Influence of drug therapy on the ischemic response to acute coronary occlusion in man: supply-side economics

1,4-Dihydropyridine derivatives as calcium channel modulators: the role of 3-methoxy-flavone moiety

It was earlier recognized that calcium antagonists, and in particular 1,4-dihydropyridines, exhibited distinct cardiovascular profiles. In addition two different splice variants of the L-type calcium channel were found in vascular and cardiac tissues. In this study, novel substituted 1,4-dihydropyridines with a 3-methoxy-flavone moiety were synthesized and structural modifications of the substituents in the dihydropyridine ring of nifedipine were carried out in order to find tissue specific compounds. The negative inotropic, chronotropic and vasorelaxant effects were investigated on guinea-pig left, right atria and aortic strips, respectively. The introduction of an heteroaromatic ring in 4-position of the 1,4-dihydropyridine nucleus led to compounds selective for cardiac tissues. Moreover, different residues in the 1,4-dihydropyridine ring could modulate the chronotropic versus inotropic activity.

Synthesis and pharmacological evaluation of piperidinoalkanoyl-1,2,3,4-tetrahydroisoquinoline derivatives as novel specific bradycardic agents

A series of piperidinoalkanoyl-1,2,3,4-tetrahydroisoquinoline derivatives were synthesized, and their bradycardic activities were investigated in the isolated right atria of guinea pigs and in conscious rats. These efforts identified the achiral compound 2f, which exhibited potent and long-lasting bradycardic activity with minimal effects on mean blood pressure in conscious rats.

(+/-)-2-(3-Piperidyl)-1,2,3,4-tetrahydroisoquinolines as a new class of specific bradycardic agents

A series of (+/-)-2-(3-piperidyl)-1,2,3,4-tetrahydroisoquinolines were prepared and their bradycardic activities were examined in isolated guinea-pigs' right atria and in anesthetized rats. Modifications on the benzyl moiety of the parent compound, 1, led to the identification of compound 11e as a potent and specific bradycardic agent.

Synthesis and pharmacological evaluation of 2-(3-piperidyl)-1,2,3,4-tetrahydroisoquinoline derivatives as specific bradycardic agents

Novel 1,2,3,4-tetrahydroisoquinoline derivatives bearing directly a cyclic amine at the 2-position were prepared and examined for their bradycardic activities in isolated right atria and in anesthetized rats. The structure-activity relationships (SAR) study revealed that the 2-(3-piperidyl)-1,2,3,4-tetrahydroisoquinoline skeleton is essential for the appearance of potent in vitro activity, and that the presence of at least one methoxy group at the 6- or 7-position of the 1,2,3,4-tetrahydroisoquinoline ring is important to exert potent in vitro activity. In vivo tests of selected compounds demonstrated that 2-(1-benzyl-3-piperidyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (6c) exhibited potent bradycardic activity with negligible influence on mean blood pressure in rats, although its potency is a half of that of Zatebradine.

Pharmacokinetic-pharmacodynamic modeling of the effects of ivabradine, a direct sinus node inhibitor, on heart rate in healthy volunteers

OBJECTIVE

Ivabradine (S-16257) is a new bradycardic agent with a direct effect on the sinus node. Its N-dealkylated metabolite, S-18982, has shown a bradycardic activity in animals. The aim of this trial was to study the correlation between drug bradycardic activity and plasma levels of the parent compound and its metabolite in healthy volunteers.

METHODS

Eighteen healthy volunteers participated in three successive study periods: an oral double-blind period with two parallel groups of doses (10 or 20 mg, single and repeated); a 10 mg intravenous bolus open period; and a final control period. The effects of ivabradine on heart rate were studied at rest and during bicycle exercise tests (at 85% of maximum workload) during 24-hour postdosing, and ivabradine and S-18982 plasma levels were determined simultaneously.

RESULTS

The maximal reductions of exercise heart rate were 11% +/- 4% (10 mg) and 18% +/- 6% (20 mg) after single oral doses (p < 0.05) and 18% +/- 4% (10 mg) and 27% +/- 6% (20 mg) after repeated doses (p < 0.01). Maximum heart rate reduction after the intravenous bolus was 19% +/- 4%. After oral administrations an indirect relationship between the bradycardic effect and the plasma concentrations of the two compounds was found. A pharmacokinetic/pharmacodynamic population analysis done with the NONMEM computer program showed that S-18982 contributes in part to the overall activity of ivabradine: modeling suggested that the metabolite is responsible for the initial bradycardic effect, whereas the parent compound is responsible for the duration of action.

CONCLUSION

This study shows that ivabradine exerts a dose-dependent bradycardic effect and that its N-dealkylated metabolite contributes to this bradycardic effect.

Interventional physiology. Part XVIII: Influence of intra-aortic balloon counterpulsation and collateral flow reversal during multivessel angioplasty

Flow velocity changes during multivessel angioplasty suggests that collateral flow has an important role in determining safety and ischemic threshold during these procedures. The physiology of collateral flow with and without intra-aortic balloon pumping has been demonstrated in this individual and provides insight into the mechanisms of reduced ischemia during high-risk coronary interventions.

Electrophysiological effects of S 16257, a novel sino-atrial node modulator, on rabbit and guinea-pig cardiac preparations: comparison with UL-FS 49

1. S 16257 is a new bradycardic agent. Its electropharmacological profile has been compared to that of the known bradycardic compound UL-FS 49 (Zatebradine). Intracellular recordings of action potentials (APs) were performed with conventional glass microelectrodes. 2. In the rabbit isolated sino-atrial node (SAN) tissue, S 16257 and UL-FS 49 (1 microM, 3 microM and 10 microM) were equipotent in slowing spontaneous APs firing predominantly by decreasing the rate of diastolic depolarization (at 3 microM, -23.8 +/- 3.9% and -27.9 +/- 2.6%, respectively). For the two compounds a maximal effect was obtained at 3 microM. In these preparations, action potential duration at 50% of total repolarization (APD50) was more affected by UL-FS 49 than S 16257 at any concentration tested (at 3 microM, +8.9 +/- 2.9% and +29.1 +/- 3.7% for S 16257 and UL-FS 49, respectively; P < or = 0.01). 3. To estimate the direct effects on AP duration, driven cardiac preparations were exposed to these agents. In guinea-pig papillary muscles, paced at a frequency of 1 Hz, increasing concentrations of S 16257 or UL-FS 49 (0.1 to 10 microM, 30 min exposure for each concentration) slightly prolonged AP repolarization. This prolongation was more marked for UL-FS 49 (at 1 microM, +6.1 +/- 0.6% and +11.2 +/- 1.3% elevation of APD50, for S 16257 and UL-FS 49, respectively). 4. Application of UL-FS 49 (3 microM) to rabbit Purkinje fibres, triggered at a frequency of 0.25 Hz, induced a marked prolongation of APD50 and APD90 (+149.4 +/- 51.2% and +86.0 +/- 15.4%, respectively). S 16257 (3 MicroM) induced only a weak prolongation of AP (+ 14.1 +/- 5.0% and + 14.8 +/- 3.3% for APD50 and APD90, respectively) significantly smaller than in the case of UL-FS 49.5. These results show that S 16257 slows the rate of spontaneous AP firing in isolated SAN mainly by a reduction of the diastolic depolarization of the cells, which suggests an inhibition of the pace-maker current (If). S 16257 and UL-FS 49 are equipotent in their bradycardic effect but S 16257 is more specific as it induces less increase in myocardial repolarization time.

Comparative effects of ischemia and hypoxemia on left ventricular systolic and diastolic function in humans

BACKGROUND

During the initial phase of an ischemic insult, left ventricular (LV) performance depends on the complex interaction between oxygen deprivation, vascular turgor, and accumulation of metabolites. In experimental preparations, low-flow ischemia decreases systolic shortening and increases diastolic LV distensibility, whereas pacing-induced ischemia or hypoxic perfusion produces smaller decreases in systolic shortening but decreases LV diastolic distensibility. The purpose of this study was to investigate the different effects of low-flow ischemia, pacing-induced ischemia, and hypoxemic perfusion on LV performance in humans.

METHODS AND RESULTS

In 20 patients with a significant stenosis in the left anterior descending coronary artery, micromanometer-tip LV pressure recordings (n = 20), LV angiography (n = 18), and coronary sinus blood sampling (n = 11) were obtained at rest and during the following conditions: pacing-induced ischemia (PI) (n = 11), low-flow ischemia of balloon coronary occlusion (CO) (n = 20), and hypoxemia induced by balloon coronary occlusion with hypoxemic perfusion distal to the occlusion (CO+P) (n = 11). LV stroke work index fell from 75 +/- 17 g.m at rest to 43 +/- 14 g.m at the end of CO (n = 18; P < .001). In addition, LV stroke work index was lower at the end of CO than during PI (50 +/- 11 vs 77 +/- 15 g.m; n = 11; P < .002) and was lower at the end of CO than at the end of CO+P (35 +/- 7 vs 46 +/- 9 g.m; n = 9; P < .02). LV end-diastolic pressure rose from 16 +/- 5 mm Hg at rest to 23 +/- 6 mm Hg at the end of CO (n = 20; P < .001). However, LV end-diastolic pressure was lower at the end of CO than during PI (20 +/- 5 vs 30 +/- 5 mm Hg; n = 11; P < .002) and was lower at the end of CO than at the end of CO+P (26 +/- 5 vs 34 +/- 7 mm Hg; n = 11; P < .01). LV end-diastolic volume index increased from 75 +/- 14 mL/m2 at rest to 79 +/- 15 mL/m2 at the end of CO (n = 18; P < .05). Left ventricular end-diastolic volume index increased to values similar to those for CO during PI (79 +/- 13 mL/m2; n = 11; P = NS) and at the end of CO+P (78 +/- 14 mL/m2; n = 9; P = NS). Higher values of LV end-diastolic pressure and unchanged values of LV end-diastolic volume index for PI and CO+P, compared with CO, suggested a lower end-diastolic LV distensibility during PI and during hypoxemia, as compared with low-flow ischemia. Upward shifts of individual diastolic LV pressure-volume curves during PI (9 of 11 patients) and at the end of CO+P (7 of 9 patients), compared with CO, were also consistent with lower LV diastolic distensibility during pacing-induced ischemia and during hypoxemia, compared with low-flow ischemia. Coronary sinus lactate, H+, and K+ levels increased after balloon deflation (CO and CO+P) and during pacing (PI).

CONCLUSIONS

Thus, during low-flow ischemia, LV systolic performance was lower and LV diastolic distensibility larger than during pacing-induced ischemia or hypoxemia. The variable response of the human myocardium to different types of ischemia was probably related to the degree of vascular turgor and accumulation of tissue metabolites.

Use of intracoronary ultrasonography in assessing pharmacotherapy for myocardial ischemia

Intracoronary ultrasonography can provide morphologic and physiologic information on coronary vasomotor responses to pharmacotherapy. Preliminary studies indicate a high correlation between dimensions determined by 2-dimensional echocardiography, angiography, and pathology. Similarly, the emerging data on intracoronary Doppler flow velocity responses beyond atherosclerotic obstructions before, during, and after coronary balloon occlusion will provide further insights into myocardial oxygen supply and its responses to pharmacotherapy during controlled myocardial ischemia.

Perspective: the cellular influences of calcium antagonists on systemic and coronary hemodynamics

Calcium antagonists may have a valuable role in ameliorating the extent and duration of myocardial ischemia following infarction. The precise cellular effects of these agents are being revealed through studies using the model of transient coronary occlusion induced by coronary angioplasty. The class of calcium antagonists is not uniform, and these diverse agents may have a favorable effect on ischemia through one or more of the following mechanisms: direct cardioprotective effects, prevention of calcium accumulation in the mitochondria in ischemic cells, reduction in oxygen consumption or in coronary artery vasoconstriction or coronary spasm, prevention of ischemia-induced arrhythmias, and increased coronary blood flow to ischemic tissue directly or through enhancement of collateral flow. Recent studies of diltiazem, nifedipine, nicardipine, nisoldipine, and amlodipine, as representative agents, are reviewed.