DPP4 and heart failure: SGLT-2: sodium-glucose cotransporter-2; DPP-4: dipeptidyl peptidase 4; MD: mean difference; HbA1c: glycated hemoglobin; FBG: fasting blood glucose; FPG: fasting plasma glucose; PPBG: postprandial blood glucose; INSITES: ProspectIve, OpeN-Label, Randomized Study Comparing EffIcacy and Safety of Teneligliptin VErsus Sitagliptin; DELIVER: Dapagliflozin Evaluation to Improve the LIVEs of Patients With PReserved Ejection Fraction Heart Failure