Tetralogy of Fallot (TOF) is the most common congenital heart defect that causes cyanosis, a blue discoloration of the skin. In this multiform heart malformation, the body and its organs are not supplied with sufficient oxygen.

Among the life-threatening consequences of the cluster of four organ malformations, first described by the French physician Étienne Fallot, is the overloading of the right ventricle due to blood backlog. The culprit is a narrowing of the right outflow tract (RVOT) below the pulmonary valve. Because the right ventricle must pump against the backlog of blood, its muscles thicken. This can lead to cardiac arrhythmias and even cardiac arrest.

Heart Correction as Gentle as Possible

As early as the mid-1950s, heart surgery ensured the survival of affected children. Today, state-of-the-art medical technology and surgical procedures ensure a gentle approach and thus a significantly improved life expectancy and quality of life. However, in each ToF, the individual malformations vary in severity, and much depends primarily on how much the outflow tract to the right ventricle is narrowed.

Targeted Relief of the Right Ventricle

During surgery, both the ventricular septal defect (VSD) associated with the malformation is closed with a patch and the right ventricular outflow tract (RVOT) is widened, either with another patch and/or also by removing muscle tissue. The aim is to relieve the musculature of the right ventricle.

In the past, the resulting leakage of the pulmonary valve often led to valve replacement. In the meantime, surgical treatment is performed in such a way that the pulmonary valve and thus the right ventricle can be preserved in its natural function.

Slight Pressure on the Ventricle

However, this often leaves a slight narrowing of the outflow tract. "Such residual constriction can be accepted as long as the pressure is not too high and the musculature of the right ventricle consequently cannot thicken to such an extent that its function is impaired," explains Heiner Latus, senior physician at the Center for Congenital Heart Defects at Klinikum Stuttgart.

But can the heart valve withstand this slight pressure in the long term? And if not: Is a renewed surgical correction of the right outflow tract worthwhile? Until now, it has been difficult to predict.

In Search of a Reliable Prognosis

A recent long-term study at the Competence Network therefore investigated the course of the disease after corrective surgery in 296 minor and adult patients, taking into account examination results on the respective pressure load on the heart muscle tissue (myocardium) of the right ventricle.

"We wanted to use the pressure gradients to find out to what extent a narrowing of the right outflow tract (RVOT) can actually be accepted, and whether there are clear indications as to when pulmonary valve replacement is unavoidable. In the interest of patients' quality of life, a reliable prognosis would be desirable here," reasons study first author Heiner Latus.

Valve Replacement Often Unavoidable

The current multicenter study provides decisive new evidence for this. Over a follow-up period of 10.1 years on average, the researchers found that more RVOT narrowing was associated with less blood return and a smaller right ventricle. At the same time, however, it was associated with a reduced load-bearing capacity of both ventricles and proved to be a clear risk factor for adverse cardiological events such as cardiac arrhythmias.

"What became clear on the basis of the comparatively young patient group with an average age between 10 and 25 years: Even a slight pressure load on the right heart valve sometimes requires pulmonary valve replacement," Heiner Latus sums up.

The researchers therefore strongly advise that the extent of blood return and the RVOT peak gradient should be considered in conjunction with the question of to what extent and at what point pulmonary valve replacement appears necessary. "Blood return greater than 25 percent and RVOT peak gradient greater than 30 mmHg are clear risk factors associated with valve replacement. On the other hand, how high precisely the pressure load may be without impairing the function of the right ventricle still needs to be determined in more detail," the researcher emphasizes.