INTERMITTENT TRANSDERMAL NITRATES DO NOT IMPROVE ISCHEMIA IN PATIENTS TAKING BETA-BLOCKERS OR CALCIUM-ANTAGONISTS - POTENTIAL ROLE OF REBOUND ISCHEMIA DURING THE NITRATE-FREE PERIOD

Objectives. This study was conducted to determine whether rebound ischemia occurs during nitrate free periods with intermittent cutaneous nitroglycerin therapy in patients with angina pectoris who are receiving background antianginal therapy. Background. Rebound angina has been suggested to be a complication of the nitrate free period with long-term cutaneous nitroglycerin therapy given intermittently to prevent tolerance. Methods. Fifty-two patients with stable effort angina taking either a beta-adrenergic blocking agent (n = 25) or diltiazem (n = 22) or their combination (n = 5) completed a randomized, double-blind, placebo controlled crossover study of cutaneous nitroglycerin patches (50 mg). Active or placebo patches were worn for 1 week applied at 8 AM and removed at 10 PM to provide a 10-h daily nitrate-free (or placebo free) period. During the last 48 h of each study phase, a Holter monitor was used to detect ischemia. Results. Only 31 patients experienced ischemia during either phase of the study (23 during the patch-off period). A total of 463 ischemic episodes were recorded: 246 during placebo and 217 during nitroglycerin (p = 0.8, for per patient comparison). The majority (88%) of ischemic episodes were silent, Mean (+/-SEM) duration of ischemia during the total 48 h period was similar during active and placebo phases (35.5 +/- 15.0 min/24 h for active therapy vs. 29.7 +/- 9.8 for placebo, p = 0.8). This was due to an increase in duration of ischemia with active therapy during the patch-off period (46.9 +/- 17.9 min/24 h for active therapy vs. 22.5 +/- 9.2 for placebo, p = 0.07) and a decrease during the patch-on period (27.5 +/- 14.0 min/24 h for active therapy vs. 34.5 +/- 11.0 min/24 h for placebo, p = 0.16). The pattern of diurnal distribution of ischemic episodes differed between active and placebo phases. During placebo there was a nadir in the incidence of ischemia in the overnight patch-off period, with a significantly lower incidence between midnight and 6 AM (25 episodes) compared with the mean number of episodes during the three other 6-h periods (73 episodes, p < 0.001). During the nitroglycerin patch off period, there was a loss of this overnight nadir, with the same incidence of ischemia between midnight and 6 AM (53 episodes) as the mean number of episodes for the three other 6-h periods (54 episodes). Conclusions. The majority of patients taking background anti anginal therapy experienced no ischemia during the patch off period. In the 44% of patients with ischemia during this period, there was a nonsignificant increase in the duration of ischemia with active therapy. Although this result was statistically inconclusive, the change in the distribution of diurnal ischemia offers suggestive evidence that rebound ischemia may be a problem with regard to intermittent cutaneous nitroglycerin.