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Objective There is a traditional assumption that to maximize stroke volume, the point beneath which the left ventricle (LV) is at its maximum diameter (P_max.LV) should be compressed. Thus, we aimed to derive and validate rules to estimate P_max.LV using anteroposterior chest radiography (chest_AP), which is performed for critically ill patients urgently needing determination of their personalized P_max.LV. Methods A retrospective, cross-sectional study was performed with non-cardiac arrest adults who underwent chest_AP within 1 hour of computed tomography (derivation:validation = 3:2). On chest_AP, we defined cardiac diameter (CD), distance from right cardiac border to midline (RB), and cardiac height (CH) from the carina to the uppermost point of left hemi-diaphragm. Setting point zero (0, 0) at the midpoint of the xiphisternal joint and designating leftward and upward directions as positive on x-and y-axes, we located P_max.LV (x_max.LV, y_max.LV). The coefficients of the following mathematically inferred rules were sought: x_max.LV = α0*CD-RB; y_max.LV = β0*CH+γ0 (α0: mean of [x_max.LV+RB]/CD; β0, γ0: representative coefficient and constant of linear regression model, respectively). Results Among 360 cases (52.0 ± 18.3 years, 102 females), we derived: x_max.LV = 0.643*CD-RB and y_max.LV = 55-0.390*CH. This estimated P_max.LV (19 ± 11 mm) was as close as the averaged P_max.LV (19 ± 11 mm, P = 0.13) and closer than the three equidistant points representing the current guidelines (67± 13, 56± 10, and 77± 17 mm; all P < 0.001) to the reference identified on computed tomography. Thus, our findings were validated. Conclusion Personalized P_max.LV can be estimated using chest_AP. Further studies with actual cardiac arrest victims are needed to verify the safety and effectiveness of the rule.

Objectives: The optimum chest compression site (P_optimum) in children is debated: European Resuscitation Council recommends one finger breadth above the xiphisternal joint, whereas American Heart Association proposes the lower sternal half. Using a coordinate system imposed on CT, we aimed to determine the pediatric P_optimum to maximize stroke volume, the key point for successful cardiopulmonary resuscitation, while minimizing hepatic injury. Design: Retrospective, cross-sectional study. Setting: University hospital. Patients: Children 1–15 years old who underwent chest CT. Interventions: None. Measurements and Main Results: We defined zero point (0, 0) as the center of the xiphisternal joint designating leftward and upward directions of the patients as positive on each axis. P_optimum (x_max. left ventricle, y_max. left ventricle) was defined as the center of the maximum diameter of the left ventricle, whereas P_aorta (x_aorta, y_aorta) as that of the aortic annulus. To compress the left ventricle exclusively, y_max. left ventricle should range above the y coordinate of hepatic dome (y_liver_dome) and below y_aorta. Data were presented as median (interquartile range) and compared among age groups 1.0–5.0, 5.1–10.0, and 10.1–15.0 years using Kruskal-Wallis test. For universal application regardless of age, y coordinates were converted into relative ones with unit of sternal top: 1 unit of sternal top was the y coordinate of the sternal top. A total of 163 patients were enrolled, median age 8.8 year (4.2–14.3 yr). Among age groups, no significant difference was observed in y_max. left ventricle, relative y_max. left ventricle, y_aorta, and y_liver_dome: 1.0 cm (0.1–1.9 cm), 0.10 unit of sternal top (0.01–0.18 unit of sternal top), 0.39 unit of sternal top (0.30–0.47 unit of sternal top), and –0.14 unit of sternal top (–0.25 to –0.03 unit of sternal top), respectively. The probability to compress the left ventricle exclusively was greater than or equal to 96% when placing hand at 0.05–0.20 unit of sternal top. Subgroup analysis demonstrated the following regression equation: x_max. left ventricle (mm) = 0.173 × (height in cm) + 13 (n = 106; p < 0.001; R 2 = 0.278). Conclusions: Theoretically, pediatric P_optimum is located 1 cm (or 0.1 unit of sternal top) above the xiphisternal joint.