Chronotropic Incompetence During Exercise in Type 2 Diabetes: Aetiology, Assessment Methodology, Prognostic Impact and Therapy.

During incremental exercise tests, chronotropic incompetence (CI), which is the inability of the heart rate (HR) to rise in proportion to an increase in metabolic demand, is often observed in patients with type 2 diabetes mellitus (T2DM). Despite the fact that CI is associated with exercise intolerance and elevated risks of development of cardiovascular disease and premature death, this clinical anomaly is often ignored or overlooked by clinicians and physiologists. CI is, however, a significant clinical abnormality that deserves further attention, examination and treatment. The aetiology of CI in T2DM remains poorly understood and is complex. Certain T2DM-related co-morbidities or physiological anomalies may contribute to development of CI, such as altered blood catecholamine and/or potassium levels during exercise, structural myocardial abnormalities, ventricular and/or arterial stiffness, impaired baroreflex sensitivity and cardiovascular autonomic neuropathy. Clinicians should thus be aware of the potential presence of yet undetected anomalies or diseases in T2DM patients who experience CI during exercise testing. However, an effective treatment for CI in T2DM is yet to be developed. Exercise training programmes seem to be the only potentially effective and feasible interventions for partial restoration of the chronotropic response in T2DM, but it remains poorly understood how these interventions lead to restoration of the chronotropic response. Studies are thus warranted to elucidate the aetiology of CI and develop an effective treatment for CI in T2DM. In particular, the impact of (different) exercise interventions on CI in T2DM deserves greater attention in future studies.