Chapter 17

Cardiac Stimulants and Depressants

The heart

Cardiac conduction p415

Autonomic innervation of the heart

Aspects of cardiac function affected by drugs p 415

• Inotropic effects: force of contractions • Chronotropic effects: heart rate• Dromotropic effects: conduction of electrical

impulses thru the myocardium

• These effects can be positive or negative.

Heart failure p416• Characterized by:

– Cardiac distention resulting from incomplete ventricle emptying

– Cardiac hypertrophy caused by heart’s adaptation to prolonged stretching (enlarged heart)

– Sodium and water retention caused by, in part, diminished renal blood flow

Symptoms of heart failure p416

• Weight gain• Peripheral edema• Shortness of breath• Pulmonary edema

Treatment of Heart Failure p416

• Cardiac glycosides: prototype: digoxin (Lanoxin)– Positive inotropic action– Negative chronotropic

action– Negative dromotropic

action

• Foxglove plant

Digoxin: Dose Considerations p416 • Long duration of action• Method of administration

– Oral route most preferable– Digitalizing dose IV

• To bring serum levels to a therapeutic level• All glycosides have a low therapeutic index

Cardiac glycosides: Side Effects p 417,418

• Gastrointestinal effects– Nausea and vomiting– Anorexia– Diarrhea

• Cardiac effects– Cardiac arrhythmias

Cardiac glycosides: Toxicity p417,418

• Neurological effects– Restlessness, confusion– Irritability– Drowsiness– Vision changes– Headache

Cardiac Glycoside Toxicity p418

• 10-20% of pt experience toxicity• Predispose to cardiac glycoside toxicity:

– Hypokalemia– Renal impairment– Rapid IV administration

Cardiac Glycoside Toxicity p418• Treatment

– Stop the drug– Physical assessment– Check potassium level

• Administer if needed– Monitor heart rate

• Administer antiarrhythmics• Digibind (digoxin immune fab)

– For life threatening toxicity

Nursing considerations when administering cardiac glycosides

• P 417 table 17-1– Administer with meals if GI upset occurs– Hold dose and report to PCP for HR < 60 bpm– Hold dose and report for HR > 100 bpm– Observe pt for signs of toxicity, document, report– Monitor labs

–K+ –dig levels

Cardiac glycoside teaching– Pt education

– teach pt to take radial pulse prior to taking his med – instruct when to hold dose and contact physician– instruct S/S dig toxicity

Antiarrhythmics and antidysrhythmics Drug Action p419

• Obliterate or diminish rhythm disturbances:– Decrease the automaticity in ectopic sites– Alter dromotropic effects– Alter the refractory period of cardiac muscle

between consecutive contractions

Table 17-3 p425-428

• Antiarrhythmic drugs – Monitor apical pulse for 1 minute prior to drug

administration– Record rate and rhythm– Patient should be supine if IV drugs

Quinidine gluconate p420, 428

• Old antidysrhythmic agent• Depressant of cardiac function

– Reduces the excitibility of cardiac muscle to electrical stimulation

– Negative chronotropic effect• SA node regains control

Quinidine toxic effects p420• Quinidine therapy is discontinued in 1/3 of pt due to toxic effects

– GI distress – N&V – anorexia– diarrhea

– Cardiovascular disorders: hypotension, AV block– Hypersensitivity

– tinnitus – N&V – headache – dizziness – impaired vision – vertigo – skin rashes

Procainamide (Pronestyl) p421, 427

• Cardiac effects are the same as quinidine, but procainamide has fewer adverse cardiovascular effects

• Pt that are allergic to “caine” local anesthetics may have a sensitivity to procainamide

Lidocaine (Xylocaine) p421, 426• Widely used as a local

anesthetic• Has antidysrhythmic

properties• Drug of choice for

treatment of premature ventricular contractions (PVCs)

• Constant EKG monitoring is necessary for all pt during administration of lidocaine as an antidysrhythmic

Beta-adrenergic Blocking Agents“beta blockers” (-olol) p423, 427

• Inhibit beta1 and beta2 sympathetic receptors• Cardiac effects of beta blockers

• negative inotropic effect• negative chronotropic effect• negative dromotropic effect

• Decrease arrhythmias • Decrease blood pressure

Beta-adrenergic blocking agents• Adverse effects

– Cause bronchoconstriction• Contraindications: pt with respiratory disease

– Cause heart failure• Contraindications: pt with heart failure

• Examples – Propanolol (Inderal) (prototype)– Metoprolol (Lopresor)– Atenolol (Tenormin)

Amiodarone HCL (Cordarone) p423425

• Effective in treating dysrythmias• Adverse effect: pulmonary toxicity

– Persistent nonproductive cough– Chest pain with deep inhalation– dyspnea

Calcium Channel Antagonists“calcium channel blockers” p424, 428

• Reduces the influx of calcium into the cell– relaxation of vascular smooth muscle

• Coronary artery dilation (treat angina)• Reduction of myocardial oxygen consumption• Lowered blood pressure• Negative dromotropic effect• Negative inotropic effect

• Example: verapamil (Calan) prototype

Drugs to treat shock p428• Adrenergic

– Causes increase in heart rate– Causes peripheral vasoconstriction– Reverses hypotension from shock

• Anticholinergic – Atropine sulfate– Frequently given to treat bradycardia