Preservation of adenosine 5'-triphosphate and mitochondrial function during hypercalcemic reperfusion using verapamil cardioplegia

Effect of verapamil and procainamide on atrial fibrillation-induced electrical remodeling in humans

BACKGROUND

Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The purpose of this study was to determine the effect of verapamil and procainamide on these manifestations of AF-induced electrical remodeling.

METHODS AND RESULTS

In adult patients without structural heart disease, the atrial ERP was measured before and after AF after pharmacological autonomic blockade and administration of verapamil (17 patients), procainamide (10 patients), or saline (20 patients). AF was then induced by rapid pacing. Immediately on AF conversion, the post-AF ERP was measured at alternating drive cycle lengths of 350 and 500 ms. In the saline group, the pre-AF and first post-AF ERPs at the 350-ms drive cycle length were 206+/-19 and 179+/-27 ms (P<.0001), respectively, and at the 500-ms drive cycle length, the values were 217+/-16 and 183+/-23 ms, respectively (P<.0001). There was a similar significant shortening of the first post-AF ERP in the procainamide group. In the verapamil group, however, there was no difference between the pre-AF and the first post-AF ERP at the 350-ms (226+/-15 versus 227+/-22 ms, P=.8) or 500-ms (230+/-17 versus 232+/-20 ms, P=.6) drive cycle length. During determinations of the post-AF ERP, 105 secondary episodes of AF were unintentionally induced in 12% of verapamil patients compared with 90% and 80% of saline and procainamide patients (P<.01 versus verapamil).

CONCLUSIONS

Pretreatment with the calcium channel antagonist verapamil, but not the sodium channel antagonist procainamide, markedly attenuates acute, AF-induced changes in atrial electrophysiological properties. These data suggest that calcium loading during AF may be at least partially responsible for AF-induced electrical remodeling.

Myocardial metabolism during graded intraportal verapamil infusion in awake dogs

Verapamil produces comparatively greater in vivo left ventricular (LV) depression than other calcium channel antagonists produce, possibly because of myocardial metabolic derangements in addition to L-channel antagonism. Therefore, we studied myocardial lipid and carbohydrate usage and the effect of insulin treatment during progressive verapamil toxicity. Verapamil was infused through the portal vein to simulate oral overdose. Eighteen mongrel dogs were instrumented to measure multiple hemodynamic and metabolic parameters. After 1-week recovery, dogs underwent control euglycemic insulin dose-response studies (n = 6) in the conscious state: at 1,000 mU/mm insulin infusion rate, myocardial glucose and lactate extraction increased seven- and threefold, respectively with no change in coronary artery blood flow or ventricular elasticity and end-systole (Ees). In 12 separate dogs, intraportal graded verapamil toxicity was induced in 3 h by increasing the infusion rate hourly: 0.04 -- 0.08 -- 0.1 mg/kg/mm. At the end of hour 3, myocardial extraction of free fatty acids decreased from 33 +/- 4 to 9 +/- 3% (mean +/- SEM, p < 0.05), without significant change in myocardial blood flow or arterial free fatty acid concentration. Verapamil toxicity increased arterial glucose from 3.5 +/- 0.16 to 6.1 +/- 1.1 mM; simultaneously, myocardial glucose extraction doubled, although endogenous insulin concentrations did not increase. Arterial lactate concentrations and net myocardial lactate uptake both increased (p < 0.05 vs basal blue). Ees decreased from 28 +/- 1 mm Hg/mm (basal) to 20 +/- 2 mm Hg/mm (end of hour 3, p <0.05). Animals were randomized into two treatment groups; either (a) insulin-glucose (1,000 mU/mm, n 6; arterial glucose was clamped +/- 10% with 50% dextrose), or (b) saline controls (n = 6) that received equivalent volume of saline. After 1-h insulin treatment, Ees increased to 34 + 3 mm Hg; in controls, Ees was 15 +/- 3 mm Hg/mm (p < 0.05). With insulin-glucose treatment, neither myocardial glucose nor lactate extraction increased significantly (p = 0.06 for lactate). Verapamil therefore inhibits myocardial fatty acid uptake and impedes insulin-stimulated myocardial glucose uptake; under these conditions, insulin-glucose treatment increases myocardial contractile function independent of increased sugar transport. These findings indicate that verapamil toxicity produces myocardial insulin resistance and, potentially, nutrient deprivation that may contribute to clinically relevant negative inotropy.