Myocardial protection through cold cardioplegia with potassium or diltiazem. Experimental evidence that diltiazem provides better protection even when coronary flow is impaired by a critical stenosis.

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Abstract
Intermittent aortic root infusion of a cold solution containing either potassium chloride (KCl) or diltiazem was performed in 32 dogs during a 2-hour aortic clamping. Half of the dogs in each group had a critical stenosis created on the circumflex artery before cardiopulmonary bypass. Global left ventricular (LV) function was determined 1 hour after bypass by means of LV pressure, peak dP/dt, LV end-diastolic pressure, cardiac and stroke work indexes. Regional function was assessed through microcrystals in the areas of the circumflex and left anterior descending coronary arteries. LV pressure decreased in all dogs, but more so with the KCl solution (p = 0.02). The stenosis had no specific effect on LV pressure, but affected peak positive dP/dt (p = 0.007) and LV end-diastolic pressure (p less than 0.0001). Cardiac and stroke work indexes decreased more in the KCl group than in the diltiazem group (p less than 0.002) with or without stenosis. Both positive and negative dP/dt were affected by the type of solution (a greater decrease with KCl), but the narrowing affected only the positive dP/dt. Regional LV function remained unchanged in the absence of a narrowing and was depressed equally in dogs with a narrowing whether they received KCl or diltiazem. Overall LV function appeared to be better preserved with diltiazem, with or without impairment of circumflex flow.