Myocardial Work in Septic Shock Patients

Myocardial strain analysis has emerged in the last decade as a reliable tool for studying myocardial mechanics, adding information on cardiac performance when compared with traditional parameters of left ventricle (LV) systolic function, such as ejection fraction (EF).

However, their relative load dependency makes the myocardial deformation indices unable to account for changes in pre- and afterload.

Myocardial work (MW) is emerging as an alternative tool for studying LV myocardial systolic function, because it incorporates both deformation and load into its analysis. In this context, MW could be considered as an advancement of myocardial strain, allowing to investigate LV performance also in cases of changes in afterload that could lead to misleading conclusions if relying only on strain analysis.

Conditions of increased afterload can in fact negatively impact on myocardial strain even if MWis normal. MW assessment was initially calculated using invasive pressure measurements, which limited its widespread use in clinical practice.

Recently, Russell et al. demonstrated that pressure-strain loops (PSLs) could estimate LV performance in a non-invasive manner, deriving LV pressure (LVP) curves from non-invasively acquired brachial artery cuff pressure. To date, the technique has been applied in myocardial ischaemia and in identification of cardiac resynchronization therapy (CRT)-responders with good results.

This clinical approach has been never tested, insofar, septic shock patients. The heart is one of the organs most frequently failing in sepsis; however, depending on the definition used, the prevalence of sepsis-induced cardiac dysfunction may vary between 10% and 70%. The sepsis-induced dysregulated inflammatory response has been directly linked to cardiomyocyte dysfunction, leading to a broad spectrum of cardiomyopathies, including ventricles' impairment during systole or diastole, inadequate cardiac output, oxygen delivery, or primary myocardial cellular injury.

Hence, in septic shocked patients, echocardiography plays a pivotal role, identifying most of the clinical cardiac patterns related to acute systolic dysfunction and chambers' dilation using basic level 2D and M-mode echocardiography. A more comprehensive diagnosis can be achieved with advanced levels of competency. Simultaneously, hemodynamic evaluation and monitoring are possible with advanced levels of competency, including the use of color Doppler, spectral Doppler, tissue Doppler imaging, and, eventually, 3D or speckled tracking. Specific pathways can now achieve all these steps of competence for skills certification, developed by intensive care medicine societies.

A variety of cardiac changes can be associated with septic shock, although a normal study is not unusual [7]. Abnormalities in LVEF (i.e., contractile impairment may be associated with either a global dysfunction or exhibited as specific patterns with apical akinesis and ballooning accompanied by good basal LV contraction and is almost always reversible over days), LV diastolic function, and right ventricular (RV) function have all been described. Since the resuscitation in septic shock is mainly focused on an aggressive and rapid fluid resuscitation associated with the administration of systemic vasopressors to optimize cardiac preload, output, and peripheral perfusion, the assessment of the basal cardiac function is critical and should be routinely performed at the bedside for this purpose.

The dynamic interaction between the heart and the systemic circulation allows the cardiovascular system to be efficient in providing adequate cardiac output and arterial pressures necessary for sufficient organ perfusion. The cardiovascular system provides adequate pressure and flow to the peripheral organs in different physiological and pathological conditions because of the continuous modulation of the arterial system compliance, stiffness and resistance with respect to LV systolic performance. This challenging interplay may lead to a condition called "ventriculo-arterial uncoupling", when the ration between myocardial performance and peripheral response (Ea/Ees) is unbalanced. The hemodynamic profile of septic shock is primarily characterized by generalized vasodilatation resulting in severe hypotension with systemic hypoperfusion. In most of the patients with septic shock, cardiovascular efficiency is impaired, and the Ea/Ees becomes uncoupled (Ea/Ees > 1). Th e hemodynamic profile is characterized by both the significant increase in Ea and the decrease in Ees. Because the increase in Ea is generally induced by pharmacological vasoconstriction. (norepinephrine) and the consequent increase in arterial tone, a decrease in Ees generally depends on the reduction in myocardial contractility. Whatever the underlying mechanism, when A-V uncoupling occurs in septic shock, the cardiac energetics are unfavorable and are often sacrificed to maintain tissue perfusion.

The purpose of this observational trial is to validate the use of MW in septic shock patients by means of consecutive echocardiographic assessment at predefined timepoints. Secondarily, we'll evaluate the impact of the vasoactive drugs used in septic shock patients (vasopressors and inotropes) on MW and on ventriculo-arterial coupling.