Outflow Tract Patency and Ventricular Compression as Determinants of CPR Hemodynamics in a TEE-Guided Swine Model of Cardiac Arrest

BACKGROUND: Perioperative cardiac arrest carries high mortality. Standard landmark-guided chest compressions (CC) frequently overlie the left ventricular outflow tract (LVOT). In the operating room, transesophageal echocardiography (TEE) can guide compression location in real time. Because LVOT-centered compressions may narrow the outflow tract and reduce direct LV compression, we hypothesized that continuous intra-arrest TEE guidance to maintain mid-LV compressions would improve hemodynamics versus LVOT-centered compressions. METHODS: In a swine model, ventricular fibrillation was induced and followed by 10 min of basic life support. Continuous mid-esophageal long-axis TEE was used to randomly deliver compressions over the mid-LV (CC-LV, n=8) or the LVOT (CC-LVOT, n=5). Primary endpoint was coronary perfusion pressure (CPP). Secondary endpoints included end-tidal CO2 (EtCO2), LV and RV compression pressures (LVP, RVP), and systolic (SAoP) and diastolic (DAoP) aortic pressures. LVOT collapse was quantified with M-mode. Linear mixed-effects models were used to examine differences in hemodynamic endpoints between the CC-LV and the CC-LVOT groups after adjusting for baseline characteristics. RESULTS: During resuscitation, after accounting for baseline imbalances between groups, CC-LV generated higher CPP than CC-LVOT (difference 15.6 mmHg; 95% CI 9.8-21.5), as well as higher systolic and diastolic aortic pressures (differences 32.4 mmHg [95% CI 12.9-51.9] and 11.3 mmHg [95% CI 3.6-19.0], respectively), and higher LVP and RVP (differences 82.4 mmHg [95% CI 31.8-132.9] and 77.5 mmHg [95% CI 17.7-137.3], respectively). EtCO2 was also higher with CC-LV (difference 11.9 mmHg; 95% CI 3.0-20.7). LVOT collapse was greater with CC-LVOT (82% vs 10%). LVOT collapse correlated with lower CPP, EtCO2, and aortic pressures, while LVP correlated positively with these variables. CONCLUSIONS: Continuous TEE-guided, LV-targeted compressions preserved LVOT patency and improved intra-arrest hemodynamics. Correlations between LVOT collapse, LV compression pressures, and perfusion variables suggest that differences between LV and LVOT compressions reflect dynamic outflow tract narrowing and reduced ventricular compression.