Autor:innen:
S. Pabel (Regensburg, DE)
M. Knierim (Göttingen, DE)
F. Alebrand (Göttingen, DE)
M. Paulus (Regensburg, DE)
T. Stehle (Regensburg, DE)
M. Sieme (Bochum, DE)
M. Herwig (Bochum, DE)
F. Barsch (Regensburg, DE)
T. Körtl (Regensburg, DE)
S. Ljubojevic (Graz, AT)
A. Pöppl (Regensburg, DE)
C. Schmid (Regensburg, DE)
T. Fischer (Würzburg, DE)
S. Sedej (Graz, AT)
D. Scherr (Graz, AT)
C. Brochhausen (Regensburg, DE)
G. Hasenfuß (Göttingen, DE)
L. Maier (Regensburg, DE)
N. Hamdani (Bochum, DE)
K. Streckfuß-Bömeke (Göttingen, DE)
S. Sossalla (Regensburg, DE)
Atrial fibrillation (AF) is often prevalent in patients with heart failure (HF). Recent clinical evidence showed that the arrhythmic component of AF alone could contribute to ventricular dysfunction. Remarkably, despite being a very frequent scenario in daily clinical practise, the pathophysiological consequences of non-tachycardic AF with arrhythmic excitation of the human LV, are unknown.
We investigated ventricular myocardium from patients with sinus rhythm (SR) or normofrequent AF in the absence of HF (compensated hypertrophy, mean EF>50%, matched clinical characteristics, derived from morrow resections during AVR). In histological analysis we detected no difference between SR (n=9 patients) vs. AF (n=6) regarding the amount and distribution of fibrosis. As Ca-handling is a major determinant of contractile function, we isolated human ventricular cardiomyocytes and studied cellular Ca-handling (Fura-2 AM). Interestingly, systolic Ca-transient amplitude was significantly reduced, and we found a significantly prolonged Ca-elimination time in AF patients (n=82 cells/ 8 patients) compared to SR (n=115/11). Patch-clamp experiments revealed a prolonged action potential duration in AF (n=16/6 vs 29/6).
For the standardized evaluation of the mechanisms of a persistent normofrequent arrhythmia, we simulated AF in vitro by using arrhythmic (60 bpm, 40% beat-to-beat variability) or rhythmic (60 bpm) field stimulation. For studying the cellular effects in a model suitable for chronic pacing (up to 7 days), we utilized human iPSC cardiomyocytes (iPSC-CM) from healthy donors (n=6). After 7 days, irregularly paced iPSC-CM (n=69 vs. 75 cells/6 differentiations each) exhibited a significantly reduced systolic Ca-transient amplitude, a prolonged Ca-elimination time as well as a reduced SR Ca-load compared to control. Confocal line-scans of arrhythmic paced cells (Fluo-4 AM, n=68 vs. 63 cells/7 differentiations) showed an increased diastolic SR Ca-leak, possibly underlying the reduced SR Ca-content. We further elucidated the underlying mechanisms of this distinct electrophysiological remodelling by showing that oxidative stress (H2O2, LPO) is increased in human ventricular myocardium from patients with AF (n=6 patients each), which was associated with an enhanced NOX2/-4 activity in patients with AF (n=7) compared to SR (n=6). Consecutively, Ca2+/calmodulin-dependent protein kinase II δ (CaMKII) was found to be more oxidized (CaMKII-Met281/282) in the ventricle of AF patients (n=7 each) leading to an increased CaMKII activity, which adversely regulated EC-coupling protein phosphorylation including RyR2 hyperphosphorylation.
This study demonstrates that normofrequent arrhythmia/AF impairs human ventricular EC-coupling via increased oxidative stress and CaMKII oxidation. Thus, this study provides the first translational mechanistic characterization and the potential negative impact of isolated AF in the absence of tachycardia on the human ventricle.