5.3 Congenital Heart Defects & CCHD Pulse Oximetry Screening

5.3 Congenital Heart Defects & CCHD Pulse Oximetry Screening

Clinical Pearl & Core Purpose: Congenital heart defects (CHD) occur in approximately 8 per 1,000 live births and represent the leading cause of infant mortality from congenital malformations. Many life-threatening cardiac anomalies remain clinically silent during the initial 24 hours of life because the ductus arteriosus remains widely patent. Low-risk neonatal nurses serve on the front lines of detection: mastery of defect classification, the Hyperoxia Test, and universal CCHD pulse oximetry screening ensures timely diagnosis before ductal closure triggers irreversible shock.

Structural Classification of Congenital Heart Defects

Congenital heart defects are classified clinically and physiologically based on pulmonary blood flow dynamics and the presence or absence of systemic cyanosis into Acyanotic and Cyanotic defects:

+-----------------------------------------------------------------------------------------+
|                        CONGENITAL HEART DEFECT CLASSIFICATION                           |
|                                                                                         |
|                     +---------------------+---------------------+                       |
|                     |                                           |                       |
|           [ ACYANOTIC DEFECTS ]                               [ CYANOTIC DEFECTS ]      |
|        (Normal Systemic Oxygenation)                      (Hypoxemia / Central Cyanosis)|
|                     |                                           |                       |
|   +-----------------+-----------------+               +---------+---------+             |
|   |                                   |               |                   |             |
|   v                                   v               v                   v             |
| [ Left-to-Right Shunts ]    [ Left Obstruction ]  [ The '5 Ts' ]    [ Single Ventricle ]|
| • VSD (Most common)         • Coarctation of Aorta• TGA (Egg/string)• HLHS (Norwood)    |
| • ASD (Fixed split S2)      • Aortic Stenosis     • TOF (Boot heart)• Single Ventricle  |
| • AV Canal (Trisomy 21)                           • Truncus Arter.                      |
| • PDA (Machinery murmur)                          • TAPVR (Snowman)                     |
|                                                   • Tricuspid Atresia                   |
+-----------------------------------------------------------------------------------------+

1. Acyanotic Congenital Heart Defects (Left-to-Right Shunts & Obstruction)

In acyanotic defects, oxygenated blood from the high-pressure left heart recirculates back into the low-pressure right heart and pulmonary circulation. Systemic arterial oxygen saturation remains normal ($SpO_2 \ge 95%$), but excessive pulmonary blood flow can lead to congestive heart failure.

• Ventricular Septal Defect (VSD):
  • Epidemiology: Most common congenital cardiac malformation, accounting for 25% to 30% of all CHD.
  • Pathophysiology: Communication between the left and right ventricles. As PVR drops over the first 2 to 6 weeks of life, left-to-right shunting increases, flooding the pulmonary vascular bed.
  • Auscultation: Harsh, blowing holosystolic (pansystolic) murmur heard loudest at the left lower sternal border (LLSB), often with a palpable systolic thrill. Smaller defects create louder, harsher murmurs due to higher velocity turbulence.
• Atrial Septal Defect (ASD):
  • Pathophysiology: Persistent opening in the interatrial septum (ostium secundum is most common, followed by ostium primum). Blood shunts left-to-right from LA to RA, causing RV and pulmonary vascular volume overload.
  • Auscultation: Soft midsystolic pulmonary flow murmur at the LUSB accompanied by a classic widely split, fixed second heart sound ($S_2$) that does not vary with respiration. Frequently asymptomatic in the newborn period.
• Atrioventricular Canal Defect (AV Canal / Endocardial Cushion Defect):
  • Pathophysiology: Defect in the center of the heart comprising an ostium primum ASD, an inlet VSD, and a single shared atrioventricular valve. Results in massive left-to-right shunting and atrioventricular valve regurgitation.
  • Chromosomal Link: Powerful association with Trisomy 21 (Down syndrome); 40% to 50% of infants with Down syndrome have CHD, with AV canal being the most prevalent.
  • Clinical Course: Rapid development of severe pulmonary overcirculation, tachypnea, diaphoresis during feeds, poor weight gain, and early congestive heart failure.
• Coarctation of the Aorta (CoA):
  • Pathophysiology: Discrete localized narrowing of the aortic arch, most commonly located juxtaductal (adjacent to the insertion of the ductus arteriosus).
  • Clinical Triad: Upper-extremity hypertension, weak, delayed, or absent femoral/pedal pulses, and a systolic blood pressure gradient > 15 to 20 mmHg higher in the right arm than in the lower extremities.
  • Critical CoA: When ductus arteriosus closes, systemic lower-body perfusion abruptly ceases, precipitating cardiogenic shock, profound oliguria, and metabolic acidosis.

2. Cyanotic Congenital Heart Defects (Right-to-Left Shunts & "The 5 Ts")

Cyanotic defects are characterized by intracardiac right-to-left shunting or parallel circulatory circuits that divert deoxygenated systemic venous blood directly into the systemic arterial circulation, producing central cyanosis and hypoxemia ($SpO_2 < 85%–90%$) that fails to correct with supplemental oxygen.

Diagnostic Testing: The Hyperoxia Test

The Hyperoxia Test is a bedside physiological challenge used to differentiate Cyanotic Congenital Heart Disease (fixed right-to-left anatomic shunt) from Parenchymal Pulmonary Disease (V/Q mismatch, RDS, TTN, MAS) or persistent pulmonary hypertension.

Hyperoxia Test Protocol & Interpretation

1. Baseline Assessment: Obtain an initial arterial blood gas (ABG) from the right radial artery (pre-ductal) while the infant breathes room air ($FiO_2 = 0.21$).
2. 100% Oxygen Administration: Place the infant in 100% ambient oxygen ($FiO_2 = 1.0$) via an oxygen hood or high-flow non-rebreather delivery system for 10 full minutes.
3. Post-Exposure ABG: Draw a repeat arterial blood gas from the right radial artery.

Universal CCHD Pulse Oximetry Screening Protocol

Critical Congenital Heart Disease (CCHD) screening via dual-site pulse oximetry is a universal, non-invasive standard of care endorsed by the American Academy of Pediatrics (AAP), American Heart Association (AHA), and the CDC. Its primary objective is to identify asymptomatic infants with life-threatening ductal-dependent defects before nursery discharge.

Screening Rules & Sensor Placement

• Timing: Performed at $\ge 24$ hours of age (or immediately prior to discharge if discharged $< 24$ hours). Performing the screen $< 24$ hours results in a high false-positive rate due to ongoing normal transitional hemodynamics.
• Sensor Sites: Must be measured simultaneously (or sequentially within minutes) at two specific sites:
  1. Pre-Ductal Site: Strictly the Right Hand (receives blood from the innominate artery prior to ductal insertion).
  2. Post-Ductal Site: Either Foot (left or right foot; receives blood from the descending aorta distal to the ductus arteriosus).
  • Clinical Warning: The left hand must NEVER be used as the pre-ductal site because the left subclavian artery originates near or distal to the ductal insertion and may reflect post-ductal flow.

Standardized AAP Screening Algorithm & Action Thresholds

+-----------------------------------------------------------------------------------------+
|                      AAP CRITICAL CONGENITAL HEART DISEASE ALGORITHM                     |
|                                                                                         |
|               Perform Pulse Oximetry Screen at ≥ 24 Hours of Life                      |
|                       (Right Hand AND Either Foot)                                      |
|                                     |                                                   |
|         +---------------------------+---------------------------+                       |
|         |                                                       |                       |
|         v                                                       v                       |
|   [ PASS / NEGATIVE ]                                   [ IMMEDIATE FAIL / POSITIVE ]   |
|   • SpO2 ≥ 95% in BOTH Hand & Foot                      • SpO2 < 90% in EITHER Hand OR Foot
|     AND                                                           |                     |
|   • Difference ≤ 3% between Hand & Foot                           v                     |
|         |                                            [ URGENT CLINICAL EVALUATION ]     |
|         v                                            • Notify provider immediately      |
|   Routine Newborn Care                               • Perform physical exam & vitals   |
|                                                      • Urgent Echocardiogram & Consult  |
|                                                                                         |
|         +-------------------------------------------------------+                       |
|         |                                                                               |
|         v                                                                               |
|   [ REPEAT / INTERMEDIATE SCREEN ]                                                      |
|   • SpO2 90% to 94% in EITHER Hand or Foot                                              |
|     OR                                                                                  |
|   • Difference > 3% between Right Hand and Foot                                         |
|         |                                                                               |
|         v                                                                               |
|   Repeat Screen in 1 Hour (Ensure proper sensor fit, warm foot, good signal)            |
|         |                                                                               |
|         +---> Pass criteria met? ------> PASS                                           |
|         +---> SpO2 < 90%? -------------> FAIL                                           |
|         +---> Still Intermediate? -----> Repeat Screen in 1 Hour (Screen #3)            |
|                                                |                                        |
|                                                +---> Pass criteria met? ---> PASS       |
|                                                +---> Any other result? ----> FAIL       |
|                                                      (3rd Intermediate = FAIL)          |
+-----------------------------------------------------------------------------------------+

Detailed Algorithm Actions

1. PASS (Negative Screen):
   • Criteria: Oxygen saturation is $\ge 95%$ in both the right hand and foot AND the absolute difference between the right hand and foot is $\le 3%$ (e.g., Right Hand 98%, Foot 96%).
   • Action: Screening is complete. The infant is cleared for routine nursery care.
2. FAIL (Positive Screen):
   • Criteria: Any oxygen saturation $< 90%$ in either the right hand or foot on any screen; OR failure to achieve a Pass result after three sequential screens (the initial screen plus two repeats spaced 1 hour apart).
   • Action: Do not discharge the infant. Immediately notify the medical provider, perform a rapid bedside assessment (evaluate perfusion, murmurs, pulses, respiratory distress), and obtain an urgent pediatric echocardiogram and cardiology consultation.
3. REPEAT (Intermediate / Equivocal Screen):
   • Criteria: Oxygen saturation is 90% to 94% in the right hand, foot, or both; OR there is a $> 3%$ absolute difference between the right hand and foot (e.g., Right Hand 96%, Foot 92%).
   • Action: Recheck probe application and signal waveform quality. Repeat the screen in exactly 1 hour (maximum of 3 screens total: initial, repeat 1, repeat 2). If the third screen does not meet Pass criteria, it is designated an automatic FAIL.