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The heart
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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