Measurement of myocardial blood flow with positron emission tomography before and after transmyocardial laser revascularization

Refractory Angina: the Current State of Mechanical Therapies

PURPOSE OF REVIEW

Refractory angina (RA), which is characterized by tissue ischemia along with neurological, mitochondrial, and psychogenic dysfunction, is becoming a major cause of morbidity in patients with advanced coronary artery disease. In this review, we discuss in detail the invasive mechanical non-cell therapy-based options, the evidence behind these therapies, and future trends.

RECENT FINDINGS

There is extensive ongoing research in the areas of spinal-cord stimulation, transmyocardial laser revascularization, sympathectomy, angiogenesis, and other non-cell-based therapies to explore the best therapy for refractory angina. There is conflicting data in the literature suggesting subjective improvement in angina, but very few studies boast improvement in core objective parameters such as myocardial blood flow, survival, or rehospitalizations. Patients with refractory angina are a complex group of patients that need novel approaches to help alleviate their symptoms and reduce mortality. A carefully selected sequence of therapies may provide the best results in this patient population.

Molecular imaging of angiogenesis after myocardial infarction by (111)In-DTPA-cNGR and (99m)Tc-sestamibi dual-isotope myocardial SPECT

Background

CD13 is selectively upregulated in angiogenic active endothelium and can serve as a target for molecular imaging tracers to non-invasively visualise angiogenesis in vivo. Non-invasive determination of CD13 expression can potentially be used to monitor treatment response to pro-angiogenic drugs in ischemic heart disease. CD13 binds peptides and proteins through binding to tripeptide asparagine-glycine-arginine (NGR) amino acid residues.

Previous studies using in vivo fluorescence microscopy and magnetic resonance imaging indicated that cNGR tripeptide-based tracers specifically bind to CD13 in angiogenic vasculature at the border zone of the infarcted myocardium.

In this study, the CD13-binding characteristics of an ¹¹¹In-labelled cyclic NGR peptide (cNGR) were determined. To increase sensitivity, we visualised ¹¹¹In-DTPA-cNGR in combination with ^99mTc-sestamibi using dual-isotope SPECT to localise CD13 expression in perfusion-deficient regions.

Methods

Myocardial infarction (MI) was induced in Swiss mice by ligation of the left anterior descending coronary artery (LAD). ¹¹¹In-DTPA-cNGR and ^99mTc-sestamibi dual-isotope SPECT imaging was performed 7 days post-ligation in MI mice and in control mice. In addition, ex vivo SPECT imaging on excised hearts was performed, and biodistribution of ¹¹¹In-DTPA-cNGR was determined using gamma counting. Binding specificity of ¹¹¹In-DTPA-cNGR to angiogenic active endothelium was determined using the Matrigel model.

Results

Labelling yield of ¹¹¹In-DTPA-cNGR was 95% to 98% and did not require further purification. In vivo, ¹¹¹In-DTPA-cNGR imaging showed a rapid clearance from non-infarcted tissue and a urinary excretion of 82% of the injected dose (I.D.) 2 h after intravenous injection in the MI mice. Specific binding of ¹¹¹In-DTPA-cNGR was confirmed in the Matrigel model and, moreover, binding was demonstrated in the infarcted myocardium and infarct border zone.

Conclusions

Our newly designed and developed angiogenesis imaging probe ¹¹¹In-DTPA-cNGR allows simultaneous imaging of CD13 expression and perfusion in the infarcted myocardium and the infarct border zone by dual-isotope micro-SPECT imaging.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-015-0081-7) contains supplementary material, which is available to authorized users.

Effectiveness of percutaneous laser revascularization therapy for refractory angina

Refractory angina is a debilitating disease characterized by persistent cardiac pain resistant to all conventional treatments for coronary artery disease. Percutaneous myocardial laser revascularization (PMLR) has been proposed to improve symptoms in these patients. We used meta-analysis to assess the effectiveness of PMLR versus optimal medical therapy for improving angina symptoms, health-related quality of life (HRQL), and exercise performance; the impact on all-cause mortality was also examined. Seven trials, involving a total of 1,213 participants were included. Our primary analyses showed that at 12-month follow-up, those who had received PMLR had ≥2 Canadian Cardiovascular Society class angina symptom reductions, OR 2.13 (95% CI, 1.22 to 3.73), as well as improvements in aspects of HRQL including angina frequency, SMD = 0.29 (95% CI, 0.05 to 0.52), disease perception, SMD = 0.37 (95% CI, 0.14 to 0.61), and physical limitations, SMD = 0.29 (95% CI, 0.05 to 0.53). PMLR had no significant impact on all-cause mortality. Our secondary analyses, in which we considered data from one trial that featured a higher-dose laser group, yielded no significant overall impact of PMLR across outcomes. While PMLR may be effective for improving angina symptoms and related burden, further work is needed to clarify appropriate dose and impact on disease-specific mortality and adverse cardiac events.

A study to assess changes in myocardial perfusion after treatment with spinal cord stimulation and percutaneous myocardial laser revascularisation; data from a randomised trial

Background

Spinal cord stimulation (SCS) and percutaneous myocardial laser revascularisation (PMR) are treatment modalities used to treat refractory angina pectoris, with the major aim of such treatment being the relief of disabling symptoms. This study compared the change in myocardial perfusion following SCS and PMR treatment.

Methods

Subjects with Canadian Cardiovascular Society class 3/4 angina and reversible perfusion defects as assessed by single-photon emission computed tomographic myocardial perfusion scintigraphy were randomised to SCS (34) or PMR (34). 28 subjects in each group underwent repeat myocardial perfusion imaging 12 months post intervention. Visual scoring of perfusion images was performed using a 20-segment model and a scale of 0 to 4.

Results

The mean (standard deviation) baseline summed rest score (SRS) and stress scores (SSS) were 4.6 (5.7) and 13.6 (9.0) in the PMR group and 6.1 (7.4) and 16.8 (11.6) in the SCS group. At 12 months, SRS was 5.5 (6.0) and SSS 15.3 (11.3) in the PMR group and 6.9 (8.2) and 15.1 (10.9) in the SCS group. There was no significant difference between the two treatment groups adjusted for baseline (p = 1.0 for SRS, p = 0.29 for SSS).

Conclusion

There was no significant difference in myocardial perfusion one year post treatment with SCS or PMR.

Influence of transmyocardial laser revascularization (TMLR) on regional cardiac function and metabolism in an isolated hemoperfused working pig heart

The mechanism of an indirect revascularization in ischemic myocardium by transmyocardial laser revascularization (TMLR) is not yet fully understood. An improvement of clinical symptoms caused by TMLR is reported in many clinical trials with patients in which a direct revascularization is not possible. An increase of myocardial perfusion through laser channels is doubtful, because the myocardial pressure in the wall is higher than in the cavum. Therefore we measured the local cardiac function (intramyocardial pressure, wall thickness, pressure-length curves) and acute metabolic changes (tissue lactate content, tissue pO2) in ischemic and nonischemic regions before and after TMLR in isolated hemoperfused pig hearts. An isolated heart was chosen because it enabled us to separate coronary flow from flow through ventricular channels. The ischemia was induced by coronary occlusion or microembolization (eight hearts each). It should be noted that microembolization leads to conditions which are more comparable with those found in patients selected for TMLR. In the isolated working heart, the coronary perfusion can be controlled independently from perfusion through the ventricular cavum. Under the ischemic conditions mentioned above, we observed that the intramyocardial pressure in the ischemic region decreased below the left ventricular pressure, so one premise for indirect perfusion was met. TMLR after microembolization led to a significant improvement of regional cardiac work and the tissue oxygen pressure. These acute effects demonstrate the possibility of functional and metabolic amelioration by TMLR after ischemia induced by microembolization in an isolated hemoperfused pig heart.

Effect of transmyocardial laser revascularization on myocardial perfusion and left ventricular remodeling after myocardial infarction in rats

PURPOSE

To monitor perfusion changes in remote myocardium caused by transmyocardial laser revascularization (TMLR) and to investigate the influence of TMLR on left ventricular morphology and function.

MATERIALS AND METHODS

The coronary arteries were ligated in 32 Wistar rats. Eight weeks later, cine magnetic resonance (MR) imaging was performed in both the treatment (n = 12) and control group (n = 8). TMLR was then performed in the remote myocardium in the treated group. Twelve weeks after myocardial infarction, cine MR imaging, including dobutamine-induced (10 micro g per kilogram of body weight per minute via the tail vein) stress, was repeated and followed with hemodynamic measurements in both groups and with perfusion MR imaging (in-plane resolution, 140 x 140 micro m) of the isolated heart at rest and during nitroglycerin-induced stress in the TMLR group (n = 10).

RESULTS

Left ventricular dilatation and hypertrophy were enhanced in the TMLR group (change in end-diastolic volume at 8-12 weeks: control group, 24.6 micro L +/- 16.7 and TMLR group, 81.7 micro L +/- 15.7; change in left ventricular mass: control group, 54.5 mg +/- 19.2 and TMLR group, 124.1 mg +/- 30.7; P <.03 for both). Ejection fractions at rest were approximately equal (control group, 40% +/- 2; TMLR group, 38% +/- 2; P value not significant), but during dobutamine-induced stress, the ejection fraction was higher in the TMLR group (54.4% +/- 4.9; control group, 47.4% +/- 4.8; P <.05). TMLR-treated areas were better perfused than was untreated myocardium (difference in perfusion: TMLR-treated vs control region, 3.89 mL/min/g +/- 0.83 at rest vs 2.29 mL/min/g +/- 1.06 during nitroglycerin-induced stress; P <.05 for both). Hemodynamic measurements revealed no differences between groups.

CONCLUSION

High-spatial-resolution perfusion MR imaging depicted a significant perfusion improvement after TMLR. Post-myocardial infarction remodeling of the left ventricle was found to be enhanced.

Alternatives to traditional coronary bypass surgery

Over 1 million percutaneous coronary interventions (PCI) and a half million surgical coronary artery bypass grafting procedures (CABG) are performed in the United States annually for treatment of coronary artery disease. With recent advances in anti-restenosis strategies, the number of PCIs is expected to increase dramatically. Still, these therapies treat relatively discrete coronary lesions. However, there is a relatively large number of patients for whom traditional therapies are not optimal, either because there are diffuse coronary artery lesions, because there are chronic total occlusions, or because, in the instance of bypass surgery, creating proximal or distal anastomoses is problematic. We review three strategies in various stages of development aimed at treating patients not optimally served by traditional forms of revascularization: transmyocardial laser revascularization, angiogenic therapies, and direct ventricle-to-coronary artery bypass.

Quantitative analysis of myocardial perfusion changes with transmyocardial laser revascularization

Transmyocardial laser revascularization (TLR) is a technique of creating left ventricular transmural channels in patients with refractory angina. We aimed to measure perfusion changes quantitatively using technetium-99m methoxyisobutyl isonitrile. Perfusion scans were performed on 94 TLRs and in 94 control patients at rest and during exercise at assessment, and 3-, 6-, and 12-month follow-up. A serial set of scans allowed direct comparison of each patient over all visits. Bull's-eyes were divided into 5 anatomic regions and a 20-region model. Severity values were calculated for rest, stress, and each cardiac region using a threshold of 1 for analysis. Higher scores indicated greater severity of ischemia and lower perfusion. At 3-month follow-up, the severity was significantly worse during TLR than in control patients both during stress (0.172 +/- 0.003 and 0.161 +/- 0.003, respectively, p = 0.007) and at rest (0.170 +/- 0.003 and 0.158 +/- 0.003, respectively, p = 0.002). At 6 months, severity during stress was 0.176 +/- 0.003 with TLR and 0.162 +/- 0.003 in controls (p = 0.001), with no significant difference at rest. At 12 months, there was no significant difference between TLR and control groups at stress and rest. Regional severity deteriorates during TLR compared with control patients anteriorly (p = 0.001, p = 0.0016, p = 0.005 at 3, 6, and 12 months), apically (p = 0.005, p = 0.0046, p = 0.032, respectively), and laterally (p <0.0001, p = 0.001, p = 0.002, respectively). An apparent improvement is observed in the inferoseptal region at 6- and 12-month follow-up-an area not lasered. Thus, TLR appears to produce deterioration in resting myocardial perfusion in lasered regions, and improvement in nonlasered regions, with no difference in exercise-induced myocardial ischemia compared with that in control patients.