Atrial fibrillation (Af) is the most common disorder of cardiac rhythm and is responsible for substantial morbidity and mortality in the general population. A recent community-based observational study revealed that diabetes and hypertension were associated with the development of Af. Since there is no definite evidence to show that type 1 diabetes is at increased risk for the development of Af, insulin resistance rather than hyperglycemia per se could explain the link between diabetes and Af. Several clinical trials suggest that the renin-angiotensin system (RAS) plays a pivotal role in the pathogenesis of insulin resistance. Indeed, interruption of the RAS with angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin II type 1 receptor blockers (ARBs) has been shown to prevent the onset of diabetes in hypertensive patients. Further, several experimental and clinical studies showed the beneficial role for the inhibition of the RAS in preventing Af as well. However, to what extent the insulin-sensitizing effects of ARBs could account for the prevention of Af remains to be clarified. Recently, telmisartan, an ARB, was found to act as a partial agonist of peroxisome proliferator-activated receptor-γ (PPAR-γ). PPAR-γ influences the gene expression involved in carbohydrate metabolism. In animal study, telmisartan administration caused a significant attenuation of weight gain and reduced glucose, insulin, and triglyceride levels in rats fed a high-fat, high-carbohydrate diet, compared with treatments of losartan, another type of ARB. Furthermore, recently, some clinical papers also reported the insulin-sensitizing effects of telmisartan in hypertensive patients. In this paper, we would like to propose the possible ways of clarifying to what extent the insulin-sensitizing effects of ARBs could account for the prevention of Af. (1) Does telmisartan reduce the development of Af in insulin resistant hypertensive patients? (2) When adjusted for blood pressure, is the effect of telmisartan superior to other ARBs? (3) Does this beneficial effect of telmisartan correlate to its insulin-sensitizing properties? Ongoing clinical trial (ONTARGET) has been designed the efficacy of telmisartan with an ACEI, ramipril, alone or in combination. This randomized, double-blind, multicenter international studies will provide further information whether telmisartan can improve insulin resistance and subsequently reduce the development of Af in high-risk hypertensive patients.
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