Does imaging-guided selection of patients with ischemic heart failure for high risk revascularization improve identification of those with the highest clinical benefit?: Myocardial imaging should not exclude patients with ischemic heart failure from coronary revascularization

Molecular In Vivo Imaging Using a Noninvasive Cardiac-Specific MLC-2v Promoter Driven Dual-Gene Recombinant Lentivirus Monitoring System

Background

Our study aimed to demonstrate the feasibility of using the sodium/iodide symporter (NIS) to monitor vascular endothelial growth factor (VEGF₁₆₅) expression in vivo.

Methods

We constructed a recombinant lentivirus plasmid with the MLC-2v promoter driving the sodium/iodide symporter (NIS) reporter gene linked to the VEGF₁₆₅ gene. Expression of NIS and VEGF gene were identified by Western blot. On days 2 and 54, ^99mTc-MIBI imaging was used to evaluate changes in myocardial ischemia. Noninvasive ¹²⁵I micro-SPECT/CT imaging was used to assess the expression of NIS reporter gene dynamically over the next 2 months.

Results

Western blot analysis showed that both NIS and VEGF₁₆₅ were highly expressed in rat cardiomyoblast H9C2 cells transduced with Lenti-MLC-2v-NIS--VEGF₁₆₅. ¹²⁵I micro-SPECT/CT reporter imaging showed higher uptake in mouse myocardium transduced with Lenti-MLC-2v-VEGF₁₆₅-IRES-NIS. NIS expression peaked on day 1 after transduction followed by a progressive decline to negligible levels by day 21. On day 1, mean ¹²⁵I activity value in group 1 was higher than that in group 2 (P<0.05). The mean ¹²⁵I activity value in group 3 was statically lower than that in group 1 and 2 (P<0.01). On day 60, ¹²⁵I uptakes in test and positive control groups became very low, and no significant differences in the mean ¹²⁵I activity values were detected between group 1 and group 2 (P = 0.531 > 0.05). In group 1 (test group), ^99mTc-MIBI SPECT/CT revealed improvements in perfusion and wall thickening in the apical anterior wall. Mean IOD values of NIS and CD₃₄ were significantly higher in group 1 than group 3 (P<0.05). Our study proved mean I-125 uptake was significantly correlated with mean IOD value of NIS and CD34 (P<0.05).

Conclusion

This study demonstrates the feasibility of using the NIS gene to monitor VEGF₁₆₅ expression in a mouse myocardial ischemia model.

Combining FDG-PET and 99mTc-SPECT to predict functional outcome after coronary artery bypass surgery

AIMS

Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) are suggested to improve clinical decision-making in ischaemic cardiomyopathy. Here, we present a unique cohort of patients who underwent nuclear medicine studies and cardiac magnetic resonance imaging (MRI) both before and 1 year after coronary artery bypass (CABG) surgery to assess benefit from surgery.

METHODS AND RESULTS

Before CABG, we applied three quantitative techniques using (18)F-fluorodeoxyglucose-PET and (99m)technetium-tetrofosmin-SPECT with a software tool to measure defects with hypoperfused but viable and non-viable myocardium in 15 patients. One method used solely PET, two others combined PET and SPECT at different thresholds. As a reference, we used change in left-ventricular (LV) function and volume by MRI. Preoperatively, ischaemic but viable areas detected by the method with a 10% threshold combining PET-SPECT and the PET-only method correlated significantly with preoperative regional wall thickening (WT; P = 0.03 and P = 0.005, respectively). When compared with global functional outcome (change in LV ejection fraction) and LV remodelling (change in end-diastolic volume) 1 year postoperatively, no correlation appeared with preoperative PET- or PET-SPECT-derived viable or non-viable tissue. Neither was any correlation observable between local change in WT and local preoperative defect size evaluated by any of these three methods.

CONCLUSION

Preoperatively, PET and PET-SPECT with 10% threshold detected dysfunctional myocardium, but all analysis methods failed to predict 1-year functional outcome assessed by MRI. In patients with three-vessel disease and heart failure, SPECT perfusion and PET viability study results show substantial heterogeneity; this should be considered when selecting patients for revascularization.

The feasibility of myocardial infarct visualization using atrial kick induced strain (AKIS) contrast

The most common mechanical measure of the heart integrates ventricular strain between end-diastole and end-systole in order to provide a measure of contraction. Here an approach is described for estimating a correlate to local passive mechanical properties. Passive strain is measured by estimating ventricular strain during atrial systole. During atrial systole the atria contract causing passive stretching in the ventricles from increased volume. This modification to traditional cardiac strain is here termed atrial kick induced strain (AKIS) imaging. AKIS imaging was evaluated in a canine ablation model of chronic infarct and a canine true chronic infarct model. AKIS images of ablation lesions were compared against acoustic radiation force impulse (ARFI) images and tissue blanching, and true chronic infarct AKIS images were compared against delayed enhanced-contrast magnetic resonance. AKIS images were made with 2-D and 3-D ultrasound data. In both studies, AKIS images and the comparison images show good qualitative agreement and good contrast and contrast-to-noise ratio.

An approach to the rational use of revascularization in heart failure patients

The most common cause of heart failure with reduced ejection fraction (HFrEF) is coronary artery disease. A multitude of factors come into play when deciding whether a patient with HFrEF and coronary artery disease should have coronary artery bypass graft (CABG) surgery, percutaneous coronary intervention, or medical therapy alone. For candidates for percutaneous coronary intervention and CABG, evidence from large registries would suggest that patients with 2-vessel coronary artery diseases and proximal left anterior descending disease and all patients with 3-vessel coronary artery disease do better with CABG. For patients that are candidates for medical therapy with or without CABG, the results of the Surgical Treatment for Ischemic Heart Failure (STICH) trial indicate that with CABG, the reduction of mortality is not statistically significant (hazard ratio [HR], 0.86; P = 0.12). However, CABG is superior in reducing cardiovascular deaths (HR, 0.81; P = 0.05), and the combination of cardiovascular deaths and cardiovascular hospitalizations (HR, 0.74; P < 0.001). Patients undergoing CABG have an upfront risk that is eliminated by 2 years and thereafter do better. The assessment of cardiac viability or reversible ischemia does not appear to be helpful in determining which individuals will improve more with CABG. Patients with severe mitral regurgitation who undergo CABG appear to benefit from simultaneous valve repair but not from the addition of surgical ventricular reconstruction of the left ventricle, although in specific patients this might be considered. The totality of evidence would thus suggest that patients with HFrEF should be evaluated for the possibility of coronary revascularization if they are candidates for CABG.

Inducible myocardial ischemia and outcomes in patients with coronary artery disease and left ventricular dysfunction

OBJECTIVES

The study objectives were to test the hypotheses that ischemia during stress testing has prognostic value and identifies those patients with coronary artery disease (CAD) with left ventricular (LV) dysfunction who derive the greatest benefit from coronary artery bypass grafting (CABG) compared with medical therapy.

BACKGROUND

The clinical significance of stress-induced ischemia in patients with CAD and moderately to severely reduced LV ejection fraction (EF) is largely unknown.

METHODS

The STICH (Surgical Treatment for IsChemic Heart Failure) trial randomized patients with CAD and EF ≤35% to CABG or medical therapy. In the current study, we assessed the outcomes of those STICH patients who underwent a radionuclide (RN) stress test or a dobutamine stress echocardiogram (DSE). A test was considered positive for ischemia by RN testing if the summed difference score (difference in tracer activity between stress and rest) was ≥4 or if ≥2 of 16 segments were ischemic during DSE. Clinical endpoints were assessed by intention to treat during a median follow-up of 56 months.

RESULTS

Of the 399 study patients (51 women, mean EF 26 ± 8%), 197 were randomized to CABG and 202 were randomized to medical therapy. Myocardial ischemia was induced during stress testing in 256 patients (64% of the study population). Patients with and without ischemia were similar in age, multivessel CAD, previous myocardial infarction, LV EF, LV volumes, and treatment allocation (all p = NS). There was no difference between patients with and without ischemia in all-cause mortality (hazard ratio: 1.08; 95% confidence interval: 0.77 to 1.50; p = 0.66), cardiovascular mortality, or all-cause mortality plus cardiovascular hospitalization. There was no interaction between ischemia and treatment for any clinical endpoint.

CONCLUSIONS

In CAD with severe LV dysfunction, inducible myocardial ischemia does not identify patients with worse prognosis or those with greater benefit from CABG over optimal medical therapy. (Comparison of Surgical and Medical Treatment for Congestive Heart Failure and Coronary Artery Disease [STICH]; NCT00023595).