Abstract WMP66: Left Atrial Appendage Flow Velocity is Associated With Ischemic Events and Brain Infarcts in Atrial Fibrillation

Objective: Clinical predictors of ischemic stroke in the setting of atrial fibrillation (AF) have been identified, but there is limited data on predictors in the context of abnormal flow originating from the left atrial appendage. We hypothesize that reduced LAA flow velocity is associated with cerebrovascular ischemic events in patients with AF.

Methods: We investigated consecutive patients with AF evaluated for ablation. Peak flow velocities at the orifice of the left atrial appendage (LAA) were obtained by transeosphageal echocardiography (TEE) studies, and elevated velocities were defined as greater than 40 cm/sec, in line with prior studies. The primary outcome was defined as the presence of any of the following: history of stroke/transient ischemic event, or non-lacunar brain infarct on brain imaging performed before the TEE. Univariate and multivariable analyses were performed to determine the association between LAA peak flow and the primary outcome, adjusting for CHADS2Vasc score.

Results: We identified 322 patients with TEE performed. The mean age was 62.1 years and 24.5% men. Patients with LAA-flow velocity < 40 cm/sec were more likely to have the primary outcome (10.7% vs 4.3%, p=0.023). This association persisted after adjusting for CHADS2VASc (OR, 2.62; 95% CI, 1.09-6.33, p = 0.032).

Conclusion: Low velocity in the LAA is associated with cerebrovascular ischemic events in patients with AF. More studies are needed to deterine whether LAA flow velocity can help risk stratify “low risk” patients with AF.

Differentiation of Papillary Muscle From Fascicular and Mitral Annular Ventricular Arrhythmias in Patients With and Without Structural Heart Disease

Background—

Idiopathic left ventricular arrhythmias (VAs) and those caused by structural heart disease can originate from the papillary muscles, fascicles, and mitral annulus. Differentiation of these arrhythmias can be challenging because they present with a right bundle branch block morphology by electrocardiography. We sought to identify clinical, electrocardiographic, and electrophysiological features that distinguish these left VAs in patients with and without structural heart disease.

Method and Results—

Patients undergoing catheter ablation for papillary muscle, fascicular, or mitral annular VAs were studied. Demographic data and electrocardiographic and electrophysiological findings were analyzed. Fifty-two VAs in 51 patients (32 [63%] male; mean age 61±15 years) with papillary muscle (n=18), fascicular (n=15), and mitral annular (n=19) origins were studied. Patients with papillary muscle VAs were older and had higher prevalence of left ventricular dysfunction (67% versus 13% of fascicular VA patients [ P =0.009]) and coronary artery disease (78% versus 37% of mitral annular VA patients [ P =0.036]). Papillary muscle VAs were distinguished electrocardiographically from fascicular VAs by longer QRS durations and lower prevalence of r<R′ V 1 QRS morphology, and from mitral annular VAs by lower prevalence of positive precordial lead concordance. Using a stepwise electrocardiographic algorithm, the accuracy rates for the diagnosis of papillary muscle VAs, fascicular VAs, and mitral annular VAs were 83%, 87%, and 89%, respectively.

Conclusions—

Specific electrocardiographic characteristics, including QRS morphology and precordial lead morphology, can help distinguish between papillary muscle, fascicular, and mitral annular VAs.

Improved conduction and increased cell retention in healed MI using mesenchymal stem cells suspended in alginate hydrogel

INTRODUCTION

Mesenchymal stem cells (MSCs) have been associated with reduced arrhythmias; however, the mechanism of this action is unknown. In addition, limited retention and survival of MSCs can significantly reduce efficacy. We hypothesized that MSCs can improve impulse conduction and that alginate hydrogel will enhance retention of MSCs in a model of healed myocardial infarction (MI).

METHODS AND RESULTS

Four weeks after temporary occlusion of the left anterior descending artery (LAD), pigs (n = 13) underwent a sternotomy to access the infarct and then were divided into two studies. In study 1, designed to investigate impulse conduction, animals were administered, by border zone injection, 9-15 million MSCs (n = 7) or phosphate-buffered saline (PBS) (control MI, n = 5). Electrogram width measured in the border zone 2 weeks after injections was significantly decreased with MSCs (-30 ± 8 ms, p < 0.008) but not in shams (4 ± 10 ms, p = NS). Optical mapping from border zone tissue demonstrated that conduction velocity was higher in regions with MSCs (0.49 ± 0.03 m/s) compared to regions without MSCs (0.39 ± 0.03 m/s, p < 0.03). In study 2, designed to investigate MSC retention, animals were administered an equal number of MSCs suspended in either alginate (2 or 1 % w/v) or PBS (n = 6/group) by border zone injection. Greater MSC retention and survival were observed with 2% alginate compared to PBS or 1% alginate. Confocal immunofluorescence demonstrated that MSCs survive and are associated with expression of connexin-43 (Cx43) for either PBS (control), 1%, or 2% alginate.

CONCLUSIONS

For the first time, we are able to directly associate MSCs with improved impulse conduction and increased retention and survival using an alginate scaffold in a clinically relevant model of healed MI.

Optical mapping of cryoinjured rat myocardium grafted with mesenchymal stem cells

Mesenchymal stem cells (MSCs) have been shown to improve cardiac electrophysiology when administered in the setting of acute myocardial infarction. However, the electrophysiological phenotype of MSCs in situ is not clear. We hypothesize that MSCs delivered intramyocardially to cryoinjured myocardium can engraft, but will not actively generate, action potentials. Cryoinjury-induced scar was created on the left ventricular epicardial surface of adult rat hearts. Within 30 min, hearts were injected with saline (sham, n = 11) or bone marrow-derived MSCs (2 × 10(6)) labeled with 1,1'-dioctadecyl-3,3,3,3'-tetramethylindocarbocyanine percholate (DiI; n = 16). At 3 wk, optical mapping and cell isolation were used to measure optical action potentials and calcium transients, respectively. Histological analysis confirmed subepicardial scar thickness and the presence of DiI-positive cells that express connexin-43. Optical action potential amplitude within the scar at MSC-positive sites (53.8 ± 14.3%) was larger compared with sites devoid of MSCs (35.3 ± 14.2%, P < 0.05) and sites within the scar of shams (33.5 ± 6.9%, P < 0.05). Evidence of simultaneous action potential upstroke, the loss of action potential activity following ablation of adjacent viable myocardium, and no rapid calcium transient response in isolated DiI+ cells suggest that the electrophysiological influence of engrafted MSCs is electrotonic. MSCs can engraft when directly injected into a cryoinjury and are associated with evidence of action potential activity. However, our results suggest that this activity is not due to generation of action potentials, but rather passive influence coupled from neighboring viable myocardium.

Plasma lipids and lipoprotein cholesterol in undernourished diabetic subjects and adults with protein energy malnutrition

Estimation of triglycerides (Tg), total cholesterol (Tc), HDLs, LDLc, and VLDLc was carried out in 46 undernourished diabetic subjects (UND); 21 untreated and 25 on insulin; 44 well-nourished diabetic subjects (WND); 22 untreated and 22 on insulin; together with 25 patients with protein energy malnutrition (PEM) and 25 healthy controls less than 50 yr of age. Compared with controls, in the untreated diabetic subjects Tg, Tc, LDLc, and VLDLc were significantly higher in both classes, while HDLc was lower only in WND. Among the treated diabetic subjects, Tg were higher in WND, LDLc lower in UND, and VLDLc higher in both. With regard to relative distribution of cholesterol in the untreated patients, HDLc/Tc was lower in WND, but this was not so in UND. HDLc/Tc was higher in treated UND. Between undernourished and well-nourished groups of diabetic subjects in the untreated patients, HDLc was significantly higher and LDLc lower in the former. Both Tc and LDLc were lower in UND on insulin compared with WND. HDLc/Tc was higher and LDLc/Tc lower in both untreated and treated UND. In adults with PEM, mean values of Tg, Tc, and LDLc were much lower than in controls, as well as in both groups of UND. On the other hand, values of HDLc/Tc were higher and LDLc/Tc lower in PEM compared with controls, but this was not so for treated UND. It is evident from the results of this study that the undernourished have lower levels of plasma lipids and a favorable distribution of cholesterol among the lipid fractions from the point of view of vulnerability to development of atherosclerosis.

Blocking by histones of accessibility to DNA in chromatin: addition of histones

The blocking effect of histones on accessibility of DNA to DNase has been studied by addition of various histones to chromatin in intact or histone-depleted thymus nuclei (those from which all lysine-rich histone was removed and those from which much of the arginine-rich histone was removed) and to deoxyribonucleoprotein (chromatin) extracted from nuclei. In each case lysine-rich histone, weight for weight, blocks accessibility more effectively than does arginine-rich histone. Fractions of the arginine-rich histone differ considerably from each other in their blocking efficacy. Phosphorylation of lysine-rich histone tempers its blocking effectiveness.