PV Loop & Coarctation Study

Arterial elastance (Ea) is measured by the pressure volume (PV) loop catheter in the left ventricle. The PV loop catheter measures pressure and volume simultaneously during the entire cardiac cycle. Arterial elastance is a measure of ventricular afterload and will be calculated using previously described formula;

Ea (arterial elastance): Ea = Pend systole/ SV

(where P, is pressure at end systole, and SV is stroke volume).

Elastance will be reported as a continuous variable in mmHg/mL with a higher number indicating an increase in elastance and a negative number indicating a decrease in elastance. Change in elastance before and after stent placement will be compared using paired T test.

The end systolic pressure volume relationship (ESPVR) summarizes ventricular systolic function and is measured as a slope of End systolic ventricular elastance (Ees) and volume-axis intercept Vo such that ESP = Ees (ESV-Vo) (ESP = end-systolic pressure, ESV = end-systolic volume, Vo represents the unstressed volume, which is the volume required to fill the ventricle before pressure rises). Shifts of the ESPVR occur with changes in ventricular contractility such that increases in contractility are associated with upward/leftward shifts of the ESPVR. ESPVR is obtained by analysing the data and PV loops obtained by PV loop catheter in the left ventricle before and after intervention. It will be depicted as a continuous variable in mmHg/ml as well as graphically as a slope. Changes before and after intervention will be compared as shifts in ESPVR.

Stroke work (SW) is a continuous variable that measures the work done by the left ventricle in ejecting blood in one cardiac cycle. It is the area under one loop and is measured in mmHg.ml. SW is obtained by analysing the data and PV loops obtained by PV loop catheter in the left ventricle before and after intervention. SW before and after intervention will be compared as continuous variables using appropriate statistical tests.

VA coupling is calculated by the ratio of effective arterial elastance (Ea), a measure of afterload, to LV endsystolic elastance (Ees), a relatively load independent measure of LV chamber performance. Both these measures are expressed in mmHg/ml and as continuous variables. Normal determined Ea and Ees values in resting subjects are 2.2 ± 0.8 mmHg/ml and 2.3 ± 1.0 mmHg/ml, respectively. When Ea/Ees ratio is approximately equal to 1.0, LV and arterial system are optimally coupled to produce stroke work, a measure of the efficiency of LV work, corresponding to the product of systolic arterial pressure and stroke volume, and related to oxygen consumption. When Ea/Ees ratio is <1.0, the stroke work remains close to optimal values, but when EA/EES ratio is >1.0, the stroke work significantly falls, and the LV becomes progressively less efficient. We will compare VA coupling before and after intervention and will be analyzed as continuous variables with appropriate statistical tests.