Abstract
BackgroundOur aim was to assess how atrial fibrillation (AF) induction, chronicity, and RR interval irregularity affect left atrial (LA) function and size in the setting of underlying heart failure (HF), and to determine whether AF effects can be mitigated by vagal nerve stimulation (VNS).MethodsHF was induced by 4-weeks of rapid ventricular pacing in 24 dogs. Subsequently, AF was induced and maintained by atrial pacing at 600 bpm. Dogs were randomized into control (n = 9) and VNS (n = 15) groups. In the VNS group, atrioventricular node fat pad stimulation (310 μs, 20 Hz, 3–7 mA) was delivered continuously for 6 months. LA volume and LA strain data were calculated from bi-weekly echocardiograms.ResultsRR intervals decreased with HF in both groups (p = 0.001), and decreased further during AF in control group (p = 0.014), with a non-significant increase in the VNS group during AF. LA size increased with HF (p<0.0001), with no additional increase during AF. LA strain decreased with HF (p = 0.025) and further decreased after induction of AF (p = 0.0001). LA strain decreased less (p = 0.001) in the VNS than in the control group. Beat-by-beat analysis showed a curvilinear increase of LA strain with longer preceding RR interval, (r = 0.45, p <0.0001) with LA strain 1.1% higher (p = 0.02) in the VNS-treated animals, independent of preceding RR interval duration. The curvilinear relationship between ratio of preceding and pre-preceding RR intervals, and subsequent LA strain was weaker, (r = 0.28, p = 0.001). However, VNS-treated animals again had higher LA strain (by 2.2%, p = 0.002) independently of the ratio of preceding and pre-preceding RR intervals.ConclusionsIn the underlying presence of pacing-induced HF, AF decreased LA strain, with little impact on LA size. LA strain depends on the preceding RR interval duration.
Highlights
The left atrium (LA) has three sequential roles during the cardiac cycle
RR intervals decreased with heart failure (HF) in both groups (p = 0.001), and decreased further during atrial fibrillation (AF) in control group (p = 0.014), with a non-significant increase in the vagal nerve stimulation (VNS) group during AF
LA size increased with HF (p
Summary
The left atrium (LA) has three sequential roles during the cardiac cycle. First, it acts as a reservoir during ventricular systole, with its compliant chamber stretching to collect incoming pulmonary vein blood while the mitral valve (MV) remains closed. [2] little is known about the severity of LA dysfunction and its relevance during AF Reasons for this include uncertainty about the role RR variability during AF, as well as the lack of agreement on a parameter that adequately reflects LA function in the absence of atrial contraction. While it appears that vagal nerve stimulation (VNS) improves LA function in HF with sinus rhythm, [3] little is known about the impact of VNS in AF. Our aim was to assess how atrial fibrillation (AF) induction, chronicity, and RR interval irregularity affect left atrial (LA) function and size in the setting of underlying heart failure (HF), and to determine whether AF effects can be mitigated by vagal nerve stimulation (VNS)
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