Actions of lofepramine, a new tricyclic antidepressant, and desipramine on electrophysiological and mechanical parameters of guinea pig atrial and papillary muscles

Tricyclic antidepressants directly depress human myocardial mechanical function independent of effects on the conduction system

OBJECTIVES

To measure the effect of tricyclic antidepressant drugs (TCAs) on human myocardial contractility.

METHODS

Human atrial tissue was obtained during cardiac bypass surgery. The tissue was harvested, suspended in a Tyrode buffer at 37 degrees C, and perfused with a 95%/5% oxygen-carbon dioxide mixture. Developed force was continuously measured using a force transducer and recorded by computer. After an equilibration period, escalating doses of amitriptyline or desipramine were added to the bath. All strips were exposed to the following five concentrations of each drug: 0 (control) 0.4, 4, 40, and 400 microM. The results for each experiment were expressed as the difference between the developed force measured prior to the addition of each concentration of drug and the developed force measured after a 30-minute exposure to the drug.

RESULTS

Desipramine decreased the developed force by 27%, 49%, and 74% at concentrations of 0.4, 40, and 400 microM, respectively. Amitriptyline decreased the developed force by 38% at the 40-microM concentration and by 89% at the 400-microM concentration. Untreated strips retained 94% of baseline developed force at 150 minutes.

CONCLUSIONS

Tricyclic antidepressants depress human myocardial function in a dose-dependent fashion independent of the effects on the cardiac conduction system. While previous work has demonstrated the effect of therapies for the reversal of impaired cardiac conduction following TCA poisoning, to the best of the authors' knowledge, no reports have documented the effects of therapy on direct myocardial depression. Additional therapies targeted at reversing the direct cardiodepressive effects of TCA may improve outcome following TCA poisoning.

Cardiac electrophysiological effects of citalopram in guinea pig papillary muscle comparison with clomipramine

The effect of citalopram, a selective serotonin reuptake inhibitor (SSRI) antidepressant, was studied on cardiac action potential configuration and compared with that of the tricyclic antidepressant (TCA) clomipramine. Conventional microelectrode techniques were used in right ventricular papillary muscle preparations of the guinea pig. Citalopram caused a concentration-dependent (10-100 microM) shortening of action potential duration (APD), depression of plateau and overshoot potential, and reduction of maximum velocity of depolarization (V(max)). No significant changes in resting membrane potential were observed. Similar results were obtained with clomipramine; however, reduction of V(max) and overshoot was more pronounced with clomipramine, whereas citalopram caused relatively greater shortening of APD. Effects of both drugs were partly reversible. The results indicate that the SSRI antidepressant citalopram, similarly to TCA compounds, alters cardiac action potential configuration in guinea pig ventricular muscle, probably owing to inhibition of cardiac Na(+) and Ca(2+) channels. Differences in cardiac side effects of the two drugs may be related to their different actions on cardiac action potential configuration.

The cardiovascular effects of antidepressants

This monograph comprises a review of the cardiovascular effects of the various types of antidepressant drugs in clinical use. The frequency, severity and clinical importance of these effects are placed in perspective. Most antidepressants can cause changes in blood pressure. Both the tricyclic type (TCA) and the monoamine oxidase inhibitors (MAOIs) can produce postural hypotension which may be dose-limiting. In addition, the MAOIs may be associated with severe hypertension when amine-containing foods or medicines are ingested. It is unlikely that therapeutic doses of any available antidepressant drug could impair cardiac contractility. Typical TCAs can cause abnormalities of cardiac conduction and arrhythmias, but this affects less than 5% of patients, mostly to a clinically insignificant extent. Newer compounds such as lofepramine, mianserin, trazodone and viloxazine seem safer in this respect. Reports of an association between therapeutic use of TCAs and sudden death are far from convincing. Overdosage with the MAOIs, lithium and carbamazepine is dangerous but not common; overdose with a TCA is a major source of morbidity and mortality. Lofepramine, mianserin and trazodone are relatively safe in overdose. The use of various antidepressants in patients with hypertension, cardiac failure, angina pectoris, myocardial infarction, or cardiac arrhythmias is discussed and guidelines suggested for the selection and use of antidepressant medication.