B78-15 Myocardial Strain at End-Exhalation Is Associated With Air Trapping: A Study From a Cohort at Risk for COPD Due to Prolonged Occupational Secondhand Tobacco Smoke Exposure

Rationale

Active smoking has been associated with impaired left ventricular (LV) systolic function as assessed by myocardial strain, but the myocardial consequences of exposure to secondhand tobacco smoke (SHS) in nonsmokers remain unclear.

Objective

To determine the relative contributions of pulmonary air trapping and cardiac structural remodeling to LV myocardial deformation.

Methods

We conducted an observational study of never-smoking individuals with prolonged occupational exposure to SHS and no overt cardiovascular disease. Participants underwent PFT and cardiac MRI acquired across respiratory phases with feature-tracking strain analysis performed using Circle cvi42 software. Air trapping was quantified using plethysmographically-measured ratio of residual volume-to-total lung capacity (RV/TLC). LV structural remodeling (LV mass index [LVMI]) and myocardial deformation (global circumferential strain [GCS] and global radial strain [GRS]) were measured during end-tidal exhalation (FRC) and end-tidal inspiration (FRC+TV) breath holds. Respiratory phase-specific differences were assessed using paired t-test. Associations of myocardial strain with RV/TLC and LVMI were examined using regression modeling adjusted for covariates.

Results

Ninety-nine participants were studied (69±8 years-old, 89% female, BMI=25±5 kg/m2, occupational SHS exposure=12±9 years, MAP=98±12 mmHg). In paired analyses, fractional wall thickness, a measure of relative LV wall thickening from diastole to systole, and LVMI did not differ between inhalation and exhalation, indicating stable LV structural remodeling across respiratory phases. LVEF was modestly lower during exhalation compared with inhalation (ΔLVEF=-1.9±4.6%, P < 0.01). Exhalation was associated with worse (increased) circumferential and (reduced) radial strain (ΔGCS = +0.9±1.8% and ΔGRS = −3.2±5.0%, both P < 0.01) (Table-top). In covariate-adjusted models including RV/TLC and LVMI, greater air trapping was independently associated with impaired strain during exhalation: each 1% increase in RV/TLC corresponded to a 0.1% and 0.5% worsening in GCS and GRS, respectively (Table-bottom). Higher LVMI was also associated with worse GCS (0.08% per g/m² increase) and showed a borderline association with worse GRS. When SHS exposure duration was excluded, associations with RV/TLC and LVMI were attenuated and no longer significant. Neither RV/TLC nor LVMI was independently associated with GCS and GRS at end-inhalation.

Conclusions

In never-smoking individuals with prolonged SHS exposure, pulmonary air trapping and left ventricular structural remodeling are associated with impaired short-axis myocardial deformation in a respiratory phase-dependent manner. These associations are evident during exhalation but not inhalation, suggesting that respiratory phase-specific ventricular loading conditions may unmask subclinical myocardial dysfunction. The attenuation of these associations after adjustment for SHS exposure duration highlights SHS exposure as a clinically relevant modifier of cardiopulmonary influences on myocardial strain, even in the setting of preserved LVEF.

This abstract is funded by: Flight Attendant Medical Research Institute (FAMRI)