Cardiac Stimulants and Depressants

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.

• 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

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

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

• 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
• Gastrointestinal effects p 417,418
– Nausea and vomiting
– Anorexia
– Diarrhea
• Cardiac effects
– Cardiac arrhythmias

Cardiac glycosides: Toxicity p417,418
• Neurological effects
– Restlessness, confusion
– Irritability
– Drowsiness
– Vision changes
– Headache

• 10-20% of pt experience toxicity
• Predispose to cardiac glycoside toxicity:
– Hypokalemia
– Renal impairment
– Rapid IV administration

• 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

– 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

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 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

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

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 beta
1 and beta
2 sympathetic receptors
• Cardiac effects of beta blockers
• negative inotropic effect
• negative chronotropic effect
• negative dromotropic effect
• Decrease arrhythmias
• Decrease blood pressure

• 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) p423
425
• 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