The Role of Left Atrial Compliance in the “Hemodynamic-Color Disconnect” in Patients Undergoing MitraClip: Results From a Single Center Registry.

Background
There is great interest in understanding left atrial (LA) hemodynamics in patients with severe mitral regurgitation (MR) undergoing MitraClip. We previously observed the phenomenon of “hemodynamic – color disconnect” (i.e. severe MR in absence of elevated LA V waves). We hypothesize these patients may have differing LA compliance (LAC) to account for their respective hemodynamic profiles. To our knowledge, LAC in patients with severe MR undergoing MitraClip therapy has not been studied to date.

Methods
We retrospectively analyzed preprocedural echocardiographic measurements and intraprocedural direct LA pressures from 95 patients enrolled in a single center registry of patients undergoing MitraClip. Direct measurement of LAC is technically difficult. Based on previously published methods, LAC was estimated by dividing the systolic rise in LA pressure into the stroke volume.

Results
All patients had 3 or 4+ symptomatic MR. The median ratio of LA V:mean LA (LAV:mLA) pressure was 1.7 (IQR 1.5 – 1.9). There were 45 patients with ratio of < 1.7 (low ratio: LR) and 50 patients with ratio ≥ 1.7 (high ratio: HR). Baseline demographics were similar between the LR and HR groups. Vena contracta, effective regurgitant orifice area and regurgitant fraction were not statistically different between groups. Additionally, indexed LA volume, heart rate, and systolic blood pressures were not statistically different between groups at the time of the procedure. However, LAC was significantly higher in the LR group vs HR (9.9 ± 7.1 vs 3.9 ± 2.9 L/mmHg, p = 0.00001).

Conclusions
The “hemodynamic-color disconnect” is commonly encountered in patients undergoing MitraClip therapy. In this single center series of patients with similar degrees of MR and loading conditions, the differences in LAV:mLA ratios can be explained by differences in left atrial compliance. Further studies are needed to evaluate the determinants of LA compliance and its impact on clinical outcomes in patients undergoing MitraClip therapy.