Key result
Induced atrial fibrillation in coronary surgery patients was associated with lower dominant frequency (75.87 vs 89.33 Hz, p<0.05) and reduced sarcolipin expression compared to sinus rhythm.
Why the study?
Are pre-existing structural and electrical substrate changes in the right atrial myocardium associated with post-operative atrial fibrillation in AF-naïve patients undergoing coronary surgery?
Observational (n=34)
Are pre-existing structural and electrical substrate changes in the right atrial myocardium associated with post-operative atrial fibrillation in AF-naïve patients undergoing coronary surgery?
Absolute Event Rate: 75.87% vs 89.33%
p-value: p=<0.05
Pre-existing electrical and structural remodeling, including altered calcium handling protein expression, is present in the right atrium of AF-naïve patients who develop post-operative AF.
May inform mechanistic AF research in surgical cohorts; leaves open clinical relevance pending prospective validation.
BACKGROUND: Post-operative atrial fibrillation (POAF) is a major health economic burden. However, the precise mechanisms in POAF remain unclear. In other forms of AF, sites of high dominant frequency (DF) in sinus rhythm (SR) may harbour 'AF nests'. We studied AF inducibility in relation to substrate changes using epicardial electrograms and cardiomyocyte calcium handling in the atria of AF naïve patients. METHOD: Bipolar electrograms were recorded from the lateral right atrial (RA) wall in 34 patients undergoing coronary surgery using a high-density array in sinus rhythm (NSR). RA burst pacing at 200/500/1000ms cycle lengths (CL) was performed, recording episodes of AF>30s. Co-localised RA tissue was snap frozen for RNA and protein extraction. RESULTS: Electrograms prolonged during AF (76.64±29.35ms) vs. NSR/pacing (p<0.001). Compared to NSR, electrogram amplitude was reduced during AF and during pacing at 200ms CL (p<0.001). Electrogram DF was significantly lower in AF (75.87±23.63Hz) vs. NSR (89.33±25.99Hz) (p<0.05), and NSR DF higher in AF inducible patients at the site of AF initiation (p<0.05). Structurally, POAF atrial myocardium demonstrated reduced sarcolipin gene (p=0.0080) and protein (p=0.0242) expression vs. NSR. Phospholamban gene and protein expression was unchanged. SERCA2a protein expression remained unchanged, but MYH6 (p=0.0297) and SERCA2A (p=0.0343) gene expression was reduced in POAF. CONCLUSIONS: Human atrial electrograms prolong and reduce in amplitude in induced peri-operative AF vs. NSR or pacing. In those sustaining AF, high DF sites in NSR may indicate 'AF nests'. This electrical remodelling is accompanied by structural remodelling with altered expression of cardiomyocyte calcium handling detectable before POAF. These novel upstream substrate changes offer a novel mechanism and manifestation of human POAF.
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Zaman et al. (2016) conducted an observational in Post-operative atrial fibrillation (n=34). Induced atrial fibrillation vs. Normal sinus rhythm was evaluated on Electrogram dominant frequency (Hz) (p=<0.05). Induced atrial fibrillation in coronary surgery patients was associated with lower dominant frequency (75.87 vs 89.33 Hz, p<0.05) and reduced sarcolipin expression compared to sinus rhythm.
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