Background and aim of the study. Left atrium (LA) is poorly understood in many pathological conditions and it is often considered a passive bystander of these pathophysiologic alterations. In the setting of impaired heart rate related LV response, the LA function could play a relevant role. The relevance of LA has been also recently demonstrated by studies which have evaluated its function by using new echocardiographic techniques such as two-dimensional speckle tracking evaluation (2D-STE). The aim of this study was to evaluate the relationship between changes in LV and LA function, assessed by 2D-STE, in response to the increase of heart rate (HR) in a group of patients carrying a pacemaker (PM) or an implantable cardioverter defibrillator (ICD).
Methods. We enrolled 45 patients. Among them, 38 were evaluated with LA strain. 31 patients were affected by CHF, among whom 18 with implanted cardioverter defibrillator (ICD), 13 with ICD and cardiac resynchronization therapy (ICD-CRT) and 7 without CHF who had a PM implanted. All were in clinically stable conditions for at least 30 days and in conventional medical therapy. Starting from basal values, HR was increased by 10 beats/min programming the implantable devices at higher atrial stimulation frequencies to max 90 beats/min. At each HR, echocardiography was performed and for left atrium the strain of reservoir (LAr), strain of conduit (LAcd) and contraction (LAct) were calculated (figure 1). Changes in left ventricle global longitudinal strain (LVGLS) were also calculated.
Results. The LAr shows a significant reduction from baseline at a heart rate of 90 bpm in conjunction with a significant change in the LAcd. No variation in LAct was observed at the various frequencies. Among the 38 patients, 29 showed a worsening of LVGLS and 9 no worsening with increasing heart rate. We demonstrated a close relationship between LV and LA function assessed by longitudinal strain measures (figure 2). A significant decrease in LAr was observed in patients with worsening LV-GLS that was not evident in patients with no or improvement.
Conclusions. Our study demonstrates that, in chronic HF outpatients, HR increase has different and heterogeneous effects on the LA function, assessed by STI and this response is more frequent among patients with LV systolic dysfunction. These results could be useful for guiding the optimal heart rate responsiveness of the implanted devices.