segments midway between laser injuries were unaffected and served as internal controls. Neointimal proliferation at 3 weeks after laser injury exhibited a clear dose dependence. Mean cross-sectional narrowing increased from 34 +/- 10% to 85 +/- 15% as laser fluence increased from 240 mJ/cm2 to 640 mJ/cm2 (r = 0.84). Similarly, cross-sectional narrowing caused by SMC neointimal proliferation increased from 20 +/- 10% to 77 +/- 17% for a fixed surface irradiation as the depth of the most superficial arterial media decreased from 600 microns to 330 microns (r = 0.94).

CONCLUSIONS

Thermal injury to the arterial wall is a potent stimulus for SMC proliferation and may necessitate reduction in laser or thermal energy used for angioplasty. Moreover, a dose-response relation exists between the degree of thermal injury and SMC proliferative response. Hence, this technique could be used as a practical model of restenosis suitable for screening therapies for inhibition of SMC proliferation.

Rabbit ear model of injury-induced arterial smooth muscle cell proliferation. Kinetics, reproducibility, and implications

Recently, considerable interest has focused on the vascular smooth muscle cell (SMC) response to injury, particularly as it relates to restenosis after angioplasty. In an effort to find an optimal experimental model of arterial SMC proliferation after injury, we examined the effects of external injury to the central artery of the rabbit ear and assessed the reproducibility, morphological changes, and time course of cellular proliferation after such an injury. With rabbits under general anesthesia, direct pressure was applied at two sites along the central artery of the ears of 19 New Zealand White rabbits. Rabbits were maintained on a diet of 2.4% fat and 0.001% cholesterol throughout the experiment. In seven rabbits examined after 21 days, marked SMC proliferation with neointimal formation was observed at all 28 sites (100%). Mean neointimal area, expressed as a percentage of the area of the tunica media, was 82 +/- 40% (range, 21-203%). Compared with the uninvolved artery displaced 2 mm from the injury site, mechanical crush caused a 38% increase in total vessel area (p less than 0.001), a 40% decrease in luminal area (p less than 0.002), and no change in the area of the media. Serial histological studies were performed 1-42 days after injury, using light and electron microscopy and bromodeoxyuridine immunohistochemistry. Beginning at day 3, activated medial SMCs were noted to migrate through defects in the internal elastic membrane, with a gradual increase in neointimal area between days 5 and 12. Peak DNA synthesis was identified in the media 5 days after injury, with proliferative activity shifting almost exclusively to the neointima thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of severity of myocardial ischemia on exercise testing in predicting the severity of myocardial ischemia during daily activities

To determine the relation between myocardial ischemic indexes on exercise testing and on ambulatory Holter recording, 60 patients with stable coronary artery disease who exhibited an ischemic response to both testing procedures were studied. All patients performed a Bruce protocol exercise test and underwent 24-hour Holter recording within 2 weeks without antianginal medications. Mean exercise duration was 7.4 +/- 2.8 minutes, mean heart rate at 1-mm ST depression was 118 +/- 20 beats/min and mean maximal ST depression during exercise was 2.2 +/- 1 mm. During Holter recording the average number of ischemic episodes was 4.7 +/- 2.6 per patient, mean duration of daily ischemia was 62 +/- 54 minutes, mean maximal ST depression was 3.2 +/- 1.3 mm and average heart rate at 1-mm ST depression was 93 +/- 17 beats/min. Overall, the correlations between ischemic indexes on both testing procedures were very weak (mean r2 = 0.054). The only exercise variable that had a significant correlation (p less than 0.05) with all Holter variables was heart rate at 1-mm ST depression, yet it correlated very weakly (0.064 less than or equal to r2 less than or equal to 0.125) with most Holter covariates and had a better correlation (r2 = 0.256) only with average heart rate at 1-mm ST depression during Holter. Thus, ischemic indexes on exercise testing cannot accurately predict ischemic indexes on ambulatory Holter recording in patients with stable coronary artery disease who exhibit ischemic changes on both tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acidic fibroblast growth factor on normal and ischemic myocardium

We sought to determine the effects of acidic fibroblast growth factor (FGF) on ischemic and normal myocardium and to determine whether direct application of acidic FGF to the heart could promote angiogenesis. Eighteen dogs underwent placement of an ameroid constrictor on the left anterior descending coronary artery (LAD). Three weeks later, a left internal mammary artery (IMA) pedicle was positioned over the LAD territory, with a sponge saturated with acidic FGF (n = 12) or saline (n = 4) interposed between the pedicle and the heart. Polytetrafluoroethylene fiber or collagen I sponges were used to deliver the acidic FGF. Weekly angiography of the IMA was performed in all dogs, but significant IMA to coronary collaterals were not demonstrable in any dog. Eight dogs had histological evidence of subendocardial infarction in the LAD territory (five acidic FGF, three control, p = NS). Striking smooth muscle cell hyperplasia was present in arterioles and small arteries exclusively in areas of subendocardial infarction in all of the acidic FGF-treated dogs but in none of the control dogs (p less than 0.05). Noninfarcted myocardium appeared normal in all dogs. In two additional dogs, ameroid constrictors were not placed on the LAD, such that acidic FGF-treated sponges were placed on normally perfused myocardium of the LAD territory. Histological evaluation of those hearts revealed normal myocardium, without evidence of myocardial infarction or smooth muscle cell hyperplasia. Thus, when acidic FGF is delivered to the myocardium via an epicardial sponge in dogs whose coronary flow is compromised, acidic FGF does not cause an angiogenic response in viable myocardium but causes vascular smooth muscle cell hyperplasia in areas subjected to ischemic injury.

Terminology of torsades de pointes

Marked prolongation of the QT interval may be associated with life-threatening ventricular tachycardia. The ventricular tachycardia has a polymorphous appearance and is usually induced by antiarrhythmic drugs. This peculiar type of ventricular tachycardia was termed by Desserstenne torsades de pointes because of its twisting ORS axis. The main reason to give this entity a special name that differentiates it from other types of ventricular tachycardia is the unique therapeutic approach to its treatment. Torsades de pointes can be suppressed by interventions that shorten the QT interval by increasing the heart rate, such as ventricular or atrial pacing, isoproterenol infusion, or atropine. Recently intravenous magnesium was also shown to be extremely effective. If torsades de pointes is treated as a conventional ventricular tachycardia by drugs that may further prolong the QT interval, it may lead to fatal results. To draw the attention of physicians to this unusual form of ventricular tachycardia, we suggest that the term torsades de pointes be kept. This specific diagnosis will hopefully guide the treating physician in selecting the appropriate mode of therapy.

Effects of nisoldipine on myocardial ischemia during exercise and during daily activity

The antiischemic properties of nisoldipine, a dihydropyridine calcium antagonist, were assessed in a multicenter, double-blind, placebo-controlled trial by repeated exercise testing and 72-hour ambulatory electrocardiographic monitoring in 82 patients with coronary artery disease. Patients with positive treadmill stress test results and greater than or equal to 2 ischemic episodes per 24 hours were included in this study. Administration of all chronic antiischemic medications except beta blockers were discontinued. During the first week all patients received placebo twice daily. During the second and third weeks, 41 patients received nisoldipine 10 mg and 41 patients received placebo twice daily. In the placebo group there were no changes in exercise parameters or in ambulatory electrocardiographic parameters. In the nisoldipine group, exercise duration increased from 403 to 448 seconds (p = 0.0035), time to 1 mm of ST depression increased from 224 to 298 seconds (p = 0.002), time to pain increased from 241 to 321 seconds (p = 0.01), and maximal ST depression was reduced from 2.6 to 2.3 mm (p = 0.002). Among the ambulatory electrocardiographic parameters in the nisoldipine group, only the number of episodes was reduced, from 14.4 to 11.6 (p = 0.0013) per patient. There was no significant reduction in total ischemic time (132 vs 120 minutes per patient). No significant side effects were observed. This is the largest clinical trial to date on the effects of nisoldipine on myocardial ischemia. The results indicate that nisoldipine was effective in improving all exercise parameters and only partially effective in suppressing ischemia during daily activity.

Changes in myocardial ischemic threshold during daily activities

This study assesses the variations in myocardial ischemic threshold (heart rate at the onset of ischemia) during daily activities in patients with ischemic episodes on Holter monitoring. Eighty patients with known coronary artery disease, positive treadmill stress test results and greater than or equal to 2 ischemic episodes during a 24-hour period of Holter monitoring were studied. The lowest and the highest ischemic thresholds were determined for each patient. The mean lowest ischemic threshold was 85 beats/min, and the mean highest ischemic threshold was 109 beats/min. The highest ischemic threshold was identical to ischemic threshold values noted during exercise. Of the 895 ischemic episodes, 654 (74%) were preceded by a moderate (greater than 10%) increase in heart rate. The variability of ischemic threshold (difference in percentage between the highest and lowest ischemic thresholds) increased with the number of ischemic episodes (range 2 to 60%). However, in different patients with a similar number of ischemic episodes, different variability was observed. These differences in ischemic thresholds are probably indirect indicators of the vasomotor activity of the coronary arteries in different patients.

Influence of extracellular magnesium on capillary endothelial cell proliferation and migration

We investigated the role of extracellular magnesium on capillary endothelial cell migration and proliferation, components of endothelial cell function that play an important role in angiogenesis and wound healing. Cell migration and proliferation were tested in six different MgSO4 concentrations and in various culture conditions. The Boyden chamber procedure was used to evaluate migration of bovine adrenal cortex capillary endothelial cells. We found that low magnesium concentration inhibited cell migration, but a dose-dependent increase in migration was observed when magnesium level was increased beyond the normal serum concentration (up to 2.4 mM magnesium; p less than 0.0001). Cell proliferation was also inhibited by very low magnesium concentration, an effect observed under all conditions studied. When cell proliferation was stimulated by acidic or basic fibroblast growth factors, it appeared that a ceiling was reached, an increasing magnesium concentration had no additional stimulatory effect. However, a dose-dependent increase in proliferation (p less than 0.005) was observed when magnesium concentration was increased above the normal serum level (0.8 mM) in culture conditions that did not cause marked cell proliferation. Thus, magnesium has an important role in endothelial cell migration and proliferation: very low extracellular magnesium concentrations inhibit and supranormal levels enhance both migration and proliferation. These results suggest that magnesium deficiency might adversely influence the healing and reendothelialization of vascular injuries and the healing of myocardial infarction and might also result in delayed or inadequate angiogenesis, effects potentially leading to infarct expansion and inadequate collateral development.

Ventricular ectopic activity during myocardial ischemic episodes in ambulatory patients

The association between ventricular ectopic activity (VEA) and ischemic episodes during everyday activities was investigated in ambulatory patients with stable angina pectoris. Seventy-five consecutive patients with proven coronary artery disease, ischemic episodes on Holter monitoring and positive treadmill tests, but without known ventricular arrhythmias, were prospectively studied. In these 75 patients, a total of 719 ischemic episodes were recorded during 127 twenty-four-hour monitoring periods. Forty-three patients had either no or only very low baseline VEA (less than 14 ventricular premature complexes [VPCs]/24 hours); none of these patients had increased VEA during any ischemic episode. However, among 32 patients who had greater than or equal to 14 VPCs/24 hours (average 243 VPCs/24 hours), increased VEA during ischemic episodes was observed in 11 (31%). These 11 patients had a total of 174 ischemic episodes and the increased VEA appeared in 47 (27%) of the episodes. During 40 of the ischemic episodes the number of single VPCs increased significantly compared to the baseline background VEA: during 4 episodes trigeminy appeared and during another 3 bigeminy was observed. More complex VEA was not observed. Among the 11 patients with increased VEA, only 4 developed VPCs during treadmill testing. No correlation was found between the severity of the ischemic episodes (degree of ST depression and duration of ischemia) and the increased VEA. In 83% of these episodes the increased VEA appeared during the last (possibly reperfusion) phase. No correlation was found between the appearance of ventricular arrhythmias during ischemic episodes and the presence or absence of chest pain at the same time.(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic significance of ischemic episodes in patients with previous myocardial infarction

This study assessed the prognostic significance of ischemic changes during daily activity as recorded by ambulatory electrocardiographic monitoring in a group of 224 low-risk postinfarction patients. Of the 224 patients studied, 74 (33%) had transient ischemic episodes on Holter monitoring. During the 28 months of follow-up the frequency of cardiac events (cardiac death, reinfarction, hospitalization for unstable angina, balloon angioplasty or coronary bypass surgery) was 51% among those with ischemic episodes on Holter monitoring, compared with 12% in those without such changes (p less than 0.0001). The 74 patients with positive results in their exercise tests and Holter monitoring had a 51% event rate, compared with 20% among the 44 patients with a positive exercise test result but negative Holter results (p less than 0.001). The event rate in those without ischemic changes either on the exercise test or on Holter was only 8.5%. Among patients with good (greater than 40%) or reduced (less than 40%) left ventricular ejection fraction, those with transient ST depression on Holter had a significantly higher cardiac event rate compared with those without it. A similar event rate was found in patients with only silent, only symptomatic and with silent and symptomatic ischemic episodes.