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Articles by S Kaab
Total Records ( 3 ) for S Kaab
  R Wakili , Y. H Yeh , X Yan Qi , M Greiser , D Chartier , K Nishida , A Maguy , L. R Villeneuve , P Boknik , N Voigt , J Krysiak , S Kaab , U Ravens , W. A Linke , G. J. M Stienen , Y Shi , J. C Tardif , U Schotten , D Dobrev and S. Nattel
  Background—

Atrial fibrillation impairs atrial contractility, inducing atrial stunning that promotes thromboembolic stroke. Action potential (AP)-prolonging drugs are reported to normalize atrial hypocontractility caused by atrial tachycardia remodeling (ATR). Here, we addressed the role of AP duration (APD) changes in ATR-induced hypocontractility.

Methods and Results—

ATR (7-day tachypacing) decreased APD (perforated patch recording) by 50%, atrial contractility (echocardiography, cardiomyocyte video edge detection), and [Ca2+]i transients. ATR AP waveforms suppressed [Ca2+]i transients and cell shortening of control cardiomyocytes; whereas control AP waveforms improved [Ca2+]i transients and cell shortening in ATR cells. However, ATR cardiomyocytes clamped with the same control AP waveform had 60% smaller [Ca2+]i transients and cell shortening than control cells. We therefore sought additional mechanisms of contractile impairment. Whole-cell voltage clamp revealed reduced ICaL; ICaL inhibition superimposed on ATR APs further suppressed [Ca2+]i transients in control cells. Confocal microscopy indicated ATR-impaired propagation of the Ca2+ release signal to the cell center in association with loss of t-tubular structures. Myofilament function studies in skinned permeabilized cardiomyocytes showed altered Ca2+ sensitivity and force redevelopment in ATR, possibly due to hypophosphorylation of myosin-binding protein C and myosin light-chain protein 2a (immunoblot). Hypophosphorylation was related to multiple phosphorylation system abnormalities where protein kinase A regulatory subunits were downregulated, whereas autophosphorylation and expression of Ca2+-calmodulin-dependent protein kinase II and protein phosphatase 1 activity were enhanced. Recovery of [Ca2+]i transients and cell shortening occurred in parallel after ATR cessation.

Conclusions—

Shortening of APD contributes to hypocontractility induced by 1-week ATR but accounts for it only partially. Additional contractility-suppressing mechanisms include ICaL current reduction, impaired subcellular Ca2+ signal transmission, and altered myofilament function associated with abnormal myosin and myosin-associated protein phosphorylation. The complex mechanistic basis of the atrial hypocontractility associated with AF argues for upstream therapeutic targeting rather than interventions directed toward specific downstream pathophysiological derangements.

  F Marroni , A Pfeufer , Y. S Aulchenko , C. S Franklin , A Isaacs , I Pichler , S. H Wild , B. A Oostra , A. F Wright , H Campbell , J. C Witteman , S Kaab , A. A Hicks , U Gyllensten , I Rudan , T Meitinger , C Pattaro , C. M van Duijn , J. F Wilson , P. P Pramstaller and on behalf of the EUROSPAN Consortium
 

Background— We set out to identify common genetic determinants of the length of the RR and QT intervals in 2325 individuals from isolated European populations.

Methods and Results— We analyzed the heart rate at rest, measured as the RR interval, and the length of the corrected QT interval for association with 318 237 single-nucleotide polymorphisms. The RR interval was associated with common variants within GPR133, a G-protein–coupled receptor (rs885389, P=3.9x10–8). The QT interval was associated with the earlier reported NOS1AP gene (rs2880058, P=2.00x10–10) and with a region on chromosome 13 (rs2478333, P=4.34x10–8), which is 100 kb from the closest known transcript LOC730174 and has previously not been associated with the length of the QT interval.

Conclusion— Our results suggested an association between the RR interval and GPR133 and confirmed an association between the QT interval and NOS1AP.

  S. C Body , C. D Collard , S. K Shernan , A. A Fox , K. Y Liu , M. D Ritchie , T. E Perry , J. D Muehlschlegel , S Aranki , B. S Donahue , M Pretorius , J. C Estrada , P. T Ellinor , C Newton Cheh , C. E Seidman , J.G Seidman , D. S Herman; , P Lichtner , T Meitinger , A Pfeufer , S Kaab , N. J Brown , D. M Roden and D. Darbar
 

Background— Atrial fibrillation (AF) is the most common adverse event following coronary artery bypass graft surgery. A recent study identified chromosome 4q25 variants associated with AF in ambulatory populations. However, their role in postoperative AF is unknown. We hypothesized that genetic variants in the 4q25 chromosomal region are independently associated with postoperative AF after coronary artery bypass graft surgery.

Methods and Results— Two prospectively collected cohorts of patients undergoing coronary artery bypass graft surgery, with or without concurrent valve surgery, at 3 US centers. From a discovery cohort of 959 patients, clinical and genomic multivariate predictors of postoperative AF were identified by genotyping 45 single-nucleotide polymorphisms (SNPs) encompassing the 4q25 locus. Three SNPs were then assessed in a separately collected validation cohort of 494 patients. After adjustment for clinical predictors of postoperative AF and multiple comparisons, rs2200733, rs13143308, and 5 other linked SNPs independently predicted postoperative AF in the discovery cohort. Additive odds ratios for the 7 associated 4q25 SNPs ranged between 1.57 and 2.17 (P=8.0x10–4 to 3.4x10–6). Association with postoperative AF were measured and replicated for rs2200733 and rs13143308 in the validation cohort.

Conclusions— In 2 independently collected cardiac surgery cohorts, noncoding SNPs within the chromosome 4q25 region are independently associated with postoperative AF after coronary artery bypass graft surgery after adjusting for clinical covariates and multiple comparisons.

 
 
 
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