Introduction

There are many research studies being undertaken within the GUCH unit at The Heart Hospital that will be ongoing at The Barts Heart Centre after our merger. We’d like to highlight some of our projects that may be interesting to the GUCH patients to participate in.

Assessment of cognitive function in GUCH patients

The steady rise in the number of adults with congenital heart disease (CHD) has shifted attention to the long-term impact of the condition for patients. Interest is also moving to long-term psychosocial outcomes such as quality of life, social functioning and wellbeing.  Research is increasingly focused on the long-term impact and late problems of these conditions and associated treatments. One potential difficultly affecting this patient group is impairment of cognitive function. Cognitive function refers to a person’s ability to process thoughts.  It primarily refers to memory, the ability to learn new information, speech and reading comprehension.

Medical literature indicates that there is a relationship between CHD, its related treatments and patients’ cognitive functioning. However most of the research to date has focused on children. The impact of CHD on cognition in adults is relatively understudied despite recent research suggesting cognitive impairment persists into adolescence.

 The primary focus of research to date has been on the assessment of IQ in both child and adult patients. A recent study suggested that IQ was adversely affected in children with complex heart defects but remained within the normal range in those with simpler forms of CHD. The limited adult literature suggests that IQ is relatively unaffected in grown up congenital heart (GUCH) patients.

Whilst informative, it fails to capture performance in specific domains of cognition, such as memory, executive functioning, verbal fluency and attention.

A series of five studies examined cognition in GUCH patients, mainly assessing IQ. A sample of patients with Tetralogy of Fallot exhibited significant impairment of executive function and attention. They had learning deficits suggesting that they may have difficulty with planning, dealing with new situations, learning and recalling information.

In collaboration with our colleagues in the department of Psychology (now based at City University), led by Professor Stanton Newman, a study was undertaken aimed at assessing cognitive function in GUCH patients with different types of CHD varying from simple lesions to more complex conditions. The study aimed to (a) assess the level of cognitive functioning in GUCH patients in comparison to age-matched norms and (b) investigate differences in cognitive function between different diagnostic groups.

Patients were classified into four groups based on the complexity of the congenital heart condition. A comprehensive range of neuropsychological tests were used to assess several cognitive domains including memory, attention, executive function and verbal fluency. Tests were undertaken to produce an estimated full scale IQ in all patients. Mood was assessed to examine whether it influenced cognitive performance.

This ongoing study of 310 patients represents one of the largest series of GUCH patients investigated, in respect of cognitive functioning later in life.  Data is being analysed and the results will be submitted for publication in a major cardiology journal.  Preliminary results indicate that impairment of cognitive function is found in some GUCH patients and is more profound the more severe the congenital heart defect is. Memory was found to be largely unaffected. Further work is now needed to identify the underlying mechanisms that can explain the specific causes of these deficits, and inform tools and interventions to evaluate and address potential deficits within clinical practice.

Acknowledgements

We are collaborating with colleagues from the Centre for Health Services Research, School of Health Sciences, City University London; the GUCH Unit, The Heart Hospital, University College of London Hospitals NHS Foundation Trust; and the Division of Cardiovascular Sciences, University College London on this study: Manavi Tyagi, Theodora Fteropoulli, Catherine Hurt, Shashivadan Hirani, Lorna Rixon, Anna Davies, Nathalie Picaut, Fiona Kennedy, John Deanfield, Shay Cullen and Stanton Newman.

Assessment of Cardiovascular Fitness

Assessment of exercise intolerance is important in patients with heart disease. Traditionally, this is achieved by measuring maximum VO2 (the amount of oxygen consumed by the body), during cardio-pulmonary exercise testing (CPEX). However, this cannot tell the difference between the work of the heart (cardiac output), and tissue extraction problems, i.e. how well the muscles use oxygen. We hypothesised that a better approach may be to assess VO2 and cardiac output simultaneously (which also allows calculation of tissue extraction). Thus, we developed magnetic resonance imaging (MRI) augmented CPEX in which real-time cardiac MRI scanning is performed at the same time as analysing the respiratory gases. Our study in healthy normal-heart volunteers has recently been published and validated. We now wish to recruit patients with congenital heart defects into this study to see how their body works differently, and whether it is their heart defect that limits their exercise capacity or whether it is a problem with the muscles extracting oxygen, in which case a reconditioning programme could improve their outcome. In particular we wish to study patients with Fontan circulations (univentricular hearts), and patients born with Tetralogy of Fallot.

When we exercise our bodies use oxygen to burn fuel in our muscles and convert this to energy.  The more fuel the body can use the more energy can be produced. In order to perform exercise the lungs must be able to extract oxygen from the air, the heart must be able to pump the oxygen rich blood to the muscles and the muscles must be able to use the oxygen.  The more efficiently these systems work the more fuel can be burned and the harder the body can exercise. VO2 max is the maximum ability of an individual’s body to use oxygen during exercise. Fitter people are able to use more oxygen than less fit people.

We would like to learn how the heart, lungs and muscles respond to exercise in people with differing levels of fitness. We would like to do this by carrying out a special scan while the patient is cycling on a bike within the MR scanner, and comparing this data to a more traditional form of cardiopulmonary exercise test performed on an exercise bike. Participants in the study will have a standard cardiopulmonary exercise test performed on an exercise bike. An ECG is recorded throughout to ensure that the heart rhythm is stable.

On a second visit, an MR scan will be performed to assess your heart function at rest and during exercise.

An MR scan uses a large magnet to get pictures of the heart. A bike will be positioned on the table. It is a special bike that can be pedalled while you are lying in the MR scanner. You will have to cycle for approximately 10 minutes while we scan your heart. We will record your electrical heart action to make sure that you are all right.  We will also ask you to wear a mask so that we can collect and analyse the air that you breathe out.

As with all studies in our department, all information that is collected during the course of the project will be kept strictly confidential. Once the study is complete and all the data has been analysed we anticipate publishing our results in one or more medical journals.

We have performed this study in normal people to ensure that it is feasible and acceptable to perform. We have compared our data with conventional exercise testing. Seventeen healthy adults underwent CPEX and MR-CPEX. 15 of the 17 volunteers completed exercise; exclusions were due to claustrophobia and inability to effectively master exercise technique. There were strong relationships between conventional and MR-CPEX for peak VO2. Other variables we looked at included the amount of carbon dioxide produced (VCO2) and the ventilation. We have so far found that MR-CPEX is feasible, acceptable and demonstrates physiology not apparent with conventional CPEX. MR-CPEX allows us to tell the difference between the cardiac output, oxygen consumption and variations in VO2.

We believe that this will be useful in understanding the origin of reduced exercise capacity in cardiac disease, and enable us to evaluate this further within the GUCH population so that we can identify the root cause of exercise intolerance and offer patients a comprehensive assessment that allows us to tailor make a treatment programme. This may involve offering further surgery, treating heart failure and designing patient specific exercise programmes.

Acknowledgements

We are collaborating with colleagues from the Institute of Cardiovascular Science, University College London, Centre for Cardiovascular Imaging; and The Heart Hospital, University London Hospital Foundation Trust on this study: Dr Nathaniel J Barber, Dr Emmanuel O Ako, Mr Grzegorz T Kowalik, Miss Jennifer A Steeden and Dr Vivek Muthurangu.

If you are interested in taking part in the Cardiovascular Fitness Study please contact either Dr Nathaniel Barber: nathaniel.barber@ucl.ac.uk or Dr Bejal Pandya: b.pandya@ucl.ac.uk.

By Dr Bejal Pandya and Dr Seamus Cullen

Consultant Cardiologists, The Heart Hospital and The Barts Heart Centre, London

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