Andersons pediatric cardiology 2021

Over time, this abnormal pressure and flow pattern can cause similar endothelial damage and intimal hypertrophy characteristic of pulmonary artery hypertension.. Transcatheter interventi

necessitates that the pulmonary arteries are exposed to higher pressures Over time, this abnormal pressure and flow pattern can cause similar endothelial

damage and intimal hypertrophy characteristic of pulmonary artery

hypertension

Pulmonary Artery Hypertension After Repair of Congenital Heart Disease

Pulmonary hypertension after repair or palliation of congenital heart disease has the same pathophysiology as described earlier Pulmonary overcirculation can occur with residual ventricular level shunts or with any significant

aortopulmonary shunts (i.e., Blalock-Taussig shunts, aortopulmonary

collaterals) Another example is residual postcapillary obstruction after repair of total anomalous pulmonary venous return Postoperative pulmonary vein

stenosis carries a poor prognosis, and progression is difficult to predict

Extension of stenosis into segmental veins carries an especially poor

prognosis.16 Currently, treatment regimens have included transcatheter

interventions, chemotherapy agents, surgical repair, and lung transplantation All treatment modalities have an unacceptably high mortality Transcatheter

interventions have been shown to be acutely successful but with extremely high reintervention rates and limited long-term benefit.17 Recently, repeated

transcatheter interventions with systemic chemotherapy targeting myofibroblast-like cells has shown promise compared with historical controls.18

Similarly, postcapillary obstruction as an etiology of long-term postoperative pulmonary vascular disease occurs in mitral valve repairs and repairs that are associated with elevated left ventricular end diastolic pressures Multilevel left- sided obstruction (e.g., Shone complex) is particularly notable because the left-sided outflow tract obstruction, including subaortic stenosis and coarctation, predispose to an elevated left ventricular end-diastolic pressure, and pulmonary venous hypertension Postcapillary obstruction is also a cause of pulmonary vascular disease in those with an atrial switch operation, usually due to

pulmonary venous baffle obstruction

Single ventricle palliation provides a unique challenge when it comes to the development of pulmonary vascular disease Due to passive pulmonary blood flow present in the Fontan circulation, pulmonary vascular resistance often

becomes the limiting factor to total cardiac output Because there is no

subpulmonary ventricle to provide a pump, even a relatively mild elevation in

the pulmonary vascular disease limits the ability of blood to flow through the lungs This can be further exacerbated by the limited growth potential of the pulmonary arteries The staged palliation currently in practice limits the volume load to the ventricle at the expense of pulmonary blood flow beginning with the Glenn operation (superior cavopulmonary anastomosis) This change in

pulmonary blood flow and the lack of pulsatility of flow in a cavopulmonary anastomosis may limit the growth potential of the pulmonary arteries and thus increases pulmonary vascular resistance.19,20 Because pulmonary vascular

resistance is the bottleneck of cardiac output in patients palliated with a Fontan circulation, targeted modulation of the pulmonary vascular systems has been proposed as a treatment for some complications of Fontan physiology Studies using phosphodiesterase inhibitors and endothelin antagonists have shown

variable effects on exercise capacity and symptoms such as protein-losing

enteropathy and plastic bronchitis, and their role remains to be determined.21,22 Further investigations into pulmonary vascular–directed therapy are currently underway in this population

Acute Postoperative Pulmonary Hypertension

Acute postoperative pulmonary hypertension is a transient clinical and

pathophysiologic condition that is a consequence of cardiopulmonary bypass and

is an important contributor to postoperative morbidity Although the

pathophysiology is incompletely understood, cardiopulmonary bypass leads to transient endothelial injury and disruption of nitric oxide production As a result, there is a transient elevation of pulmonary vascular resistance and increased sensitivity to vasoconstrictive stimuli The resistance can be lowered by

supplementation of elements from the l-arginine–nitric oxide pathway and by blockade of the endothelin receptors, suggesting a combined pathophysiology of different pathways as a cause This pathophysiology may persist for several days, in extreme cases making the lung very vulnerable to different stimuli such

as handling, suctioning, movement, and hypoventilation Such stimuli can be associated with life-threatening pulmonary vasospasm This is the so-called pulmonary hypertensive crisis, which results in a sharp increase in pulmonary vascular resistance and pulmonary arterial pressure, acute right ventricular

decompensation with raised central venous pressure, decreased pulmonary blood flow with cyanosis, and left atrial and systemic hypotension (Fig 75.2A) In infants and young patients, this phase is directly associated with a decrease in

lung compliance (see Fig 75.2B), hypoventilation, hypercarbia, and further pulmonary vascular restriction, producing a vicious circle that can only be interrupted by manual forced and energetic hyperventilation and that may

require other immediate measures aimed at resuscitation (Fig 75.3).23 This bronchopulmonary interaction has also been described elsewhere, such as in the variation of both pulmonary compliance and flow of blood to the lungs and asthma in pulmonary hypertension

FIG 75.2 (A) Original hemodynamic pressure tracing of a pulmonary hypertensive crisis, which resolved with the prompt administration of inhaled nitric oxide (inh NO) The sharp increase of the pulmonary arterial

pressures (lower half of the panel, upper tracing) is accompanied by systemic hypotension (upper half of the panel) and an increase of central

venous pressure as a sign of acute right heart decompensation (lower half

of panel, lower tracing) The situation reverses promptly within less than a

minute upon inhalation of 20 ppm nitric oxide (B) The bronchopulmonary

interaction during such a pulmonary hypertensive crisis The rise and fall of

mean pulmonary arterial pressure (mPA) are accompanied by reverse changes in dynamic lung compliance, in response to the unsuccessful attempt to wean from inhaled nitric oxide (5 ppm) and the decision to

recommence the inhalation.