Predictability of O₂ consumption from contractility and mechanical energy of absolute arrhythmic beats in canine heart

Left ventricular (LV) O₂ consumption (VO₂) per minute is measurable for both regular and arrhythmic beats. LV VO₂ per beat can then be obtained as VO₂ per minute divided by heart rate per minute for regular beats, but not for arrhythmic beats. We have established that VO₂ of a regular stable beat is predictable by VO₂ = a PVA + b E_max + c, where PVA is the systolic pressure-volume area as a measure of the total mechanical energy of an individual contraction and E _max is the end-systolic maximum elastance as an index of ventricular contractility of the contraction. Furthermore, a is the O₂ cost of PVA, b is the O₂ cost of E_max, and c is the basal metabolic VO₂ per beat. We considered it theoretically reasonable to expect that the same formula could also predict LV VO₂ of individual arrhythmic beats from their respective PVA and E_max with the same a, b, and c. We therefore applied this formula to the PVA - E_max data of individual arrhythmic beats under electrically induced atrial fibrillation (AF) in six canine in situ hearts. We found that the predicted VO₂ of individual arrhythmic beats highly correlated linearly with either their VO ₂ (r = 0.96 ± 0.01) or E_max (0.97 ± 0.03) while both also highly correlated linearly with each other (0.88 ± 0.04). This suggests that the above formula may be used to predict LV VO₂ of absolute arrhythmic beats from their E_max and PVA under AF.