Integrated 3D structural-functional mapping of diseased human right atria ex vivo revealed that the complex atrial microstructure caused significant differences between Endo vs. Epi activation during pacing and sustained AF driven by intramural re-entry anchored to fibrosis-insulated atrial bundles.

Rationale: Transmural dispersion of repolarization has been shown to play a role in the genesis of ventricular tachycardia and fibrillation in different animal models of heart failure (HF). Heterogeneous changes of repolarization within the midmyocardial population of ventricular cells have been considered an important contributor to the HF phenotype. However, there is limited electrophysiological data from the human heart. Objective: To study electrophysiological remodeling of transmural repolarization in the failing and nonfailing human hearts. Methods and Results: We optically mapped the action potential duration (APD) in the coronary-perfused scar-free posterior-lateral left ventricular free wall wedge preparations from failing (n‫)5؍‬ and nonfailing (n‫)5؍‬ human hearts. During slow pacing (S1S1‫0002؍‬ ms), in the nonfailing hearts we observed significant transmural APD gradient: subepicardial, midmyocardial, and subendocardial APD80 were 383؎21, 455؎20, and 494؎22 ms, respectively. In 60% of nonfailing hearts (3 of 5), we found midmyocardial islands of cells that presented a distinctly long APD (537؎40 ms) and a steep local APD gradient (27؎7 ms/mm) compared with the neighboring myocardium. HF resulted in prolongation of APD80: 477؎22 ms, 495؎29 ms, and 506؎35 ms for the subepi-, mid-, and subendocardium, respectively, while reducing transmural APD80 difference from 111؎13 to 29؎6 ms (P<0.005) and presence of any prominent local APD gradient. In HF, immunostaining revealed a significant reduction of connexin43 expression on the subepicardium. Conclusions: We present for the first time direct experimental evidence of a transmural APD gradient in the human heart. HF results in the heterogeneous prolongation of APD, which significantly reduces the transmural and local APD gradients. (Circ Res. 2010;106:981-991.)Key Words: heart failure Ⅲ repolarization Ⅲ transmural gradient Ⅲ optical mapping Ⅲ connexin43 H eart failure (HF) claims more than 200 000 lives annually in the US alone. 1,2 Approximately a half of these deaths are sudden and presumably caused by ventricular tachyarrhythmias. Pathophysiological remodeling of cardiac function occurs at multiple levels and includes the alterations in a host of ion channels, Ca 2ϩ -handling proteins, and proteins mediating cell-cell coupling, predisposing to arrhythmias and sudden death. 3 Numerous animal models have shown the importance of such electrophysiological (EP) remodeling in the mechanisms of HF-related arrhythmogenesis. 4 Prolongation of the repolarization is a hallmark of cells and tissues isolated from failing hearts independent of the cause, which has been observed in isolated myocytes 5 and intact ventricular preparations. 4,6 This fundamental change in myocyte biology underlies QT-interval prolongation of the surface ECG in patients with HF. The action potential (AP) prolongation is heterogeneous, resulting in exaggeration of the physiological heterogeneity of electric properties in the failing heart. 1,4 These cellular EP changes were linked to down...

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Background The site of origin and pattern of excitation within the human sinoatrial node (SAN) has not been directly mapped. Objective We hypothesized that the human SAN is functionally insulated from the surrounding atrial myocardium except for several exit pathways which electrically bridge the nodal tissue and atrial myocardium. Methods The SAN was optically mapped in coronary perfused preparations from non-failing human hearts (n=4, age 54±15 years) using dye Di-4-ANBDQBS and Blebbistatin. SAN 3D structure was reconstructed using histology. Results Optical recordings from the SAN had diastolic depolarization and multiple upstroke components, which corresponded to the separate excitations of the SAN and atrial layers. Excitation originated in the middle of the SAN (66±17 BPM), then slowly (1–18 cm/s) and anisotropically spread. After a 82±17 ms conduction delay within the SAN, the atrial myocardium was excited via superior, middle, and/or inferior sinoatrial conduction pathways. Atrial excitation was initiated 9.4±4.2 mm from the leading pacemaker site. The oval 14.3±1.5 × 6.7±1.6 × 1.0±0.2 mm SAN structure was functionally insulated from the atrium by connective tissue, fat, and coronary arteries, except for these pathways. Conclusion These data demonstrated for the first time the location of the leading SAN pacemaker site, the pattern of excitation within the human SAN, and the conduction pathways into the right atrium. The existence of these pathways explained why, even during normal sinus rhythm, atrial breakthroughs could arise from a region parallel to the CT that is significantly larger (26.0±7.8 mm) than the area of the anatomically defined SAN.

Abstract-Surface electrode recordings cannot delineate the activation within the human or canine sinoatrial node (SAN) because they are intramural structures. Thus, the site of origin of excitation and conduction pathway(s) within the SAN of these mammals remains unknown. Canine right atrial preparations (nϭ7) were optically mapped. The SAN 3D structure and protein expression were mapped using immunohistochemistry. SAN optical action potentials had diastolic depolarization and multiple upstroke components that corresponded to the separate excitations of the node and surface atrial layers. Pacing-induced SAN exit block eliminated atrial optical action potential components but retained SAN optical action potential components. Excitation originated in the SAN (cycle length, 557Ϯ72 ms) and slowly spread (1.2 to 14 cm/sec) within the SAN, failing to directly excite the crista terminalis and intraatrial septum. After a 49Ϯ22 ms conduction delay within the SAN, excitation reached the atrial myocardium via superior and/or inferior sinoatrial exit pathways 8.8Ϯ3.2 mm from the leading pacemaker site. The ellipsoidal 13.7Ϯ2.8/4.9Ϯ0.6 mm SAN structure was functionally insulated from the atrium. This insulation coincided with connexin43-negative regions at the borders of the node, connective tissue, and coronary arteries. During normal sinus rhythm, the canine SAN is functionally insulated from the surrounding atrial myocardium except for 2 (or more) narrow superior and inferior sinoatrial exit pathways separated by 12.8Ϯ4.1 mm. Conduction failure in these sinoatrial exit pathways leads to SAN exit block and is a modulator of heart rate. The clinical signs of SAN dysfunction include bradycardia, sinus pauses, sinus arrest, sinus exit block, and reentrant arrhythmias. 3,4 Although the syndrome may have many causes and commonly affects elderly persons, it usually is idiopathic. 5 Studies of human SAN function are complicated by the inability of epior endocardial mapping to detect the origin and slow propagation of action potentials (APs) within the SAN before it activates adjacent atrial myocardium. 6,7 Sinus rhythm (SR) is physiologically controlled by autonomic modulation of pacemaker ion channels, 8 calcium handling, 9 and shifts of the leading pacemaker site. 10 -12 Anatomic structure and electrophysiological heterogeneity play important roles in SAN excitation under various conditions. 6 Recently, we investigated activation patterns in the rabbit SAN using optical mapping, 13 which is the only available technology that allows the resolution of simultaneous changes in the activation pattern and AP morphology from multiple sites. In that study, we demonstrated that the rabbit SAN is functionally insulated from the atrial septum. 13 However, the rabbit SAN is essentially a 2D structure 14 in contrast to the 3D structure of the canine 7,15,16 and human 17,18 SANs. Bromberg et al 7 suggested that the canine SAN may be functionally insulated from the surrounding atrial myocytes, except for a limited number of exit si...

Background Excitation-contraction (EC) coupling is altered in the end-stage heart failure (HF). However, spatial heterogeneity of this remodeling has not been established at the tissue level in failing human heart. The objective is to study functional remodeling of EC coupling and calcium handling in failing and nonfailing human hearts. Methods and Results We simultaneously optically mapped action potentials (AP) and calcium transients (CaT) in coronary-perfused left ventricular wedge preparations from nonfailing (n = 6) and failing (n = 5) human hearts. Our major findings are: (1) CaT duration minus AP duration was longer at sub-endocardium in failing compared to nonfailing hearts during bradycardia (40 beats/min). (2) The transmural gradient of CaT duration was significantly smaller in failing hearts compared with nonfailing hearts at fast pacing rates (100 beats/min). (3) CaT in failing hearts had a flattened plateau at the midmyocardium; and exhibited a “two-component” slow rise at sub-endocardium in three failing hearts. (4) CaT relaxation was slower at sub-endocardium than that at sub-epicardium in both groups. Protein expression of sarcoplasmic reticulum Ca2+-ATPase 2a (SERCA2a) was lower at sub-endocardium than that at sub-epicardium in both nonfailing and failing hearts. SERCA2a protein expression at sub-endocardium was lower in hearts with ischemic cardiomyopathy compared with nonischemic cardiomyopathy. Conclusions For the first time, we present direct experimental evidence of transmural heterogeneity of EC coupling and calcium handling in human hearts. End-stage HF is associated with the heterogeneous remodeling of EC coupling and calcium handling.

These data indicate that although both autonomic systems play a role in AF, cholinergic stimulation is likely the main factor for spontaneous AF initiation in this animal model. Adrenergic tone modulates the initiation and maintenance of cholinergically mediated AF.

Background Several arrhythmogenic mechanisms have been inferred from animal heart failure (HF) models. However, the translation of these hypotheses is difficult due to lack of functional human data. We aimed to investigate the electrophysiological substrate for arrhythmia in human end-stage non-ischemic cardiomyopathy. Methods and Results We optically mapped the coronary-perfused left ventricular wedge preparations from human hearts with end-stage non-ischemic cardiomyopathy (HF, n=10) and non-failing hearts (NF, n=10). Molecular remodeling was studied with immunostaining, Western blotting, and histological analyses. HF produced heterogeneous prolongation of action potential duration (APD) resulting in the decrease of transmural APD dispersion (64±12 ms vs 129±15 ms in NF, P<0.005). In the failing hearts, transmural activation was significantly slowed from the endocardium (39±3 cm/s versus 49±2 cm/s in NF, P=0.008) to the epicardium (28±3 cm/s versus 40±2 cm/s in NF, P=0.008). Conduction slowing was likely due to Cx43 downregulation, decreased colocalization of Cx43 with N-cadherin (40±2% versus 52±5% in NF, P=0.02), and an altered distribution of phosphorylated Cx43 isoforms by the upregulation of the dephosphorylated Cx43 in both the subendocardium and subepicardium layers. Failing hearts further demonstrated spatially discordant conduction velocity alternans which resulted in nonuniform propagation discontinuities and wavebreaks conditioned by strands of increased interstitial fibrosis (fibrous tissue content in HF 16.4±7.7 versus 9.9±1.4% in NF, P=0.02). Conclusions Conduction disorder resulting from the anisotropic downregulation of Cx43 expression, the reduction of Cx43 phosphorylation, and increased fibrosis is likely to be a critical component of arrhythmogenic substrate in patients with non-ischemic cardiomyopathy.