COVID-19 vaccine-induced myocarditis vs. immune checkpoint inhibitor-induced myocarditis – same but different?

Background

While immune checkpoint inhibitors (ICI) -induced myocarditis and coronavirus disease 2019 (COVID-19) vaccine-induced myocarditis are considered to be rare; they are both significant side effects, suggested being caused by activation of the immune system against the myocardium. We aimed to assess whether both phenomena share similar presenting characteristics.

Methods

We included patients diagnosed with either ICI or COVID-19 vaccine-induced myocarditis at our medical center. We performed a retrospective assessment of clinical presentation, blood tests, and advanced echocardiography, including speckle strain.

Results

We included 18 patients diagnosed with ICI (ICI group) or COVID-19 vaccine (COVID-19 group)-induced myocarditis, and 20 patients with viral myocarditis (Viral group) as a control group. The median age was significantly older in the ICI group (74 years) compared to the COVID-19 and Viral groups (20 and 24 years), p<0.001. The clinical presentation in the COVID-19 group was more similar to the Viral group, presenting mainly with chest pain and fever, while the ICI group presented mainly with dyspnea. ST-elevation was frequent in the COVID-19 and Viral groups and absent in the ICI group, p=0.004. Median peak high sensitivity troponin I values were markedly lower in the ICI group compared to the COVID-19 and Viral groups (619 ng/L vs. 15527 ng/L vs. 7388 ng/L, p=0.004). While the median left ventricular ejection fraction was 60% among all groups, patients in the ICI group presented with mean lower LV global longitudinal strain (−13%) and left atrial conduit strain (17%), compared to the COVID-19 (−17% and 30%) and Viral groups (−18% and 37%), p=0.016 and p=0.001.

Conclusions

While the suspected mechanism is an activation of the immune system in both ICI and the COVID-19 vaccine-induced myocarditis, we found that the clinical presentation, cardiac biomarkers, and advanced echocardiography of the COVID-19 vaccine, are more similar to viral myocarditis than to ICI-induced myocarditis.

Funding Acknowledgement

Type of funding sources: None.

Early detection of inflammation-prone STEMI patients using the CRP Troponin Test (CTT)

Background

Elevated concentrations of C-reactive protein (CRP) early after acute coronary syndrome (ACS) may reflect the magnitude of the inflammatory response to myocardial damage and are associated with worse outcome. However, the routine measurement of both CRP and cardiac troponin simultaneously in the setting of ST segment myocardial infarction (STEMI) is not used broadly. Here, we sought to identify and characterize individuals who are prone to an elevated inflammatory response following STEMI using the CRP Troponin test (CTT) and determine their short- and long-term outcome.

Material and methods

We retrospectively examined 1,186 patients with the diagnosis of acute STEMI, who had at least two successive measurements of combined CRP and cardiac troponin (up to 6 hours apart), all within the first 48 hours of admission. We used Chi-Square Automatic Interaction Detector (CHAID) tree analysis to determine which parameters, timing (baseline vs. serial measurements), and cut-offs should be used to predict mortality.

Results

Patients with high CRP concentrations (above 90th percentile, >33mg/L) had higher 30 day- and all-cause mortality rates regardless of their troponin test status (above or below 118,000 ng/L); 14.4% vs 2.7%, p<0.01. Furthermore, patients with both high CRP and high Troponin levels on their second measurement had the highest 30-day mortality rates compared to the rest of the cohort; 21.4% vs. 3.7%, p<0.01. These patients also had the highest all-cause mortality rates after a median follow up of 4.5 years compared to the rest of the cohort; 42.9% vs 12.7%, p<0.01 (Figure 1).

Conclusions

In conclusion, serial measurements of both CRP and cardiac troponin might detect patients at increased risk for short-and long-term mortality following STEMI. We suggest the future use of the combined CRP Troponin-test (CTT) as a potential early marker for inflammatory-prone patients with worse outcomes following ACS. This sub-type of patients might benefit from early anti-inflammatory therapy such as colchicine and anti-IL-1β agents.

Funding Acknowledgement

Type of funding sources: None.

Valvular changes following anthracycline therapy: is it time to look beyond ejection fraction?

Background

Advancements in early detection and treatment of breast cancer have improved survival, but with the costs of side effects, with cardiotoxicity being the most significant one. Anthracycline (ANT) is the most recognized therapy leading to cardiotoxicity, mainly manifested as left ventricle (LV) dysfunction. While the changes in LV ejection fraction (LVEF) are well studied, little is known about the effect of ANT on valvular function. We aimed to evaluate the change in valvular function following ANT therapy in patients diagnosed with breast cancer.

Methods

The study population is part of the Israel Cardio-Oncology Registry (ICOR). All patients performed serial echocardiography; before (T1), during (T2), at the end (T3), and following (T4) ANT therapy, assessing valvular changes. Exclusion criteria included age below 18 and baseline LVEF <55%.

Results

The study included 141 female patients diagnosed with breast cancer and treated with ANT with a mean age of 51±12 years (Table 1). During a median follow-up of 255 [IQR 214–313] days, from T1 to T4, we observed a significant increase in the portion of patients developing new mitral regurgitation (MR) (3.5% to 18.7%, p<0.0001), with a trend for developing moderate and above MR (0.7% to 3.3%, p=0.13). While a statistically significant reduction in mean LVEF (60.2%±1.5 to 59.2%±2.7, p=0.0004) and median LV global longitudinal strain (LV GLS) (−21.6% [−20.0 to −23.0] to −20.0% [−19.1 to −21.1], p<0.0001) was observed (Figure 1), the values remain within the normal range with no significant clinical change. In a multivariate binary logistic regression model, age (OR 1.06, 95% CI: 1.01–1.11) and trastuzumab therapy (OR 5.59, 95% CI: 1.95–16.6) were strong independent predictors for MR development, while medical history was not.

Conclusions

MR development following ANT exposure is frequent, increasingly after the completion of ANT therapy. The parallel reduction in LV function might imply a functional mechanism. Larger trials are needed to evaluate the MR prognostic clinical role in cancer patients.

Funding Acknowledgement

Type of funding sources: None.

Microvascular dysfunction in patients with angina and non-obstructive coronary artery disease – preliminary data from a single center registry

Introduction

About 50% of patients referred for coronary angiography because of angina and/or myocardial ischemia are found to have non-obstructive coronary artery disease (CAD). The role of microvascular dysfunction as the cause of angina or ischemia is becoming increasingly recognized.

Purpose

Our aim was to describe coronary physiology and microvascular function in patients with angina and ischemia and non-obstructive CAD (ANOCA/INOCA).

Methods

Patients with angina, referred for coronary angiography and found to have non-obstructive CAD enter a prospective registry and undergo invasive coronary physiology evaluation. Fractional flow reserve (FFR), coronary flow reserve (CFR), index of myocardial resistance (IMR) and resistive reserve ratio (RRR) are recorded. Patients with obstructive CAD (≥50% diameter stenosis and/or FFR≤0.8), acute coronary syndrome and/or hemodynamic instability are excluded. Microvascular dysfunction is considered significant if either CFR<2.5, IMR≥25 and/or RRR≤3.5.

Results

58 patients with ANOCA or INOCA were studied. Mean age was 64.8±10.4 and 65.5% were females. Hyperlipidemia, hypertension, and obesity were the most frequent cardiovascular risk factors (65.5%, 55.1% and 39%, respectively), and approximately 25% had known ischemic heart disease with a previous percutaneous coronary intervention. Microvascular dysfunction was found in 29 (52.7%) of the patients. 10 (18.2%) had CFR<2.5, 20 (34.5%), had IMR≥25, and 27 (50%) had RRR≤3.5. Among patients with IMR≥25, mean CFR and RRR were 2.1±0.5 and 2.4±6.8, respectively.

Conclusion

Microvascular dysfunction is present in approximately half of the patients with angina and/or ischemia referred for coronary angiography and found to have non-obstructive CAD.

Funding Acknowledgement

Type of funding sources: None.

Invasive- versus computed tomography-angiography for the evaluation of coronary artery disease among elderly patients undergoing transcatheter aortic valve implantation

Background

Coronary artery disease (CAD) is common among elderly patients with severe aortic stenosis undergoing transcatheter aortic valve implantation (TAVI). Current guidelines recommend that percutaneous coronary intervention (PCI) of >70% proximal coronary lesions prior to TAVI. The aim of the current study was to evaluate two approaches to CAD diagnosis pre-TAVI.

Methods

We investigated 2,027 patients undergoing TAVI for severe aortic stenosis at two large centers with different pre-procedural CAD assessment: pre-TAVI computed tomography angiography (CTA) with selective invasive angiography according to CTA results (N=831) or mandatory invasive angiography (IA) (N=1,196). Peri-procedural complications were documented according to the VARC-2 criteria. Mortality rates were prospectively documented.

Results

Mean age of the study population was 86±4, of whom 55% were female. Patients in the IA group had significantly higher rates of pre-TAVI PCI compared to the CTA group (32% vs. 17%, p<0.001). Following TAVI, peri-procedural myocardial infarction (MI) rates were significantly lower among the IA group (0.1% vs. 1.5%, p=0.001). However, multivariate binary logistic regression analysis adjusted for age, gender and cardiovascular risk factors failed to show association between centers strategy and peri-procedural MI. Periprocedural bleeding rates were similar between the groups (3.5% vs. 2.9%, p=0.477). Thirty day, and 1-year mortality crude rates were similar between the groups (2.5% vs. 3.4%, p=0.25, and 10.2% vs. 12.0%, p=0.19). Multivariate cox regression adjusted for age, gender and cardiovascular risk factors did not find association between CAD clearance strategy and outcome.

Conclusions

In elderly patients, CTA driven approach for CAD evaluation pre-TAVI is a valid strategy with similar outcome as compared to invasive approach. CTA strategy significantly reduces invasive procedures rates without compromising patient's outcome.

Funding Acknowledgement

Type of funding source: None

P1423 Significantly higher 1-year mortality rate in patients undergoing TAVR with higher right ventricular volumes, as calculated by pre-procedural CT angiography

Background

Cardiac gated computed tomography angiography (CCTA) is the mandatory pre-interventional imaging planning procedure in patients eligible for trans-catheter valve implantation (TAVR). Automated analysis of the cardiac chambers" volumes including the right ventricle (RV), can be obtained from the CCTA and thus contribute to patient selection.

Objectives

To assess the prognostic implications of increased RV volume using a fast automated volumetric analysis software on preprocedural CCTA data among patients undergoing TAVR.

Methods

CCTA of patients who underwent TAVR at two medical centers – Stanford University Medical Center (California, USA) and Tel Aviv Medical Center (Israel) – between 2013 and 2016 were analyzed by an automatic four chamber volumetric analysis (4CVA) software, and grouped according to their RV volume index, into those with the largest RV (upper 5th percentile of RV volume index (>120 ml/m2; n = 16) versus those within the 95th percentile lower volumes index (≤120 ml/m2; n = 307). Differences in baseline characteristics between the groups were adjusted for with a propensity score. The risk for one year mortality following the TAVR was compared between the two groups.

Results

In total 323 patients were included. There were no major differences in background and demographic characteristics between the study groups. A significantly higher 1-year mortality rate was found for patients with large RV (31.3% vs. 7.5%, p = 0.008). After adjustment for clinical characteristics, patients with RV volume index >120 ml/m2 were at almost a 5 times higher risk for 1-year mortality compared to patients with smaller RV (HR 4.9, 95% CI 1.8-13.1, p = 0.002). The addition of echocardiographic parameters to the propensity score did not eliminate the significance of RV volume index >120 ml/m2 as an independent predictor for mortality at 1-year. An analysis of RV as a continuous variable demonstrated that the risk for 1-year mortality increased by 2% for every 1 ml/m2 RV volume enlargement (p = 0.013).

Conclusions

Cardiac volumetric data by CCTA performed for procedural planning may help predict outcome in patients undergoing TAVR.

Abstract P1423 Figure. Cox survival curves according to RVi

P3378Differences in valve morphology and aortopathy between patients with bicuspid and tricuspid aortic valves: a Computed Tomography Study

Background

Transcatheter aortic valve implantation (TAVI) has been shown safe and feasible in patients with bicuspid aortic valve (BAV) morphology. Evaluation of differences in valve morphology and aortic root dimensions in patients with BAV in comparison to patients with tricuspid aortic valve (TAV) is important for the spread of TAVI in patients with BAV.

Purpose

The present study evaluated the prevalence of BAV subtypes and the differences in valve morphology and aortic root dimensions between BAV and TAV in patients undergoing computed tomography (CT) before TAVI.

Methods

In five medical centers in Israel, 104 patients (69±13.5 years) with BAV and 105 patients (81±8.22 years) with TAV underwent CT angiography. BAV morphology was defined according to the number of commissures and raphe following Siever's classification. Functional BAV was defined as 3 cusps with focal fusion of 1, 2, or 3 commissures. Aortic root dimensions were measured at the level of the aortic annulus, sinus of Valsalva (SOV), sino-tubular junction (STJ), and ascending aorta (AA). Membranous septum (MS) length was measured in coronal view. The volume and agatston score of aortic valve calcification were evaluated.

Results

Type 0 account for 22% (23/104), type IA for 58% (60/104), Type IC for 9% (9/104), functional BAV for 11% (12/104). Type IB and II were not found in the studied population. As compared with TAV, patients with BAV have significantly larger aortic annulus area, SOV area, STJ area and AA Area; however, the ellipticity index of aortic annulus, SOV, STJ, and AA were similar. MS length was significantly smaller in patients with BAV compared to patients with TAV (6.4±2.3 mm vs. 8.1±2.7mm; retrospectively; P<0.001) and the volume of aortic valve calcifications was significantly higher in BAV compared to TAV patients: 2.3±1.6 ml3 vs. 1.4±1.2 ml3 retrospectively; P=0.003).

Conclusions

In Israel, patients with BAV showed more frequently type 1A BAV. BAV patients have larger aortic root dimensions than patients with TAV without difference in regard to the ellipticity index. MS length was smaller and the amount of aortic leaflet calcifications was higher in patients with BAV. These findings may have important impact on procedural outcome.

Sexual activity and erectile dysfunction in elderly men with angiographically documented coronary artery disease

We studied the prevalence of erectile dysfunction (ED) in elderly men, aged 65 years or above, with coronary artery disease (CAD) documented by coronary angiography. A total of 123 men (112 men with CAD and 11 men without CAD), mean age 74.6+/-5.9 years, was included. To detect ED and assess its severity, all participants were asked to complete the Sexual Health Inventory for Males (SHIM) questionnaire. Lack of sexual activity was more prevalent among men with CAD relative to men without CAD (31.3 vs 0.0%). Among the sexually active men, ED was more prevalent among men with CAD relative to men without CAD (85.7 vs 72.7%). A general linear model showed that age was the only factor associated with SHIM scores among the sexually active men with CAD (P=0.001). Other factors, such as the number of occluded coronary arteries, diabetes mellitus, hypertension, smoking, various medications and marital status, were not associated with SHIM scores in elderly men with CAD. We conclude that lack of sexual activity and ED are very common in elderly men with CAD. Among the sexually active men with CAD, ED severity is associated only with age.

LDL-C goal attainment with the addition of ezetimibe to ongoing simvastatin treatment in coronary heart disease patients with hypercholesterolemia

OBJECTIVE

To evaluate the addition of ezetimibe or placebo to on-going simvastatin treatment on attaining the LDL-C treatment target of </= 2.60 mmol/L (100 mg/dL) in coronary heart disease (CHD) patients with hypercholesterolemia.

METHODS

Patients with documented CHD were recruited if they were on a stable dose of simvastatin 10 mg or 20 mg for at least 6 weeks, had LDL-C > 2.60 mmol/L and </= 4.20 mmol/L (> 100 mg/dL and </= 160 mg/dL), triglycerides </= 4.00 mmol/L (355 mg/dL) and hepatic transaminases and creatine kinase </= 50% above the upper limit of normal. After a 4-week placebo and diet run-in period, eligible patients were randomized to a double-blind, placebo-controlled comparative study with ezetimibe 10mg co-administered with on-going simvastatin 10mg or 20 mg (n = 208) versus placebo to match ezetimibe co-administered with simvastatin 10mg or 20mg for 6 weeks (n = 210).

RESULTS

When ezetimibe was added to on-going simvastatin therapy, a significantly greater percentage of patients attained the LDL-C target of </= 2.60 mmol/L after 6 weeks of treatment compared to placebo added to on-going simvastatin (80.4% vs. 17.4%, respectively;p </= 0.001). When co-administered with on-going simvastatin therapy, mean percentage reduction in LDL-C from baseline was significantly larger in the ezetimibe group compared to placebo (27.1% vs. 4.1%, respectively; p </= 0.001). The co-administration of ezetimibe or placebo to on-going simvastatin treatment was generally well tolerated.

CONCLUSIONS

Ezetimibe co-administered with on-going simvastatin 10 mg or 20 mg treatment enabled more CHD patients with hypercholesterolemia to attain the LDL-C treatment target of </= 2.60 mmol/L.

Initial and long-term results with the CrossFlex stent--data from a national registry

The Cordis CrossFlex trade mark stent is a balloon expandable helical coil made of stainless steel. OBJECTIVE: To assess the short- and long-term safety and efficacy of this stent by conducting a multi-center national registry. METHODS: One hundred and sixteen stents were implanted in 109 patients (mean age 59 3 10 years, 95 males). The lesions were classified as type B2 or C in 56 patients (51%). Successful deployment was achieved in 103 patients (94.5%). Failure was due to damage to the stent (two patients) or inability to reach the lesion (four patients). High-pressure deployment (>14 atm) was used in 68% of cases. RESULTS: Edge dissections occurred in nine patients after high-pressure deployment and necessitated implantation of a second stent. One patient with a large acute myocardial infarction died during hospitalization. Side branch occlusion occurred in five patients (4.6%). Subacute thrombosis occurred in two patients (1.8%) during the first four weeks. During a six-month follow-up period, 18 patients (16.5%) were rehospitalized with recurrent angina. Fifteen patients had coronary angiography and 13 (12.1%) needed additional target lesion revascularization (TLR). Twelve patients required a second PTCA for in-stent restenosis, and one needed a coronary artery bypass graft operation. CONCLUSIONS: The CrossFlex coronary stent can successfully be used in complex coronary lesions, with few short-term complications and a low TLR rate. Operators should be aware of the possibility of edge dissection during high-pressure implantation.

Formulation and delivery mode affect disposition and activity of tyrphostin-loaded nanoparticles in the rat carotid model

Poor drug residence in the arterial wall hinders clinical implementation of local drug delivery strategies for the treatment of restenosis. A rat carotid model of vascular injury and intraluminal delivery of tyrphostin-containing polylactic acid (PLA) nanoparticles (NPs) were used to determine the relationship between residence properties and biological activity of different formulations and administration modes. The effects of delivery modes (denudation and delivery time) and formulation variables (adsorbed vs encapsulated drug, and NP size) on arterial drug/NP retention were examined. Antirestenotic effects of large (160 nm) and small (90 nm) tyrphostin-containing NPs, surface-absorbed tyrphostin, and systemic treatment were compared. Fluorescent NPs were used to study the spatial distribution of the carrier in the arterial wall. The decrease in arterial tyrphostin level over time fitted a biexponential model. Delivery time and pressure, endothelium integrity, particle size, and drug-polymer association affected local pharmacokinetics and the antirestenotic results after 14 days. The PLA-based tyrphostin NP formulation ensured a prolonged drug residence at the angioplasty site after single intraluminal application. Several readily adjustable formulation and procedural factors considerably modified arterial ingress of the drug-loaded NPs and governed their subsequent redistribution, tissue binding, elimination, and ensuing antirestenotic effect.

Nanoparticulate delivery system of a tyrphostin for the treatment of restenosis

Restenosis, the principal complication of percutaneous transluminal coronary angioplasty is responsible for the 35-40% long-term failure rate following coronary revascularization. The neointimal formation, a morphological substrate of restenosis, is dependent on smooth muscle cells (SMC) proliferation and migration. Signal transduction through the platelet-derived growth factor (PDGF)/PDGF receptors system is involved in the process of post-angioplasty restenosis. The unsuccessful attempts to control restenosis by systemic pharmacological interventions have prompted many researchers to look for more promising therapeutic approaches such as local drug delivery. Tyrphostins are low molecular weight inhibitors of protein tyrosine kinases. We assessed the release kinetics and in vivo effects of nanoparticles containing PDGF-Receptor beta (PDGFRbeta) tyrphostin inhibitor, AG-1295. AG-1295-loaded poly(DL-lactide) (PLA) nanoparticles were prepared by spontaneous emulsification/solvent displacement technique. In vitro release rate and the impact of drug/polymer ratio on the nanoparticle size were determined. The degree of tyrosine phosphorylation was assessed by Western blot with phosphotyrosine-specific antibody in rat SMC extracts. Several bands characteristic of PDGF BB-stimulated SMC disappeared or weakened following tyrphostin treatment. Local intraluminal delivery of AG-1295-loaded PLA nanoparticles to the injured rat carotid artery had no effect on proliferative activity in medial and neointimal compartments of angioplastisized arteries, indicating a primary antimigration effect of AG-1295 on medial SMC.

Local delivery of platelet-derived growth factor receptor-specific tyrphostin inhibits neointimal formation in rats

Signal transduction through the platelet-derived growth factor (PDGF)/PDGF receptor (PDGFR) system is involved in the process of postangioplasty restenosis. Tyrphostins are low molecular weight inhibitors of protein tyrosine kinases. We assessed the antiproliferative effects of PDGFRbeta-specific tyrphostin AG-1295 in vitro and in vivo. AG-1295 significantly inhibited rat smooth muscle cell growth stimulated by PDGF-BB or FCS. This antiproliferative effect was paralleled by reversible reduction of the total phosphotyrosine level and the degree of PDGFRbeta phosphorylation by the drug in vitro. Local sustained delivery of the drug from perivascularly implanted polymeric matrices resulted in focal AG-1295 levels of 711 and 29.1 ng/mg of dry arterial tissue 1 and 14 days after implantation in rats. AG-1295 delivered from polymeric matrices resulted in a 35% reduction of neointimal formation on day 14 after balloon injury in the rat carotid model. Tyrosine phosphorylation of certain transduction proteins in arterial tissue extracts was significantly upregulated by balloon injury on day 3 but was essentially returned to or below basal levels 14 days after injury. Tyrphostin treatment decreased tyrosine phosphorylation at both time points below the basal levels. Moreover, the enhancement of PDGFRbeta expression 3 and 14 days after arterial injury was strongly inhibited by AG-1295 treatment. It can be concluded that AG-1295 reduces neointimal formation by inhibiting PDGFbeta-triggered tyrosine phosphorylation.

Protection of thrombin receptor expression under hypoxia

Thrombin receptor (ThR) plays a significant role in myocyte contractility and hypertrophy. Heart myocyte ischemic damage, caused by insufficient blood supply, is the leading cause of heart infarction. Here we demonstrate that when primary myocyte cultures are subjected to hypoxic stress, ThR mRNA levels are reduced markedly. This takes place also in vivo in a model of ischemic pig heart, exhibiting reduced levels of ThR compared with normal heart sections. Prior activation of ThR however, by either thrombin receptor-activating peptide (TRAP) or by alpha-thrombin resulted in full protection of ThR mRNA levels under hypoxia. The effect appeared specific to ThR because the addition of TRAP did not affect the hypoxic damage as shown by the levels of lactic dehydrogenase release and up-regulated GLUT-1, a glucose transporter gene. This protection effect took place not only in primary myocytes but also in NIH3T3 fibroblasts. ThR protection occurs via specific cell signaling events because activation of the receptor by TRAP, following interruption of the signaling cascade by calphostin C, a protein kinase C inhibitor, resulted in loss of ThR mRNA protection. Because Ras and Src are part of the ThR signaling cascade, the introduction of either dominant ras or src oncogenes to NIH3T3 murine fibroblasts gave rise to similar protection of ThR mRNA levels under hypoxic conditions without the exogenous addition of TRAP. Likewise, ThR mRNA protection was obtained after transfection with proto-oncogene vav. The 95-kDa protein Vav undergoes tyrosine phosphorylation after ThR activation, serving thus as part of the receptor machinery cascade. We therefore conclude that the initiation of the signaling cascades either exogenously by TRAP or within the cell via src or ras, as well as via vav oncogene interconnecting G-binding protein to the tyrosine kinase pathway, ultimately results in ThR protection under hypoxia. We present hereby, a novel concept of activated receptors, which under minimal oxygen tension protect their otherwise decaying mRNA. Maintaining the level of ThR that plays an active role in normal myocyte function may provide a significant repair mechanism in ischemic tissue, assisting in the regaining of normal myocyte functions.

[Use of abciximab (Reopro) in the catheterization laboratory and in unstable coronary syndromes]

Blockage of platelet glycoprotein IIb/IIIa receptor by Reopro (c7E3 Fab-abciximab) has been shown to reduce markedly ischemic complications during and following elective and high-risk coronary intervention (CI). Between July '96 and February '98, 120 consecutive patients (85 men and 34 women, aged 34-90--mean 62) received Reopro (20 mg bolus, followed by 10 micrograms/min for 12-48 hours). 100 were treated with Reopro in the catheterization laboratory, in 76 as prophylactic treatment preceding high-risk CI and in 24 as bailout treatment for acute complications during CI. 20 additional patients were treated in the CCU for acute coronary syndromes, 17 of whom underwent CI 6-48 hours later. Coronary angiography demonstrated multivessel disease in 66 (56%), and the target lesions were LAD--77, RCA--41, LCX--22, SVG--6, and 2 unprotected LMCA (total: 148 lesions dilated in 117 patients). Of the 117 CI, 44 were PTCA alone, and 73 included stenting. Indications for prophylactic Reopro for high risk CI were: acute MI (< or = 48 hours), early post-MI angina, unstable AP, and/or complex anatomy with visible thrombus. In this high-risk population the overall success rate (open artery, no MI, discharged alive, no need for urgent re-vascularization) was 97% when Reopro was given prophylactically prior to CI. The success rate was lower (87.5%) when Reopro was given in bailout situations. In 20 patients with acute coronary syndromes treated in the CCU while receiving maximal combined conventional therapy (including full-dose heparin), all symptoms and dynamic ischemic ECG changes disappeared within minutes following Reopro. 17 underwent successful CI during hospitalization and 3 were treated medically. Reopro given prior to high risk CI was associated with a very low rate of complications. In a few cases with acute coronary syndromes, Reopro given in the CCU cases immediate relief of myocardial ischemia and reduced the need for urgent coronary intervention.

Hirudin reduces tissue factor expression in neointima after balloon injury in rabbit femoral and porcine coronary arteries

BACKGROUND

Tissue factor (TF) is a transmembrane glycoprotein that, after binding to factor VII/VIIa, initiates the extrinsic coagulation pathway, resulting in thrombin generation and its sequelae. Thrombin has been shown to induce TF mRNA in endothelium, monocytes, and smooth muscle cells, further perpetuating the thrombogenic cycle. This study was designed to determine the effect of specific inhibition of thrombin by recombinant hirudin (r-hirudin) on TF distribution after balloon angioplasty in the cholesterol-fed rabbit femoral artery and porcine coronary artery models.

METHODS AND RESULTS

Thirty-five femoral arteries from 32 cholesterol-fed New Zealand White rabbits and 84 coronary arteries from 55 Yorkshire-Albino swine were studied by use of a recently developed in situ method of TF localization based on digoxigenin labeling of recombinant factor VIIa (Dig-VIIa), with correlative studies of TF immunoreactivity by use of anti-rabbit (AP-1) or anti-human (sTF) antibodies. At sites of balloon angioplasty in rabbit femoral or pig coronary arteries (double or single injury), TF-antibody and Dig-VIIa staining were noted in association with endothelial cells, smooth muscle cells, and foam cells and within the fibrous tissue matrix primarily of the adventitia and neointima. Staining was significantly greater after balloon angioplasty than in vessels that had not undergone angioplasty but was similar after single and double balloon injury. Animals treated with r-hirudin (rabbits, 1 mg/kg bolus plus 2-hour infusion; pigs, 1 mg/kg bolus plus 0.7 mg x kg(-1) x d(-1) infusion for 14 days with implantable pump) had diminished TF-antibody and Dig-VIIa staining 28 days after balloon angioplasty compared with controls (bolus heparin only). This effect was more prominent on the neointima and was more striking in the porcine than the rabbit model.

CONCLUSIONS

TF expression, persistent 1 month after balloon angioplasty in rabbit femoral arteries and porcine coronary arteries, is attenuated by specific thrombin inhibition with hirudin. These results suggest that thrombin inhibition, in addition to its effect on acute thrombus formation and its effect on luminal narrowing by plaque in experimental animals, may result in a prolonged reduction in thrombogenicity of the restenotic plaque through this effect on TF expression.

PDGF-receptor tyrosine kinase blocker AG1295 selectively attenuates smooth muscle cell growth in vitro and reduces neointimal formation after balloon angioplasty in swine

BACKGROUND

Signaling through protein tyrosine kinases (PTKs) is a major contributor to the transmission of mitogenic stimuli to the interior of the cell and nucleus. The present study was designed to determine the effect of the tyrphostin AG1295, a selective blocker of PDGF-receptor PTK, on the growth of porcine and human smooth muscle cells (SMCs) in culture, on the outgrowth kinetics of SMCs from porcine and human arterial explants, and on neointimal formation after balloon injury in pigs.

METHODS AND RESULTS

SMCs for culture were obtained from porcine abdominal aortas, human internal mammary arteries, and endarterectomy tissue from a single human carotid artery. Addition of AG1295 to SMCs before PDGF stimulation completely inhibited PDGF-beta-receptor tyrosine phosphorylation without affecting the level of PDGF-beta-receptor. AG1295 resulted in a selective, reversible inhibition of SMC proliferation in culture (76%) with only mild (13.5%) inhibition of endothelial cell proliferation. The number of SMCs accumulating around explants of porcine carotid arteries and human endarterectomy specimens 12, 15, 19, 22, and 24 days after plating was reduced by 82% to 92% in AG1295-treated compared with nontreated specimens, and initiation of SMC outgrowth was markedly delayed. The numbers of cells accumulated 10 days after initiation of outgrowth were significantly lower in treated versus control explants. Local intravascular delivery of AG1295-impregnated polylactic acid-based nanoparticles (130+/-25 nm) to the site of balloon injury to porcine femoral arteries resulted in significant reductions in intima/media area ratio and luminal cross-sectional area narrowing by neointima compared with contralateral control arteries to which empty nanoparticles were applied (0.15+/-0.07 versus 0.09+/-0.03, P=.046 and 20+/-4% versus 10+/-4%, P=.0009, n=6 for both).

CONCLUSIONS

The tyrphostin AG1295, a selective blocker of PDGF-receptor kinase, exerts a marked inhibitory effect on the activation, migration, and proliferation of porcine and human SMCs in vitro and an approximately 50% inhibitory effect on neointimal formation after balloon injury in porcine femoral arteries when delivered via biodegradable nanoparticles. Further studies appear to be warranted to evaluate the applicability of this novel approach to the interventional setting.

Predictors of luminal narrowing by neointima after angioplasty in atherosclerotic rabbits

OBJECTIVE

The present study was designed to identify the predictors of cross-sectional area narrowing by neointima (%CSAN-N) after balloon angioplasty (BA) in the cholesterol fed rabbit model.

METHODS

Angiographic, histomorphometric, and immunohistochemical data were analyzed from 91 femoral arteries of New Zealand white rabbits. Focal atherosclerosis was induced by air desiccation of the endothelium followed by a 2% cholesterol diet for 28 days. The rabbits received heparin (150 U/kg) at the time of BA (2.5 mm; three, 60-second, 10-atm inflations). Arteries were perfusion-fixed and excised 7 (n = 16), 14 (n = 11), 21 (n = 9), or 28 (n = 20) days after BA. Non-angioplastied arteries were de-endothelialized (cholesterol-fed [n = 12] or normal diet [n = 8]), non-injured but cholesterol-fed (n = 7), or normal (n = 8).

RESULTS

Univariate regression across all groups showed that the absolute area of the lumen by histomorphometry (LA) correlated significantly with the area bounded by the external elastic lamina (EEL) (vessel size), but no correlation was found with the absolute area of neointima or media, the percentage disruption of the internal elastic lamina (IEL), or the percentage of neointima and media occupied by foam cells. However, %CSAN-N correlated significantly with the area bounded by the EEL, significantly with the absolute neointimal area, and negatively with the absolute LA (p < 0.0001). Significant correlations were also found between %CSAN-N and the % IEL disrupted, the area of neointima and media occupied by RAM-11 + foam cells, and the loss of alpha-actin positivity in the media (p < 0.0001).

CONCLUSIONS

These studies show that neointimal formation contributes significantly to luminal narrowing 1 month after angioplasty in this model, that the degree of vascular injury and the extent of foam cell accumulation in the neointima and media are significant independent predictors of neointimal formation, and that the area of the neointima, and the percent narrowing by neointima, are important predictors of remodeling itself (EEL area). These predictors were not identifiable when the analysis was focused on the determinants of absolute luminal area alone.

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.