Neovascularization after transmyocardial laser revascularization in a model of chronic ischemia

Effects of needle puncturing on re-vascularization and follicle survival in xenotransplanted human ovarian tissue

BACKGROUND

Ovarian tissue transplantation can restore fertility in young cancer survivors, however the detrimental loss of follicles following transplantation of cryopreserved ovarian tissue is hampering the efficiency of the procedure. This study investigates whether needle puncturing prior to transplantation can enhance revascularization and improve follicle survival in xenotransplanted human ovarian cortex.

METHODS

Cryopreserved human ovarian cortex pieces (N = 36) from 20 women aged 24-36 years were included. During the thawing process, each piece of tissue was cut in halves; one half serving as the untreated control and the other half was punctured approximately 150-200 times with a 29-gauge needle. The cortex pieces were transplanted subcutaneously to immunodeficient mice for 3, 6 and 10 days (N = 8 patients) and for 4 weeks (N = 12 patients). After 3, 6 and 10 days, revascularization of the ovarian xenografts were assessed using immunohistochemical detection of CD31 and gene expression of angiogenic factors (Vegfα, Angptl4, Ang1, and Ang2), and apoptotic factors (BCL2 and BAX) were performed by qPCR. Follicle density and morphology were evaluated in ovarian xenografts after 4 weeks.

RESULTS

A significant increase in the CD31 positive area in human ovarian xenografts was evident from day 3 to 10, but no significant differences were observed between the needle and control group. The gene expression of Vegfα was consistently higher in the needle group compared to control at all three time points, but not statistically significant. The expression of Ang1 and Ang2 increased significantly from day 3 to day 10 in the control group (p < 0.001, p = 0.0023), however, in the needle group this increase was not observed from day 6 to 10 (Ang2 p = 0.027). The BAX/BCL2 ratio was similar in the needle and control groups. After 4-weeks xenografting, follicle density (follicles/mm³, mean ± SEM) was higher in the needle group (5.18 ± 2.24) compared to control (2.36 ± 0.67) (p = 0.208), and a significant lower percentage of necrotic follicles was found in the needle group (19%) compared to control (36%) (p = 0.045).

CONCLUSIONS

Needle puncturing of human ovarian cortex prior to transplantation had no effect on revascularization of ovarian grafts after 3, 6 and 10 days xenotransplantation. However, needle puncturing did affect angiogenic genes and improved follicle morphology.

Effects of Er:YAG laser treatment on re-vascularization and follicle survival in frozen/thawed human ovarian cortex transplanted to immunodeficient mice

PURPOSE

The huge loss of ovarian follicles after transplantation of frozen/thawed ovarian tissue is considered a major drawback on the efficacy of the procedure. Here we investigate whether Er:YAG laser treatment prior to xenotransplantation can improve re-vascularization and subsequently follicle survival in human ovarian tissue.

METHODS

A total of 99 frozen/thawed human ovarian cortex pieces were included of which 72 pieces from 12 woman were transplanted to immunodeficient mice. Tissues from each woman were included in both an 8-day and an 8-week duration study and treated with either full-beam laser (L1) or fractionated laser (L2), or served as untreated controls. Vascularization of the ovarian xenografts were evaluated after 8 days by qPCR and murine Cd31 immunohistochemical analysis. Follicle densities were evaluated histologically 8 weeks after xenografting.

RESULTS

Gene expression of Vegf/VEGF was upregulated after L1 treatment (p=0.002, p=0.07, respectively), whereas Angpt1, Angpt2, Tnf-α, and Il1-β were significantly downregulated. No change in gene expression was found in Cd31/CD31, ANGPT1, ANGPT2, ANGTPL4, XBP1, or LRG1 after any of the laser treatments. The fraction of Cd31 positive cells were significantly reduced after L1 and L2 treatment (p<0.0001; p=0.0003, respectively), compared to controls. An overall negative effect of laser treatment was detected on follicle density (p=0.03).

CONCLUSIONS

Er:YAG laser treatment did not improve re-vascularization or follicle survival in human ovarian xenografts after 8 days and 8 weeks grafting, respectively. However, further studies are needed to fully explore the potential angiogenic effects of controlled tissue damage using different intensities or lasers.

Transmyocardial revascularization (TMR): current status and future directions

Purpose

Cardiac surgeons are increasingly faced with a more complex patient who has developed a pattern of diffuse coronary artery disease (CAD), which is refractory to medical, percutaneous, and surgical interventions. This paper will review the clinical science surrounding transmyocardial revascularization (TMR) with an emphasis on the results from randomized controlled trials.

Methods

Randomized controlled trials which evaluated TMR used as sole therapy and when combined with coronary artery bypass grafting were reviewed. Pertinent basic science papers exploring TMR's possible mechanism of action along with future directions, including the synergism between TMR and cell-based therapies were reviewed.

Results

Two laser-based systems have been approved by the United States Food and Drug Administration (FDA) to deliver laser therapy to targeted areas of the left ventricle (LV) that cannot be revascularized using conventional methods: the holmium:yttrium-aluminum-garnet (Ho:YAG) laser system (CryoLife, Inc., Kennesaw, GA) and the carbon dioxide (CO₂) Heart Laser System (Novadaq Technologies Inc., (Mississauga, Canada). TMR can be performed either as a stand-alone procedure (sole therapy) or in conjunction with coronary artery bypass graft (CABG) surgery in patients who would be incompletely revascularized by CABG alone. Societal practice guidelines have been established and are supportive of using TMR in the difficult population of patients with diffuse CAD.

Conclusions

Patients with diffuse CAD have increased operative and long-term cardiac risks predicted by incomplete revascularization. The documented operative and long-term benefits associated with sole therapy and adjunctive TMR in randomized trials supports TMR's increased use in this difficult patient population.

Ten-year follow-up after combined coronary artery bypass grafting and transmyocardial laser revascularization in patients with disseminated coronary atherosclerosis

Coronary artery disease involving heavily calcified lesions has been associated with worse short- and long-term outcomes including increased mortality. This paper aims to evaluate long-term survival benefit when CABG + transmyocardial laser revascularization (TMLR) are performed on the hearts of patients with disseminated coronary atherosclerosis (DCA). This novel retrospective study was conducted between 1997 and 2002 and followed 86 patients with ischemic heart disease and severe DCA who underwent TMLR using a Holmium:YAG laser and/or CABG. There were 46 patients who had CABG plus TMLR on at least one heart wall ("combined therapy group") and 40 patients who had CABG or TMLR separately on at least one heart wall ("single therapy group"). For the whole group, actuarial survival at 10 years was 78.3% in the combined group compared to 72.5% in the single therapy group (p = 0.535). Ten-year survival in the combined vs. single therapy group for the anterior heart walls was 100 vs. 72.2% (p = 0.027). For the lateral and posterior heart walls were 73.7 vs. 73.3% (p = 0.97) and 84.2 vs. 72% (p = 0.27), respectively. Kaplan-Meier survival analysis showed benefit only for the anterior heart wall (F Cox test, p = 0.103). Single therapy procedures on all heart walls (odds ratio 1.736, p = 0.264) or on the anterior heart wall only (odds ratio 3.286, p = 0.279) were found to be predictors of 10-year late mortality. Combined therapy (TMLR + CABG) provides benefit for perioperative mortality and long-term survival only when provided on the anterior heart wall. For patients with disseminated coronary atherosclerosis, cardiac mortality was found to be increased when followed up 6 years later, regardless of the therapy applied.

Transmyocardial revascularization devices: technology update

Transmyocardial laser revascularization (TMR) emerged as treatment modality for patients with diffuse coronary artery disease not amendable to percutaneous or surgical revascularization. The procedure entails the creation of laser channels within ischemic myocardium in an effort to better perfuse these areas. Currently, two laser devices are approved by the US Food and Drug Administration for TMR – holmium:yttrium–aluminum–garnet and CO₂. The two devices differ in regard to energy outputs, wavelengths, ability to synchronize with the heart cycle, and laser–tissue interactions. These differences have led to studies showing different efficacies between the two laser devices. Over 50,000 procedures have been performed worldwide using TMR. Improvements in angina stages, quality of life, and perfusion of the myocardium have been demonstrated with TMR. Although several mechanisms for these improvements have been suggested, evidence points to new blood vessel formation, or angiogenesis, within the treated myocardium, as the major contributory factor. TMR has been used as sole therapy and in combination with coronary artery bypass grafting. Clinical studies have demonstrated that TMR is both safe and effective in angina relief long term. The objective of this review is to present the two approved laser devices and evidence for the safety and efficacy of TMR, along with future directions with this technology.

Holmium:YAG laser system for transmyocardial revascularization

Transmyocardial revascularization, using the US FDA-approved holmium: yttrium-aluminum-garnet (Ho:YAG) laser system, is a surgical option for patients with debilitating angina caused by diffuse coronary artery disease in areas of the heart not amenable to complete revascularization using conventional treatments. Increased utilization of this therapy is warranted, in parallel with continuing research into therapeutic or cell-based methods for enhancing the clinically relevant, positive outcomes. This article will review the clinical science surrounding Ho:YAG transmyocardial revascularization with an emphasis on the randomized controlled trials performed in these patient groups.

Cardiomyocyte regeneration in pericicatricial zone of the myocardium after laser tunneling and implantation of bone marrow mononuclear cells

Using canine model of chronic postinfarction myocardial ischemia we evaluated angiogenesis and cardiomyogenesis after combined revascularization by laser tunneling of the pericicatricial zone followed by implantation of bone marrow mononuclear cells into the channels. It was shown that the numerical density of arterioles and capillaries considerably increased 1 month after revascularization. We also observed a considerable increase in the density of cardiomyocyte nuclei in the test area, a 2-fold increase in the total area of nuclei, and an increase in the mean area of cardiomyocyte nuclei. The number of PNCA-positive cardiomyocytes significantly increased after combined revascularization. Our findings suggest that combined revascularization of the pericicatricial zone of the myocardium promoted angiogenesis and stimulates regeneration of cardiomyocytes.

Long-Term Outcomes After CABG With Concomitant CO2 Transmyocardial Revascularization in Comparison With CABG Alone

OBJECTIVES

: Transmyocardial revascularization (TMR) has been used as an isolated or adjunctive revascularization therapy in patients presumed to have nonbypassable coronary artery disease. The purpose of this study is to evaluate the short- and midterm mortality for patients with complete revascularization using TMR and coronary artery bypass grafting (CABG) compared with those patients with incomplete CABG revascularization and to document long-term follow-up in patients receiving TMR + CABG.

METHODS

: Seventy TMR + CABG patients were cohort matched with 70 patients undergoing isolated CABG with circumflex coronary artery disease, but with no bypassable distal targets, from 1999 to 2005 at Emory University Hospital. The data were retrospectively reviewed from a database after being prospectively entered. Results are presented in mean ± standard deviation, and Kaplan-Meier curves were created for long-term all-cause mortality.

RESULTS

: The TMR + CABG patients had a similar incidences to the CABG only group for preoperative ejection fraction (50.9 ± 11.2% vs. 50.7 ± 10.3%, P = 0.93), number of grafts (2.6 ± 1.1 vs. 2.5 ± 1.3, P = 0.5), and number of diseased vessels (2.8 ± 0.3 vs. 2.9 ± 0.4, P = 0.26). Off-pump surgery was used more often in the CABG alone group versus the TMR combined with CABG group (74.3% vs. 41.4%, P < 0.001). Postoperatively, there was no statistical difference among the TMR + CABG and the CABG alone groups for intensive care unit length of stay (4.3 ± 7.8 days vs. 2.6 ± 3.4 days, P = 0.026), postsurgical length of stay (7.6 ± 6.1 days vs. 6.8 ± 4.5 days, P = 0.31), stroke events (1.4% vs. 1.4%, P = 1.00), myocardial infarction (4.3% vs. 2.9%, P = 0.65), and 30-day mortality (5.7% vs. 4.3%, P = 0.70). Long-term survival rate was not statistically significant. In addition, 4-year follow-up in the TMR + CABG group had symptom improvement with reduction in New York Heart Association classification for class III/IV (P < 0.0001, baseline vs. 4-year follow-up).

CONCLUSIONS

: The combination of TMR and CABG for complete revascularization is safe and carries no further risk to patients compared with CABG only. CABG + TMR patients tend to have increased resource utilization. Long-term follow-up shows similar survival between the groups. TMR can be a useful adjunct to CABG for complete revascularization.

Intramyocardial injection of autologous platelet-rich plasma combined with transmyocardial revascularization

Transmyocardial revascularization (TMR) can improve refractory angina but does not consistently demonstrate an effect on myocardial function. Recent studies suggest a synergistic effect between TMR and exogenously supplied growth factors. We evaluated the clinical role of intramyocardial injection of autologous platelet-rich plasma (PRP) in conjunction with TMR. Twenty-five nonrevascularizable patients with class III/IV angina underwent minimally invasive sole therapy TMR during a 5-year period at a single institution. Group 1 (14 patients) underwent TMR alone while group 2 (11 patients) underwent TMR plus injection of PRP (Magellan plasma separator) between TMR channels. Blinded angina assessment and ejection fraction (EF) were measured preoperatively and at 6 months postoperatively. Baseline EF (57 +/- 10% vs. 50 +/- 7%), angina class (3.7 +/- 0.5 vs. 3.7 +/- 0.5), and the number of channels (48 +/- 5 vs. 48 +/- 4) were statistically similar in both groups. At 6 months, two class angina relief was similar in both groups (92% vs. 100%, p = 0.4); however, the TMR + PRP group had a lower average angina score (1.3 vs. 0.4, p = 0.07) and more were angina free (23% vs. 78%, p = 0.04) than the TMR-alone group. EF improved in the TMR + PRP group (-2.0% vs. +9.0%, p = 0.07) compared to the TMR-alone group. Two 30-day morbidities occurred in the TMR-alone group (atrial fibrillation and left pleural effusion) and one mortality occurred in the TMR + PRP group. Intramyocardial injection of autologous PRP combined with TMR may be more efficacious at relieving angina and improving myocardial function than TMR alone.

Effects of Transmyocardial Revascularization on Myocardial Perfusion and Systolic Function Assessed by Nuclear and Magnetic Resonance Imaging Methods

OBJECTIVE

There is no obvious explanation, except placebo, to the symptomatic effect of transmyocardial laser revascularization (TMR) in patients with refractory angina. Whether TMR improves myocardial perfusion or relieves symptoms without altering cardiac function is not clarified.

METHODS

One hundred patients with refractory angina were randomized 1:1 to TMR (CO2 laser) and medical treatment, or medical treatment alone. Technetium 99m (99mTc)-tetrofosmin myocardial perfusion tomography (SPECT), quantitative myocardial perfusion gated SPECT (QGSPECT), technetium 99m (99mTc) multiple gated acquisition radionuclide ventriculografi (MUGA) and cine-magnetic resonance imaging (cine-MRI) were performed at baseline and after 3 and 12 months.

RESULTS

Following TMR, a slight reduction in left ventricular ejection fraction (LVEF) (p < 0.05) was observed (MUGA and QGSPECT) compared to baseline. Inclusion of incomplete studies (QGSPECT) revealed a significant reduction in LVEF and increase in left ventricular end-diastolic volume (LVEDV) (p < 0.05) compared to a control group. Otherwise, no between-group comparisons showed statistically significant differences.

CONCLUSION

TMR did not improve myocardial perfusion, but led to a reduction in LVEF and increase in LVEDV, however not significantly different from the control group.

Myocardial Laser Revascularization in the Year 2000 as seen by a Norwegian Specialist Panel. The Process of Evaluating and Implementing New Methods in Clinical Practice

OBJECTIVE

In Norway "Transmyocardial laser revascularization" as a routine method was prohibited by the Ministry of Health in 1995 due to lacking evidence of treatment effect and concerns about procedural morbidity and mortality. In 1999 Norwegian health authorities asked for a re-evaluation of the method based on a systematic review of literature.

METHODS

Medline and Embase were searched and a total of 267 articles were identified. Publications were classified by an expert panel according to type of study and importance for the project.

RESULTS

Based on the literature review the panel concluded that heart laser treatment does not have a life-saving effect, nor does it improve myocardial function. However, the method has a considerable short-term symptomatic effect, the mechanism of which is not understood. Neoangiogenesis, denervation and placebo may play a role. Based on the report the Norwegian health authorities recommended use of this method be restricted to scientific trials only.

CONCLUSIONS

Based on a systematic literature review it was concluded that the only documented effect of heart laser treatment is symptom relief, the mechanism for which is unclear. It could partly or totally be a placebo effect. A conflict of interest may arise when new technologies are to be implemented in health care. The communication between professionals evaluating scientific results and decision makers is challenging. Quality assurance of this process may be obtained by use of expert panels working under the auspices of an official institution.

Transmyocardial laser revascularization: from randomized trials to clinical practice. A review of techniques, evidence-based outcomes, and future directions

Cardiac surgeons are increasingly faced with a more complex patient who has developed a pattern of diffuse coronary artery disease that cannot be completely revascularized by CAGB alone. Considering the increased operative and long-term cardiac risks predicted by incomplete revascularization, and the documented operative and long-term benefits associated with sole therapy and adjunctive TMR in randomized patients with diffuse coronary artery disease, increased use of sole therapy and adjunctive TMR therapy is warranted.

Transmyocardial laser revascularization

It has been almost a decade since transmyocardial laser revascularization (TMR) was approved for clinical use in the United States. The safety of TMR was demonstrated initially with nonrandomized studies in which TMR was used as the only treatment for patients with severe angina. TMR efficacy was proven after multiple randomized controlled trials. These revealed significant angina relief compared to maximum medical therapy in patients with diffuse coronary disease not amenable to conventional revascularization. In light of these results, TMR has been used as an adjunct to coronary artery bypass grafting (CABG). By definition, patients treated with this combined therapy have more severe coronary disease and comorbidities that are associated with end-stage atherosclerosis. Combination CABG + TMR has resulted in symptomatic improvement without additional risk. The likely mechanism whereby TMR has provided benefit is the angiogenesis engendered by the laser-tissue interaction. Improved perfusion and concomitant improvement in myocardial function have been observed post-TMR. Additional therapies to enhance the angiogenic response include combining TMR with stem cell-based treatments, which appear to be promising future endeavors.

Transmyocardial revascularization ameliorates ischemia by attenuating paradoxical catecholamine-induced vasoconstriction

BACKGROUND

The mechanism by which transmyocardial revascularization (TMR) offers clinical benefit is controversial. We hypothesized that TMR ameliorates ischemia by reversing paradoxical catecholamine-induced vasoconstriction.

METHODS AND RESULTS

Chronic ischemic cardiomyopathy was created in 11 dogs by placing ameroid constrictors on the proximal coronary arteries and their major branches. Six weeks later, 35 channels were created percutaneously in the left circumflex artery region, with the left anterior descending artery region serving as control. At rest, wall thickening and myocardial blood flow did not change in the treated region, whereas they deteriorated in the control bed. Contractile and myocardial blood flow reserve increased in the treated region but deteriorated in the control region. There was diminished iodine 123 metaiodobenzylguanidine uptake and a significant reduction in noradrenergic nerves in the treated region compared with the control region, with a corresponding reduction in tissue tyrosine hydroxylase activity.

CONCLUSIONS

We conclude that the absence of a catecholamine-induced reduction in MBF reserve and contractile reserve in the TMR-treated region with associated evidence of neuronal injury indicates that the relief of exercise-induced ischemia after TMR most likely results from reversal of paradoxical catecholamine-induced vasoconstriction. These findings may have implications in selecting patients who would benefit from TMR.

Targeted Therapeutic Applications of Acoustically Active Microspheres in the Microcirculation

The targeted delivery of intravascular drugs and genes across the endothelial barrier with only minimal side effects remains a significant obstacle in establishing effective therapies for many pathological conditions. Recent investigations have shown that contrast agent microbubbles, which are typically used for image enhancement in diagnostic ultrasound, may also be promising tools in emergent, ultrasound-based therapies. Explorations of the bioeffects generated by ultrasound-microbubble interactions indicate that these phenomena may be exploited for clinical utility such as in the targeted revascularization of flow-deficient tissues. Moreover, development of this treatment modality may also include using ultrasound-microbubble interactions to deliver therapeutic material to tissues, and reporter genes and therapeutic agents have been successfully transferred from the microcirculation to tissue in various animal models of normal and pathological function. This article reviews the recent studies aimed at using interactions between ultrasound and contrast agent microbubbles in the microcirculation for therapeutic purposes. Furthermore, the authors present investigations involving microspheres that are of a different design compared to current microbubble contrast agents, yet are acoustically active and demonstrate potential as tools for targeted delivery. Future directions necessary to address current challenges and advance these techniques to clinical practicality are also discussed.

Transmyocardial Revascularization

Low-powered lasers were first used in the 1980s to produce transventricular channels as an adjunct to coronary artery bypass surgery. High-powered lasers, which were introduced in the 1990s, are powerful enough to create transmyocardial channels with minimal damage to surrounding tissues. Clinical studies were first carried out in patients with inoperable coronary artery disease and angina pectoris refractory to medical therapy. Based on these studies, the Food and Drug Administration granted approval of transmyocardial revascularization (TMR) as a sole therapy. Recently, TMR has been combined with coronary artery bypass surgery and 2 types of laser systems are currently available which have not been compared. The results of clinical trials provide contrasting findings regarding benefit, and the procedure is associated with potential morbidity and mortality risk. Furthermore, the mechanism of action of TMR remains undefined. Additional studies need to be done with TMR to assess whether it is a useful treatment or an addition to the list of placebo therapies initially thought to have been of benefit in the therapy for angina pectoris.

Only transient increase of vascular growth factors and microvascular density after percutaneous myocardial laser

OBJECTIVE

We tested the hypothesis that percutaneous myocardial laser may stimulate microvascular growth in areas surrounding the laser channels.

METHODS

We conducted a study of 24 domestic pigs, which underwent percutaneous myocardial laser to left ventricular myocardium using holmium:YAG laser. The pigs were sacrificed in groups of four after one day, 3-4 days, one week, three weeks and six weeks. Frozen sections from both normal and treated myocardium were prepared for immunofluorescence microscopy and stained with antibodies against von Willebrand factor, vascular endothelial growth factor (VEGF) and Extra Domain-A cellular fibronectin (ED-AcFN). Microvascular density (MVD) and vascular area (VA) were determined in sections stained with antibodies against von Willebrand factor VIII using a digitised image analysis system. When determined in laser treated areas, channel core remnants were excluded from analysis.

RESULTS

Within the laser channel remnants and in the tissue closely surrounding these, expression of VEGF and ED-AcFN increased significantly after treatment at one, 3-4, and seven days and decreased to normal at three and six weeks. Expression of ED-AcFN was detected adjacent to endothelial cells of microvessels. The original laser channels were rapidly invaded by granulation tissue. There was no sign of recanalization at any stage during the six weeks. Morphometric analysis showed no increase in MVD and VA in the myocardium surrounding the laser channels.

CONCLUSION

An increase of VEGF and ED-AcFN after myocardial laser is transient and is not associated with increase of MVD or VA in myocardium not involving laser channel remnants.

What is the Optimal Channel Density for Transmyocardial Laser Revascularization?

BACKGROUND

Transmyocardial laser revascularization (TMR) has demonstrated reproducible relief of angina in patients with end-stage coronary disease. However, the optimum dose or channel density has not been elucidated.

METHODS

Using a porcine model of chronic myocardial ischemia, 14 animals were treated with CO2 TMR and randomized as follows: group 1 was 1 channel per 2 cm2; group 2 was 1 channel per 1 cm2; and group 3 was 2 channels per 1 cm2. Left ventricular myocardial viability and function were assessed by magnetic resonance imaging (MRI) and echocardiography pretreatment, and repeated 6 weeks later.

RESULTS

The MRI assessment of group 1 (1 channel/2 cm2) and group 2 (1 channel/cm2) demonstrated similar improvement in segmental contractility posttreatment of 12.11% +/- 5.15% and 12.47% +/- 9.51%, respectively. In contrast, group 3 (2 channels/cm2) showed significantly worse segmental contractility posttreatment: -18.52% +/- 7.16% (p = 0.01). Echocardiographic imaging revealed significant improvements in wall thickening in the ischemic zone for group 1 at 0.91 +/- 0.07 cm pretreatment versus 1.30 +/- 0.09 cm posttreatment, (p = 0.01); and for group 2 at 0.93 +/- 0.11 cm versus 1.42 +/- 0.18 cm, (p = 0.01). No significant improvement in wall thickening was seen in group 3 (0.84 +/- 0.06 cm versus 0.88 +/- 0.09 cm, p = n.s.).

CONCLUSIONS

These data corroborate the empiric finding of an effective therapeutic dose range for TMR, 1 channel per 1 to 2 cm2. These results also demonstrate a detrimental effect when channel density is increased above the clinical standard of 1 channel per cm2 to a density of 2 channels per 1 cm2.

Treatment of acute myocardial infarction by hepatocyte growth factor gene transfer: the first demonstration of myocardial transfer of a "functional" gene using ultrasonic microbubble destruction

OBJECTIVES

We examined whether ultrasonic microbubble destruction (US/MB) enables therapeutic myocardial gene transfer of hepatocyte growth factor (HGF) for acute myocardial infarction (MI).

BACKGROUND

Hepatocyte growth factor gene transfer provides cardioprotective effects in MI, which requires direct intramyocardial injection or special vectors. Although US/MB was used in myocardial gene transfer, its feasibility in transfer of a therapeutic gene with non-viral vector remains unknown.

METHODS

In a rat model of acute MI, naked plasmid (pVaxl) encoding human HGF (1,500 microg) was infused into the left ventricular (LV) chamber during US/MB (HGF-US/MB) or insonation only (HGF-US) or alone (HGF-alone), while control MI rats received empty pVaxl during US/MB (pVaxl-US/MB). For US/MB, transthoracic intermittent insonation with a diagnostic transducer (1.3 MHz) was performed for 2 min at a peak negative pressure of -2,160 kPa during intravenous 20% Optison.

RESULTS

Baseline risk area was comparable among the groups. Immunohistology seven days after treatment revealed significant myocardial expression of HGF protein only in HGF-US/MB. At three weeks, LV weight in HGF-US/MB (0.89 +/- 0.03 g) was significantly lower than those in HGF-alone (1.09 +/- 0.08 g), HGF-US (1.04 +/- 0.07 g), and pVaxl-US/MB (1.04 +/- 0.05 g). Moreover, scar size was significantly smaller (16 +/- 6% vs. 39 +/- 5%, 41 +/- 6%, and 40 +/- 4% of total myocardial circumferential length, respectively), while capillary density (49 +/- 8 vs. 34 +/- 5, 37 +/- 6, and 36 +/- 4 capillaries/high-power field, respectively) and arterial density (37 +/- 7 vs. 15 +/- 9, 18 +/- 4, and 14 +/- 11 arterioles/high-power field, respectively) in the risk area were higher in HGF-US/MB than the other groups.

CONCLUSIONS

Ultrasound-mediated microbubble destruction may enable myocardial HGF gene transfer with systemic administration of naked plasmid, which enhances angiogenesis, limits infarction size, and prevents LV remodeling after MI.

[Long-term results of percutaneous transmyocardial laser revascularization therapy at the University of Vienna Medical Center]

INTRODUCTION

Percutaneous transmyocardial laser revascularization (PTMR) was used for treating patients with therapy refractory angina pectoris who are not amenable for angioplasty or bypass surgery ("no-option patients"). The aim of this study was to evaluate the short- and long-term results of PTMR-interventions performed at the University of Vienna between February 1999 and May 2000.

PATIENTS AND METHODS

Twenty-four "no-option" patients underwent PTMR. The chronically ischemic myocardial areas were determined by perfusion scintigraphy; after coronary angiography and contrast ventriculography 10 patients were treated with the Biosense laser using 3D-NOGA-mapping guidance and 14 patients with the Eclipse laser using biplane fluoroscopic guidance. After an average follow-up period (FUP) of 7.7 +/- 4.2 months, all patients underwent perfusion scintigraphy, coronary angiography and contrast ventriculography. Global and regional left ventricular (LV) function were calculated by the area-length method.

RESULTS

The ischemic myocardial areas of the patients were treated with an average of 16 laser points. In one patient, an intramural hematoma caused by the Biosense laser catheter was observed, in another patient the ventricular wall was perforated by the Eclipse laser (both events were resolved conservatively); during the in-hospital stay 2 patients suffered from severe angina pectoris and in one patient a pacemaker was implanted. During the 7-month-FUP one patient had a myocardial infarction; in one patient a stent implantation, in another one coronary bypass surgery had to be performed (in not-lasered areas), 2 patients died. Thus, the composite MACE rate was 33.3%. Angina class improved significantly during the FUP, but a trend to deterioration of global ejection fraction was observed. The rest and late rest myocardial perfusion remained unchanged.

CONCLUSION

While the angina class of the patients improved significantly, no significant change of myocardial perfusion but a trend to deterioration of LV function after the FUP were observed.

Therapeutic angiogenesis in chronically ischemic porcine myocardium: comparative effects of bFGF and VEGF

BACKGROUND

Both vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) have been used in preclinical studies to induce new blood vessel growth in ischemic cardiac muscle with promising results. However, clinical trials have been much less convincing and further work is needed. This study expands on prior work by comparing the long-term proangiogenic effects of direct intramyocardial (IM) injection of bFGF, as well as IM and intravenous (IV) VEGF in a porcine model of chronic hibernating myocardium.

METHODS

Mini-swine with proximal 90% left circumflex (LCx) coronary stenosis subtending chronically ischemic, viable (hibernating) myocardium by positron emission tomography (PET) and dobutamine stress echocardiography (DSE) were randomized to IM bFGF (n = 5), IM VEGF(165) (n = 5), IV VEGF(165) (n = 5), IM vehicle (n = 5), or sham redo-thoracotomy (n = 4). The bFGF protein was administered in a total dose of 1.35 microg divided into 30 IM injections. IM VEGF(165) protein was administered in a total dose of 15 microg/kg divided into 30 injections; IV VEGF(165) was given at a dose of 50 ng. kg(-1). min(-1) for 200 minutes at three 72-hour intervals (30 microg/kg total dose). After 3 and 6 months the PET and DSE studies were repeated, and the animals were sacrificed for tissue vascular density and angiogenic protein analysis.

RESULTS

Myocardial blood flow (MBF) by PET was significantly improved 3 months posttreatment in the IM bFGF and IM VEGF(165) groups, differences that were sustained at 6 months. There was no significant increase in MBF 3-months posttreatment in the IV VEGF(165) group; however, at 6 months MBF was significantly improved. No change in MBF was seen in the IM vehicle or sham groups. Regional wall motion at rest and peak stress in the LCx region demonstrated small but statistically significant improvements by 6 months in the IM bFGF and IV VEGF(165) groups only; no improvement was seen in the IM VEGF(165), IM vehicle, or sham groups. Quantitative vascular density was significantly increased in the LCx regions of all treatment groups (IM bFGF, IM VEGF(165), IV VEGF(165)) 6-months postoperatively. No significant increase in LCx region myocardial bFGF or VEGF protein levels was seen in the treated animals at 6 months.

CONCLUSIONS

The IM bFGF, IM VEGF(165), and IV VEGF(165) all improve regional perfusion and vascular density 6-months posttherapy in the animal model utilized. Functional improvements were less consistent. Both bFGF and VEGF(165) may be useful therapies for improving regional perfusion in chronically ischemic myocardium, although combination therapy with additional growth factors or cellular therapies may be necessary if concomitant improvements in function are to be seen.

Chronic effects of transmyocardial laser revascularization in the nonischemic myocardium: a word of caution

BACKGROUND

Transmyocardial laser revascularization (TMLR) has been shown to induce angiogenesis and improve regional myocardial blood flow. However, the biological response to laser of different energy doses in nonischemic myocardium has not been well studied. We study the time course of histological appearance following high- and low-energy TMLR in a rodent model of normal myocardium.

METHODS

The animals were randomized to two groups (high-energy (1.4 J/pulse) TMLR group and low-energy (0.6 J/ pulse) TMLR group). TMLR was applied to the anterolateral wall of the left ventricle. Then the animals were sacrificed (one every 2 or 3 days up to 6 weeks, then one every week) to give a series of hearts from 1 week to 12 weeks following TMLR.

RESULTS

No patent laser channels were identified. All laser channel remnants were composed of granulation tissue, fibrosis, and various amounts of vascular structures. Changes in vascular density demonstrated a similar pattern in both groups over time. The initial increase in vascular density within the laser channel remnants and the surrounding areas was more marked in group I than in group II. Gradual decline of vascular density occurred during a later follow-up. More fibrosis and less vasculature were demonstrated 12 weeks after laser therapy in group I.

CONCLUSION

Angiogenic response to the Holmium:YAG laser in the nonischemic myocardium is nonspecific and unsustainable. TMLR might chronically impair the myocardium function by enhancing regional scar formation. Therefore, we should clearly identify the ischemic area for laser therapy. Reduction of laser energy might prevent this potential complication.

Mechanisms and Results of Transmyocardial Laser Revascularization

Transmyocardial laser revascularization (TMR) is a technique that has been performed on over 10,000 patients around the world. Most of the patients were not suffering from heart failure. TMR is principally used for the treatment of angina, but in patients with significant reversible ischemia that is not amenable to conventional therapy, TMR may also improve myocardial function. The results of using TMR as a treatment for angina show a dramatic improvement in symptoms and quality of life. This paper reviews the current status of TMR techniques, mechanisms and results.

Regional Cardiac Sympathetic Innervation Early and Late After Transmyocardial Laser Revascularization

BACKGROUND

Prior experimental and clinical studies have drawn disparate conclusions regarding the effects of transmyocardial laser revascularization (TMR) on regional cardiac innervation in the treated regions. Regional afferent denervation has been proposed as a potential mechanism of action of the procedure, although this as yet remains unproven. The purpose of the present study was to evaluate regional myocardial sympathetic innervation both early (3 days) and late (6 months) after TMR.

METHODS

Mini-swine in the early group were randomized to be sacrificed 3 days after holmium:YAG TMR (n = 5) or sham thoractomy (n = 3). In the late group, mini-swine with hibernating myocardium in the left circumflex (LCx) region were randomized to sham redo-thoracotomy (n = 5), TMR of the LCx distribution with a carbon dioxide (n = 5), holmium:YAG (n = 5), or excimer (n = 5) laser. Six months postoperatively the animals were sacrificed. Additional animals in both the early (n = 2) and late (n = 2) groups served as age- and weight-matched normal controls. Immunohistochemistry and Western blot analysis for tyrosine hydroxylase (TYR-OH), a neural-specific enzyme found in sympathetic efferent nerves and a commonly used anatomic marker of regional innervation, were performed on lased and nonlased LCx and septal regions.

RESULTS

Immunohistochemical staining for TYR-OH was markedly diminished in the lased myocardial regions 3 days after TMR. This staining was significantly reduced compared to untreated septal regions, sham-operated, and normal LCx myocardium. Quantitative immunoblotting confirmed a significant reduction in TYR-OH (p < 0.05) protein concentration in the lased regions 3 days after TMR. On the contrary, TYR-OH staining was present in LCx myocardium surrounding the laser channels of all animals in all groups 6 months postoperatively. Staining was not different from controls. Similarly, there was no difference in LCx TYR-OH protein concentration between the normal, sham, or 6 months postoperative lased groups (p > 0.2 by one-way ANOVA).

CONCLUSIONS

TMR-treated myocardium demonstrates anatomic evidence of regional sympathetic denervation 3 days postoperatively, although myocardium lased with each of the three lasers currently in clinical use is reinnervated by 6 months as evidenced by immunoblotting and immunohistochemistry for TYR-OH. These results suggest that mechanisms other than denervation may account for the long-term reductions in angina seen after TMR.

Intramyocardial and intracoronary basic fibroblast growth factor in porcine hibernating myocardium: a comparative study

OBJECTIVE

Therapeutic angiogenesis is an alternative method of revascularization for end-stage coronary artery disease. We determined the effects of intramyocardial and intracoronary basic fibroblast growth factor 2 on myocardial blood flow and function in a porcine model of hibernating myocardium.

METHODS

Twenty-four mini-swine with 90% left circumflex artery stenosis and documented hibernating myocardium by positron emission tomography and dobutamine stress echocardiography were randomized to intramyocardial basic fibroblast growth factor 2 at 0.6 microg/kg (mid-dose, n = 6, 30 injections/animal), 6 microg/kg (high-dose, n = 6, 30 injections/animal), or intramyocardial vehicle control (n = 6). The intracoronary group received 6 microg/kg basic fibroblast growth factor 2 (n = 6) into the right and left circumflex artery coronary arteries. Positron emission tomography and dobutamine stress echocardiography were repeated at 1 and 3 months.

RESULTS

In the vehicle group, normalized left circumflex artery myocardial blood flow was 0.74 +/- 0.04 at 1 month and 0.75 +/- 0.07 at 3 months compared with 0.68 +/- 0.03 at baseline. In the intracoronary group, myocardial blood flow was 0.71 +/- 0.03 at 1 month and 0.72 +/- 0.04 at 3 months compared with 0.67 +/- 0.04 at baseline. In the mid group, myocardial blood flow was 0.73 +/- 0.06 at 1 month and 0.85 +/- 0.05 at 3 months (P <.001) compared with 0.67 +/- 0.04 at baseline. In the high group, myocardial blood flow was 0.81 +/- 0.06 at 1 month and 0.83 +/-.04 at 3 months (P =.03) compared with 0.71 +/- 0.02 at baseline. No significant improvements in ischemia were demonstrated in any of the groups by dobutamine stress echocardiography at 1 or 3 months.

CONCLUSIONS

In porcine hibernating myocardium, intramyocardial basic fibroblast growth factor 2 significantly improved regional myocardial blood flow 3 months after treatment. There was no significant change in function in any of the 4 groups. These data suggest that intramyocardial dosing of basic fibroblast growth factor 2 (0.6 microg/kg) may be an optimal dose for improving perfusion in the treatment of end-stage coronary artery disease.

Evaluation of myocardial perfusion and left ventricular function six months after percutaneous transmyocardial laser revascularization: Comparison of two Ho-YAG laser systems with the same wavelength, but different energy delivery and navigation systems

BACKGROUND AND OBJECTIVES

Myocardial perfusion and left ventricular function (LVF) were assessed after percutaneous transmyocardial laser revascularization (PTMR) in patients not amenable to conventional revascularization, with a comparison of two laser systems.

STUDY DESIGN/MATERIALS AND METHODS

PTMR was performed with an Eclipse laser in 15 patients, and with a Biosense DMR in 10 patients. (201)Thallium scintigraphy, coronary angiography, and ventriculography were performed at baseline and at the 7.5+/-4.3-month follow-up. All patients in the Biosense DMR group and 10 in the Eclipse group underwent NOGA mapping before PTMR and after follow-up.

RESULTS

The event-free survival rates were comparable, and the angina scores of all patients improved significantly, but more so in the Biosense DMR group than in the Eclipse group (1.2+/-1.1 vs. 2.3+/-0.9, P < 0.05). Both, the electrical activity assessed by NOGA mapping and the normalized (201)thallium uptake at redistribution improved significantly in the treated segments after Biosense DMR, while the global LVF decreased insignificantly in the Eclipse group.

CONCLUSIONS

PTMR resulted in significant improvements in the clinical symptoms, but the electrical activity improved only in the Biosense DMR group, without transforming to a better LVF.

Laser revascularization of ischemic skeletal muscle

BACKGROUND

Clinical trials have shown that transmyocardial laser revascularization is an effective secondary treatment for ischemic heart disease patients. Laser revascularization may also provide an alternative method for treating peripheral vascular disease.

METHODS

The purpose of this study was to investigate the potential for laser revascularization in ischemic skeletal muscle. Eighteen rabbits (3-4 kg) were instrumented chronically with transit time ultrasound flowprobes on both common iliac arteries. All rabbits performed graded exercise tests on a treadmill where maximal blood flow was recorded. Unilateral hindlimb ischemia was produced by ligation of one femoral artery. At week 3 postligation, 10 rabbits received laser therapy and 8 underwent a sham surgery. In each of four muscles (gracilius, medialis, sartorius, and biceps femoris) 5 to 22 laser channels were created (average = 52 channels per leg).

RESULTS

At week 3 postligation the maximal blood flow of the ischemic limb for the treated group was 64 +/- 3 ml/min (mean +/- SEM) and at 6 weeks postlaser therapy maximal blood flow increased to 75 +/- 5 ml/min. The sham surgery group had a maximal blood flow of 58 +/- 4 ml/min at week 3 postligation and 66 +/- 3 ml/min at week 6 postsham surgery.

CONCLUSION

These results indicate that laser therapy does not induce angiogenesis and vascular remodeling in the ischemic hindlimb of a rabbit which exceeds that seen with a sham surgery.

From controlled trials to clinical practice

OBJECTIVES

We sought to examine trends in the use and outcomes of transmyocardial revascularization (TMR) in community practice. We also identified important risk factors for TMR and compared outcomes of TMR combined with coronary artery bypass graft surgery (TMR + CABG) versus bypass alone in patients receiving incomplete revascularization.

BACKGROUND

Although it is approved for use as a stand-alone procedure, there are limited data on the outcomes of (TMR + CABG).

METHODS

We identified 3,717 patients receiving TMR at 173 U.S. hospitals participating in the Society of Thoracic Surgeons (STS) National Cardiac Database. Baseline characteristics and outcomes in these patients were compared with those from six published randomized TMR trials. Multivariable logistic regression was used to identify clinical risk factors for mortality with TMR. Risk-adjusted mortality was also compared for TMR + CABG relative to CABG only in patients not amenable to complete traditional revascularization.

RESULTS

Between January 1998 and December 2001, the number of STS hospitals performing TMR and total procedural counts increased markedly, driven predominately by more TMR + CABG cases. Overall mortality rates for TMR-alone and TMR + CABG were 6.4% and 4.2%, respectively. Operative risks were significantly higher in those patients with recent myocardial infarction, unstable angina, and depressed ventricular function. Among patients receiving incomplete revascularization, TMR + CABG was not associated with decreased mortality risk compared with CABG alone, adjusted odds ratio 1.11 (95% confidence interval 0.74 to 1.67).

CONCLUSIONS

The use of TMR, and in particular, TMR + CABG, is expanding in community practice. Although procedural risks are high, there is room for optimization through improved patient selection and timing of the procedure. Further studies of TMR + CABG are needed given its growing use and unclear benefits.

Alternative therapeutic strategies for patients with severe end-stage coronary artery disease not amenable to conventional revascularization

Although there have been remarkable advances in medical therapy, percutaneous coronary interventions, and coronary artery bypass graft surgery, complete revascularization remains a challenge given the more complex coronary artery disease prevalent in contemporary practice. The lack of donors for cardiac transplantation will fuel the search for effective alternative strategies for dealing with patients with severe ischemic heart disease not amenable to conventional revascularization techniques. Percutaneous laser revascularization clearly diminishes anginal symptoms; however, the blinded trials have provided conflicting results, with one study showing a definite decrease in angina and another suggesting that the placebo effect may play a major role in this modality. Similarly, surgical transmyocardial laser revascularization is limited by the lack of consistent improvement in objective measurements of ischemia and the potential confounding mechanisms of denervation and the placebo effect, and thus should be reserved for only the most highly selected patients. Although enhanced external counterpulsation is associated with an improvement in anginal symptoms and exercise tolerance, this modality is limited by its availability, tolerability, and rigid exclusion criteria. Of the alternative strategies available, therapeutic angiogenesis holds the most promise. However, the long-term results of ongoing randomized clinical trials require further scrutiny. Novel methods for vascular reconstruction are evolving techniques, but should be viewed currently as mainly experimental methods. The common goals of these new treatment options would be to reduce symptoms, decrease morbidity, and potentially improve mortality by reducing ischemia through favorably impacting myocardial oxygen supply and demand. The optimal management of patients with severe end-stage coronary artery disease not amenable to conventional revascularization techniques will continue to remain a challenge for the clinician and will be the main focus of basic cardiovascular research and clinical trials in the new millennium.

Translational physiology: porcine models of human coronary artery disease: implications for preclinical trials of therapeutic angiogenesis

"Therapeutic angiogenesis" describes an emerging field of cardiovascular medicine whereby new blood vessels are induced to grow to supply oxygen and nutrients to ischemic cardiac or skeletal muscle. Various methods of producing therapeutic angiogenesis have been employed, including mechanical means, gene therapy, and the use of growth factors, among others. The use of appropriate large-animal models is essential if these therapies are to be critically evaluated in a preclinical setting before their use in humans, yet little has been written comparing the various available models. Over the past decade, swine have been increasingly used in studies of chronic ischemia because of their numerous similarities to humans, including minimal preexisting coronary collaterals as well as similar coronary anatomy and physiology. Consequently, this review describes the most commonly used swine models of chronic myocardial ischemia with special attention to regional myocardial blood flow and function and critically evaluates the strengths and weaknesses of each model in terms of utility for preclinical trials of angiogenic therapies.

Percutaneous myocardial laser revascularization in patients with refractory angina pectoris

This study aimed to determine the safety and efficacy of percutaneous myocardial laser revascularization (PMLR). Seventy-three patients with stable angina pectoris (class III or IV) who were unsuitable for conventional revascularization and had evidence of reversible ischemia by thallium-201 scintigraphy, ejection fraction of > or =25%, and myocardial wall thickness > or =8 mm were randomized to optimal medical therapy alone (n = 37) or PMLR with optimal medical therapy (n = 36). Patients were followed up at 3, 6, and 12 months. The primary end point was exercise time. Secondary end points included angina scores, left ventricular ejection fraction, quality of life, changes in medical therapy, and hospitalizations. All 36 patients randomized to PMLR underwent the procedure successfully with no periprocedure deaths. One patient developed sustained ventricular tachycardia that required electrical cardioversion, and 1 patient developed cardiac tamponade that required surgical drainage. At 12 months, exercise times improved by 109 seconds in the PMLR group but decreased by 62 seconds in the control group (p <0.01). Angina scores improved by 2 classes in 36% of PMLR-treated patients at 12 months compared with 0% of the control patients (p <0.01). We conclude that PMLR is a relatively safe procedure that provides patients with symptomatic angina relief and improvement in exercise capacity and quality of life.

Myocardial laser revascularization for the treatment of end-stage coronary artery disease

Myocardial laser revascularization is a novel therapeutic technique aimed at delivering oxygenated blood via a series of channels to the ischemic regions of the heart. These channels may be created surgically or via a less invasive percutaneous approach. In patients with end-stage coronary artery disease, both transmyocardial laser revascularization (TMR) and percutaneous myocardial laser revascularization (PMR) have been associated with a reduction in symptoms, improved exercise tolerance, and enhanced quality of life. However, the mechanism of action of laser therapy is incompletely understood, the results of objective cardiac perfusion measurements are inconclusive, and multiple randomized trials have failed to demonstrate an increase in survival. In addition, the positive results seen in TMR trials have been questioned because of a lack of blinding, raising the possibility that the benefit may have been due to the placebo effect. Finally, two recent sham-controlled, randomized clinical trials of PMR have not shown any benefit of the procedure, but instead have highlighted the important role of the placebo effect in the response to PMR. Further research is, therefore, needed to elucidate the value of myocardial laser revascularization.

35 years of experimental research in transmyocardial revascularization: what have we learned?

In the past 35 years many experimental studies have been performed to investigate the revascularization potential of transmyocardial revascularization and the possible working mechanisms underlying the observed clinical improvement in angina pectoris after this treatment. In this review of the experimental literature, the various methods that have been used to create transmyocardial channels and the most supported hypotheses on the working mechanism (channel patency, angiogenesis and myocardial denervation) are discussed and evaluated.

Transmyocardial coil implants: a novel approach to transmyocardial revascularization

BACKGROUND

Transmyocardial laser revascularization (TMLR) has potential benefit for patients with end-stage coronary artery disease and intractable angina not amenable to conventional revascularization techniques. Neovascularization has been proposed to occur around the laser channels. Our aim was to determine the feasibility of a novel nonlaser myocardial revascularization technique and its effect on angiogenesis in a nonischemic porcine model.

METHODS

In the first phase, six transmyocardial stainless steel coil implants (TMI) were deployed to the lateral wall of the left ventricle in each of 6 pigs. The animals were sacrificed at 8 and 12 weeks, with a single animal dying prematurely at 4 weeks, and the myocardium was assessed for new vessel growth. In the second phase, 8 implants were deployed in each of 12 pigs with regular fluoroscopic follow-up until sacrifice at 2 weeks to assess implant stability.

RESULTS

The deployment procedure was safe and feasible with no complications evident. A significant increase in new vessels at implant sites with 5.43 +/- 3.67, 4.97 +/- 2.44, and 3.57 +/- 2.29 seen per high power field at 12, 8, and 4 weeks, respectively, compared to 1.00 +/- 1.06 (p < 0.0001) in control myocardium. There was no evidence of implant migration in Phase 2.

CONCLUSIONS

TMIs can feasibly be deployed in the nonischemic pig model with a high success rate. The presence of angiogenesis at the implant site and the maintenance of this reaction for 3 months implies that TMI may offer an alternative to TMLR while providing a platform for delivery of angiogenic factors.

Contrast ultrasound targeted drug and gene delivery: an update on a new therapeutic modality

The effective delivery of intravascular drugs and genes to regions of pathology is dependent on a number of factors that are often difficult to control. Foremost is the site-specific delivery of the payload to the region of pathology and the subsequent transport of the payload across the endothelial barrier. Ultrasound contrast agent microbubbles, which are typically used for image enhancement, are capable of amplifying both the targeting and transport of drugs and genes to tissue. Microbubble targeting can be achieved by the intrinsic binding properties of the microbubble shells or through the attachment of site-specific ligands. Once microbubbles have been targeted to the region of interest, microvessel walls can be permeabilized by destroying the microbubbles with low-frequency, high-power ultrasound. A second level of targeting specificity can be achieved by carefully controlling the ultrasound field and limiting microbubble destruction to the region of interest. When microbubbles are destroyed, drugs or genes that are housed within them or bound to their shells can be released to the blood stream and then delivered to tissue by convective forces through the permeabilized microvessels. An alternative strategy is to increase payload volume by coinjecting drug- or gene-bearing vehicles, such as liposomes, with the microbubbles. In this manifestation, microbubbles are used for creating sites of microvessel permeabilization that facilitate drug or gene vehicle transport. Recent work in the emerging field of contrast ultrasound-based therapeutics, with particular emphasis on the delivery of drugs and genes to tissue through microvascular networks is reviewed.

Factors influencing results and outcome after transmyocardial laser revascularization

BACKGROUND

Transmyocardial laser revascularization (TMR) has been increasingly used during the recent past for patients with diffuse coronary artery disease. Because this operation is associated with significant morbidity and mortality, it is important to select patients for TMR who are likely to benefit from the procedure.

METHODS

We performed an univariate logistic regression analysis of 20 factors on the benefits and outcomes of 134 patients who underwent isolated TMR at our institution between November 1994 and May 2000.

RESULTS

Responders and nonresponders differed significantly with regard to the incidence of diabetes mellitus. For diabetic patients the chance of profiting from the TMR operation was only 43% of that of nondiabetic patients (odds ratio = 0.43 [0.20 to 0.92]). Furthermore, patients with a preoperative body mass index of less than 25 had a threefold increase in the probability of death during the first year after TMR as compared to patients whose body mass index was 25 or more (odds ratio = 2.97 [1.05 to 8.40]). The incidence of diabetes was also slightly but not significantly different between 1-year survivors and nonsurvivors.

CONCLUSIONS

In diabetic patients we recommend caution in selecting therapeutic TMR because outcomes are less satisfactory than in nondiabetics. Furthermore, patients with a body mass index below 25 have a significantly higher risk for death during the first postoperative year. Studies based on larger patient populations should follow.

A comparison of mechanical and laser transmyocardial revascularization for induction of angiogenesis and arteriogenesis in chronically ischemic myocardium

OBJECTIVES

The purpose of the present study was to compare the use of a mechanical transmyocardial implant (TMI) device with transmyocardial laser revascularization (TMR) for induction of therapeutic angiogenesis and arteriogenesis in the chronically ischemic heart.

BACKGROUND

Prior experimental studies have demonstrated evidence for neovascularization after both mechanical and laser transmyocardial revascularization, although a long-term comparison of the two techniques has not been performed.

METHODS

Using an established model of chronic hibernating myocardium, mini-swine underwent 90% proximal left circumflex (LCx) coronary artery stenosis. One month later, baseline positron emission tomography (PET) and dobutamine stress echocardiography (DSE) were performed to quantitate regional myocardial blood flow (MBF) and function. Animals then underwent TMR with a holmium:yttrium-aluminum-garnet (holmium:YAG) laser (n = 5), TMI (n = 5), or sham redo-thoracotomy (n = 5). In the TMR group, the entire LCx region was treated with transmural laser channels at a density of 1/cm(2). Transmyocardial implants were placed transmurally at a similar density in the LCx region of the TMI group. Six months later, the PET and DSE studies were repeated, and the animals were euthanized.

RESULTS

Six months after TMR, there was a significant increase over baseline in resting MBF to the lased LCx region (68.9 +/- 4.6% vs. 89.3 +/- 3.0% reference non-ischemic septal segments; p < 0.001). This increased MBF was accompanied by a significant improvement in LCx regional wall motion during peak dobutamine stress (p = 0.04). Compared with baseline, there was no change in LCx region MBF six months after either TMI (72.9 +/- 4.8% vs. 85.7 +/- 3.4%; p = 0.10) or sham redo-thoracotomy (75.6 +/- 4.6% vs. 80.1 +/- 5.0%; p > 0.2). Likewise, there was no significant change in rest or stress wall motion by DSE six months postoperatively in either group. Overall vascular density was increased only in the TMR-treated regions six months postoperatively. The difference between groups was most notable for a twofold increase in the number of small arterioles seen in the lased (4.4 +/- 0.3 arterioles per high power field; p < 0.001 vs. both TMI and sham) compared with TMI (2.2 +/- 0.2) and sham (1.9 +/- 0.2)-treated regions.

CONCLUSIONS

Mechanical transmyocardial revascularization with a TMI device does not appear to promote physiologically significant angiogenesis or arteriogenesis in the chronically ischemic porcine heart and cannot be recommended for clinical trials at this time. Infrared laser-mediated injury mechanisms may be important for inducing therapeutic neovascularization with direct myocardial revascularization techniques.

Magnetic resonance imaging demonstrates improved regional systolic wall motion and thickening and myocardial perfusion of myocardial territories treated by laser myocardial revascularization

OBJECTIVES

This study was designed to investigate the use of magnetic resonance (MR) functional and perfusion imaging to evaluate laser myocardial revascularization (LMR).

BACKGROUND

Most clinical studies of LMR have shown improvements in angina class and exercise capacity, with minimal or absent improvements in myocardial perfusion and function.

METHODS

Fifteen patients who underwent percutaneous Biosense-guided holmium:yttrium aluminum garnet LMR to areas of viable but ischemic myocardium were followed clinically and underwent functional and perfusion MRI at baseline, 30 days and 6 months.

RESULTS

The mean age was 64 +/- 11 years; four patients were women. The ejection fraction was 47.4 +/- 14.0%. Angina class at baseline was 3.4 +/- 0.6 and improved to 2.5 +/- 1.4 at six months (p = 0.054). Exercise time at baseline was 298 +/- 97 s and increased to 350 +/- 95 s at 30 days and 365 +/- 79 s at six months, p = 0.04. There were no significant changes in nuclear perfusion scans. Although MR determined that resting radial motion and thickening of the target wall were significantly less than normal at baseline (p < 0.001), they improved significantly during follow-up (wall thickening: baseline, 30.6 +/- 11.7%; day 30, 41.2 +/- 13.3% and day 180, 44.2 +/- 11.9%, p = 0.01). The size of the underperfused myocardial area was 14.5 +/- 5.4% at baseline and was reduced to 6.3 +/- 2.8% at 30 days and 7.7 +/- 3.7% at 6 months (p < 0.001).

CONCLUSIONS

This small phase I, open-label, uncontrolled study of MR functional and perfusion imaging in patients undergoing Biosense-guided LMR suggests a beneficial effect of this treatment strategy on myocardial function and perfusion. The efficacy of Biosense-guided LMR is being evaluated in a large phase II, randomized, blinded placebo-controlled trial with an MRI substudy (DIRECT).

Excimer laser (308 nm) based transmyocardial laser revascularization: effects of the lasing parameters on myocardial histology

BACKGROUND AND OBJECTIVE

The effect of the excimer laser (308 nm) parameters on transmyocardial revascularization (TMR) channels is not well defined. This study investigates the influence of the pulse repetition rate, the size of the delivery catheter and its advancement speed on the morphology of TMR channels in vivo.

STUDY DESIGN/MATERIALS AND METHODS

Myocardial ablation was performed in a porcine model (N = 27) using multifiber catheters of 1.0 and 1.4 mm in diameter. The catheters were advanced into the myocardium at different speeds (1.27 and 2.54 mm/sec) while ablating at various repetition rates (10-80 Hz). The radiant exposure was kept at 35 mJ/mm(2) throughout the experiments. The channel histology was quantified by digital microscopy.

RESULTS

The channel cross-sectional area and the extent of the thermal damage decrease as the catheter advancement speed exceeds the ablation speed and vice versa. Within the parameters tested, advancement speed of about 1.3 mm/sec and pulse repetition rates of 40 Hz produce channels of size comparable to the catheter's diameter with moderate thermomechanical damage.

CONCLUSIONS

The repetition rate, catheter size, and catheter advancement speed are closely intertwined and crucial to the histological outcome of excimer laser based TMR.

First experience with hybrid percutaneous transmyocardial laser revascularization and angioplasty in patients with lesions at high risk for restenosis: Results of a phase I feasibility study

BACKGROUND

Prior studies have suggested that percutaneous transmyocardial laser revascularization (PTMR) may be effective as a sole treatment modality in reducing angina in patients with severe coronary artery disease and no revascularization alternatives. The safety and efficacy of the hybrid or adjunctive use of PTMR during the same procedure as percutaneous intervention (PCI) has not previously been reported.

METHODS

A US phase I feasibility study was therefore performed to determine whether PTMR performed in the same myocardial territory as PCI is able to ameliorate symptomatic recurrence from restenosis.

RESULTS

After successful and uncomplicated PCI in 26 patients with class III-IV angina and lesion(s) at high risk for restenosis, PTMR was performed in the same myocardial territories subtended by the treated vessel(s). Major periprocedural adverse events (death, Q-wave myocardial infarction, and bypass surgery) occurred in 3 (11.5%) patients, as the result of subacute vessel closure in 2 patients, and tamponade in the third. Cumulative 6-month mortality rate was 19.2%, including 2 late deaths between 3 and 4 months after discharge (1 death caused by late stent closure and 1 unexplained death during sleep.) Late repeat revascularization for restenosis in the PCI plus PTMR treated target vessel was required in 19.2% of patients, and an additional 11.5% of patients had class III-IV angina at 6-month follow-up.

CONCLUSIONS

These data demonstrate that in a patient population at high risk for restenosis, recently created PTMR channels are not protective against severe ischemia caused by acute vessel closure and that late symptomatic restenosis after PCI may still frequently occur despite PTMR in the same region.

Intramyocardial delivery of FGF2 in combination with radio frequency transmyocardial revascularization

Therapeutic angiogenesis and percutaneous transmyocardial revascularization (PMR) are potentially synergistic modalities to improve myocardial perfusion. To evaluate the efficiency of FGF2 delivery into an area that has been radio frequency (RF) ablated, we studied two catheter-based delivery methods, a direct injection system (Stiletto) and a combined RF ablation-delivery system (RF-PMR). Four groups (n = 3/group) of pigs received six transendocardial injections of (125)I-FGF2/fluorescent microspheres with either the Stiletto or the RF-PMR catheter. RF-PMR injections were preceded by a 0.6 sec RF ablation step. After either 1 or 24 hr, hearts and other tissues were harvested. Intramyocardial deposition sites were located with UV light and isolated. Specific activity per site was expressed as a percentage of total activity injected per site corrected for quenching. Injection site recovery was high for both catheter systems (average = 88%) and systemic uptake was low (< 6% in the liver). FGF2 retention was significantly higher with the Stiletto than the RF-PMR catheter (Stiletto 1 hr 41% +/- 17%, 24 hr 26% +/- 10%, RF-PMR 1 hr 21% +/- 14%, 24 hr 13% +/- 8%; P < 0.001), principally explained by the differences in catheter design. The Stiletto has a retractable needle and is optimized for intramyocardial delivery, whereas infusion from the RF-PMR device occurs at the endocardial surface and relies on channels created during RF ablation. Overall, FGF2 retention after transendocardial intramyocardial delivery by the Stiletto or the RF-PMR system is significantly higher than previously observed for intracoronary, intravenous and intrapericardial delivery. In conclusion, the combination of RF ablation and growth factor delivery using the RF-PMR system is feasible and efficient. Cathet Cardiovasc Intervent 2001;53:429-434.

Combined percutaneous biosense-guided laser myocardial revascularization and coronary intervention

Laser myocardial revascularization is a promising new treatment strategy for patients with severe ischemic heart disease who are not candidates for conventional percutaneous or surgical revascularization. The open chest surgical approach to transmyocardial revascularization has been approved by the FDA for the treatment of angina in inoperable patients, but has had limited use as a stand-alone procedure. More recently, use of fiber-optic catheters has made it possible to use a holmium:yttrium aluminum garnet laser to perform percutaneous catheter-based transmyocardial revascularization. To the extent that many patients have a combination of ischemic sources, some amenable to conventional revascularization and some not, combination or hybrid approaches have been considered. We report herein two patients with class IV angina who underwent laser myocardial revascularization using the Biosense system and complex percutaneous coronary intervention during the same procedure. Areas amenable to conventional percutaneous coronary intervention (PCI) were so treated, and viable but ischemic areas were supplied by totally occluded native vessels and bypass grafts underwent Biosense-guided laser myocardial revascularization (LMR). As the results of more controlled and blinded studies of laser myocardial revascularization become available (if results continue to be promising) and a better understanding of the mechanism of action of this treatment modality is achieved, LMR-PTCA hybrid will be performed in increasing frequency. However, even after establishing LMR efficacy, studies of LMR-PTCA hybrid should be conducted to determine the efficacy of this approach.

Spinal Cord Stimulation: A Comparison of Efficacy versus Other Novel Treatments for Refractory Angina Pectoris

Recently much attention has been directed toward novel treatment alternatives for refractory angina pectoris. Refractory angina is persistent stable class III or IV angina despite maximally tolerated medical treatment in patients with end-stage coronary artery disease. Transmyocardial laser revascularization (TMLR), gene therapy, intermittent urokinase therapy, enhanced external balloon counterpulsation, and spinal cord stimulation have all been employed to treat refractory angina pectoris. TMLR and gene therapy are invasive open-chest procedures that have yielded controversial results. Intermittent urokinase and enhanced external balloon counterpulsation studies have limited follow-up times and require multiple clinic visits for treatment. Spinal cord stimulation has a proven short- and long-term efficacy and cost-effectiveness in the treatment of refractory angina. When compared to coronary artery bypass grafting (CABG), it has been shown to decrease the frequency of anginal attacks and consumption of short-acting nitrates to the same extent in refractory angina. Spinal cord stimulation's safety profile has also been well established and it can be used concurrently with cardiac pacemakers or MRI systems, provided the proper precautions are taken. Since spinal cord stimulation is a minimally invasive procedure with a favorable efficacy and safety profile, it should be considered as a valid treatment alternative after medical management has failed in refractory angina prior to implementing invasive modalities such as TMLR or gene therapy.

Acute and chronic effects of transmyocardial laser revascularization in the nonischemic pig myocardium by using three laser systems

BACKGROUND AND OBJECTIVE

Transmyocardial laser revascularization (TMLR) improves symptoms in patients with coronary heart disease. It is based on the hypothesis of direct perfusion of ischemic myocardium by means of laser-created channels. Three different lasers were used to study alternative effects on myocardium.

STUDY DESIGN/MATERIALS AND METHODS

The present study was conducted to evaluate comprehensively and compare the short and long-term tissue effects and the basic interaction mechanisms of CO2, Ho:YAG, and Er:YAG laser radiation with myocardium. The dynamics of laser-induced impacts in gel used as tissue phantom was visualized by time-resolved flash photography. Pressure measurements performed during perforation of myocardium in vitro revealed the explosive character of the ablation process. Channels made into the left ventricle of normal pig hearts were examined immediately and 6 weeks after creation.

RESULTS

Regardless of laser source, all channels became occluded within 6 weeks by scar. Minimal acute thermal damage by Er:YAG laser corresponded to smaller scars. Pulsed Ho:YAG caused stronger tissue tearing than continuous wave CO2 irradiation. An increased volume density of intramyocardial vessels was found about the scars 6 weeks after treatment with all lasers.

CONCLUSION

The laser sources permitted to study outcome of pressure effects and thermal damage in vivo. There were only minor differences between the three laser systems used. Rapid channel occlusion suggests that rather than revascularization, subsidiary physiologic tissue effects elicited by the thermal, oxidative, or mechanical action of the laser impact may contribute to the beneficial clinical effects of TMLR.

Laser revascularization in the management of coronary artery disease

In recent years, laser therapy has been evaluated for the treatment of patients with angina who have coronary artery disease which is not amenable to conventional revascularization techniques. The results of transmyocardial revascularization and percutaneous myocardial revascularization are reviewed.