Nitrates decrease myocardial consumption of oxygen by all of the following mechanisms except

Nitrates decrease end diastolic pressure by causing venodialtation. Administered by carefully titrated i.v. infusion to avoid hypo- tension and tachycardia, GTN is frequently used during evolving MI with the aim of relieving chest pain, pulmonary congestion and limiting the area of necrosis by ourably altering O2 balance in the marginal paially ischaemic zone (a consequence of preload reduction). However, the evidence that it decreases moality is not robust; prognostic benefits appear marginal. Proper patient selection is impoant. GTN should not be administered if: * Systolic BP is < 90 mm Hg * Hea rate is < 50 or > 100 beats/min * Right ventricular infarction is suspected * Hypotension caused by nitrate limits the administration of b blockers which have more powerful salutary effects.* * Patient has taken sildenafil in the past 24 hour Refer kDT 6/e p526