Study Notes on Ischemic Heart Disease and Conduction Disorders

Davis Advantage for Capriotti

Pathophysiology: Introductory Concepts and Clinical Perspectives

Anatomy of the Heart

General Structure

  • Size: Comparable to a human fist.

  • Location: Mediastinum.

  • Base: Upper part of the heart.

  • Apex: Pointed end.

  • Key Conditions:

    • Acute Coronary Syndrome (ACS): Results from ischemia.

    • Myocardial Infarction (MI): Caused by prolonged ischemia leading to cell death.

Heart Structure

Layers of the Heart Wall

  • Epicardium: The outer layer.

  • Myocardium: The muscular middle layer responsible for contraction.

  • Endocardium: Lines the interior of the heart chambers.

Coronary Arteries

Overview

  • Right and Left Coronary Arteries.

  • Left Coronary Artery: Further divided into:

    • Left Anterior Descending (LAD) artery.

  • Role of Exercise: Increases formation of coronary collateral vessels, increasing blood supply.

Circulatory System Overview

Circuits

  • Pulmonary Circuit:

    • Low-pressure system.

    • Transports deoxygenated blood from right ventricle (RV) to lungs and returns oxygenated blood to left atrium (LA).

  • Systemic Circuit:

    • High-pressure system.

    • Delivers oxygenated blood from the left ventricle (LV) to body tissues and returns deoxygenated blood to right atrium (RA).

Blood Flow Components

  • Chambers:

    • Right Atrium: Receives deoxygenated blood.

    • Right Ventricle: Pumps blood to lungs.

    • Left Atrium: Receives blood from pulmonary veins.

    • Left Ventricle: Pumps blood to the body.

Blood Pressure

  • Systolic Blood Pressure (SBP): Indicates pressure during heart contractions.

  • Diastolic Blood Pressure (DBP): Indicates pressure during heart relaxation.

Heart Conduction System

Components

  • Sinoatrial Node (SA Node): Primary pacemaker of the heart.

  • Atrioventricular Node (AV Node): Regulates electrical impulses between atria and ventricles.

  • Bundle of His, Bundle Branches: Conduct impulses through the ventricles.

  • Purkinje Fibers: Distribute impulses throughout the ventricles, causing contraction.

Cardiac Muscle Action Potential

Phases of Cardiac Action Potential

  • Phase 0: Fast sodium channels open, depolarizing from -90 mV to +20 mV.

  • Phase 1: Abrupt closure of fast sodium channels.

  • Phase 2: Plateau phase with slow sodium-calcium channels active.

  • Phase 3: Repolarization as potassium channels open.

  • Phase 4: Resting potential is maintained by sodium/potassium pump.

Electrocardiogram (ECG)

Functionality

  • Purpose: Measures electrical activity of the heart; time on the X-axis, millivolts on the Y-axis.

  • Key Waveforms:

    • P Wave: Atrial depolarization.

    • QRS Complex: Ventricular depolarization.

    • T Wave: Ventricular repolarization.

  • 12-Lead ECG: Provides 12 different views of the heart's electrical activity.

Interpretation

  • Standard Intervals:

    • PR Interval: Time between atrial and ventricular depolarization.

    • QT Interval: Time taken for the heart to contract and then recover.

    • ST Segment: Represents the period between depolarization and repolarization of the ventricles.

Acute Coronary Syndrome (ACS)

Definitions

  • Ischemia of the Heart: Includes unstable angina and myocardial infarction.

  • Angina Pectoris: Chest pain due to myocardial ischemia, categorized into:

    • Unstable Angina: New or intensifying episodes, not relieved by rest, considered a medical emergency.

    • Chronic Stable Angina: Consistent symptom episodes often relieved with medications like nitroglycerin.

Unstable Angina

Incidence and Pathophysiology

  • Increasing Incidence: Particularly in the United States.

  • Causes:

    • Myocardial ischemia due to coronary thrombosis or atherosclerotic plaque.

    • Coronary artery vasospasm (Prinzmetal’s angina).

  • Risk Factors: Includes arteriosclerosis.

Clinical Presentation

  • Symptoms:

    • Chest pain, often described as crushing on the left side, may radiate to shoulders, jaw, and arms.

    • Precipitated by stress or exertion, lasts 1-5 minutes.

  • Diagnosis: ECG, high sensitivity cardiac troponin tests, and cardiac enzymes.

  • Management: Use of nitrates, aspirin, and oxygen administration.

Myocardial Infarction (MI)

Classification

  • Types of MI:

    • Type 1: Spontaneous due to plaque/thrombus.

    • Type 2: MI due to lack of oxygen without atherothrombotic occlusion.

    • Type 3: Death before cardiac troponin measurement.

    • Type 4 & 5: MI related to stent insertion/CABG.

Damage Assessment

  • Critical Factors: Time duration of ischemia, location, and available collateral circulation.

  • Types of Damage:

    • Zone of Injury: Surrounding area to ischemia with some recoverable cells.

    • Necrotic Cells: Cause ECG changes and release cardiac markers (e.g., troponin).

MI Symptoms and Diagnosis

Clinical Signs

  • Symptoms include:

    • Crushing chest pain, often described using Levine’s sign.

    • Pain may radiate to shoulder and arm, with accompanying symptoms like sweating and nausea.

  • Silent MI: Occurs without typical symptoms.

Diagnostic Tests

  • ECG: Can show STEMI (full thickness wall) or NSTEMI (partial thickness).

  • Blood Tests: Cardiac markers like CPK-MB and troponins.

Management Strategies

  • Treatment includes anti-platelet medications, beta-blockers, nitrates, and possible surgical interventions such as PCI or CABG.

Complications of Myocardial Infarction

Relevant Issues

  • Dysrhythmias: Risk increases post-MI.

    • Issue arises when ischemic areas lead to abnormal impulse conduction.

  • Papillary Muscle Rupture: May lead to mitral insufficiency.

  • Heart Failure and Cardiogenic Shock: Complications that may arise from severe MI, characterized by inadequate cardiac output.

Infective and Inflammatory Heart Diseases

Infectious Endocarditis

Overview

  • Usually bacterial, with Staphylococcus aureus being common; associated with prosthetic valves and IV drug use.

  • Diagnosis: Involves echocardiographic and blood tests.

  • Treatment: Prolonged antibiotic therapy and possible surgical intervention as required.

Myocarditis

  • Symptoms: Include fever, myalgia, and palpitations; often viral in origin.

  • Treatment Protocols: Restrict activity and manage with medications to decrease workload.

Pericarditis

  • Symptoms: Similar to MI with chest pain worsening during inspiration.

  • Possibility of Cardiac Tamponade if fluid accumulation compresses the heart.

  • Management: Varies depending on etiology.

Cardiac Tamponade

  • Presents with a classic triad of hypotension, jugular vein distention, and muffled heart sounds (Beck's triad).

Dysrhythmias and Conduction Disorders

Types

  • Supraventricular: SA node issues, atrial fibrillation, etc.

  • Ventricular: Issues affecting the conduction system.

  • Bradyarrhythmias and Tachyarrhythmias: Disturbances of heart rates.

  • Heart Block: Conduction impairment, particularly of the AV node, where atria and ventricles beat independently.

Atrial Fibrillation

Features and Risks

  • Absence of coordinated contractions; increase thrombus risk leading to potential strokes.

Treatment Options

  • Device options include cardiac plug devices or surgical strategies.

Alerts and Important Notes

Nitroglycerin Use

  • Dosage: Sublingual 0.3 to 0.6 mg; maximum dosage parameters and emergency indications.

  • Cautions: May cause severe hypotension; contraindicated with ED drugs.

Ventricular Dysrhythmias

  • Their dangerous potential, especially in the context of acute myocardial infarction.

Conclusion

  • Understanding these various aspects of ischemic heart disease is crucial for effective management and treatment of affected patients.