Surgical implications of pulmonary hypertension in congenital heart disease

Progressive Memory Decline in a Patient With Atrial Septal Defect: Case Report and Literature Review

Atrial septal defect (ASD) is a common congenital anomaly that increases the risk of heart failure as well as strokes which can lead to cognitive impairment. The risk of stroke is higher when pulmonary hypertension develops and there is reversal of shunt. Stroke in ASD may be due to paradoxical emboli from the right heart or a left ventricular thrombus which develops as a result of atrial fibrillation, a common arrhythmia in ASD. We present a case of a 32-year-old Ghanaian man with history of ASD who presented with progressive memory loss with magnetic resonance imaging scan of the brain showing multiple infarcts, microvascular disease, and cerebral atrophy.

Canadian Cardiovascular Society 2022 Guidelines for Cardiovascular Interventions in Adults With Congenital Heart Disease

Interventions in adults with congenital heart disease (ACHD) focus on surgical and percutaneous interventions in light of rapidly evolving ACHD clinical practice. To bring rigour to our process and amplify the cumulative nature of evidence ACHD care we used the ADAPTE process; we systematically adjudicated, updated, and adapted existing guidelines by Canadian, American, and European cardiac societies from 2010 to 2020. We applied this to interventions related to right and left ventricular outflow obstruction, tetralogy of Fallot, coarctation, aortopathy associated with bicuspid aortic valve, atrioventricular canal defects, Ebstein anomaly, complete and congenitally corrected transposition, and patients with the Fontan operation. In addition to tables indexed to evidence, clinical flow diagrams are included for each lesion to facilitate a practical approach to clinical decision-making. Excluded are recommendations for pacemakers, defibrillators, and arrhythmia-directed interventions covered in separate designated documents. Similarly, where overlap occurs with other guidelines for valvular interventions, reference is made to parallel publications. There is a paucity of high-level quality of evidence in the form of randomized clinical trials to support guidelines in ACHD. We accounted for this in the wording of the strength of recommendations put forth by our national and international experts. As data grow on long-term follow-up, we expect that the evidence driving clinical practice will become increasingly granular. These recommendations are meant to be used to guide dialogue between clinicians, interventional cardiologists, surgeons, and patients making complex decisions relative to ACHD interventions.

Mechanical forces alter endothelin-1 signaling: comparative ovine models of congenital heart disease

The risk and progression of pulmonary vascular disease in patients with congenital heart disease is dependent on the hemodynamics associated with different lesions. However, the underlying mechanisms are not understood. Endothelin-1 is a potent vasoconstrictor that plays a key role in the pathology of pulmonary vascular disease. We utilized two ovine models of congenital heart disease: (1) fetal aortopulmonary graft placement (shunt), resulting in increased flow and pressure; and (2) fetal ligation of the left pulmonary artery resulting in increased flow and normal pressure to the right lung, to investigate the hypothesis that high pressure and flow, but not flow alone, upregulates endothelin-1 signaling. Lung tissue and pulmonary arterial endothelial cells were harvested from control, shunt, and the right lung of left pulmonary artery lambs at 3–7 weeks of age. We found that lung preproendothelin-1 mRNA and protein expression were increased in shunt lambs compared to controls. Preproendothelin-1 mRNA expression was modestly increased, and protein was unchanged in left pulmonary artery lambs. These changes resulted in increased lung endothelin-1 levels in shunt lambs, while left pulmonary artery levels were similar to controls. Pulmonary arterial endothelial cells exposed to increased shear stress decreased endothelin-1 levels by five-fold, while cyclic stretch increased levels by 1.5-fold. These data suggest that pressure or an additive effect of pressure and flow, rather than increased flow alone, is the principal driver of increased endothelin signaling in congenital heart disease. Defining the molecular drivers of the pathobiology of pulmonary vascular disease due to differing mechanical forces will allow for a more targeted therapeutic approach.

Alterations in cGMP, soluble guanylate cyclase, phosphodiesterase 5, and B-type natriuretic peptide induced by chronic increased pulmonary blood flow in lambs

OBJECTIVE

The objective of the study was to determine alterations in cGMP, soluble guanylate cyclase (sGC), phosphodiesterase type 5 (PDE5), and B-type natriuretic peptide (BNP), in an animal model of a congenital cardiac defect with increased pulmonary blood flow.

DESIGN

Prospective, comparative, experimental study.

SUBJECTS

Lambs, from birth until 8 weeks of age.

METHODOLOGY

Late gestation fetal lambs underwent in utero placement of an 8 mm aortopulmonary vascular graft (shunt). In shunted and normal age-matched control lambs, at 2, 4, and 8 weeks of age, cGMP and BNP levels were measured, and sGC subunit and PDE5 protein expression were determined by Western blot analysis and immunohistochemistry.

RESULTS

In shunted lambs, tissue and plasma cGMP levels were greater than normal throughout the 8-week study period (P < 0.05). sGCalpha protein was greater at 2 and 4 weeks (P < 0.05), and sGCbeta and PDE5 protein were greater at 4 weeks in shunted lambs (P < 0.05). Plasma BNP levels did not change in normal lambs but increased in shunted lambs by 8 weeks of age (P < 0.05). BNP levels were greater in shunted lambs than normal at 4 and 8 weeks (P < 0.05).

CONCLUSIONS

Alterations in sGC subunit protein expression during the first post-natal month, and increased BNP levels during the second post-natal month contribute to elevations in plasma and lung tissue cGMP in lambs with increased pulmonary blood flow.

Upregulation of collagens detected by gene array in a model of flow-induced pulmonary vascular remodeling

We recently reported localized increased pulmonary arterial resistance, neointimal lesions, and medial thickening induced by aortopulmonary anastomosis in young pigs. This model was used to investigate changes in expression of genes potentially involved in pulmonary vascular remodeling employing a high throughput Atlas Human Cardiovascular Array carrying approximately 600 cardiovascular-related cDNA sequences. Data were confirmed by Northern analysis, Western blots, and histological examination. With the use of lower stringency conditions for hybridization, 56% of the 588 human genes on the array showed visible signal after autoradiography. Approximately 10% of the genes with visible hybridization were altered by shunt-induced high flow. Extracellular matrix and cell adhesion molecules were the most highly represented group of upregulated genes. To our knowledge, our data are the first to demonstrate flow-induced changes in gene expression using a combination of cross species cDNA arrays, homologous hybridization, immunospecific protein, and histology. Our observations expand the list of genes as putative candidates in pulmonary vascular remodeling and support the utility of cross-species microarray analysis in such applications.

Systemic lobar shunting induces advanced pulmonary vasculopathy

OBJECTIVES

We characterized the morphology and vasomotor responses of a localized, high-flow model of pulmonary hypertension.

METHODS

An end-to-side anastomosis was created between the left lower lobe pulmonary artery and the aorta in 23 piglets. Control animals had a thoracotomy alone or did not have an operation. Eight weeks later, hemodynamic measurements were made. Then shunted and/or nonshunted lobes were removed for determination of vascular resistance and compliance by occlusion techniques under conditions of normoxia, hypoxia (FIO (2) = 0.03), and inspired nitric oxide administration. Quantitative histologic studies of vessel morphology were performed.

RESULTS

Eighty-three percent of animals having a shunt survived to final study. Aortic pressure, main pulmonary artery and wedge pressures, cardiac output, blood gases, and weight gain were not different between control pigs and those receiving a shunt. Six of 9 shunted lobes demonstrated systemic levels of pulmonary hypertension in vivo. Arterial resistance was higher (24.3 +/- 12.0 vs 1.3 +/- 0. 2 mm Hg. mL(-1). s(-1), P =.04) and arterial compliance was lower (0. 05 +/- 0.01 vs 0.16 +/- 0.03 mL/mm Hg, P =.02) in shunted compared with nonshunted lobes. Hypoxic vasoconstriction was blunted in shunted lobes compared with nonshunted lobes (31% +/- 13% vs 452% +/- 107% change in arterial resistance, during hypoxia, P <.001). Vasodilation to inspired nitric oxide was evident only in shunted lobes (34% +/- 6% vs 1.8% +/- 8.2% change in arterial resistance during administration of inspired nitric oxide, P =.008). Neointimal and medial proliferation was found in shunted lobes with approximately a 10-fold increase in wall/luminal area ratio.

CONCLUSIONS

An aorta-lobar pulmonary artery shunt produces striking vasculopathy. The development of severe pulmonary hypertension within a short time frame, low mortality, and localized nature of the vasculopathy make this model highly attractive for investigation of mechanisms that underlie pulmonary hypertension.

Effects of chronic pulmonary overcirculation on pulmonary vasomotor tone

BACKGROUND

A model of shunt-induced pulmonary hypertension was used to study the effects of pulmonary overcirculation on endothelial nitric oxide synthase (eNOS) and cytochrome P450-4A (cP450-4A) vasodilatory mechanisms and related hemodynamic responses.

METHODS

An aortopulmonary shunt was constructed in 6-week-old piglets (n = 7, sham-operated controls n = 8). Hemodynamic measurements were made 4 weeks later under serial experimental conditions: baseline (fractional concentration of oxygen, 0.4); inhaled nitric oxide, 25 ppm (INO); hypoxia (fractional concentration of oxygen, 0.14); hypoxia + INO; N(omega)-nitro-L-arginine methylester (L-NAME 30 mg/kg intravenously, competitive NOS inhibitor); and L-NAME + INO. Lung protein levels of eNOS and cP450-4A and NOS activity were compared between groups.

RESULTS

Shunted animals had a higher baseline pulmonary artery pressure (p < 0.05). L-NAME resulted in a greater increase in pulmonary vascular resistance in shunted animals (150% +/- 26% shunt versus 69% +/- 14% control; p = 0.01). The INO administered during baseline conditions decreased pulmonary vascular resistance only in control animals (p < 0.05). Protein levels of eNOS and NOS activity were similar in both groups; however, cP450-4A protein levels were decreased in the shunted group (p = 0.02).

CONCLUSIONS

The NO production was preserved in shunted animals but they demonstrated greater vasodilatory dependence on NO, evidenced by an exaggerated increase in pulmonary vascular resistance after NOS inhibition. Loss of the cP450-4A vasodilatory system may be the driving force for NO dependency in the shunted pulmonary circulation.

Management of adults with congenital bidirectional cardiac shunts, cyanosis, and pulmonary vascular obstruction: successful operative repair in 3 patients

Patients with congenital cardiac shunts in whom marked functional disability, cyanosis and pulmonary arterial hypertension develop have been considered inoperable or at exceedingly high risk. Three adult patients, 2 with atrial septal defect (ASD) and 1 with patent ductus arteriosus (PDA), presented with New York Heart Association class IV symptoms, bidirectional shunting with cyanosis, polycythemia, severe pulmonary hypertension, and increased pulmonary vascular resistance. Pulmonary arterial pressure did not decrease in response to administration of 100% oxygen in any patient, and 2 had lung biopsy results showing advanced pulmonary vascular obstruction. While a right-to-left shunt caused cyanosis in all patients, the net shunt was left to right (Qp/Qs greater than 1) and the resistance ratio (Rp/Rs) less than 0.5. All 3 patients survived operation, became acyanotic with normal hematocrit, and are in functional class I or II a mean of 36 months postoperatively. At repeat cardiac catheterization, pulmonary arterial pressure and resistance had decreased substantially. This high-risk group of patients with bidirectional shunts, in whom cyanosis due to pulmonary vascular obstruction and polycythemia develop and who appear to be at very high operative risk, should still be considered for surgical correction if the usual criteria for operability exist: net left-to-right Qp/Qs and Rp/Rs less than 0.50.