Intro and Diag Tech CHD Part 2

Introduction and Diagnostic Techniques in Congenital Heart Disease

Echocardiography Overview

Types of Echocardiography

Transthoracic Echocardiogram (TTE)

  • Functionality: Utilizes sound waves to produce images of the heart.

  • Principles of Operation:

    • M-mode: Time-motion display along a single ultrasound line; utilized for measuring chamber size and wall thickness.

    • 2-D modality: Offers spatial orientation of cardiac anatomy; crucial for identifying atrial septal defects (ASD), ventricular septal defects (VSD), heart valves, and ventricular size.

    • Doppler: Measures blood flow velocity and calculates pressure gradients across valves or shunts.

    • Color Doppler: Visualizes flow direction (red indicates flow towards the probe, blue indicates flow away) and visualizes turbulence using a mosaic pattern.

Standard Echocardiographic Windows (TTE)

A. Parasternal View

  • I. Long Axis

    • Visualizes left ventricle.

  • II. Short Axis Aortic Valve Level

  • III. Short Axis Mitral Valve Level

  • IV. Short Axis Papillary Muscle Level

  • V. Short Axis Apical Level

B. Apical View

  • I. Four Chamber

  • II. Five Chamber

  • III. Apical Long Axis Left Ventricle

  • IV. Two Chamber

C. Subcostal View

  • I. Four Chamber

D. Suprasternal View

  • I. Long Axis Aortic Arch

Transesophageal Echocardiogram (TEE)

  • Indications:

    • Before CPB: Confirm diagnosis, document additional findings, provide anatomic information for repair, and establish baseline heart function.

    • After CPB: De-airing, assessing for residual defects, evaluating the adequacy of correction, and conducting function assessment.

Cardiac MRI

  • Utility: Provides detailed imaging of cardiac structures, assisting in diagnostic clarifications where echocardiography may have limitations.

Cardiac Catheterization Measurements

  • Assesses:

    • Anatomic abnormalities.

    • Pulmonary/systemic shunt ratios.

    • Pressures in heart chambers and vessels.

    • Cardiac output and oxygen saturations.

    • Valve gradients and reactivity of pulmonary vascular bed.

    • Coronary artery anatomy.

Normal Intracardiac Pressures

Age

RA (mmHg)

RV (mmHg)

PA (mmHg)

PCWP (mmHg)

LA (mmHg)

LV (mmHg)

Ao (mmHg)

Newborn

0-4

65-80

0-6

65-80

35-50

Child 6-9

3-6

65-80

0-6

65-80

45-60

Child 2-6

15-25

3-7

15-25

10-14

5-10

90-110

7-9

Adult

90-110

7-9

90-110

65-75

Detection of Shunt by Oxygen Saturation

  • An increase in oxygen saturation of:

    • 8-10% indicates a left-to-right shunt at the atrial level.

    • 6-8% indicates a left-to-right shunt at the ventricular level.

Common Interventional Procedures in the Catheterization Lab

  • Intracardiac electrophysiology studies.

  • Balloon atrial septostomy.

  • Balloon dilation procedures for coarctation and pulmonary arteries.

  • Balloon valvuloplasty.

  • Transcatheter closure of ASD using a clamshell device.

  • PDA stenting.

  • Transcatheter valve interventions.

Surgical Status Classification

  • Uncorrected: No surgical intervention has been performed.

  • Palliated: Surgical interventions have been performed to alleviate symptoms without complete repair.

  • Partially repaired: Some surgical correction has been undertaken, but further interventions are necessary.

  • Complete repair: Full correction of the defect has been achieved surgically.

Palliative Surgical Procedures

Goals of Palliative Procedures

  • Increase pulmonary blood flow: These include:

    • Shunts.

  • Decrease pulmonary blood flow: Utilizing procedures like pulmonary artery banding and modified Blalock-Taussig shunt.

Types of Palliative Procedures

  • Potts Shunt: Connects the descending aorta to the left pulmonary artery.

  • Glenn Shunt: Connects the superior vena cava to the right pulmonary artery.

  • Waterston Shunt: Connects the ascending aorta to the pulmonary artery.

  • Blalock-Taussig Shunts: Connecting the right subclavian artery to the pulmonary artery; can be classic, modified BT, or central shunts.

Preparation for CPB Workup

Key Elements to Assess

  • Patient’s history, physical examination findings, laboratory results, catheterization results, presence of shunts, or previous surgical interventions.

  • Patient size and calculated flow rates.

Equipment Selection

  • Essential equipment includes:

    • Tubing pack.

    • Oxygenator.

    • Filter cannulas.

    • Hemoconcentrator.

    • CDPG circuit.

    • Temperature regulation tools.

    • Hematocrit monitoring devices.

    • Allergies (important for antibiotic selection).

    • Blood products based on calculations.

Classification of Congenital Heart Defects (CHD)

Types

  • Simple CHD: Characterized by shunt or obstructive lesion.

  • Complex CHD: Involves a combination of shunt and obstructive lesions.

Overview

  • There are 35 different types of congenital heart defects, categorized into four primary categories:

    • Increased Pulmonary Blood Flow (Acyanotic, Left-to-Right Shunt): Examples include Patent Ductus Arteriosus (PDA), ASD, VSD, AV canal, Truncus Arteriosus, Single Ventricle.

    • Decreased Pulmonary Blood Flow (Cyanotic, Right-to-Left Shunt): Disorders include Tetralogy of Fallot, pulmonary atresia, tricuspid atresia.

    • Obstructive Lesions (No Flow): Such as coarctation of the aorta, aortic stenosis, pulmonic stenosis.

    • Mixed Lesions: Conditions where blood flows in both directions, causing both cyanotic and acyanotic symptoms (e.g., Transposition of the Great Vessels).

Flow Distribution Factors

Increasing Pulmonary Output

  • Factors:

    • Decreased pulmonary vascular resistance (due to hypocapnia, pulmonary vasodilators like nitric oxide).

    • Systemic factors that increase systemic vascular resistance (sympathetic stimulation, vasoconstriction).

Decreasing Pulmonary Output

  • Factors:

    • Increased pulmonary vascular resistance (due to hypoxemia, hypercapnia, high hematocrit conditions).

    • Positive pressure ventilation.

    • Metabolic acidosis leading to changes in blood flow dynamics.

Strategies to Change Pulmonary Blood Flow

Increasing Blood Flow

  • Provide increased oxygen and perform hyperventilation.

  • Induce alkalosis post-operative physiological conditions.

  • Administer PGE1 (prostaglandin) or vasodilators such as nitric oxide.

Decreasing Blood Flow

  • Reduce oxygen supply or induce hypoventilation.

  • Induce acidosis or manage hypervolemia.

  • Utilize anesthetics judiciously in clinical settings.

Lifelong Journey of CHD Patients

Stages of Life:

  • Infancy, Early Childhood: Surgical or catheter reparative interventions are common; usually associated with low mortality, leading to a good quality of life.

  • Teenage Years: Characterized by a 'honeymoon period'; a crucial time to educate patients on lifestyle choices, including dietary habits and exercise importance.

  • Adulthood: Patients often require reintervention; the focus remains on ongoing education, empowerment, and planning for life trajectories.

  • Elderly Years: Increasing numbers of patients reach old age. Long-term considerations include preventative care for other diseases, ongoing reinterventions, and holistic end-of-life support.