The Influence of Heart Rate Limitation on Exercise Tolerance in Pacemaker Patients.

Inclusion criteria

We will only include patients able to give informed written consent, which will be obtained in all subjects, and those capable of performing a peak exercise test. Since we are performing the study on three groups of patients, further inclusion criteria for each group are outlined below.

Inclusion criteria - CRT-sinus rhythm group We will enrol 25 patients with severe CHF on otherwise optimally tolerated medical therapy who have undergone cardiac resynchronisation therapy at least 3 months previously. These individuals will be on optimal medical therapy for their heart failure with no change in medication or exacerbation for the preceding 3 months. They will not currently be taking ivabradine.

Inclusion criteria - CRT-atrial fibrillation group We will enrol 25 patients with severe CHF on otherwise optimally tolerated medical therapy who have undergone cardiac resynchronisation therapy at least 3 months previously. All patients will be previously pacemaker dependant or have 'blocked' atrial fibrillation either due to medical therapy or previous atrio-ventricular nodal ablation.

Inclusion criteria - control group The control subjects (n=25) will be recruited from the general pacemaker clinic. They will undergo echocardiography to exclude structural heart disease. They will have no contraindications to exercise testing or ivabradine.

Exclusion Criteria

We will exclude subjects with musculoskeletal disorders limiting exercise capacity, patients with peripheral vascular disease, those with inflammatory disorders such as rheumatoid arthritis, and airways disease. Other exclusions include contraindications to ivabradine use such as severe hepatic impairment, significant renal impairment (creatinine clearance <15ml.min-1), and long QT syndrome. We will only include patients able to give informed written consent, which will be obtained in all subjects.

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