Calcium channel blocking agents and the heart

In The Line of Treatment: A Systematic Review of Paroxysmal Supraventricular Tachycardia

Paroxysmal supraventricular tachycardia (PSVT) is a common tachyarrhythmia, and an electrocardiogram is the best tool for making a diagnosis. If Valsalva maneuvers and carotid sinus massage do not give positive results, then the next choice is either adenosine or calcium channel blockers. At this time, adenosine is the drug of choice of treatment. Verapamil and diltiazem are the most commonly used calcium channel blockers (CCBs). This review aimed to compare the efficacy of both drugs in the treatment of PSVT.

We utilized the databases PubMed Central and Medline by using keywords: "calcium channel blockers OR adenosine AND supraventricular tachycardia." In the end, we finalized 32 studies, including observational studies, literature reviews, systematic reviews/metanalysis, and randomized control trials. We included articles only in the English language and related to humans. Two authors completed the quality assessment and evaluation of bias according to specific guidelines. Only high-quality studies were included in this systematic review based on the cut-off score of seven or above. Calcium channel blockers have a longer half-life than adenosine and were previously used as the drug of choice in the treatment of PSVT. Calcium channel blockers are safe if given slowly; however, adenosine is safer and useful when an electrocardiogram is uncertain. We compared both drugs in certain aspects and found equal efficacy. Though safer, adenosine was found to have a higher cost and a higher probability of re-initiation arrhythmia compared to calcium channel blockers. 

Effect of delayed administration of activated charcoal on the absorption of conventional and slow-release verapamil

OBJECTIVE

To investigate the effect of simultaneous and delayed administration of activated charcoal on the absorption of two verapamil formulations.

METHODS

In the first study, 9 healthy volunteers received the following treatments: 1) verapamil 80 mg (conventional formulation) with 50 mL water only, 2) verapamil 80 mg and 25 g activated charcoal immediately afterwards, and 3) verapamil 80 mg with 50 mL water, followed by 25 g charcoal 2 h after verapamil ingestion. In the second study, 8 healthy volunteers received the following treatments: 1) verapamil 240 mg (slow-release formulation) with 50 mL water only, 2) verapamil slow-release 240 mg and 25 g activated charcoal immediately afterwards, 3) verapamil slow-release 240 mg with 50 mL water, followed by 25 g charcoal 2 h after verapamil ingestion, and 4) verapamil slow-release 240 mg with 50 mL water, followed by 25 g charcoal 4 h later. Plasma verapamil concentrations over 24 h were measured by high performance liquid chromatography.

RESULTS

Activated charcoal given immediately after the conventional formulation of verapamil reduced the AUC0-24 h by 99% (p < 0.0005) and the Cmax by 98% (p < 0.0005). When the administration of charcoal was delayed 2 h, no significant change in verapamil absorption was observed. With the slow-release formulation of verapamil, charcoal given immediately after verapamil ingestion reduced the verapamil AUC0-24 h by 86% (p = 0.001) and the Cmax by 82% (p = 0.002). When the administration of charcoal was delayed 2 or 4 h, the AUC0-24 h was reduced by 35% (p = 0.04) and 32% (p = 0.001), respectively, but the Cmax was decreased by 13% (p = NS) and 9% (p = NS) only.

CONCLUSIONS

Activated charcoal was effective in preventing absorption of verapamil when it was administered immediately after verapamil ingestion. In the case of slow-release formulation, charcoal reduced verapamil absorption by over 30% even when given 4 h after verapamil.

Management of massive verapamil overdose

A 53-year-old man presented to hospital after an overdose (4.8 g) of verapamil. He developed profound bradycardia and hypotension, requiring treatment with calcium salts, dobutamine, isoprenaline and cardiac pacing. As calcium channel blockers are more widely used, self-poisoning will become more common. The effects, although serious, are self-limiting and recovery within 48 hours is the rule provided adequate support is given.

Acute hemodynamic effects of intravenous diperdipine, a new dihydropyridine derivative, in coronary heart disease

The acute hemodynamic effects of a new dihydropyridine calcium channel blocker, diperdipine, which is suitable for intravenous administration, were studied by right and left cardiac catheterization in 16 patients with coronary heart disease. Diperdipine markedly reduced systemic vascular resistance and improved stroke index and left ventricular ejection fraction. Mean pulmonary artery and wedge pressures were slightly increased as a possible consequence of enhanced venous return, whereas right atrial and left ventricular end-diastolic pressures were not significantly changed. Nevertheless, an increase in preload was clearly indicated by an augmented left ventricular end-diastolic volume index after administration of diperdipine. Left ventricular contractility, which was estimated by the end-systolic pressure-volume ratio and by dP/dt max was not significantly changed, though analysis of individual data suggests a minimally negative inotropic effect. However, such a minor effect on left ventricular contractility was largely counterbalanced by the marked reduction of afterload, which produced a sharp improvement of stroke index. Enhancement of left ventricular ejection fraction and reduction in systemic vascular resistance were inversely and directly correlated to control values. Overall, diperdipine was well tolerated, but one patient had a major untoward reaction that consisted of an ischemic episode that was possibly related to drug administration. In conclusion, intravenous diperdipine appears to be a potent arteriolar dilating agent that does not affect left ventricular contractility.

Rheology of the sickle cell disorders

The sickling process causes secondary changes in cell shape, size, cation and water content, and membrane structure that contribute to the impairment of intrinsic cell deformability (Figure 2). This rheological defect is partially compensated by a low haematocrit, which moderates the rise in whole-blood viscosity, and by a rise in cardiac output which increases capillary flow velocity (Berger and King, 1982). A delicate balance exists between these mechanisms and any local disturbance of this balance by pathological changes in factors extrinsic to the sickle cell (Figure 2) can precipitate vaso-occlusion. There is still considerable controversy over the site (arteriolar, capillary, or venular) of vaso-occlusion, the type of sickle cell (reversibly sickled or irreversibly sickled) that is primarily involved, and the relative importance of extra-erythrocytic precipitating factors such as stasis, hypoxia, hyperosmolality, acidosis, alteration in temperature, acute-phase rise in plasma proteins and leukocytes, prothrombotic changes in coagulation factors and platelets, and adhesion of blood cells to vascular endothelium (Figure 2). A low-grade hypercoagulable state has been described in patients with SS (Leichtman and Brewer, 1978; Richardson et al, 1979) which may be related to the procoagulant effect of the shift of phosphatidyl serine to the outer lipid bilayer of the sickle cell (Chiu et al, 1981; Franck et al, 1985). Platelets appear to accumulate at sites of vaso-occlusion (Siegel et al, 1985) and their migration to the vessel wall may be enhanced by the presence of poorly deformable erythrocytes (Aarts et al, 1984). Endothelial cell damage in the arterial or venous circulation may also contribute (Klug et al, 1982). Thus vaso-occlusion appears to result from a complex interaction between blood cells, plasma proteins and endothelium and any one of several precipitating factors may disturb the fragile steady state and cause a painful crisis. The study of sickle cells by rheological methods has considerable potential for investigating the pathophysiology of vaso-occlusive episodes in the SCD and for monitoring, both in vitro and ex vivo, the efficacy of antisickling compounds. Because of the multiple intrinsic and extrinsic factors that contribute to the rheological defect, it is not yet known which of these should be the primary target for an antisickling agent. In-vitro rheological studies in which different metabolic stresses can be applied to intact sickle cells in the presence of a putative antisickling drug should help to answer this question.(ABSTRACT TRUNCATED AT 400 WORDS)

Nifedipine in the treatment of myotonia in myotonic dystrophy

Abnormal calcium transport may be implicated in the membrane defect in myotonic dystrophy. A single blind crossover trial of placebo (t.i.d.), nifedipine 10 mg (t.i.d.) and nifedipine 20 mg (t.i.d.), was performed in 10 patients with myotonic dystrophy. The severity of myotonia was assessed by measuring finger extension time after maximum voluntary finger flexion. A significant improvement in myotonia, after nifedipine, was recorded by this technique and supported by a subjective improvement in 50% of patients and clinical improvement of greater than 20% in five patients. Initial grip strength and muscle fatiguability measured by grip strength ergometry were not significantly altered.