Right Heart Failure in Pediatric Pulmonary Hypertension
hassan esmaeili M.D,Assistant professor of Gorgan University of medicine
PH is an important cause of morbidity and mortality in pediatric patients of diverse causes.
Although advances in the understanding of pathology of pulmonary arterial hypertension (PAH) have led to novel therapies, there is no cure for many forms of PH. Right ventricular function is a major determinant of prognosis in severe PH.
MPAP greater of 25 mmHg
PAH, a subtype of PH, is also defined :
MPAP greater of 25 mmHg
normal pulmonary artery wedge pressure less than 15 mmHg
increase in (PVRI) greater than 3 wood units × m2.
in children younger than 3 months of age:
MPAP is typically referenced to the systemic pressure with an abnormal value greater than half the SBP.
Normal pulmonary circulation is low pressure and low resistance and large reserve of low perfused pulmonary capillaries
The RV is thin walled and is able to accommodate large changes in volume or preload . however limited contractile reserve to compensate for an increase In impedance or afterload ,increase in afterload and decrease in RV stroke volume and output
bulging of the IVS into the LV leading to decrease LV filling and to further decrease LV output.
An elevation of RV pressure and volume cause dilation and thus may cause TR,
reduces forward cardiac output and ultimately end organ perfusion.
In many patients with chronic PH, the increase in PVR occurs gradually in the RV initially hypertrophies (adaptive response).
At a later stage the RV begins to fail and dilate with reduced cardiac output and elevated filling pressure (maladaptive response)
RV perfusion at diastole and systole because of low wall tension.
When PAP becomes systemic the perfusion of the RV is markedly diminished leading to a spiral decrease in overall cardiac output
Right heart failure
clinical syndrome that is characterized by elevated venous pressure and/or decreased delivery of blood to the pulmonary circulation .
RV failure is a major component of right heart failure and occurs when cardiac output and blood pressure drop despite an increase in RVEDP. A surrogate for this is an elevation of RA pressure leading to an increase CVP
pulmonary artery compliance is crucial to the success of the RV in maintaining cardiac output
Compliance of the pulmonary vasculature :how the blood volume is ejected and can be estimated SV/PP.
Recent measures of pulmonary vascular input impedance have been shown to have added value in the measure of RV afterload
Cardiac catheterization is mandatory for the diagnosis of PH. Evaluation shows clues of right heart failure by evaluation of cardiac output, right atrial pressure, PVRI, and PAP.
All of the measures are predictors of adverse outcome. In particular, cardiac output and right atrial pressure are better predictors of outcome in PH than pulmonary artery pressure (PAP) alone
MANAGEMENT OF ACUTE RIGHT VENTRICULAR FAILURE
In a patient with acute elevations of PAP and afterload, there is decreased in RV contractility with RV dilation in an effort to increase RV volume and improve cardiac output by the Frank–Starling mechanism.
In patients with chronic PH, the RV compensates with myocardial hypertrophy that reduces wall stress. Despite the hypertrophic mechanism the RV can easily be overwhelmed and result in failure. RVH is associated with an increase in myocardial demand leading to a supply demand mismatch.
Thus, patients with chronic PAH who have an upper-respiratory infection, pneumonia, marked changes in preload, or medication noncompliance can rapidly develop right ventricular failure. As these compensatory mechanisms unravel, RV stroke volume continues to decrease leading to an under filled LV with a drop in systemic blood pressure. This leads to a decrease in aortic and coronary perfusion and RV ischemia. This circular abnormality mandates rapid changes in preload, ventricular function, and afterload .