Cbnidine

Cocaine

Dexmedetomidine Digoxin Diltiazem D'pyridamole Disopyrarnide Donepezil Dronedarone Flecainide

Fluoxetine

Haiothane

Isradipine

Neostigmine

Nicardipine

Nitroglycerin

Paclitaxel

Propafenone

Propofol

Sevoflurane

Sotalol

Succinylcholine

Thalidomide

Verapamil

FromRefs. 12,13.

Acute treatment of the symptomatic patient consists primarily of administration of the anticholinergic drug atropine, which may be given in doses of 0.5 mg IV every 3 to 5 minutes. The maximum recommended total dose of atropine is 3 mg;14 however, this total dose should not be administered to patients with sinus bradycardia, but rather should be reserved for patients with cardiac arrest due to asystole, as complete vagal inhibition at this dose can increase myocardial oxygen demand and precipitate ischemia or tachyarrhythmias in patients with underlying coronary artery disease (CAD). Therefore, for management of sinus bradycardia, the maximum atropine dose should be approximately 2 mg. In patients with hemodynamically unstable or severely symptomatic sinus bradycardia that is unresponsive to atropine and in whom temporary or transvenous pacing is not available or is ineffective, epinephrine (2-10 mcg/ min, titrate to response) and/or dopamine (2-10 mcg/kg/min) may be administered. 4 Both drugs stimulate adrenergic a- and P-receptors.

In patients with sinus bradycardia due to underlying correctable disorders (such as electrolyte abnormalities or hypothyroidism), management consists of correcting those disorders.

Nonpharmacologic Therapy

Long-term management of patients with sick sinus syndrome requires implantation of a permanent pacemaker.12

Outcome Evaluation

• Monitor the patient's heart rate and alleviation of symptoms.

• Monitor for adverse effects of medications, such as atropine (dry mouth, mydriasis, urinary retention, and tachycardia).

AV Nodal Blockade

AV nodal blockade occurs when conduction of electrical impulses through the AV node is impaired to varying degrees. AV nodal blockade is classified into three categories. First-degree AV block is defined simply as prolongation of the PR interval to greater than 0.2 seconds. During first-degree AV block, all impulses initiated by the SA node that have resulted in atrial depolarization are conducted through the AV node; the abnormality is simply that the impulses are conducted more slowly than normal, resulting in prolongation of the PR interval.15 Second-degree AV block is further distinguished into two types: Mobitz type I (also known as Wenckebach) and Mobitz type II. In both types of second-degree AV block, some of the impulses initiated by the

SA node are not conducted through the AV node. This often occurs in a regular pattern; for example, every third or fourth impulse generated by the SA node may not be conducted. During third-degree AV block, which is also referred to as "complete heart block," none of the impulses generated by the SA node are conducted through the AV node. This results in "AV dissociation," during which the atria continue to depolarize normally as a result of normal impulses initiated by the SA node; however, the ventricles initiate their own depolarizations, because no SA node-generated impulses are conducted to the ventricles. Therefore, on the ECG, there is no relationship between the P waves and the QRS complexes.

Epidemiology and Etiology

The overall incidence of AV nodal blockade is unknown. AV nodal blockade may be caused by degenerative changes in the AV node. In addition, there are many other possible etiologies of AV nodal blockade including drugs (Table 9-3).12,13,15

Pathophysiology

First-degree AV nodal blockade occurs due to inhibition of conduction within the upper portion of the node.15 Mobitz type I second-degree AV nodal blockade occurs as

12 15

a result of inhibition of conduction further down within the node. Mobitz type

II second-degree AV nodal blockade is caused by inhibition of conduction within or

12 15

below the level of the bundle of His. ' Third-degree AV nodal blockade may be a result of inhibition of conduction either within the AV node or within the bundle of

12,15

His or the His-Purkinje system. ' AV block may occur as a result of age-related AV node degeneration.

Treatment Desired Outcomes

The desired outcomes of treatment are to restore normal sinus rhythm and alleviate patient symptoms.

Table 9-3 Etiologies of AV Nodal Blockade idiopathic degeneration of Lhe AV node Myocardial ischemia or infarction Neurocardiac syncope

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

Get My Free Ebook


Post a comment