Acute hypertensive stress imaged by cardiac hyperpolarized [1- 13 C]pyruvate magnetic resonance.

PURPOSE: Deranged metabolism is now recognized as a key causal factor in a variety of heart diseases, and is being studied extensively. However, invasive methods may alter metabolism, and conventional imaging techniques measure tracer uptake but not downstream metabolism. These challenges may be overcome by hyperpolarized MR, a noninvasive technique currently crossing the threshold into human trials. The aim of this study was to image metabolic changes in the heart in response to endogastric glucose bolus and to acute hypertension.

METHODS: Five postprandial pigs were scanned with hyperpolarized [1-13 C]pyruvate cardiac MR at baseline, after oral glucose bolus, and after infusion of angiotensin-II.

RESULTS: No effect of glucose bolus was seen using hyperpolarized [1-13 C]pyruvate MR despite changes in circulating substrates. During angiotensin-II infusion, blood pressure increased 179% (P = 0.008) and ejection fraction decreased from 54 ± 2% to 47 ± 6% (P = 0.03) The hemodynamic changes were accompanied by increases in the hyperpolarized [1-13 C]pyruvate MR derived ratios of lactate/alanine (from 0.58 ± 0.13 to 0.78 ± 0.06, P = 0.03) and bicarbonate/alanine (from 0.55 ± 0.12 to 0.91 ± 0.14, P = 0.007).

CONCLUSION: Glucose loading did not alter cardiac metabolism, but during acute hypertensive stress, cardiac aerobic, carbohydrate metabolism, and pyruvate-lactate exchange was altered. Hyperpolarized MR allows noninvasive evaluation of acute changes in cardiac metabolism. However, hemodynamics must be taken into account when interpreting the results.