The Force Frequency Relationship in Heart Failure and Diabetes Mellitus: a Metabolic Aetiology?

RESEARCH QUESTION Hypothesis: The abnormal cardiac force-frequency relationship (FFR) and peripheral autonomic activation are the result of cardiac and peripheral metabolic abnormalities.

Fundamental aims: to determine whether impaired metabolism is a mechanism underlying the failing FFR in patients with heart failure and to determine whether diabetes mellitus is a contributing factor to the development of heart failure through its adverse effect on metabolism reflected in an abnormal FFR.

Secondary aims - this project will provide answers to a series of important questions through a single protocol which are potentially of direct and longer term importance to patients:

1. What metabolic pathways are abnormal in people with heart failure, diabetes mellitus and both? 2. What is the relationship between skeletal muscle metabolic abnormalities and those of the myocardium? 3. Can we identify using metabolomics, a substrate or compound that underlies the metabolic abnormalities? 4. What is the effect of diabetes mellitus on cardiac (glucose) and peripheral metabolism at rest and with increased heart rate? 5. Is cardiac metabolism abnormal at higher heart rates despite adequate perfusion? 6. Is abnormal cardiac metabolism related to that of the peripheral muscles? 7. Does this 'cross-talk' have a negative influence on the FFR and how does this relationship change with increased heart rate? 8. Can the improved FFR with CRT be explained by improved cardiac metabolism across the entire heart rate range? 9. Is peripheral autonomic activation at higher heart rates reflected in higher activation of cardiac sympathetic tone in HFrEF? 10. Do the laboratory data about muscle, fat and metabolomics relate to clinical variables, response to therapy and prognosis? 11. Do the haemodynamic responses to heart rate increase predict outcomes following pacemaker insertion?

STUDY DESIGN AND SETTING This will be a UK-based, unblinded, observational, mechanistic study carried out in patients receiving a pacemaker device as standard of care.

PARTICIPANT RECRUITMENT AND ELIGIBILITY CRITERIA Identification, approach and consent: Patients with and without heart failure as well as with and without type 2 diabetes mellitus receiving a clinically indicated pacemaker implantation will be approached. The selection of patients for device therapy is based on the current European guidelines on heart failure and also the European Guidelines on Pacemaker Therapy from the European Society of Cardiology (ESC) 2021. The diagnosis of T2DM is made based on HbA1c, fasting glucose, existing antidiabetic medication and/or a pathological glucose tolerance test. Patients with impaired glucose tolerance, as a precursor to overt T2DM, will also be included. In study participants of childbearing age, pregnancy is routinely excluded for clinical reasons before device implantation due to the potential risk of exposure to X-rays.

The clinical teams will approach, and the research team will follow-up these approaches, aiming for an estimated 180 patients, to achieve 160 participants (40 with CHF and DM, 40 with CHF but without DM, 40 without CHF but with DM, and 40 with neither CHF nor DM).

Participants will not be paid for participation, although reasonable travel costs will be refunded according to guidelines laid out by INVOLVE.

STUDY CLINICAL PROCEDURES:

Baseline visit (pre-implantation): Patients will be approached by the study team only after their clinical team has identified that they are suitable and interested. Patients will be offered an information sheet and be given a week to read and consider it. They will then receive a telephone call from the study nurse or doctor prior to attending the baseline visit to check if they are interested and to answer any outstanding questions.

If they agree to participate, they will attend for their baseline visit around one week prior to the day of the procedure. This visit will be combined with the pre-assessment visit for the pacemaker device implant to save them a second hospital attendance.

At the baseline visit the following tests will be done:

1. Demographics, co-morbidities, medical therapies, height, weight: These will also be entered on the pre-assessment form for the pacemaker procedure. 2. Two quality of life questionnaires (the Kansas City Cardiomyopathy Questionnaire and EQ5D-5L) (research activity)

2\) Frailty assessment: Frailty is an important risk factor for adverse outcomes in heart failure. One component contributing to frailty is muscle strength. Hence, we will include an assessment of frailty known as the clinical frailty scale (CFS). This is not a questionnaire and requires no input from the patients and is routinely collected for the pacemaker procedure. They will also complete a questionnaire specific for sarcopenia to improve the identification muscle loss (research activity).

3\) Echocardiography: This is routinely in use in research projects in Leeds. In this protocol it would be a research activity unless not done clinically in the last 6 months, in which case it would have been repeated prior to the pacemaker implantation. All participants will undergo complete echocardiography with two-dimensional grayscale and tissue Doppler images recorded in two- and four-chamber. The images are stored in the "Echopac" digital imaging system and analyzed offline (GE, Milwaukee, WI, USA). This analysis includes a calculation of LV end-diastolic and end-systolic volumes using the biplane disk method (modified Simpson method). The frame at the R wave is taken as end diastole and the frame with the smallest LV volume is taken as end systole. The LV end-systolic volume (ESV) index (ESVi) is calculated as ESV/body surface area (BSA) in each phase. Each measurement is averaged from three beats. BSA is calculated using the Mosteller equation. Our data to date have confirmed good reproducibility. This method of LV volume calculation is not only widely used and accepted, , but the key variable is the ESV, which has a particularly high reproducibility.

4\) An exercise ECG with metabolic gas analysis (cardiopulmonary exercise test) will be performed depending upon pacemaker indication. This is a common functional test established in the clinic to assess a patient's performance. The patient will walk continuously on a treadmill until exhaustion. The aim is to evaluate the patient's maximum performance. As part of the examination, blood pressure, pulse and oxygen saturation will be measured at three minute intervals. A stress ECG is usually carried out to assess progress before and after therapy (in this case CRT implantation) and is normally therefore carried out on an outpatient basis before CRT implantation and 6 months afterwards. For those receiving a pacemaker for intermittent bradycardia this will be done approximately 6 weeks after implantation of the pacemaker system to avoid the confounding of a bradycardia.

5\) Handgrip strength (research activity): Lower handgrip strength is a marker of adverse outcome in CHF,\[ \] and we have previously demonstrated a relationship to exercise capacity. As a non-invasive marker of skeletal muscle function each will be asked to perform maximal handgrip strength assessment using a standard handgrip dynamometer (Jamar). This will be recorded as the best of three attempts on the non-dominant arm.

6\) Bioimpedance to assess lean mass (research activity): Higher lean muscle mass and higher fat mass are associated with better outcomes in people with heart failure. Body composition assessment may help define and clarify the obesity paradox in heart failure where, despite a higher rate of heart failure in obese people, worse rates of diabetes (an adverse factor in CHF) and lesser exercise tolerance, obesity is associated with better outcomes in cohort studies of people with prevalent heart failure. A portable bioelectrical impedance device will be used to assess the proportion of muscle and fat.

7\) Blood tests for kidney function, glucose levels and HbA1c (routine clinical activity but blood also taken for research purposes and results used for research database): Those data collected for this study that are relevant to clinical care (peak oxygen consumption and echocardiography) including this exercise test will be added to the medical record to save the patient multiple exercise tests.

During the procedure: The device implantation will be performed according to standard protocols, within two weeks of the preassessment.

Once the routine implantation of the leads has taken place, the participant will be asked to confirm that they remain comfortable and happy to continue with the study procedures of heart rate adjustment and blood sampling.

Patients receiving a pacemaker routinely receive a venous cannula to allow provision of drugs including antibiotics and fluids.

1. Optional thigh muscle biopsy (research procedure): Prior to the start of the pacemaker procedure, a thigh muscle biopsy will be done in a subgroup of patients. This will be included as an optional procedure in those participants that have agreed and provided consent to this additional procedure. Many previous studies that have assessed skeletal muscle function in both CHF patients as well as numerous other populations have used muscle biopsies from the vastus lateralis muscle of the thigh. This particular muscle is considerably more susceptible to the effects of training and detraining. Therefore in order to establish the differences in patients that are attributable to detraining as opposed to systemic differences, a biopsy will be taken from both muscles (pectoralis major and vastus lateralis). 2. Invasive arterial monitoring (research procedure): In patients with HF, an arterial pressure catheter is often placed for invasive blood pressure monitoring (usually radial artery). In addition, there is one peripheral venous access as standard. In patients undergoing a standard pacemaker implantation, this would be a study-related procedure. 3. Invasive haemodynamics (research procedure): In addition, in a subgroup of people in each group (n=40 in total), using the venous access required for the pacemaker implantation, we will pass a catheter through the heart into the pulmonary artery to measure the pressures 'behind' the left ventricle (the main pumping chamber). This is a routine procedure in the assessment of severe heart failure. The measurement of pulmonary artery and left atrial pressure in this way would represent a research procedure for those people having a pacemaker that do not have heart failure. 4. Non-invasive cardiac monitoring (research procedure): Cardiac output and pulse pressure will be assessed through small blood pressure cuffs on patients' fingers throughout the procedure and specifically at different heart rates. 5. Pectoralis muscle and subcutaneous adipose tissue sampling (research procedure): During creation of the pacemaker pocket, muscle and fatty tissue are exposed and three samples of muscle and three samples of fatty tissue each less than 2mm x 2mm will be taken and immediately frozen in liquid nitrogen. The sampling is painless. 6. Lead implantation (routine clinical activity): The cardiac leads are inserted into the heart via the subclavian vein. A lead is first implanted in the right ventricle and, if indicated, a lead is placed in the right atrium. 7. Coronary sinus cannulation (research/standard activity): To insert the CS lead for CRT pacemaker implantation, the coronary sinus is routinely first cannulated using a guide catheter, through which blood can be taken easily. The coronary sinus represents the venous drainage system of the heart and a comparison of the coronary sinus blood ("output") with the arterial blood ("input") allows conclusions to be drawn about cardiac metabolism. This method for studying cardiac metabolism is recognized and has been used by numerous other groups. Most recently this technique has been use