Heart rate reduction in the treatment of chronic stable angina pectoris: experiences with a sinus node inhibitor

Prognostic significance of double product and inadequate double product response to maximal symptom-limited exercise stress testing after myocardial infarction in 6296 patients treated with thrombolytic agents. GISSI-2 Investigators. Grupo Italiano per lo Studio della Sopravvivenza nell-Infarto Miocardico

BACKGROUND

The aim of this study was to evaluate the prognostic significance of the pressure-rate product (PRP) obtained during exercise stress testing and of its change from rest to maximal exercise (dPRP) in a population of survivors of acute myocardial infarction treated with thrombolytic agents.

METHODS AND RESULTS

Survivors of acute myocardial infarction (n = 6251) from the GISSI-2 database, who underwent a maximal symptom-limited exercise test with either bicycle ergometer or treadmill, were followed up for 6 months. PRP and dPRP values were dichotomized (</=21,700 and >21,700, </=11, 600 and >11,600, respectively) and analyzed in a multivariate Cox model individually and simultaneously with other ergometric variables. Six-month mortality rate was 0.8% in the high PRP group and 2.0% in the low PRP group. Low PRP was an independent predictor of 6-month mortality rate (relative risk [RR] 1.97, 95% confidence interval [CI] 1.24 to 3.13). Patients with low dPRP had mortality rates higher than patients with high dPRP (2.1% vs 0.8%). At the multivariate analysis, low dPRP showed negative predictive value (RR 1.97, 95% CI 1.23 to 3.16). A further multivariate analysis was performed with PRP and dPRP, also adjusting for low work capacity, abnormal systolic blood pressure response to exercise, and symptomatic-induced ischemia. The results showed that low work capacity, low PRP, and symptomatic exercise-induced ischemia were still significantly associated with higher 6-month mortality rate (P =.04,.02, and.05; RR = 1.68, 1.71, and 1.78 respectively).

CONCLUSIONS

PRP is a predictive index to assess prognosis in survivors of acute myocardial infarction treated with thrombolytic agents able to perform an exercise test after acute myocardial infarction, but its usefulness appears to be limited, considering that these patients were at low risk.

Selective cardiodepressant activity of fluodipine, a fluorenone-1,4-dihydropyridine derivative

The effect of the dihydropyridine derivative, 1,4-dihydro-2,6-dimethyl-4-(fluorenon-4-yl)pyridine-3,5-dicarboxyl ic acid diallyl ester (fluodipine) was studied in vitro in different rabbit, rat and guinea pig preparations and in vivo in the rabbit in order to characterize its pharmacological profile at cardiac and at vascular sites. Compared to nifedipine, fluodipine showed a similar cardiodepressant activity, and a much lower inhibitory activity on vascular contraction. The highest tissue selectivity was observed in guinea pig preparations: fluodipine was about 2-3 times more effective than nifedipine on chronotropism and inotropism in isolated atria, and about 150 times less effective on aortic strip contraction. Accordingly, fluodipine (i) showed high-affinity binding to guinea pig ventricular L-type cardiac Ca2+ channels (Ki=2.57 nM), (ii) was about 80 times less effective than nifedipine to inhibit Ca2+ influx in vascular smooth muscle cells and (iii) induced a significant reduction of heart rate in the anesthetized rabbit (ID25=8.5 mg kg(-1), i.v.) without affecting the blood pressure up to 20 mg kg(-1), whereas nifedipine showed a significant hypotensive effect at very low doses (ID25=0.18 mg kg(-1), i.v.). The pacemaker current If of rabbit sino-atrial node myocytes was not affected by fluodipine. These findings demonstrate that fluodipine exerts selective cardiodepressant activity, likely due to a higher affinity for cardiac than for vascular Ca2+ channels.

Relationships between heart rate and heart rate variability: study in conscious rats

Heart rate (HR) and heart rate variability (HRV) are risk markers in cardiac disease. HRV is also an index of the sympathovagal modulation of heart rate. Their relations have been rarely analyzed. We aimed to study such relations in normal adult conscious rats by using a novel bradycardic agent, a sinus node inhibitor, S-16257. Placebo-drug crossover designs were used while monitoring HR with telemetry and analyzing HRV in both time and frequency domains. S-16257 (2 mg/kg; n = 10) decreased HR by 29% and markedly increased HRV in parallel. By using various combinations of S-16257, atropine (2 mg/kg), and propranolol (4 mg/kg), a positive relation was shown between RR interval and various indexes of HRV: the slower the HR, the greater the HRV. Nevertheless, there is one exception to this correlation. When S-16257 was associated with both atropine and propranolol, the deep bradycardia was accompanied by a reduction of HRV, which indicates that the physiologic negative correlation between HR and HRV is not an intrinsic property of the pacemaker but is highly dependent on the two components of the autonomic system.