Late-onset pulmonary hypertension in adults after atrial switch for transposition of the great arteries

Background:

The pathophysiology of pulmonary hypertension (PH) in patients with Transposition of Great Arteries (TGA) after atrial switch intervention remains to be elucidated. Different factors have been associated with the development of PH in this group of patients, such as older age at surgery, obstruction in systemic atrial baffles, residual hemodynamic lesions, systemic right ventricle (sRV) systolic dysfunction or sRV diastolic dysfunction.

Some degree of sRV systolic dysfunction is the rule in adults with TGA and atrial switch surgery, but there is not a clear correlation between reduced systolic function, functional capacity and PH development. Conversely, impaired systemic RV filling has been increasingly involved in the late functional deterioration after atrial switch. In this sense, impaired systemic RV filling due to stiff atrial baffles has been incriminated as the cause of failure of RV stroke volume to increase during exercise or dobutamine stress.

Diastolic dysfunction is another concern in these patients, in whom the RV is chronically exposed to increased afterload (systemic arterial pressure). Nevertheless, there is scarce data on systemic RV filling pressures late after atrial switch intervention. The authors of this article tried to find out more about it.

Study summary:

This is a single-center retrospective cohort study of forty-two adults with complete TGA and atrial switch palliation identified between January 2004 and December 2018 at Mayo Clinic. The aim of this study was to assess the prevalence of pulmonary arterial hypertension and to describe the hemodynamic profile in this group of patients.

Mean age at the time of catheterisation was 37.6 ± 7.9 years and median age at atrial switch operation was 15 months. The Mustard palliation was the most common surgery (91% of the individuals). 36 patients (85.7%) had moderate or severe systemic RV systolic dysfunction, with an estimated ejection fraction of 33.3% ± 10.9%. Fifteen patients (35.7%) had ≥ moderate tricuspid regurgitation.

During cardiac catheterization pulmonary venous baffle obstruction was diagnosed in seven patients (16.7%) and systemic venous baffle obstruction in 23 (54.7%).

PH (defined as PAPm ³25 mmHg) was present in 47.5% of patients (17 patients) and median PVR was 1.3 Wood units. Among those with PH, only in one patient PAWP was 15 mmHg, all the remaining patients had PAWP >15 mmHg. Those with PH had a higher prevalence of atrial arrhythmia (26.3% vs 0%, p=0.02) and diuretic treatment (68.4% vs 23.8%, p=0.01) compared with those without PH.

Elevated systemic RV end-diastolic pressure (sRVEDP) (>15 mmHg) was obtained in 13 patients (35.1%), whereas a pulmonary artery wedged pressure (PAWP) >15 mmHg was present in 23 (58.9%). Most of the patients with an elevated sRVEDP had elevated PAWP (83%), whilst only 50% of patients with high PAWP had elevated sRVEDP.

Noteworthy, those with elevated PAWP had poorer functional class (New York Heart Association functional class ≥3 56.6% vs 12.5%, p=0.008), higher prevalence of diuretic therapy (65.2% vs 18.8%; p=0.008) and ≥moderate sRV systolic dysfunction (78.3% vs 37.5%; p=0.02). After excluding patients with pulmonary venous baffle obstruction results remained unchanged.

Discussion:

This article shows a high prevalence of late-onset PH in adults with TGA and atrial switch intervention, being mainly postcapillary. PAWP was increased in all but one patient, while sRVEDP was significantly lower, suggesting that impaired RV filling takes part as an important factor in the development of PH in default of normal atrial contractionin this group of patients. 

Despite the high prevalence of systemic RV systolic dysfunction, elevated sRVEDP was barely found in 35% of patients, whereas high PAWP was obtained in 83%, highlighting the role of pulmonary atrial baffle in the pathophysiology of pulmonary hypertension among these patients. 

The findings of this study suggest that the combination of stiff, small and non-compliant pulmonary atrial baffle and the absence of atrial contraction contribute to the development of late-onset postcapillarypulmonary hypertension in patients with TGA and atrial switch intervention, being present in up to 48% of this cohort.

Furthermore, individuals with higher PAWP and PH have worse prognosis, with poorer functional class, greater need of diuretic therapy and increased prevalence of atrial arrythmias. Hence, the decreased pulmonary venous atrial compliance can explain why some patients develop atrial arrythmias or symptoms on exertion in the absence of a significant systemic RV dysfunction or atrioventricular valve dysfunction. Moreover, impaired systemic RV filling during an effort has been previously involved in the functional limitation of adults with TGA and atrial switch surgery.

Conclusion

To conclude, understanding the pathophysiology is vital for a better care and surveillance of these patients and further investigations in this issue are warranted