Sinus drugs

Class II drugs are classical (3-adrenoceptor antagonists such as propranolol, atenolol, metoprolol or the short-acting substance esmolol. These drugs reduce sinus rate, exert negative inotropic effects and slow atrioventricular conduction. Automaticity, membrane responsiveness and effective refractory period of Purkinje fibres are also reduced. The typical extracardiac side effects are due to (3-adrenoceptor blockade in other organs and include bronchospasm, hypoglycemia, increase in peripheral vascular resistance, depressions, nausea and impotence. 

Class II antiarrhythmic drugs are (3-adrenoceptor antagonists such as propranolol, metoprolol or atenolol. (3-adrenoceptor antagonists slow sinus rate and atrioventricular conduction and exert negative inotropic effects. 

Class IV antiarrhythmic drugs are Ca2+ channel blockers, which predominantly slow sinus rate and atrioventricular conduction and thus are used in the treatment of supraventricular tachyarrhythmias. These drugs exert a pronounced negative inotropic effect. 

These drags are contraindicated in patients with an allergy to the (3 blockers, in patients with sinus bradycardia, second- or third-degree heart block, heart failure, and those with asthma, emphysema, or hypotension. The drug are used cautiously in patients with diabetes, thyrotoxicosis, and peptic ulcer. 

The hydantoins are contraindicated in patients widi known hypersensitivity to die drug s. Phenytoin is contraindicated in patients widi sinus bradycardia, sinoatrial block, second and diird degree AV block, and Adams-Stokes syndrome it also is contraindicated during pregnancy (ediotoin and phenytoin are Pregnancy Category D) and lactation. Ediotoin is contraindicated in patients widi hepatic abnormalities. 

These drug are used cautiously in patients with renal or hepatic disease, bladder obstruction, seizure disorders, sick sinus syndrome, gastrointestinal bleeding, and asthma Individuals with a history of ulcer disease may have a recurrence of the bleeding. 

Drugs related to PCP are known to alter the carotid sinus reflex. Mechanical stimulation of the carotid sinus in the neck normally results in a slowing of heart rate and a decrease in blood pressure. Carotid sinus stimulation, coupled with the effects of PCP on blood vessels, might result in a marked fall in the blood pressure that could lead, ultimately, to death. Individuals intoxicated with PCP may be at a higher risk to complications of carotid compression neck holds. Hence, additional cases would be expected to become medicolegal issues. 

Compare and contrast the mechanisms of action of drugs used for ventricular rate control, conversion to sinus rhythm and maintenance of sinus rhythm in patients with AF, and explain the importance of anticoagulation for patients with AF. 

Design individualized drug therapy treatment plans for patients with (1) sinus bradycardia (2) AV nodal blockade (3) AF (4) PSVT (5) VPDs (6) VT (including torsades de pointes) and (7) VF. 

Numerous drugs ((1-blockers, diltiazem, verapamil, digoxin, and amiodarone) can cause bradyarrhythmias (sinus bradycardia and AV nodal blockade). 

Antiarrhythmic drug therapy for maintenance of sinus rhythm/reduction in frequency of episodes of AF should be initiated only in patients in whom symptoms persist despite maximal doses of drugs for ventricular rate control. 

Sick sinus syndrome leading to sinus bradycardia may be caused by degenerative changes in the sinus node that occur with advancing age. However, there are other possible etiologies of sinus bradycardia, including drugs (Table 6-2).13... 

Determine whether the patient is taking any drugs known to cause sinus bradycardia. If the patient is currently taking digoxin, determine the serum digoxin concentration and ascertain whether it is supratherapeutic (greater than 2 ng/mL [2.56 nmol/L]). 

Treatment of sinus bradycardia is only necessary in patients who become symptomatic. If the patient is taking any med-ication(s) that may cause sinus bradycardia, the drug(s) should be discontinued whenever possible. If the patient remains in sinus bradycardia after discontinuation of the drug(s) and after five half-lives of the drug(s) have elapsed, then the drugs(s) can usually be excluded as the etiology of the arrhythmia. In certain circumstances, however, discontinuation of the medication(s) may be undesirable, even if it may be the cause of symptomatic sinus bradycardia. For example, if the patient has a history of myocardial infarction or HF, discontinuation of a (3-blocker is undesirable, because (3-blockers have been shown to reduce mortality and prolong life in patients with those diseases, and the benefits of therapy with... 

Conversion to Sinus Rhythm Termination of AF in hemodynami-cally stable patients may be performed using antiarrhythmic drug therapy or elective DCC. Drugs that may be used for conversion to sinus rhythm are presented in Table 6-7 these agents... 

In recent years, numerous studies have been performed to determine whether drug therapy for maintenance of sinus rhythm is preferred to drug therapy for ventricular rate control.28-31 In these studies, patients have been assigned randomly to receive therapy either with drugs for rate control or with drugs for rhythm control (Table 6-8). These studies have found... 

TABLE 6-7. Drugs for Conversion of Atrial Fibrillation to Normal Sinus Rhythm... 

TABLE 6-8. Drugs for Maintenance of Sinus Rhythm/ Reduction in the Frequency of Episodes of Atrial Fibrillation... 

The desired outcomes for treatment are to terminate the arrhythmia, restore sinus rhythm, and prevent recurrence. Drug therapy is employed to terminate the arrhythmia and restore sinus rhythm nonpharmacologic measures are employed to prevent recurrence. 

Patients who may benefit from allergen immunotherapy include those who do not tolerate traditional drug therapy (e.g., nosebleeds with intranasal steroids or sedation with antihistamines), suffer from severe symptoms, have comorbid conditions (e.g., asthma or sinusitis), fail drug therapy, or prefer not to take long-term medication. 

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