Mechanisms of luminal enlargement and quantification of vessel wall trauma following balloon coronary angioplasty and directional atherectomy

Low incidence of restenosis after successful balloon pulmonary angioplasty in patients with chronic thromboembolic pulmonary hypertension

Balloon pulmonary angioplasty (BPA) is now a treatment option for patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). However, the incidence of restenosis and long-term changes in vessel diameters in pulmonary arteries after BPA are unknown. The present study investigated the incidence of restenosis by measuring changes in vessel diameter after BPA. We reviewed 58 patients (168 lesions) with CTEPH who underwent single dilation for the target lesion (type A/B/C lesions) during BPA procedure followed by selective pulmonary angiography more than 6 months after the final BPA procedure. The outcomes of BPA were assessed in terms of pulmonary artery diameters. In a median follow-up of 1.9 (1.2-2.7) years, restenosis occurred in only one case with a type C lesion after BPA (0.6%). In type A/B lesions, the minimal lumen diameter was significantly enlarged at follow-up after BPA [3.48 (2.59-4.34) to 4.22 (3.31-4.90) mm]. In type C lesions, the minimal lumen diameter was unchanged at follow-up after BPA [3.15 (1.96-3.64) to 3.28 (2.38-4.61) mm]. The present results revealed that restenosis after BPA rarely occurs in type A/B/C lesions. Minimal lumen diameters for type A/B lesions continually increased and those for type C lesions did not decrease. Stent implantation in type A/B/C lesions would be unnecessary after BPA.

Directional coronary atherectomy: a time for reflection. Should we let it go?

A series of interventional tools have emerged since the advent of percutaneous coronary angioplasty. Several are fundamental and used routinely, while others less favourable have fallen short of mainstream therapy and/or have settled as a niche device. We present an overview of the evolution of directional coronary atherectomy (DCA), a unique device that was originally conceived in 1984 to solve the limitations of balloon angioplasty. Unfortunately, we have witnessed its use fall significantly out of favour due to premature and controversial study results. In many interventional laboratories DCA is no longer available. However, we strongly feel that allowing DCA to join the list of extinct interventional tools would be very unfortunate. We, herein, present a series of complex percutaneous coronary procedures to illustrate the convenience of DCA use as a lesion-specific niche device. Finally, DCA offers a valuable distinct clinical research function as it allows for in vivo pathological coronary tissue examination. In conclusion, we plead for its continued production and use as an interventional niche device for the wellbeing of our patients.

The eccentric lumenology

Coronary angiography has a poor predictive value for the detection of eccentric plaque morphology. Many reports have demonstrated discordance between the angiographic classification and the intravascular ultrasound (IVUS) classification. Although eccentricity is usually considered a dichotomous character, more than two-thirds of all coronary stenosis have some degree of eccentricity. The American College of Cardiology/American Heart Association (ACC/AHA) Task force included lesion eccentricity as a risk factor for moderate procedural success (60-85%) and moderate complications (type B). Although lesion eccentricity has been implicated as a risk factor for reduced short-term procedural results, current available data does not support the adverse impact of eccentricity on procedural success or restenosis. The present article reviews the incidence and the various clinical scenarios known to be associated with the eccentric lumenogram and the impact of coronary artery remodeling contributing to misinterpretation of disease eccentricity. Various therapeutic modalities with reference to eccentric lesions are also considered.

Mechanism of lumen enlargement with direct stenting versus predilatation stenting: influence of remodelling and plaque characteristics assessed by volumetric intracoronary ultrasound

OBJECTIVE

To compare the effects of arterial remodelling and plaque characteristics on the mechanisms of direct stenting and predilatation stenting. Direct stenting has become routine in some laboratories and differs technically from predilatation stenting.

METHODS

Pre- and post-interventional volumetric intravascular ultrasound (IVUS) was undertaken in 30 patients with direct stenting and in 30 with predilatation stenting of non-calcified native coronary lesions, using the same stent design and stent length. Lumen, vessel (external elastic membrane (EEM)), and plaque (plaque + media) volumes were calculated. Remodelling was determined by comparing the EEM area at the centre of the lesion with the EEM areas at proximal and distal reference sites. Plaque eccentricity was defined as the thinnest plaque diameter to the thickest plaque diameter ratio. Plaque composition was characterised as soft, mixed, or dense.

RESULTS

All volumetric IVUS changes were similar in the two groups. Pre-intervention remodelling remained uninfluenced after direct stenting, but was neutralised after predilatation stenting. Eccentric lesions responded to intervention by a greater luminal gain owing to greater vessel expansion in direct stenting. Plaque composition influenced luminal gain in direct stenting, the gain being greatest in the softest plaques; in predilatation stenting, luminal gain was equivalent but vessel expansion was greater for "dense" plaque and plaque reduction greater for "soft" plaque.

CONCLUSIONS

In non-calcified lesions, the mechanisms of lumen enlargement after direct or predilatation stenting are significantly influenced by atherosclerotic remodelling, plaque eccentricity, and plaque composition.

Intracoronary ultrasound in acute coronary syndromes: from characterization of vulnerable plaques to guidance of percutaneous treatment of complex stenoses

Our current knowledge on the substrate and genesis of acute coronary syndromes (ACS) results from the integration of pathological, angiographic, and intracoronary imaging techniques. To summarize briefly the current paradigm, eight differentiated stages of development of atherosclerotic lesions are currently accepted, defined not only by the cellular elements involved, but also by the appearance of sudden alterations of plaque structure and coronary thrombosis. The latter constitutes not only the dominant substrate for the most devastating manifestations of coronary artery disease, but also accelerates plaque size at a faster pace than in earlier stages. The composition of atherosclerotic plaque varies significantly along the different evolutive stages, and thus includes cellular (macrophage, smooth muscle cells) and noncellular elements (glicosaminglycan or collagen-rich cellular matrix, extracellular lipid deposits, calcification, fresh, or organized thrombus) in a varying proportion. Furthermore, a dynamic process of vessel remodeling occurs along the atherosclerotic process, resulting, in most cases, in a protective mechanism against myocardial ischemia by preserving luminal dimensions during plaque enlargement. Intravascular ultrasound (IVUS) is one of the intracoronary imaging techniques that has contributed to the understanding of these changes in man. In addition, IVUS has the potential of being a useful clinical tool for predicting the chances of future acute coronary events by identifying vulnerable plaques, of characterizing which is the culprit lesion in ACS, and in guiding revascularization procedures in the treacherous field of thrombotic coronary syndromes. In this article, we review the current evidence on the potential of IVUS imaging for fulfilling these purposes.

Mechanisms of acute lumen gain following cutting balloon angioplasty in calcified and noncalcified lesions: an intravascular ultrasound study

Several studies have shown that mechanisms for lumen enlargement following conventional balloon angioplasty (BA) consist of plaque reduction and vessel expansion. To assess the mechanisms of lumen enlargement after Cutting Balloon (CB) angioplasty, intravascular ultrasound images were analyzed in 180 lesions (89 CB and 91 BA). External elastic membrane (EEM) cross-sectional area (CSA), lumen CSA, and plaque plus media (P+M) CSA were measured before and after angioplasty. In the CB group, lower balloon pressure was utilized (P < 0.0001). DeltaP+M CSA was significantly larger (P = 0.02) and deltalumen CSA showed a trend toward being larger (P = 0.07) compared to BA group. For noncalcified lesions, CB resulted in a larger deltaP+M CSA (P < 0.05) and a smaller deltaEEM CSA (P = 0.10) than BA. For calcified lesions, deltalumen CSA was significantly larger in the CB group (P < 0.05) without significant differences in deltaEEM CSA and deltaP+M CSA. Dissections complicated with calcified lesions were associated with larger deltalumen CSA for the CB group. In conclusion, for noncalcified lesions, CB achieves similar luminal dimensions with larger plaque reduction and less vessel expansion compared to BA. On the other hand, for calcified lesions, the CB achieves larger lumen gain, especially in lesions with evidence of dissections.

Suppression of arterial intimal hyperplasia by cilostamide, a cyclic nucleotide phosphodiesterase 3 inhibitor, in a rat balloon double-injury model

The effects of cilostamide, a cyclic nucleotide phosphodiesterase 3 (PDE3) selective inhibitor, on vascular intimal hyperplasia were evaluated using a single-balloon injury model and a double-injury model in which the rat common carotid artery was subjected to a second injury at a site injured 14 days previously. In the double-injury model, the second balloon injury caused more severe intimal hyperplasia (intima/media (IM) ratio, 1.88+/-0.10) than in the single-injury model (1.09+/-0.08). Histopathological study revealed that vascular smooth muscle cells (VSMC) were the predominant cell-type in the affected neointimal area. Oral administration of cilostamide for 2 weeks after the second injury suppressed intimal hyperplasia in the double-injury model (30 mg kg(-1) bid, 83% inhibition in terms of the IM ratio, P<0.05; 100 mg kg(-1) bid, 69% inhibition, P<0.05). Similar effects were also observed in the single-injury model with oral administration of cilostamide for 2 weeks (100 mg kg(-1) bid, 36% inhibition, P<0.01). Cilostamide inhibited DNA synthesis of cultured VSMC stimulated by foetal calf serum or different kinds of growth factors, but did not affect their migration stimulated by platelet-derived growth factor (PDGF)-BB. Cilostamide significantly increased the cyclic AMP concentration of VSMC dose-dependently. These results indicate that cilostamide suppresses intimal hyperplasia both in the single- and double-injury models of rat, presumably by inhibiting proliferation rather than migration of VSMC. It is suggested that PDE3 inhibitors might find application in preventing intimal hyperplasia following angioplasty such as percutaneous transluminal coronary angioplasty (PTCA) or stent.

Propensity and mechanisms of restenosis in different coronary stent designs: complementary value of the analysis of the luminal gain-loss relationship

OBJECTIVES

This study sought to investigate the influence of stent design on the long-term angiographic outcome.

BACKGROUND

The proportional relationship between vessel injury and late luminal loss in percutaneous revascularization should be best appreciated in coronary stenting, where recoil and shrinkage are theoretically minimal. It is unclear whether all stent designs can counterbalance this reactive loss by achieving a large initial luminal gain (bigger is better).

METHODS

In 523 lesions successfully stented, the long-term angiographic results of slotted-tube (n = 331), coil (n = 85), multicellular (n = 70) and self-expandable mesh (n = 37) stent designs were compared using the angiographic gain-loss relationship (GLR).

RESULTS

Restenosis rate was 10% for multicellular, 20% for slotted-tube, 46% for coil and 49% for self-expandable designs (p = 0.001). At a difference with other designs, no significant GLR was found in coil stents, suggesting additional mechanisms of luminal loss (i.e., plaque protrusion, stent compression) to neointimal proliferation. Significant differences in late loss between stents were found within each quartile of luminal gain, suggesting a specific role of design in luminal loss. Multivariate analysis identified use of coil and self-expandable stents, vessel size, minimal luminal diameter preintervention, luminal gain and stent length as variables with independent predictive value for several indices of angiographic long-term outcome.

CONCLUSIONS

The analysis of GLR: 1) demonstrates that stent design influences late luminal loss; 2) challenges the applicability of the widely accepted "bigger is better" approach to all stent designs; and 3) appears as a valuable tool in assessing long-term stent performance.

Impact of residual plaque burden on clinical outcomes of coronary interventions

In this study, we summarize the role of residual plaque burden, as determined by intravascular ultrasound, on the development of restenosis following percutaneus coronary interventions. Several clinical trials have shown that the amount of residual plaque is a consistent and independent predictor of subsequent restenosis. The impact of residual plaque burden on late lumen loss is particularly augmented by negative vessel remodeling that is commonly seen after balloon angioplasty and atherectomy. However, early evidence suggests that the importance of plaque burden also applies in the context of stenting. The cotreatment of debulking may further improve the long-term outcome of stenting by maximizing an acute lumen gain with less vessel stretching, preventing stent edge problems and possibly reducing the cell source involved in the intimal hyperplastic process. Evaluation of residual plaque burden with on-line intravascular ultrasound could lead to definitive therapies via risk stratification of the treated segments.

Elastic response of human iliac arteries in-vitro to balloon angioplasty using high-resolution CT

Previous angioplasty studies have used angiography and intravascular ultrasound to obtain vascular dimensions. These imaging methods do not always provide reliable measurements due to limitations in image orientation and resolution. In this study, high-resolution (0.1 x 0.1 x 0.5 mm) transverse CT slices were obtained from human common-iliac arteries in vitro to study their elastic response pre- and post-angioplasty. Seven iliacs from five patients were imaged over the physiological pressure range both pre- and post-angioplasty. Contrast was obtained with humidified air surrounding the artery. Angioplasty was done with 10 or 12 mm diameter Medi-Tech balloon catheters with a balloon pressure of 300 kPa held for 30 s. Lumen circumference, c, measured from the images, was plotted against pressure, P, and curve fitting showed c = A(1 - e(-KP)) + B where A, K, and B are fitting parameters. Six lesions appeared soft and were compressed, while one was calcified and partially lifted off the wall. Normalized changes in parameters B and K were much higher post-angioplasty in the calcified lesion, and were over 3 standard deviations from the means of the normalized changes in the six compressed lesions. Balloon/stenosed lumen diameter ratios greater than 1.2 produced a lumen area increase of 38.6 +/- 4.1%(S.D.)(n = 3); ratios less than 1.2 produced an increase of 4.4 +/- 5.1%(S.D.)(n = 4). There was no correlation between area increase and balloon/normal lumen diameter ratio (the value used clinically). Arteries with lesions containing stiffer plaques that tear from the artery wall during angioplasty appear more distensible over the physiological pressure range post-angioplasty.

Coronary artery stenting: indications and cost implications

The practice of coronary stenting is evolving rapidly, with new stent designs, deployment techniques, and adjunctive therapy. In many respects, clinical practice is changing in advance of the availability of supporting data. The consistent excellent angiographic result with stent deployment exceeds that achieved by any other previous interventional device, and the extent to which this accounts for the exponential increase in stent utilization cannot be accurately determined but is undoubtedly considerable. Controlled randomized trials have confirmed that stent deployment is superior to balloon angioplasty in certain lesion subsets or clinical scenarios. These include focal de novo native vessel lesions, lesions with late recoil after balloon angioplasty, acute closure after balloon angioplasty, and proximal left anterior descending coronary artery lesions. In addition, observational data is persuasive in focal coronary saphenous vein graft lesions and aorto-ostial lesions. On the other hand, the evidence supporting the use of stents strictly to improve on a suboptimal result, possibly the most frequent indication, is indirect and circumstantial. Stents are expensive, but it was anticipated that with the reduction in restenosis not only would they be cost-effective but also ultimately would reduce costs. This hope has not as yet been realized. However, there is little question that the introduction of intracoronary stents has been the most significant and exciting development since the introduction of percutaneous revascularization almost 20 years ago. It has revitalized the field.

Clinical and angiographic comparison of matched patients with successful directional coronary atherectomy or stent implantation for primary coronary artery lesions

OBJECTIVES

This study was designed to compare the long-term clinical and angiographic effects of successful directional atherectomy and stent implantation and to examine whether restenosis is related to the mechanism of lumen improvement as well as the extent of lumen gain.

BACKGROUND

Directional atherectomy and coronary stent implantation have been shown to achieve a more optimal immediate result that may lead to a more favorable long-term angiographic outcome and fewer target vessel revascularizations than does angioplasty. However, it remains to be determined whether one of the devices used in these interventions provides consistently better results than the other.

METHODS

To allow meaningful comparisons a prospectively collected series of 117 patients successfully treated with atherectomy were individually matched with a prospectively collected series of 117 patients successfully treated with stent implantation. Matching for baseline characteristics identified patients with identical lesion location and lesion severity, and immediate and late angiographic and clinical outcome were compared. To evaluate the possibility of a procedure effect on restenosis, patients were further matched for both immediate angiographic outcome and baseline characteristics, providing 150 matched patients for comparison. As confirmatory analysis, multivariate models were constructed to predict late lumen diameter.

RESULTS

Matching resulted in two comparable groups with equivalent baseline clinical and stenosis characteristics (n = 117 pairs). Atherectomy led to a smaller immediate gain than stenting and, because late loss was similar in both groups, stenting resulted in a larger late lumen (1.96 +/- 0.51 vs. 1.66 +/- 0.55 mm, p < 0.0001). When patients were matched for immediate gain and baseline characteristics (n = 75 pairs), lumen loss was more pronounced after atherectomy, and thus the minimal lumen diameter at follow-up differed significantly between the two groups (1.66 +/- 0.53 vs. 1.90 +/- 0.47 mm, p = 0.004). This beneficial angiographic effect of stenting was accompanied by a reduced need for repeat interventions. Multivariate analysis confirmed the independent effect of the interventional device used, whereby less loss and greater lumen diameter at follow-up were predicted for stent implantation than for atherectomy.

CONCLUSIONS

Successful stent implantation provided a more favorable long-term angiographic outcome and lower rates of restenosis and need for target lesion revascularization than did atherectomy. This favorable effect of stenting not only is related to a larger, immediate gain, but also seems to attenuate late lumen loss.