Comparison of endocardial electromechanical mapping with radionuclide perfusion imaging to assess myocardial viability and severity of myocardial ischemia in angina pectoris

Coronary Guidewires in Temporary Cardiac Pacing and Assessment of Myocardial Viability: Current Perspectives and Future Directions

Intracoronary guidewires used in percutaneous coronary intervention can also be configured to provide temporary ventricular pacing. Trans coronary electrophysiological parameters recorded by employing coronary guidewires may have a potential role in assessing myocardial viability and could provide a means to make an immediate on-table decision about revascularisation. To date, some small studies have demonstrated the safety of this technique in temporary cardiac pacing, but further research is required to refine this approach and establish its clinical utility in myocardial viability assessment. In this review we discuss the potential role of trans coronary electrophysiology in the assessment of myocardial viability.

Contact-force monitoring increases accuracy of right ventricular voltage mapping avoiding “false scar” detection in patients with no evidence of structural heart disease

Purpose

Electroanatomical mapping (EAM) could increase cardiac magnetic resonance imaging (CMR) sensitivity in detecting ventricular scar. Possible bias may be scar over-estimation due to inadequate tissue contact. Aim of the study is to evaluate contact-force monitoring influence during EAM, in patients with idiopathic right ventricular arrhythmias.

Methods

20 pts (13 M; 43 ± 12 y) with idiopathic right ventricular outflow tract (RVOT) arrhythmias and no structural abnormalities were submitted to Smarttouch catheter Carto3 EAM. Native maps included points collected without considering contact-force. EAM scar was defined as area ≥1 cm² including at least 3 adjacent points with signal amplitude (bipolar <0.5 mV, unipolar 3,5 mV), surrounded by low-voltage border zone. EAM were re-evaluated offline, removing points collected with contact force <5 g. Finally, contact force-corrected maps were compared to the native ones.

Results

An EAM was created for each patient (345 ± 85 points). After removing poor contact points, a mean of 149 ± 60 points was collected. The percentage of false scar, collected during contact force blinded mapping compared to total volume, was 6.0 ± 5.2% for bipolar scar and 7.1 ± 5.9% for unipolar scar, respectively. No EAM scar was present after poor contact points removal. Right ventricular areas analysis revealed a greater number of points with contact force < 5 g acquired in free wall, where reduced mean bipolar and unipolar voltage were recorded.

Conclusions

To date this is the first work conducted on structurally normal hearts in which contact-force significantly increases EAM accuracy, avoiding “false scar” related to non-adequate contact between catheter and tissue.

Comparison of NOGA endocardial mapping and cardiac magnetic resonance imaging for determining infarct size and infarct transmurality for intramyocardial injection therapy using experimental data

Objectives

We compared the accuracy of NOGA endocardial mapping for delineating transmural and non-transmural infarction to the results of cardiac magnetic resonance imaging (cMRI) with late gadolinium enhancement (LE) for guiding intramyocardial reparative substance delivery using data from experimental myocardial infarction studies.

Methods

Sixty domestic pigs underwent diagnostic NOGA endocardial mapping and cMRI-LE 60 days after induction of closed-chest reperfused myocardial infarction. The infarct size was determined by LE of cMRI and by delineation of the infarct core on the unipolar voltage polar map. The sizes of the transmural and non-transmural infarctions were calculated from the cMRI transmurality map using signal intensity (SI) cut-offs of>75% and>25% and from NOGA bipolar maps using bipolar voltage cut-off values of <0.8 mV and <1.9 mV. Linear regression analysis and Bland-Altman plots were used to determine correlations and systematic differences between the two images. The overlapping ratios of the transmural and non-transmural infarcted areas were calculated.

Results

Infarct size as determined by 2D NOGA unipolar voltage polar mapping correlated with the 3D cMRI-LE findings (r = 0.504, p<0.001) with a mean difference of 2.82% in the left ventricular (LV) surface between the two images. Polar maps of transmural cMRI and bipolar maps of NOGA showed significant association for determining of the extent of transmural infarction (r = 0.727, p<0.001, overlap ratio of 81.6±11.1%) and non-transmural infarction (r = 0.555, p<0.001, overlap ratio of 70.6±18.5%). NOGA overestimated the transmural scar size (6.81% of the LV surface) but slightly underestimated the size of the non-transmural infarction (−3.04% of the LV surface).

Conclusions

By combining unipolar and bipolar voltage maps, NOGA endocardial mapping is useful for accurate delineation of the targeted zone for intramyocardial therapy and is comparable to cMRI-LE. This may be useful in patients with contraindications for cMRI who require targeted intramyocardial regenerative therapy.

A randomized study of transendocardial injection of autologous bone marrow mononuclear cells and cell function analysis in ischemic heart failure (FOCUS-HF)

BACKGROUND

Autologous bone marrow mononuclear cell (ABMMNC) therapy has shown promise in patients with heart failure (HF). Cell function analysis may be important in interpreting trial results.

METHODS

In this prospective study, we evaluated the safety and efficacy of the transendocardial delivery of ABMMNCs in no-option patients with chronic HF. Efficacy was assessed by maximal myocardial oxygen consumption, single photon emission computed tomography, 2-dimensional echocardiography, and quality-of-life assessment (Minnesota Living with Heart Failure and Short Form 36). We also characterized patients' bone marrow cells by flow cytometry, colony-forming unit, and proliferative assays.

RESULTS

Cell-treated (n = 20) and control patients (n = 10) were similar at baseline. The procedure was safe; adverse events were similar in both groups. Canadian Cardiovascular Society angina score improved significantly (P = .001) in cell-treated patients, but function was not affected. Quality-of-life scores improved significantly at 6 months (P = .009 Minnesota Living with Heart Failure and P = .002 physical component of Short Form 36) over baseline in cell-treated but not control patients. Single photon emission computed tomography data suggested a trend toward improved perfusion in cell-treated patients. The proportion of fixed defects significantly increased in control (P = .02) but not in treated patients (P = .16). Function of patients' bone marrow mononuclear cells was severely impaired. Stratifying cell results by age showed that younger patients (≤60 years) had significantly more mesenchymal progenitor cells (colony-forming unit fibroblasts) than patients >60 years (20.16 ± 14.6 vs 10.92 ± 7.8, P = .04). Furthermore, cell-treated younger patients had significantly improved maximal myocardial oxygen consumption (15 ± 5.8, 18.6 ± 2.7, and 17 ± 3.7 mL/kg per minute at baseline, 3 months, and 6 months, respectively) compared with similarly aged control patients (14.3 ± 2.5, 13.7 ± 3.7, and 14.6 ± 4.7 mL/kg per minute, P = .04).

CONCLUSIONS

ABMMNC therapy is safe and improves symptoms, quality of life, and possibly perfusion in patients with chronic HF.

Human hepatocyte growth factor (VM202) gene therapy via transendocardial injection in a pig model of chronic myocardial ischemia

BACKGROUND

Hepatocyte growth factor (HGF) may stimulate angiogenesis. We examined the safety and therapeutic potential of the HGF plasmid (VM202) in pigs with chronic myocardial ischemia.

METHODS AND RESULTS

We delivered VM202 or vehicle transendocardially to 4 groups of pigs: vehicle control (n = 9); high-dose VM202 (n = 9); low-dose VM202 (n = 3); and normal control (no ischemia; n = 1). Pigs were killed 3, 30, and 60 days after injection. No adverse events were associated with VM202 treatment or delivery. Quantitative polymerase chain reaction indicated that heart injection sites had the highest levels of VM202 (day 3), which became almost undetectable by 30-60 days. Most nontarget tissues showed clearance of VM202 plasmid by day 30. Control and VM202-treated pigs did not differ in global functional data. Dobutamine-stressed myocardial-contrast echocardiogram suggested that VM202 may help preserve microvascular perfusion at 30 days; reperfusion velocity in ischemic myocardium decreased significantly in control (baseline to follow-up, 5.1 ± 1.9 to 2.7 ± 1.0; P = .031) but not in VM202 groups (high-dose: 3.1 ± 1.1 vs 3.1 ± 1.5 [P = .511]; low-dose: 3.8 ± 1.1 vs 3.9 ± 1.5 [P = .559]). Linear local shortening increased significantly from day 0 to 30 in VM202-treated versus control pigs (5.0 ± 4.7% vs 9.2 ± 7.5% vs 0.9 ± 5.8% [high-dose, low-dose, control, respectively]; P = .021).

CONCLUSIONS

Transendocardial delivery of VM202 was safe and may help to preserve microcirculatory perfusion and improve wall motion.

Prognostic validation of an algorithm to convert myocardial perfusion SPECT imaging data from a 12-segment model to a 17-segment model

BACKGROUND

A 17-segment model has become the standard for interpreting myocardial perfusion single-photon emission computed tomography (SPECT). Methods for converting pre-existing databases from 12-segment models to the 17-segment model are needed for ongoing prognostic studies.

METHODS AND RESULTS

To develop the conversion algorithm, 150 consecutive SPECT studies (82 abnormal) were read by both a 12-segment and the standard 17-segment models. Summed stress scores (SSSs) were calculated from a 17-segment model derived from the 12-segment data and compared to those of the standard 17-segment model. The effect of the conversion algorithm on prognostic data derived from the 12-segment model was evaluated in 25,876 patients from the Duke Nuclear Cardiology Database, including a sample of 3,205 patients with known covariates for adjusted analysis. The derived 17-segment SSS from the 12-segment model was highly correlated (R = 0.99) to the SSS from the standard 17-segment model. In both unadjusted and adjusted analysis, there was no difference in the prognostic information.

CONCLUSIONS

An algorithm for conversion of 12-segment perfusion scores to 17-segment scores has been developed which is highly correlated to visual interpretation by the 17-segment model with nearly identical prognostic information.

Catheter-based stem cell and gene therapy for refractory myocardial ischemia

Intramyocardial delivery of genes and cells derived from bone marrow has been evaluated in several small studies of 'no-option' symptomatic patients with chronic ischemic coronary artery disease. Clinical experience with intramyocardial gene delivery is limited to genes encoding isoforms of vascular endothelial cell growth factor. In the largest study (Euroinject One), 80 patients were randomized to receive a plasmid encoding vascular endothelial cell growth factor 165 or placebo. The results of this study suggested no beneficial therapeutic effect of this strategy. The experience with stem cells is limited to use of autologous, nonexpanded, nonmanipulated bone-marrow-derived cells; thus, the number of injected stem cells reflects their natural proportion within the bone marrow. The results of these preliminary studies suggest this approach is feasible and has a high safety profile. Although no conclusion can yet be made regarding efficacy, the improved myocardial perfusion in all four studies described in this Review is encouraging. Data from assessments of individual patients, however, suggests a wide variability in response, underscoring the need for further bench and clinical investigations.

Safety and feasibility of transendocardial autologous bone marrow cell transplantation in patients with advanced heart disease

The present report contains the final results of a Phase I study that evaluated the feasibility, safety, and potential efficacy of intramyocardial injection of autologous bone marrow (BM) in "no-option" patients with refractory angina and myocardial ischemia. Twenty-seven patients underwent electromechanic mapping-guided transendomyocardial injections (n = 12, 0.2 ml each) of unfractionated autologous BM cells directed to ischemic, noninfarcted myocardial territory. Patients were injected with 28 +/- 27 x 10(6)/ml nucleated cells containing 2.2 +/- 1.4% CD34+ cells. The autologous BM injection procedure was successful in all patients and was associated with no adverse events. At 3 months, the Canadian Cardiovascular Society angina score (3.2 +/- 0.5 vs 2.0 +/- 0.91, p = 0.001) and treadmill exercise duration (418 +/- 136 vs 489 +/- 142 seconds, p = 0.017) had improved significantly. The stress-induced ischemia score within the injected territories (118 segments) had also improved (2.2 +/- 0.8 vs 1.7 +/- 1.1, p < 0.001). At 1 year, the clinical improvement was sustained, although 5 patients had undergone revascularization procedures. The number of total injected nucleated cells (CD45+), progenitor cells (CD34+), and the magnitude of secreted vascular endothelial growth factor and macrophage chemoattractant protein-1 by cultured BM cells failed to predict the clinical response. In conclusion, the 3- and 12-month study results have indicated the safety of catheter-based transendocardial delivery of autologous BM cells in patients with advanced symptomatic ischemic heart disease and may suggest sustained potential efficacy. The cellular and humeral characteristics of autologous BM cells did not predict the clinical response, underscoring the advisability of additional mechanistic exploration.

Correlation between endocardial voltage mapping and myocardial perfusion: implications for the assessment of myocardial ischemia

BACKGROUND

Recent clinical studies using a non-fluoroscopic three-dimensional (3D) left ventricular (LV) mapping system suggested reduced endocardial voltage amplitudes measured in zones sustaining myocardial ischemia or infarction. However, the direct relationship between myocardial perfusion and endomyocardial voltage amplitudes has not been fully elucidated.

METHODS

In a pig model of chronic myocardial ischemia (n = 20), LV endocardial unipolar voltage (UpV) mapping was performed using the Biosense 3D navigation system (Johnson and Johnson, Warren, New Jersey, USA) 4 weeks after ameroid constrictor placement around the left circumflex coronary artery. Echocardiography was used to assess regional changes in myocardial wall thickening (MT) and fluorescent microspheres (4 x 10/injection) were used to quantify rest regional myocardial blood flow (MBF) in ischemic (left circumflex) and remote non-ischemic (left anterior descending) regions.

RESULTS

UpV measurements were reduced in ischemic compared to non-ischemic zones (9.9+/-3.3 compared with 13.3+/-3.3 mV, P = 0.03). This corresponded to changes in endocardial MBF and MT, which were both noted to be significantly reduced in the ischemic compared to the non-ischemic area (MBF, 0.50+/-0.16 compared with 0.74+/-0.15 ml/g per min, P = 0.001; MT, 26.1+/-12.0 compared with 37.4+/-10.1%, P=0.003). A positive linear correlation was found between UpV at rest and endomyocardial (but not epicardial) perfusion: UpV (mV) = 7.8+5.9xMBFendocardial (r = 0.32, P = 0.05).

CONCLUSIONS

Chronic myocardial ischemia, resulting in reduced perfusion and function at rest (that is, hibernating myocardium), is characterized by a significant reduction ( approximately 25%) in endocardial UpV potentials, which correlates with reduced endomyocardial blood flow and tissue perfusion at rest.

Electromechanical mapping identifies improvement in function and retention of contractile reserve after revascularization in ischemic cardiomyopathy

BACKGROUND

We hypothesized that (1) a significant proportion of ischemic dysfunctional segments that do not improve function will demonstrate postrevascularization contractile reserve and (2) electromechanical mapping (EMM) can identify segments that improve function as well as those with postrevascularization contractile reserve, a potential indicator of delayed functional improvement.

METHODS AND RESULTS

Eighteen patients with severe ischemic left ventricular dysfunction underwent EMM and dobutamine (D) cardiac magnetic resonance imaging (CMR) followed by revascularization. Four months after revascularization, all patients underwent a repeated D-CMR, and at 35 months, a subgroup (n=6) underwent a third CMR. Of 120 dysfunctional segments, 60 segments had improved rest function (IRF) and 60 did not. Twenty-eight of 60 segments (47%) that did not improve RF demonstrated postrevascularization contractile reserve (CR), and 32 of 60 segments (53%) that demonstrated neither IRF nor CR were persistently dysfunctional (PD). CR segments recovered significantly greater late function compared with IRF or PD: 14+/-12% vs 2+/-5% and 4+/-7%, respectively; P<0.05. EMM ratio, defined as the unipolar voltage divided by linear shortening, was significantly higher in IRF segments compared with segments that did not improve RF: 2.4+/-4.5 vs 0.7+/-3.5, P<0.05. Unipolar voltage was stepwise lower in normal, IRF, CR, and PD segments (10.5+/-4.7, 9.3+/-3.9, 8.8+/-3.2, and 7.4+/-2.3 mV, respectively; P<0.01 for trend).

CONCLUSIONS

Almost half of dysfunctional myocardial segments in chronic ischemic heart disease that do not improve RF early after revascularization demonstrate early CR and delayed functional recovery. EMM parameters can identify segments that improve RF and retain CR early after revascularization.

Myocardial gene and cell delivery

Although we now have the tools to introduce vectors and stem cells into specific myocardial locations, these devices are yet to be matched by comparable advances in molecular virology, cell biology, and our understanding of the pathophysiology of ischaemic heart disease

Electromechanical mapping for detecting myocardial viability and ischemia in patients with severe ischemic cardiomyopathy

This study was designed to evaluate several electromechanical mapping parameters for assessment of myocardial viability and inducible ischemia as defined by dipyridamole single-photon emission computed tomographic (SPECT) imaging at rest in patients with severe ischemic cardiomyopathy. Unipolar voltage, normalized unipolar voltage, bipolar voltage, and fragmentation were compared with tracer uptake at rest and reversibility on stress or rest quantitative technetium-99m sestamibi SPECT imaging in 32 patients with severe ischemic cardiomyopathy (left ventricular ejection fraction 0.24 +/- 0.08). In dysfunctional myocardial segments, logistic regression showed unipolar voltage, normalized unipolar voltage, and bipolar voltage to be predictive of viable myocardium (> or = 60% tracer uptake at rest) and was significantly higher in viable than in nonviable segments (p <0.01). A unipolar voltage of > or = 7.1 mV was the best predictor of viable myocardium. In dysfunctional viable segments, unipolar voltage was significantly higher in reversible than in fixed segments (p <0.001), and a unipolar voltage of > or = 8.5 mV had optimal power for identifying reversibility on dipyridamole SPECT imaging. We conclude that in patients with severe ischemic cardiomyopathy, unipolar voltage can identify viable from nonviable myocardium and reversible from fixed viable defects as defined by dipyridamole technetium-99m sestamibi SPECT imaging.

Assessing myocardial viability and infarct transmurality with left ventricular electromechanical mapping in patients with stable coronary artery disease: validation by delayed-enhancement magnetic resonance imaging

BACKGROUND

This study was designed to define myocardial viability and establish practical cut-off values for differentiating normal myocardial tissue from subendocardial and transmural scar tissue by using electromechanical mapping (EMM). We validated our results by delayed-enhancement cardiac MRI (DE-MRI).

METHODS AND RESULTS

We prospectively studied 15 ambulatory patients with stable coronary disease who were candidates for cardiac catheterization. Within 48 hours of EMM, DE-MRI was performed. Using EMM software, we created a bull's eye precisely matched to that generated by DE-MRI. Segment by segment, we compared the MRI results to the corresponding unipolar voltage value for that same segment in the EMM bull's eye. Of 300 total segments, 275 were compared. The segments were divided into normal (n=211), subendocardial scar (n=49), and transmural scar (n=15). We found that subendocardial (6.8+/-2.9 mV) and transmural (4.6+/-1.9 mV) scar segments had significantly less unipolar voltage than normal (11.6+/-4.5 mV) segments (P<0.05 for each comparison). When normal myocardium was compared with myocardium with subendocardial scar, the threshold for differentiating between the two areas was 7.9 mV (sensitivity, 80%; specificity, 80%). Comparison of normal tissue to transmural scar yielded a threshold of 6.9 mV (sensitivity, 93%; specificity, 88%).

CONCLUSIONS

Our results demonstrate that normal myocardium can be accurately distinguished from myocardium with subendocardial or transmural infarcts on the basis of unipolar voltage values obtained through EMM. This is the first study to validate these results by using cardiac DE-MRI in humans.

Electromechanical assessment of left ventricular function following successful percutaneous coronary revascularization

Percutaneous electromechanical mapping was applied to evaluate the impact of coronary revascularization on electrical and mechanical parameters in patients with prior myocardial infarction. In 15 patients with prior (> or = 4 weeks) myocardial Q-wave infarction and regional wall motion abnormalities, left ventricular endocardial mapping was performed immediately prior to percutaneous coronary revascularization. Patients underwent repetitive mapping during 6-month follow-up angiography with good revascularization results in all patients. Mean regional unipolar electrogram (UP) amplitude of all regions remained unchanged (10.4 +/- 4.2 mV prerevascularization vs. 10.2 +/- 4.4 mV postrevascularization), whereas mean local shortening (LS) of all regions increased from 6.0% +/- 5.8% to 9.7% +/- 5.3% (P < 0.001). The percentage of electromechanical match regions (LS < 6% and UP < 9 mV) remained unchanged after revascularization (15% vs. 10%; NS), whereas the percentage of mismatch regions (LS < 6% and UP > 9 mV) declined from 38% to 10% (P < 0.0001). We conclude that electromechanical mapping allows the sensitive detection of improved mechanical function after successful revascularization. Electrical activity remains unchanged 6 months after revascularization and the number of regions with an electromechanical mismatch decrease.

Three-dimensional electromechanical mapping: imaging in the operating room of the future

BACKGROUND

Three-dimensional electromechanical mapping has previously been shown to be a clinically important tool for cardiac imaging and intervention. We hypothesized that this technology may be beneficial as an intraoperative modality for assessing cardiac hemodynamics and viability during cardiac surgery. We report here the use of this technology as an imaging modality for intraoperative cardiac surgery.

METHODS

The tip of a locatable catheter connected to an endocardial mapping and navigating system is accurately localized while simultaneously recording local electrical and mechanical functions. Thus the three-dimensional geometry of the beating cardiac chamber is reconstructed in real time. The system was tested on 6 goats that underwent acute dynamic cardiomyoplasty and on 5 dogs that underwent left anterior descending (LAD) coronary artery ligation.

RESULTS

The electromechanical mapping system provided an accurate three-dimensional reconstruction of the beating left ventricle during cardiomyoplasty. After the wrapping procedure, significant end-diastolic area reduction was noted in the base and mid parts of the heart (948 +/- 194 mm2 vs 1245 +/- 33 mm2, p = 0.021; and 779 +/- 200 mm2 vs 1011 +/- 80 mm2, p = 0.016). The area of the cross-section of the apex did not change during the operation. Acute infarcted tissue was characterized 3 days after LAD ligation by concomitant deterioration in both electrical and mechanical function.

CONCLUSIONS

By providing both a clear view of the anatomical changes that occur during cardiac surgery, and an accurate assessment of tissue viability, electroanatomic mapping may serve as an important adjunct tool for imaging and analysis of the heart during cardiac surgery