1.2-DRUGS-AFFECTING-CVS (1)

Introduction to Cardiovascular Drugs

Cardiovascular drugs play a vital role in managing various heart and vascular conditions. This set of notes focuses on cardiotonic agents, phosphodiesterase inhibitors, antianginals, and antihypertensives, outlining their mechanisms, indications, dosages, contraindications, and nursing responsibilities.

Cardiotonics

Definition

Cardiotonic agents are essential drugs utilized to augment the contractility and output of a hypodynamic heart without proportionately increasing oxygen consumption. These medications are commonly employed in treating heart failure (HF).

Mechanism of Action

Cardiotonic (inotropic) drugs impact intracellular calcium levels in heart muscle, which enhances contractility. This enhancement leads to increased cardiac output, which subsequently improves renal blood flow and urine production.

Types of Cardiotonic Drugs

  1. Cardiac Glycosides

    • Example: Digoxin (Lanoxin), which was derived from the Digitalis purpurea plant.

  2. Phosphodiesterase Inhibitors

Cardiac Glycosides - Digoxin

Mechanism of Action: Digoxin boosts intracellular calcium, allowing more calcium to enter myocardial cells during depolarization, leading to:

  1. Increased force of myocardial contraction (a positive inotropic effect).

  2. Enhanced cardiac output and renal perfusion.

  3. Slowed heart rate due to delayed repolarization (a negative chronotropic effect).

  4. Decreased conduction velocity through the atrioventricular (AV) node.

Indications for Digoxin

  • Heart failure (HF)

  • Atrial flutter

  • Atrial fibrillation

  • Paroxysmal atrial tachycardia.

Dosage

  • Oral: 0.75-1.25 mg PO

  • IV: 0.125-0.25 mg

  • Onset of action is 30-120 minutes orally and 5-30 minutes intravenously.

Contraindications

  • Hypersensitivity to digitalis preparations

  • Ventricular tachycardia or fibrillation

  • Heart block or sick sinus syndrome

  • Acute MI

  • Renal failure.

Adverse Effects

  • Common: Headache, weakness, drowsiness, and vision changes.

  • Serious: Digitalis toxicity (normal level: 0.5 - 2.0 ng/ml), presenting symptoms include anorexia, nausea, vomiting, malaise, depression, and abnormal heart rhythms.

Nursing Responsibilities

  • Assess for contraindications and perform physical assessments, closely monitoring the cardiac status, including pulse and blood pressure.

  • Hold the dose if the pulse is less than 60 beats/min in adults or less than 90 beats/min in infants.

  • Administer intravenous doses slowly to avoid arrhythmias.

  • Perform thorough patient education on the drug, dosage, monitoring pulse, and reporting toxicity signs.

Phosphodiesterase Inhibitors

Example: Milrinone (Primacor)

Mechanism of Action: Blocks the enzyme phosphodiesterase, increasing myocardial cAMP levels, which elevate calcium in myocardial cells.

Indications for Milrinone

  • Short-term treatment of heart failure unresponsive to digoxin or diuretics.

Dosage

  • IV: 50 micrograms/kg IV bolus, followed by 0.4-1.0 micrograms/kg/min infusion.

Contraindications

  • Hypersensitivity to phosphodiesterase inhibitors

  • Severe aortic or pulmonic valvular disease

  • Acute myocardial infarction.

Adverse Effects

  • Ventricular arrhythmias potentially leading to fatal ventricular fibrillation, hypotension, chest pain.

  • GI effects include nausea, vomiting, and thrombocytopenia.

Nursing Responsibilities

  • Assess for contraindications, monitor vital signs, and provide patient education about the drug's use and warning signs of adverse effects.

Antianginals

Definition

Antianginal drugs improve oxygen delivery and reduce demand in the myocardium, thereby managing angina.

Types of Antianginals

  1. Nitrates: E.g., Glyceryl trinitrate, Isosorbide dinitrate.

  2. Beta-Blockers: E.g., Atenolol, Propranolol.

  3. Calcium Channel Blockers: E.g., Amlodipine, Diltiazem.

  4. Potassium Channel Openers: E.g., Nicorandil.

Mechanism of Action of Nitrates

Nitrates relax and dilate blood vessels, increasing blood flow to the heart and reducing systemic blood pressure by decreasing preload and afterload. They can be used for both short-term relief of acute angina and for long-term management.

Nursing Responsibilities for Antianginals

  • Monitor vital signs and educate patients on the administration and management of medications, including proper techniques for sublingual doses and awareness of expiration dates.

Antihypertensives

Definition

Antihypertensives are medications utilized to lower blood pressure.

Classifications

  • Diuretics: e.g., Furosemide, Hydrochlorothiazide, Spironolactone.

  • Adrenergic Inhibitors: Centrally acting (e.g., Clonidine) and peripherally acting (e.g., Prazosin).

  • Calcium Channel Blockers: E.g., Amlodipine, Nifedipine.

  • Angiotensin Inhibitors: ACE inhibitors (e.g., Captopril) and ARBs (e.g., Losartan).

  • Direct Vasodilators: E.g., Nitroglycerin.

Diuretics

Loop Diuretics

  • Mechanism: Inhibits sodium and chloride reabsorption in the loop of Henle (e.g., furosemide).

Thiazide Diuretics

  • Inhibit sodium and chloride reabsorption in the distal convoluted tubule and are the first-line therapy for hypertension (e.g., hydrochlorothiazide).

Potassium-Sparing Diuretics

  • Prevent potassium loss (e.g., spironolactone).

Side Effects

  • Loop and thiazide diuretics: Hypokalemia, weakness, muscle cramps.

  • Potassium-sparing diuretics: Hyperkalemia, lethargy, muscle cramps.

Nursing Responsibilities

  • Regular monitoring of vital signs and patient education to ensure proper medication adherence, caution regarding potassium levels, and awareness of side effects.