Children with dysfunction of the right heart chamber (ventricle), which pumps blood to the lungs, have lower tolerance to exercise and are at risk of sudden cardiac death in more severe cases. This dysfunction usually sets in progressively and detection at earlier stages is crucial to guiding therapies and interventions that improve symptoms and survival. New ultrasound techniques, make it easier detect and quantify the problem.

Assessing the right ventricular function has always been challenging with conventional ultrasound techniques. However, using the new high frame-rate ultrasound imaging techniques combined with speckle tracking (both developed at NTNU), we are now able to measure the energy that is lost in the blood. This is a promising new way of detecting ventricular dysfunction.

In the case of high blood pressure in the lungs (pulmonary hypertension), an early diagnosis is crucial to direct therapies, which can lower the resistances in the lung vessels and facilitate the function of the right ventricle, and reduce the risk of heart failure and sudden cardiac death.  We have included 9 children, aged 5 months to 8 years of age, to study energetics and flow patterns within the right ventricle and pulmonary arteries, and compare these to controls.

Another particularly challenging group with regards to assessing cardiac function, is patients with single ventricle physiologies. This type of circulation refers to situations where one of the ventricles is inadequate to participate in pumping the blood to the body or to the lungs. The entire pumping function then falls on one ventricle instead if two.  This type of circulation depends heavily on good ventricular performance and a large number of these patients experience ventricular dysfunction during adulthood. This can even go as far as requiring heart transplant, although this has limited success. Recognising dysfunction before patients develop symptoms is very important as it can offer a window of opportunity to intervene, either with medication or surgery, to improve cardiac function.  Flow dynamics and energetics are particularly interesting to study in these patients as they may reflect dysfunction earlier than conventional echocardiographic parameters. We have included 21 patients, aged 4 to 9 years old, with this condition and will shortly start studying their intracardiac flow characteristics, including energy loss.

Studying these flow phenomena by imaging requires high frame rates because the blood moves much faster than the heart muscle (myocardium), with important phenomena occurring in short times intervals. Recent advances in imaging technologies have given us access to characterising the speed and volume of the blood flow (blood flow velocities) as never before. Blood speckle tracking, which is the technique our group is working with, combines ultra-high frame rate imaging (in the KHz range – see figure below), and tracking of speckles within the blood pool. From there, the velocities of these speckles can be measured without the use of contrast agents or the need for mathematical assumptions. These velocities measurements enable us to, amongst other things, to assess the energy loss.

Previously, we have studied cardiac flow dynamics in repaired tetralogy of Fallot, a condition where there is narrowing between the right ventricle and the lung artery requiring surgery. After the surgical repair, there is a necessary incompetence of the lung valve, which causes gradual dilatation and dysfunction of the right ventricle. A total of 57 children aged two weeks to 10 years were included. Of this group, 21 had repaired tetralogy of Fallot and 11 had an atrial septal defect (ASD) which is a hole between the upper chambers of the heart also causing right ventricular dilatation. In the latter 2 group, we found significantly higher diastolic energy loss compared to normal controls. Inefficiencies within the heart has long been suspected but to demonstrate these using non-invasive, ultrasound imaging is very promising in allowing early detection of flow inefficiencies at an earlier stage where interventions might be more beneficial.

Now that these techniques are available more widely, there are many challenges for our community to better understand, validate and compare flow parameters in normal and abnormal hearts. More technical improvements are needed with regard to developing 3D techniques, where NTNU is making great leaps.

How these new insights alter our management to improve our patients’ outcomes is to be seen as our community continues to explore these new imaging technologies.

Using a new ultrasound technique, we have been able to visualize and measure how efficiently blood flows through the heart chambers in young children with congenital heart disease. We studied 37 children aged two weeks to 10 years, and among the 26 children, which had congenital heart disease, we found less efficient hearts, meaning they use more energy than a normal heart. The technology, known as blood speckle tracking, has been developed by our colleagues at CIUS.

Tetralogy of Fallot is one of the most common types of congenital heart disease, accounting for 10% of all congenital heart disease. It consists mainly of a large hole between the pumping chambers and narrowing below the lung artery valve. The surgical repair is usually undertaken within the first 6 months of life but comes at the cost of causing a severe leak of the lung artery valve. Although well tolerated in young age, this can cause the right ventricle, the ventricle pumping through the lung artery valve, to become progressively bigger and increasingly dysfunctional with an increasing risk of life-threatening events. It is thought that replacing the lung artery valve can interrupt the progression and prevent these adverse events from occurring.

Predicting these events and intervening preventatively has been the focus of much work but remains challenging, with cutoffs of ventricular volumes measured by cardiac MRI constantly being changed. Lung artery replacement has been shown to procure some symptomatic relief, however, no survival benefit has been demonstrated. Given this realization, we can wonder whether ventricular volumes are really the best guide to optimally time surgery for these patients or is there a better avenue?

It has been suggested, from foetal life and beyond, that the shape and size of cardiac structures change in response to changes in blood flow patterns. These flow patterns are now within the reach of a new echocardiographic imaging technique combining high-frame-rate imaging of clusters of red blood cells. The resulting images open a window into the disturbed flow patterns of these patients. Abnormalities in flow result in ventricular inefficiencies and energy-losses which can now be quantified and localized using custom software, PyUSview. This analysis tool is the result of a tight collaboration between the clinicians and engineers in our group lead by Lasse Løvstakken at CIUS.

High frame rate blood flow speckle tracking echocardiography: Blood flow patterns and energy loss maps. using in-house developed software, 2D blood velocity fields were processed without in-plane flow assumptions. Energy losses were calculated within a region encompassing the RV, using a spline-based segmentation and reconstruction approach.

Using PyUSview, we studied a group of patients with repaired tetralogy of Fallot with severe lung artery leak (15 patients). We compared them to a group with another type of congenital heart disease, atrial septal defect (ASD) (communication between the upper chambers of the heart; 11 patients) and 11 healthy controls. We calculated energy-loss in the right ventricle during contraction (systole) and relaxation (diastole) and found that energy-loss in diastole was similar for both groups with congenital heart lesions, but significantly higher than controls.

A most interesting finding came from inspecting the location of maximal energy-loss, with marked differences between the groups (Figure 1). In the ASD group, the pattern of energy-loss was similar to that of normal controls. In the repaired tetralogy of Fallot group however, there was an additional area of increased energy loss at the right ventricular apex, corresponding to the collision of blood leaking back from the lung artery and the blood coming in normally to the ventricle during filling.

This is the first study of ventricular energetics in a paediatric population with dilated right ventricles. The methodology behind the imaging, its planned integration into the newest release of the GE Vivid E95 scanner as well as our results were presented by our group at the 2017 American Society of Echocardiography meeting (Pic 1-4).  Although the clinical significance of these findings is not yet clear, ventricular energetics, as assessed by echocardiography, may become a valuable tool in developing an approach based on blood flow patterns and energy-loss calculations to select a more optimal time for intervention.

Wadi Mawad was awarded a top 25 investigator prize for his presentation at the ASE-meeting 2017.