Beta-adrenergic blocking drugs in the treatment of congestive heart failure

Combined effect of the force-frequency and length-tension mechanisms on left ventricular function in patients with dilated cardiomyopathy

BACKGROUND

The myocardial length-tension and the force-frequency relations are important mechanisms that regulate the contractile strength of the heart.

AIMS

To evaluate in humans the effect on left ventricular function of the interaction between the myocardial length-tension and force-frequency relations.

METHODS AND RESULTS

Eight patients with dilated cardiomyopathy (DCM) and 6 control subjects underwent radionuclide monitoring of left ventricular function during atrial pacing, saline loading and atrial pacing at the end of saline loading. In controls, atrial pacing reduced left ventricular end-diastolic (P < 0.001) and end-systolic volumes (P < 0.001) with no change in ejection fraction whereas after volume expansion end-diastolic volume (P < 0.001) and ejection fraction (P < 0.001) increased. Atrial pacing after volume expansion increased ejection fraction (P < 0.05). In patients with DCM, ejection fraction was reduced during atrial pacing (P < 0.001) and volume expansion (P < 0.05) due to an increase in left ventricular end-systolic volume (P < 0.001). Pacing tachycardia after volume expansion further increased end-systolic volume and reduced ejection fraction with a significant 'pacing by load' interaction (P < 0.001). Peak filling rate increased at each step in controls while it remained unchanged in patients with DCM.

CONCLUSION

The heart rate increase during left ventricular distension improves ventricular function in normals and has detrimental effects in patients with DCM.

Combined phosphodiesterase inhibition and beta-blockade in the GI104313, decreases ischemia-induced arrhythmias in the rat

PURPOSE

The purpose of the present study was to evaluate the effects of GI104313, a chimeric molecule containing a phosphodiesterase inhibiting pyradazinone and a blocking phenoxpropanolamine, on ischemia-induced arrhythmias in anesthetized rats.

METHOD

The coronary artery was occluded 15 min after commencing drug administration and myocardial ischemia was maintained for 30 min during which the heart rate and mean blood pressure were recorded. Cyclic AMP and GMP were determined by radio-immunoassay.

RESULTS

GI104313 (0.1 micromol x kg(-1) plus 0.01 micromol x kg(-1) x min(-1) or 1 micromol x kg(-1) plus 0.1 micromol x kg(-1) x min(-1)) decreased the incidence of ventricular tachycardia (86% and 75%), ventricular fibrillation (28%, P <0.01 and 12%, P <0.001) and premature ventricular beats (164 +/- 27.0 and 114 +/- 28.5, P <0.05) following coronary artery ligation, resulting in a decrease in mortality (29% and 12%, P <0.05). Changes in cyclic nucleotide concentrations have been implicated in the genesis of ischemia-induced arrhythmias. However, in the present study GI104313 did not change the concentrations of adenosine 3':5'-cyclic monophosphate (cyclic AMP) (1.0 +/- 0.07 pmol x mg(-1), 1.0 +/- 0.05 pmol x mg(-1)) or guanosine 3':5'-cyclic monophosphate (cyclic GMP) (0.025 +/- 0.008 pmol x mg(-1) protein, 0.017 +/- 0.004 pmol x mg(-1) protein) in the left ventricle during ischemia-induced arrhythmias in anesthetized rats compared to saline (0.9 +/- 0.1 pmol x mg(-1) and 0.013 +/- 0.002 pmol x m(-1), respectively).

CONCLUSION

Our results demonstrate that, in rats, GI104313 induced a decrease in both incidence of arrhythmias and mortality which was not associated with changes in ventricular cyclic nucleotide content.

Electropharmacological effects of UK-1745, a novel cardiotonic drug, in guinea-pig ventricular myocytes

Effects of (2RS, 3SR)-2-aminomethyl-2,3,7,8-tetrahydro-2,3,5,8, 8-pentamethyl-6H-furo-[2,3-e] indol-7-one hydrochloride (UK-1745), a novel cardiotonic drug with beta-adrenoceptor blocking property and antiarrhythmic activity, on the action potentials of isolated papillary muscles and the membrane currents of single ventricular myocytes of guinea pigs were examined and compared with those of milrinone using conventional microelectrode and patch-clamp techniques. In papillary muscles, UK-1745 (3-100 microM) produced a mild positive inotropic response and depressed the maximum upstroke velocity of the action potential (V(max)) at 100 microM. Milrinone, a phosphodiesterase III inhibitor, markedly shortened the action potential duration with a significant increase in developed tension. In enzymatically-dissociated ventricular myocytes, UK-1745 failed to increase the L-type Ca(2+) current (I(Ca)) at 10 and 30 microM and rather decreased I(Ca) at 100 microM. The high concentration of UK-1745 slightly inhibited the delayed rectifier K(+) current (I(K)). Although UK-1745 antagonized the isoproterenol-induced increase in I(Ca), it potentiated the histamine-induced increase in I(Ca). On the other hand, milrinone per se significantly increased I(Ca) and markedly enhanced the isoproterenol-induced increase in I(Ca). It can be concluded that UK-1745 is a unique cardiotonic drug possessing beta-adrenoceptor blocking and weak phosphodiesterase-inhibitory actions in addition to direct inhibitory actions on the Na(+), Ca(2+) and K(+) channels with its high concentrations.

A prospective study of the efficacy and safety of adjuvant metoprolol and xamoterol in combination with amiodarone for resistant ventricular tachycardia associated with impaired left ventricular function

Combination antiarrhythmic drug therapy may be more effective than treatment with a single agent for control of refractory cases of sustained ventricular tachycardia (VT). In a prospective randomized crossover study of 20 patients with impaired left ventricular function (ejection fraction of 28% +/- 8%) and recurrent VT in spite of treatment with amiodarone, we compared the efficacy and safety of adjuvant therapy with metoprolol, 50 mg two times daily and xamoterol, 200 mg two times daily. Metoprolol caused hemodynamic deterioration in five patients, and only one also experienced intolerance to xamoterol. Sustained VT was inducible in all 20 patients who were receiving amiodarone alone but was suppressed or rendered nonsustained in 8 of 20 patients during treatment with amiodarone plus xamoterol and in 6 of 17 patients during treatment with amiodarone plus metoprolol. Addition of xamoterol restored sinus rhythm in four patients who presented with incessant VT, and metoprolol was effective for three of them. Neither beta-blocker significantly altered tachycardia cycle length or any electrophysiologic parameter other than the slowing of the sinus rate. Both beta-blockers suppressed exercise-induced VT in 3 of 4 patients, and addition of xamoterol significantly increased treadmill exercise duration (7.1 +/- 1.8 min) compared with administration of amiodarone alone (3.8 +/- 1.5 min; p < 0.01). Fourteen patients were discharged with prescriptions for amiodarone-beta-blocker combinations. During a mean follow-up period of 13 months (range, 2 to 24 months), there were three cases of recurrent VT (in all patients VT remained inducible) and no sudden deaths.(ABSTRACT TRUNCATED AT 250 WORDS)