Veterinary Cardiac and Renal Pharmacology Study Guide

Introduction to Cardiac and Renal Pharmacology

• Overview of cardiac and renal pharmacology in veterinary medicine.
• Importance of understanding drugs that impact cardiac output, myocardial function, and renal function.

Cardiac Output

• Definition: Cardiac output (CO) is a measure of the volume of blood the heart pumps in a given time.
• Formula: $CO = HR imes SV$ (where HR is heart rate, SV is stroke volume).
• **Components: **
  • Stroke Volume (SV): The volume of blood ejected by the heart in one contraction.
  • Heart Rate (HR): The number of heartbeats per minute.
• Changes in either heart rate or stroke volume will affect cardiac output.

Factors Affecting Cardiac Output

• Cardiac Cycle and Action Potential:
  • Drugs may influence the cardiac cycle and cardiac action potential by affecting the movement of sodium, calcium, and potassium ions across the cardiac membrane.
  • Sodium, calcium, and potassium are key ions involved in the generation of action potentials in cardiac myocytes.

Example of Cardiac Output Calculation

• Hypothetical Case:
  • Assume stroke volume (SV) is 6 mL.
  • If HR is 10 beats in 10 seconds:
  • $CO = 10 imes 6 = 60 mL/10s$ or 600 mL/min.
  • If HR is 4 beats in 10 seconds:
  • $CO = 4 imes 6 = 24 mL/10s$ or 144 mL/min.
  • Variations based on body condition:
  • Different animals will exhibit different cardiac outputs based on their physiology and condition.

Stroke Volume Contributions

• Blood Volume and Vascular Resistance:
  • Stroke volume is influenced by blood volume and the resistance in the vascular system.
  • Example Scenario:
  • If vascular resistance decreases (vasodilation), stroke volume may increase as the heart can push more blood without obstruction, e.g., aortic output.
  • Conversely, vasoconstriction leads to increased vascular resistance, reducing stroke volume.

Active Bleeding and Cardiac Output

• Active bleeding decreases blood volume.
• Resulting impact on cardiac output:
  • Heart rate may increase as a compensatory mechanism to maintain CO, but stroke volume is directly affected due to insufficient blood volume in the heart.
• Overall cardiac output decreases due to insufficient blood returning to the heart.

Cardiovascular Adaptations

• Homeostatic responses during hemostasis often lead to compensatory mechanisms, such as increased heart rate, to counteract decreased stroke volume due to blood loss.
  • Increased heart rate attempts to maintain overall cardiac output despite reduced stroke volume.

Cardiac Conditions and Drug Interventions

• Common Conditions:
  • Congestive Heart Failure (CHF)
  • Dilated Cardiomyopathy (DCM)
  • Hypertrophic Cardiomyopathy (HCM)
• Symptoms include:
  • Pulmonary edema, ascites, lethargy, etc.
• Medications:
  • Positive Inotropes, Antiarrhythmics, etc., are tailored to supporting heart function and correcting rhythm disorders.

Classification of Cardiac Drugs

• Positive Inotropes: Improve heart contractility.
  • E.g., Epinephrine: Nonselective alpha-beta agonist, used in cardiac resuscitation.
• Antiarrhythmics: Correct cardiac rhythm abnormalities.
  • E.g., Amiodarone, Lidocaine: Modify electrical conduction in the heart.
• Vasodilators: Decrease vascular resistance and lower blood pressure.
  • E.g., Amlodipine: Calcium channel blocker.

Renal Pharmacology

• Renal and Urinary Drugs: Impact urine production and renal function.
• Examples:
  • Diuretics: Reduce fluid buildup in conditions such as CHF or renal failure.
  • Furosemide: Increases renal excretion of water and electrolytes; can cause electrolyte imbalances and ototoxicity.
  • Renal Protective Agents: Enhance renal perfusion and support renal function, e.g., ACE inhibitors (Enalapril).

Specific Drug Mechanisms and Applications

Anticholinergics

• Atropine and Glycopyrrolate: Used for bradycardia, pre-anesthetics.
  • Side effects include tachycardia and decreased secretions.

Dietary Management of Cardiac Health

• Importance of taurine in diet, especially for cats; deficiency can lead to cardiomyopathy.
• Taurine supplementation may be necessary for cardiac support in deficient animals.

Summary of Key Points

• Understanding cardiac output, stroke volume, heart rate, and the physiological response to drugs is crucial.
• Familiarity with specific drugs, indications, contraindications, and potential effects, both therapeutic and adverse, is essential for effective veterinary nursing and patient care.