Transmural Scar Tissue Research Articles

Lesion formation following pulsed field ablation for pulmonary vein and posterior wall isolation.

Pulsed field ablation (PFA) results in unique lesion formation, but there is lack of in-vivo validation in terms of scar formation following atrial fibrillation (AF) ablation. We aimed to access atrial lesion formation based on late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) following PFA for pulmonary vein (PV) and posterior wall isolation (PWI). AF ablation was performed in 10 patients using a 31mm pentaspline PFA catheter. After pulmonary vein isolation (PVI; n=8 PFA-applications/ PV; n=4 in basket and n=4 in flower configuration), another eight applications in flower configuration were conducted for concomitant PWI. Patients underwent LGE CMR 3 months after ablation aiming for quantification of left atrial (LA) scar. Acute procedural success was achieved in all patients. Mean procedure duration was 62±7min. and mean LA dwell time of the PFA catheter was 13±2min. Mean post ablation total LA scar burden was 8.1±2.1% and mean scar width was 12.8±2.1mm. At the posterior LA, 22.6±2.2% of the anatomical segment resulted in chronic scar tissue, concentrated at the PW. Postablation CMR found no evidence for PV stenosis or collateral damage of adjacent structures. At 7 months of follow-up, 9/10 patients (90%) were free from arrhythmia recurrence. PFA for AF resulted in durable and transmural atrial scar tissue at the PVs and PW. LGE CMR found a very homogeneous and contiguous lesion pattern with no signs for collateral damage.

F18-FDG Cardiac PET/CT: An alternative tool for myocardial viability determination prior to coronary revascularization decision in severe ventricular dysfunction

Purposes: The aim of the present study was to evaluate clinical value and accuracy of Fludeoxyglucose Cardiac Positron Emission Tomography Computerized Tomography (FDG C-PET/CT) as an alternative tool for myocardial viability determination prior to coronary revascularization decision in lower left ventricular ejection fraction (LVEF) patients. We accepted lower LVEF as 35% or less for the study. FDG C-PET/CT is reported to be the gold standart for myocardial viability detection among other techniques such as thallium-201 rest-redistribution scintigraphy myocardial perfusion imaging and dobutamine stress echocardiography.
 Materials and Methods: Between the dates of 01.01.2010 and 10.07.2019, 191 consecutive patients (mean age 64±9.1 years) underwent CABG operations with severe LVEF dysfunction with 35% or less. These impaired LVEF patients were calculated as the 4.4% total CABG cases. Myocardial viability was also studied and elaborated by F18-FDG C-PET/CT for all cases. Elaboration was detailed as viable myocardial tissue, hibernated myocardial tissue or necrosis areas (scars, nonviable tissue) via segmentally images of the heart. Final surgical decision was primarily depended on F18-FDG C-PET/CT for the majority of cases.
 Results: 191 CABG operations were performed. Perioperative deaths occured in 18 (9.4%) cases. Mortality reasons were prolonged CPB in 4 (2%) cases, severe and unmanageable ventricular arrhytmias in 5 (2.6%) cases, MOD with prolonged intubation in 6 (3.1%) cases and major neurological complication in 2 (1%) cases. Our mean coronary graft number was 3.5±0.8. LIMA was used in the majority of cases (n=176, 92.1%). LIMA was anastomosed to LAD for each case. IABP insertions were applied in 81(42.4%, 43 cases intraoperatively, 38 cases at ICU) patients. 236 patients with impaired LVEF and severe coronary artery disease were evaluated by F18-FDG C-PET/CT prior to operation. 191 cases (80.9%) were accepted as canditates for revascularization with multiple viable segments.45 cases (19.1%) presented transmural scar tissue (non-viable) images by FDG uptake analysis. This group cases were considered to be with non-beneficial results from revascularization. Thus, these patients were referred to medical treatments. Mean number of viable segments on F18-FDG C-PET/CT were calculated as 5.2±1.4 for each patient.
 Conclusions: The presence of myocardial viability is crucial to define reasonable canditates for revascularization in cases with lower LVEF. Among other preoperative viability detection techniques such as dobutamin echocardiography and myocardial perfusion scintigraphies, F18 FDG cardiac PET/CT is accepted as the ‘Gold Standart’ for segmental analysis on basis of distinguishing scar tissue from viable components. We strongly advocate F18-FDG cardiac PET/CT to be a suitable and effective tool to evaluate CABG indications in severe ventricular dysfunction.

Left Ventricular Lead Position Guided by Parametric Strain Echocardiography Improves Response to Cardiac Resynchronization Therapy

There is still a significant proportion of patients with heart failure who fail to improve after cardiac resynchronization therapy (CRT). The investigators used parametric two-dimensional speckle-tracking echocardiography with polar plots of the amplitude and timing of left ventricular (LV) longitudinal strain to guide implantation of the LV lead, with the aim of increasing CRT response. Sixty-four patients who underwent LV lead implantation guided by two-dimensional speckle-tracking echocardiography (study group) and 64 patients treated with standard CRT implantation (control group) were retrospectively analyzed in this study. A positive response to CRT was defined as a reduction of ≥15% in LV end-systolic volume 6 months after implantation. Parametric two-dimensional speckle-tracking echocardiographic evaluation was associated with myocardial end-diastolic wall thickness assessment for recognition of nonviable or irreversibly damaged myocardial tissue. Compared with the control group, the number of responders increased in the study group (75% vs 48%, P=.002) and in the subgroups of nonischemic (85% vs 59%, P=.022) and ischemic (65% vs 38%, P=.032) patients. The magnitude of echocardiographic LV response also increased in the overall study group and subgroups. In the ischemic patients, the size of transmural scar area correlated with LV reverse remodeling (r=0.693, P<.001). Echocardiography-guided LV lead implantation on the basis of parametric polar plots of LV longitudinalmyocardial strain increases both the number of responders and the magnitude of echocardiographic response to CRT. In ischemic patients, size of transmural scar tissue negatively affects CRT response, even when LV lead position is optimized.

Association of mean platelet volume with presence of non-viable myocardium in ischaemic cardiomyopathy.

Parameters derived from complete blood count, such as mean platelet volume (MPV), neutrophil-to-lymphocyte ratio (NLR), and platelet-to-lymphocyte ratio (PLR), have recently been proposed as measures of inflammation in addition to C-reactive protein (CRP), a classical inflammatory marker. Significant association of these parameters with atherosclerosis and complications have increasingly been reported. The aim of the study is to evaluate the relationship between these parameters and the presence of myocardial viability assessed with positron emission tomography (PET) in patients with ischaemic cardiomyopathy (ICM). A total of 122 ICM patients who had undergone PET were enrolled in this study. The patients were dichotomised depending on the presence of transmural scar. Group 1 consisted of 21 patients who had transmural scar tissue only, who were accepted as the group having non-viable myocardium. Group 2 consisted of 101 patients who had hibernation and/or non-transmural scar, who were accepted as the group having viable myocardium. Haematological parameters within 30 days of PET imaging were retrospectively analysed. There were no significant differences between the two groups regarding values of white blood cell, neutrophil, lymphocyte, platelet, haemoglobin, red cell distribution width, CRP, PLR, and NLR. Patients with non-viable myocardium have significantly higher levels of MPV (p = 0.002). In multiple logistic regression analysis, MPV (odds ratio [OR] = 0.373, 95% confidence interval [CI] 0.20-0.69, p = 0.002), was identified as an independent predictor of non-viable myocardium. In receiver-operator characteristic (ROC) analysis, a cut-point of 8.19 identified patients with non-viable myocardium (area under curve: 0.72, 95% CI 0.60-0.84). An MPV value greater than 8.19 demonstrated a sensitivity of 76% and a specificity of 55%. \ CONCLUSIONS: The present study showed that MPV is an inexpensive, clinical, and routinely measurable parameter that is associated with the presence of viable myocardium in ICM.

Scar tissue–guided left ventricular lead placement for cardiac resynchronization therapy in patients with ischemic cardiomyopathy: An acute pressure-volume loop study

Response to cardiac resynchronization therapy (CRT) is hampered by the extent and location of left ventricular (LV) scar tissue. It is commonly advised to avoid scar tissue while placing the LV lead. However, whether individual patients benefit from this strategy remains unclear. Thirty-two CRT candidates with ischemic cardiomyopathy were enrolled from 2 successive clinical trials (TBS and E-pot study). Magnetic resonance imaging with late contrast enhancement was performed to assess location, degree and transmurality of LV scar tissue. Patients underwent invasive pressure-volume loop measurements to assess acute LV pump function changes during pacing at posterolateral (PL) and anterolateral LV sites. In the study population (26 [81%] men, ejection fraction [EF] 22% ± 8%, QRS 149 ± 20 milliseconds), baseline mean stroke work (SW) and dP/dtmax were 4.4 ± 2.2 L∙mmHg and 849 ± 212 mmHg/s, respectively. The extent of scar tissue was inversely related to the acute increase in SW during pacing (R = -0.53, P = .002). Stimulating PL scar tissue resulted in deterioration of pump function (∆SW -17% ± 17%, P = .018), whereas pacing PL viable tissue led to an increase in pump function (∆SW +62% ± 51%, P < .001). Switching from pacing at the location of scar tissue, irrespective of the scar location, to viable tissue showed a significant increase in SW (-8% ± 20% vs +20 ± 40, P = .004). The extent of LV scar tissue is inversely related to acute pump function improvement during CRT. Pacing at the location of (transmural) scar tissue at any site of the LV will generally deteriorate LV pump function. Placing the LV lead over viable myocardium significantly improves pump function as compared with pacing at the location of scar tissue in patients with ischemic cardiomyopathy.

Prevalence of Regional Myocardial Thinning and Relationship With Myocardial Scarring in Patients With Coronary Artery Disease

Regional left ventricular (LV) wall thinning is believed to represent chronic transmural myocardial infarction and scar tissue. However, recent case reports using delayed-enhancement cardiovascular magnetic resonance (CMR) imaging raise the possibility that thinning may occur with little or no scarring. To evaluate patients with regional myocardial wall thinning and to determine scar burden and potential for functional improvement. Investigator-initiated, prospective, 3-center study conducted from August 2000 through January 2008 in 3 parts to determine (1) in patients with known coronary artery disease (CAD) undergoing CMR viability assessment, the prevalence of regional wall thinning (end-diastolic wall thickness ≤5.5 mm), (2) in patients with thinning, the presence and extent of scar burden, and (3) in patients with thinning undergoing coronary revascularization, any changes in myocardial morphology and contractility. Scar burden in thinned regions assessed using delayed-enhancement CMR and changes in myocardial morphology and function assessed using cine-CMR after revascularization. Of 1055 consecutive patients with CAD screened, 201 (19% [95% CI, 17% to 21%]) had regional wall thinning. Wall thinning spanned a mean of 34% (95% CI, 32% to 37% [SD, 15%]) of LV surface area. Within these regions, the extent of scarring was 72% (95% CI, 69% to 76% [SD, 25%]); however, 18% (95% CI, 13% to 24%) of thinned regions had limited scar burden (≤50% of total extent). Among patients with thinning undergoing revascularization and follow-up cine-CMR (n = 42), scar extent within the thinned region was inversely related to regional (r = -0.72, P < .001) and global (r = -0.53, P < .001) contractile improvement. End-diastolic wall thickness in thinned regions with limited scar burden increased from 4.4 mm (95% CI, 4.1 to 4.7) to 7.5 mm (95% CI, 6.9 to 8.1) after revascularization (P < .001), resulting in resolution of wall thinning. On multivariable analysis, scar extent had the strongest association with contractile improvement (slope coefficient, -0.03 [95% CI, -0.04 to -0.02]; P < .001) and reversal of thinning (slope coefficient, -0.05 [95% CI, -0.06 to -0.04]; P < .001). Among patients with CAD referred for CMR and found to have regional wall thinning, limited scar burden was present in 18% and was associated with improved contractility and resolution of wall thinning after revascularization. These findings, which are not consistent with common assumptions, warrant further investigation.

Role of dyssynchrony in optimization of CRT implantation: a time to re-think?

Optimizing the treatment strategy and patient selection have been the challenging areas for cardiac resynchronization therapy (CRT) since the introduction of the therapy in the beginning of the Millennium. To optimize the treatment strategy, it is commonly related to the implantation of the left ventricular (LV) lead—its location with respect to the anatomical location of the LV, the presence of transmural scar tissue in the pacing site, its relationship with respect to the mechanical delay, and also the number of LV pacing sites. To achieve this task, there are two prerequisites that need to be fulfilled—the use of an appropriate imaging technology that allows the identification of the potentially optimal LV lead location and the use of a right implantation strategy that permits the secure placement of the LV lead in the target location. Factors that may affect the efficacy of LV pacing may include the presence of transmural scar tissue and the degree of the mechanical contractile delay at the location where the LV lead is placed. To assess the transmurality of LV scar tissue, cardiac MRI with delay enhancement is currently the preferred imaging of choice. It has been observed that patients who had a transmural scar at the postero-lateral wall in which the LV lead was placed would have a significantly a lower response rate than those …

Pacing transmural scar tissue reduces left ventricle reverse remodeling after cardiac resynchronization therapy

BackgroundIn patients with ischemic heart failure undergoing cardiac resynchronization therapy (CRT) the underlying myocardial substrate at the left ventricle (LV) pacing site may affect CRT response. However, the effect of delivering the pacing stimulus remote, adjacent to or over LV transmural scar tissue (TST) identified by echocardiography is still unknown. MethodsFirst, 35 patients with healed myocardial infarction (57±11 years) were prospectically studied to demonstrate the capability of echocardiographic end-diastolic wall thickness (EDWT) to identify LV-TST as defined by delayed enhancement magnetic resonance imaging (DE-MRI). Subsequently, in 136 patients (65±10 years) who underwent CRT, EDWT was retrospectively evaluated at baseline. The LV catheter placement was defined over, adjacent to and remote from TST if pacing was delivered at a scarred segment, at a site 1 segment adjacent to or remote from scarred segments. CRT response was defined as LV end-systolic volume (ESV) decrease by at least 10% after 6months. ResultsA EDWT≤5mm identified TST at DE-MRI with 92% sensitivity and 96% specificity. In the 76 CRT responders, less overall and posterolateral TST segments and more segments paced remote from TST areas were found. At the multivariate regression analysis, the number of TST segments and scar/pacing relationship showed a significant association with CRT response. ConclusionsIn addition to LV global scar burden, CRT response relates also to the myocardial substrate underlying pacing site as evaluated by standard echocardiography. This information may expand the role of echocardiography to guide pacing site avoiding pacing at TST areas.

Transmurality of scar influences the effect of a hybrid-intervention with autologous bone marrow cell injection and aortocoronary bypass surgery (MNC/CABG) in patients after myocardial infarction

BackgroundCell therapy (CTx) is a strategy to support cardiac regeneration after myocardial infarction (MI). Thus far, clinical studies provided mixed results. Here, we investigated whether transmurality of the infarct may play a relevant role. Methods18 patients (63±3years, 15 male) undergoing elective coronary artery bypass graft (CABG) surgery 2.2±0.7months post MI participated. 10 had transmural and 8 non-transmural infarct scars assessed by Tc-99m-MIBI Single-Photon Emission Computed Tomography (SPECT) and F18-FDG-Positron-Emission-Tomography (PET). During surgery, 10ml of sternal bone marrow were obtained, mononuclear cells (MNC) were isolated. At the end of surgery MNC were injected into the infarctions' center and border zones (10 injections, 2ml total, 6.6±1.3×107 MNC). ResultsNo major complications attributable to cell therapy were observed. The sizes of non-transmural scars were reduced at 3 and 24months after treatment (7.7±1.1% and 5.5±1.8 vs. 17.5±4.9%, P=0.05 and P=0.04), while transmural scars remained unchanged (23.5±2.6% and 23.8±3.2 vs. 23.5±2.6%, P>0.99 and P=0.95). A trend towards improved LVEF was seen in patients with non-transmural scars (MRI: 48.8±5.1% vs. 30.6±8.7%, P=0.3; SPECT: 54.1±3.1 vs. 41.0±4.0, P=0.086), but not in patients with transmural scars (MRI: 36.7±3.9 vs. 34.3±5.0, P=0.63, SPECT: 37.8±3.1 vs. 37.9±2.3%, P=0.96). ConclusionsA single hybrid intervention of MNC recovery, purification and injection with CABG-surgery (MNC/CABG) may be an attractive modality for cell therapy. However, no regeneration of avital transmural scar tissue seems to occur, while the contribution of MNC to improved perfusion in non-transmural myocardial infarct scars remains to be determined.

Cardiac resynchronization therapy; evaluation by advanced imaging techniques

Cardiac resynchronization therapy; evaluation by advanced imaging techniques

Validation of Echocardiographic Two-Dimensional Speckle Tracking Longitudinal Strain Imaging for Viability Assessment in Patients With Chronic Ischemic Left Ventricular Dysfunction and Comparison With Contrast-Enhanced Magnetic Resonance Imaging

The purpose of the present study was to compare longitudinal strain assessed by two-dimensional speckle tracking with scar tissue on contrast-enhanced magnetic resonance imaging (MRI) in patients with chronic ischemic left ventricular (LV) dysfunction. The aim was also to define a cutoff value for regional strain to discriminate between viable myocardium and transmural scar. Ninety patients with chronic ischemic LV dysfunction underwent transthoracic echocardiography to measure global and segmental (regional) longitudinal LV strain using two-dimensional speckle tracking and cine MRI followed by contrast-enhanced MRI to assess segmental LV function and the segmental/global (transmural) extent of scar tissue. The optimal cutoff value for regional strain to discriminate between segments with viable myocardium and segments with transmural scar was also determined. A good correlation was found between global LV strain and the global extent of scar tissue on contrast-enhanced MRI (R = 0.62, p <0.001). The mean segmental strain in segments without scar tissue was -10.4% +/- 5.2% compared with 0.6% +/- 4.9% in segments with transmural scar tissue (p <0.001). A strain value of -4.5% discriminated between segments with viable myocardium and segments with transmural scar tissue on contrast-enhanced MRI with a sensitivity of 81.2% and specificity of 81.6%. In conclusion, global and regional longitudinal strain measured with two-dimensional speckle tracking is associated with the global and regional (transmural) extent of scar tissue on contrast-enhanced MRI. A cutoff value of -4.5% for regional strain discriminated between segments with viable myocardium and those with transmural scar tissue on contrast-enhanced MRI with a sensitivity of 81.2% and specificity of 81.6%.

Agreement and disagreement between contrast-enhanced magnetic resonance imaging and nuclear imaging for assessment of myocardial viability

The purpose of this study was to compare contrast-enhanced MRI and nuclear imaging with (99m)Tc-tetrofosmin and (18)F-fluorodeoxyglucose ((18)F-FDG) single photon emission computed tomography (SPECT) for assessment of myocardial viability. Included in the study were 60 patients with severe ischaemic left ventricular (LV) dysfunction who underwent contrast-enhanced MRI, (99m)Tc-tetrofosmin and (18)F-FDG SPECT. Myocardial segments were assigned a wall motion score from 0 (normokinesia) to 4 (dyskinesia) and a scar score from 0 (no scar) to 4 (76-100% transmural extent). Furthermore, (99m)Tc-tetrofosmin and (18)F-FDG segmental tracer uptake was categorized from 0 (tracer activity >75%) to 3 (tracer activity <25%). Dysfunctional segments were classified into viability patterns on SPECT: normal perfusion/(18)F-FDG uptake, perfusion/(18)F-FDG mismatch, and mild or severe perfusion/(18)F-FDG match. Minimal scar tissue was observed on contrast-enhanced MRI (scar score 0.4+/-0.8) in segments with normal perfusion/(18)F-FDG uptake, whereas extensive scar tissue (scar score 3.1+/-1.0) was noted in segments with severe perfusion/(18)F-FDG match (p < 0.001). High agreement (91%) for viability assessment between contrast-enhanced MRI and nuclear imaging was observed in segments without scar tissue on contrast-enhanced MRI as well as in segments with transmural scar tissue (83%). Of interest, disagreement was observed in segments with subendocardial scar tissue on contrast-enhanced MRI. Agreement between contrast-enhanced MRI and nuclear imaging for assessment of viability was high in segments without scar tissue and in segments with transmural scar tissue on contrast-enhanced MRI. However, evident disagreement was observed in segments with subendocardial scar tissue on contrast-enhanced MRI, illustrating that the nonenhanced epicardial rim can contain either normal or ischaemically jeopardized myocardium.

Abstract 4192: Unrecognized Myocardial Infarctions are Common in Cardiac Asymptomatic Subjects at High Vascular Risk

Unrecognized myocardial infarction (UMI), generally assessed by the presence of a Q-wave on the electrocardiogram, is commonly found. Furthermore, mortality associated with UMI appears to be similar as for recognized myocardial infarction. With delayed enhancement cardiac MRI (DE-CMR) both Q-wave and non-Q wave infarctions can be identified. The aim of this study was to investigate the prevalence and determinants of UMI in high risk subjects without symptomatic coronary artery disease using DE-CMR. A DE-CMR was performed in 502 subjects with clinically manifest non-coronary atherosclerotic disease or marked risk factors for atherosclerosis. As all subjects had no known history of coronary artery disease, subendocardial and transmural scar tissue on DE-CMR was considered an UMI. In all subjects information on atherosclerotic risk factors was collected. Multivariable logistic regression was used to study the relation of risk factors with UMI. DE-CMR was of sufficient image quality in 480 (95.6%) subjects. Interobserver agreement was excellent (weighted kappa = 95%). An UMI was present in 45 (9.4%) of all subjects, and in 38 (13.1%) of 291 men and in 7 (3.7%) of 189 women. The risk of UMI increased from 6.0% (95%CI 2.2 – 9.8%) in those with two risk factors up to 26.2% (95%CI 15.2 – 37.3%) in those with 4 or 5 risk factors (male gender, age above mean of 53 years, ever smoking, history of stroke, and history of aneurysm of the abdominal aorta (AAA)). In multivariable analysis the risk of UMI was related to male gender (OR 2.6 (95%CI 1.1– 6.3)), age (OR 1.0 (95%CI 1.0 –1.1) per year), ever smoking (OR 3.1 (95%CI 1.0 –9.0), history of stroke (OR 2.1 (95%CI 1.0 – 4.4)) and history of AAA (OR 2.3 (95%CI 0.9 –5.9)). In high risk cardiac asymptomatic subjects UMI is common. The risk of UMI increases with increasing presence of risk factors.

Quantitation of Myocardial Borderzone Using Reconstructive 3-D Echocardiography After Chronic Infarction in Rats—Incremental Value of Low-Dose Dobutamine

Myocardial remodeling determines the degree of left ventricular dysfunction and mortality after transmural chronic myocardial infarction (CMI). Noninvasive characterization and quantitation of myocardial borderzone and collagenous scar are therefore parameters of clinical interest. The aims of this study were (i) to measure accuracy of reconstructive 3-D echocardiography (3DE) in scar and myocardial borderzone size assessment and (ii) to investigate the incremental value of low-dose dobutamine stress. 3DE was performed in 14 immunodeficient rats (rnu-rnu, 180–200 g) with anterior CMI 25 d after coronary ligation. Briefly, consecutive parallel short-axis cineloops were obtained electrocardiogram-gated starting from base to the apex. Morphology (mass, surface) and function (contractility, contractile reserve) of different compartments were assessed and correlated with 3-D histomorphometry. Histology was done using picrosirius red for collagen staining. 3DE left ventricular mass correlated closely with histomorphometry (y = 0.89x + 155, p < 0.0001, r = 0.80). Hypo- and akinetic myocardial surface correlated well with borderzone myocardium (y = 0.34x + 17, p = 0.009, r = 0.62) and collagenous scar (y = 1.9x + 4.4, p < 0.0001, r = 0.79), respectively. Extent of abnormal wall motion was closely related to borderzone and scar tissue area (y = 0.82x + 7, p < 0.0001, r = 0.77). 3DE quantitation of borderzone myocardium, but not collagenous scar, was more closely correlated to histomorphometry during inotropic stimulation. Global contractile reserve is positively associated with the size of myocardial borderzone. Regional contractile reserve of borderzone myocardium is not negatively associated with its collagen content. 3DE allows precise quantitation of myocardial borderzone and identification of transmural scar tissue noninvasively. Assessment of contractile reserve improves characterization and estimation of myocardial borderzone after CMI. (E-mail: ghanem@uni-bonn.de)

Impact of viability and scar tissue on response to cardiac resynchronization therapy in ischaemic heart failure patients

At present, 20-30% of patients do not respond to cardiac resynchronization therapy (CRT). In this study, the relation between the extent of viable myocardium and scar tissue vs. response to CRT was evaluated. In addition, the presence of scar tissue in the left ventricular (LV) lead position was specifically related to response to CRT. A total of 51 consecutive patients with ischaemic heart failure and substantial LV dyssynchrony undergoing CRT were included. All patients underwent gated SPECT before CRT implantation to determine the extent of scar tissue and viable myocardium. Clinical and echocardiographic parameters were assessed at baseline and after 6 months of CRT. The results demonstrated direct relations between the response to CRT and the extent of viable myocardium and scar tissue. In addition, the 15 patients (29%) with transmural scar tissue (< 50% tracer activity) in the region of the LV pacing lead showed no improvement after 6 months of CRT. The extent of scar tissue and viable myocardium were directly related to the response to CRT. Furthermore, scar tissue in the LV pacing lead region may prohibit response to CRT. Evaluation for viability and scar tissue may be considered in the selection process for CRT.

Effect of Posterolateral Scar Tissue on Clinical and Echocardiographic Improvement After Cardiac Resynchronization Therapy

Currently, one third of patients treated with cardiac resynchronization therapy (CRT) do not respond. Nonresponse to CRT may be explained by the presence of scar tissue in the posterolateral left ventricular (LV) segments, which may result in ineffective LV pacing and inadequate LV resynchronization. In the present study, the relationship between transmural posterolateral scar tissue and response to CRT was evaluated. Forty consecutive patients with end-stage heart failure (NYHA class III/IV), LV ejection fraction < or =35%, QRS duration >120 ms, left bundle-branch block, and chronic coronary artery disease were included. The localization and transmurality of scar tissue were evaluated with contrast-enhanced MRI. Next, LV dyssynchrony was assessed at baseline and immediately after implantation with tissue Doppler imaging. Clinical parameters, LV volumes, and LV ejection fraction were assessed at baseline and at a 6-month follow-up. Fourteen patients (35%) had a transmural (>50% of LV wall thickness) posterolateral scar. In contrast to patients without posterolateral scar tissue, these patients showed a low response rate (14% versus 81%; P<0.05) and did not show improvement in clinical or echocardiographic parameters. In addition, LV dyssynchrony remained unchanged after CRT implantation (84+/-46 versus 78+/-41 ms; P=NS). Patients without posterolateral scar tissue and severe baseline dyssynchrony (> or =65 ms) showed an excellent response rate of 95% compared with patients with a posterolateral scar and/or absent LV dyssynchrony (11%). CRT does not reduce LV dyssynchrony in patients with transmural scar tissue in the posterolateral LV segments, resulting in clinical and echocardiographic nonresponse to CRT.

Subendocardial and intramural temperature response during radiofrequency catheter ablation in chronic myocardial infarction and normal myocardium.

The ability of radiofrequency energy to extend across scar tissue is unknown. We investigated the effects of radiofrequency catheter ablation on intramural temperature in experimental chronic myocardial infarction. Myocardial infarction was induced in eight dogs by a transcatheter coronary artery occlusion-reperfusion technique. The dogs were reanesthetized after 15 to 24 days. Four additional dogs served as controls. The freshly excised preparations were cut and placed in a saline bath at 37 degrees C. Temperature-guided energy applications with a preselected catheter tip temperature of 80 degrees C were performed for 60 seconds with a 7F ablation catheter. Thermoelements were inserted into the ventricular muscle at depths of 2.5 to 3.0 mm ("subendocardial") and 5.5 to 6.0 mm ("intramural"). Surviving muscle fibers were interspersed among the transmural scar tissue. The maximal temperatures did not differ significantly between normal hearts and chronic infarctions at the subendocardial (64.5+/-6.4 degrees C versus 66.7+/-6.6 degrees C) or intramural thermo-element (51.9+/-5.7 degrees C versus 52.3+/-5.7 degrees C). The myocardial temperature rise was slow, and steady-state temperatures had not been reached after 60 seconds. The intramural temperatures in chronic infarctions measured 49.0+/-4.3 degrees C after 40 seconds of energy delivery and were still below the critical tissue temperature of 50 degrees C that is necessary to induce permanent myocardial damage. Temperature-guided radiofrequency ablation in a dog model of chronic myocardial infarction may induce tissue temperatures >50 degrees C at a depth of 5.5 to 6.0 mm. The intramural temperature rise was slow, indicating that long energy applications might be necessary if the arrhythmogenic substrate is subepicardial.

901-59 Right Coronary Artery Obstruction After Radiofrequency Current Application at Right Atrial Myocardium in Young Pigs

Anatomical sequelae after creation of right atrial myocardial lesions by radiofrequency current (RFC) application have not been studied in detail in young subjects. During general anesthesia, a steerable 6 French electrode catheter, equipped with a thermistor at the 4 mm tip electrode, was positioned at the lateral atrial aspect of the tricuspid valve anulus in 10 piglets (german landrace, age 6 weeks, mean body weight 12.5 kg). RFC (500 kHz) was delivered temperature-guided (75 °C) over 30 sec. Right atrial RFC lesions were studied macroscopically and microscopically in 5 animals after 48 hours, the remaining 5 animals were examined after 6 months. After 48 hours, RFC lesions presented as transmural grey-white coagulation necrosis. Lesions were sharply demarcated by a lymphocytic wall. Lymphocytic infiltration around the lesions extended to the right coronary artery in 4/5 animals and to right ventricular myocardium in 3/5 piglets. After 6 months, lesions consisted of transmural white scar tissue extending to the right ventricular myocardium in 2/5 animals. Layers of the right coronary artery were affected in 4/5 pigs. In 2 animals, the lumen of the right coronary artery was obstructed due to intimal thickening by 25 and 40%, respectively. Results should be taken into account when radiofrequency current application at the atrial aspect of the tricuspid valve anulus is considered in infants and small children.