Blockers potency, cardiac

Assessment of physical, as well as psychiatric status, is also critically important. The presence of intercurrent medical disorders, as well as any medication used to manage them, increases the likelihood of an adverse outcome with an otherwise appropriate medication. With a recent history of myocardial infarction, certain tricyclic antidepressants (TCAs) or low-potency antipsychotics might be contraindicated due to potential adverse effects on cardiac function. Another example is the avoidance of carbamazepine in a bipolar patient with a persistently low white blood cell count. Finally, b-blockers are typically contraindicated in a patient with asthma. 

Important differences in vascular selectivity exist among the calcium channel blockers. In general, the dihydropyridines have a greater ratio of vascular smooth muscle effects relative to cardiac effects than do diltiazem and verapamil. Furthermore, the dihydropyridines may differ in their potency in different vascular beds. For example, nimodipine is claimed to be particularly selective for cerebral blood vessels. Splice variants in the structure of the cq channel subunit appear to account for these differences. 

They antagonize the positive inotropic and chronotropic effects of catecholamines. Cardiac arrhythmias associated with excessive adrenergic stimulus, released endogenous catecholamines or sensitization of the heart by anes-thetics or cardiac glycosides may effectively be treated by 6-blockade. Some B-blockers also possess membrane or local anesthetic action and are effective against arrhythmias due to ischemia or cardiac glycoside toxicity as well. This membrane action was shown to be independent of 6-blockade since resolved isomers of B-blockers possessed equal antiarrhythmic potency but unequal B-blocking action. 

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