Relationship between arterial dp/dt and left ventricular ejection fraction by modified Simpson’s method using cardiac ultrasound: An observational analytical study

Hemodynamic monitoring is one of the most important parameters in managing hemodynamically unstable patients, particularly in perioperative and ICU settings. The left ventricular ejection fraction is often taken as an indicator for left ventricular function and is a cornerstone for deciding management and interventions. The plan for management of the patient depends on the ventricular contractility, which will direct us to decide between inotropes, fluids or vasopressor administration. This is one of the most crucial steps towards the management of the patient who remains hypotensive or in failure, since fluid therapy may lead to worsening in case of decreased contractility of the left ventricle.

Studies show that peak left ventricular dp/dt (change in pressure over time) during iso-volumeteric contraction is a good indicator of ventricular contractility and performance that is not influenced by afterload, wall motion abnormalities, or the variation in ventricular anatomy and morphology. LV dp/dtmax is closely correlated to ejection fraction. However, catheterisation of the left ventricle for routine monitoring is neither feasible nor practical and can be done only in catheterisation laboratories.

Left ventricular ejection function (LVEF), is a commonly used method to determine ventricular contractility that can be measured non- invasively. There are, however, different methods to calculate LVEF using cardiac ultrasound. The standard accepted method is the modified Simpson’s method. This entails calculation of end-diastolic volume (EDV) and end-systolic volume (ESV) from the area of left ventricle using two views, thereby calculating LVEF. This measurement may not be accurate if the window is poor or the left ventricle is not visible. Further, it has limitations such as inter-observer variability, operator dependency and the inability to provide continuous real time data. Echocardiography doesn’t reflect the data continuously. It has to be repeated in order to assess the contractility of the heart.

Recent advancements in arterial waveform analysis have introduced arterial dp/dt – the maximal rate of pressure rise during systole; as a potential indicator of left ventricular contractility.4 Arterial dp/dt provides reasonably good tracking of LV contractility changes as loading and ionotropic conditions are varied. Arterial dp/dt measurement via pulse contour analysis from a peripheral arterial line, is minimally invasive. Strong correlation between arterial and LV dp/dtmax during manipulations of afterload and inotropic state was found, despite the influence of vascular tone. It can be monitored continuously and may be used as a surrogate for left ventricular contractility monitoring.

Studies have shown that arterial dp/dt mimics ventricular dp/dt, which is a good indicator of left ventricular contractility. Arterial dp/dt and end systolic elastance (Ees) correlate during various hemodynamic conditions, though arterial dp/dt has been found to be more accurate for assessing LV contractility with an adequate vascular volume.

There are only a few reported studies establishing a relationship between peripheral arterial waveform analysis, i.e., arterial dp/dt and LVEF. There is no universal equation available to calculate left ventricular ejection fraction from arterial dp/dt. This study is therefore being designed to find the relationship of dp/dt through arterial pulse contour and LVEF measured by modified Simpson’s method and to derive and validate a generalized equation to determine whether or not arterial dp/dt can be used as a surrogate for LVEF.