Will metformin improve exercise capacity in chronic heart failure patients who has insulin resistance (pre-diabetic- means before they become diabetic)?

Exercise incapacity is one of the major debilitating symptoms of heart failure patients. Studies showed that heart failure patients will become insulin resistance (IR) or vice versa, severity of heart failure also correlates with the severity of insulin resistance. A recent study demonstrated that if we correct diabetic patient insulin resistance by giving them a drug to make them more sensitive to the effects of insulin, their exercise capacity improves. Therefore, we think that the same effects might happen in heart failure patients who have been identified to the insulin resistance by blood test. Insulin resistance means that they have not yet become diabetic and it is a stage the diabetic patients go through before they develop diabetes.

Therefore, we plan to use a drug called metformin (a diabetic drug), give it to heart failure patients who also have IR for 4 months and examine the effects before and after 4 months of treatment. It is a double blind control study, therefore, neither the examiner nor the patient know which drug they receive (either active drug- Metformin, or a placebo).

The main objective is to assess their exercise capacity using an exercise test called Innocor System. It is a bicycle based exercise test that involves patient breathing into a mouth piece before and during exercise in order for the machine to work out the maximum oxygen consumption and pumping power of the heart.

The other objectives of the trial are looking at the possible mechanisms of improving exercise capacity. We aim to answer the following questions by doing the following tests:

Does exercise capacity improve because of

1. The effect of metformin on the heart? We will answer this question by doing an ultrasound scan of the heart (Echocardiography)
2. The effects on the blood vessels? We plan to perform a test called flow-mediated dilatation, it is an ultrasound scan of the artery in the arm and also assess the blood flow in the skin using a test called Laser Doppler scan (small amount of medication will be delivered through a small electric current and the blood vessels response will be assessed using the laser doppler scan)
3. The effects on the muscle? We will do a muscle biopsy looking at the enzymes activities in the muscle before and after taking 4 months of medication.

Inclusion Criteria:

• Patients aged 25-80 yrs with compensated CHF in NYHA functional I-III with evidence of insulin resistance [fasting insulin resistance index values of > 2.7 are said to have insulin resistance].
• Documented Left ventricular systolic dysfunction or LV ejection fraction < 35%

Exclusion Criteria:

• Elderly patients (aged >80 yrs);
• Patients with decompensated CHF (NYHA functional class IV and /or signs of decompensated CHF);
• Renal dysfunction (serum creatinine > 160 mmol/L);
• Patients who are unable to exercise including patients that will be excluded for reasons of safety or potential effects on exercise performance. Therefore, patients with angina or other cardiac or pulmonary symptoms potentially limiting exercise performance will be excluded.
• Systolic blood pressure >190 mmHg at rest or >250 mmHg with exercise or diastolic blood pressure >95 mmHg at rest or >105 mmHg with exercise will also be a reason for exclusion;
• Patients with underlying disease likely to limit life span and/or increase risk of interventions will be excluded i.e., cancer; cardiovascular disease .i.e., uncontrolled hypertension: SBP>180 mmHg or DBP, recent stroke, any severe chronic disease (including renal and hepatic disease).