What could be the cause of weakness, dyspnea, headache, and spotty vision in a post-operative HLHS patient with a known left bundle branch block and normal vital signs?

Acute Cardiac Decompensation with Possible Ischemia or Arrhythmia

This 14-year-old with post-operative hypoplastic left heart syndrome (HLHS) presenting with weakness, dyspnea, headache, and visual disturbances most likely has acute heart failure decompensation, potentially complicated by myocardial ischemia or a symptomatic arrhythmia, despite the "normal" vital signs. 1

Critical Immediate Assessment

The blood pressure of 128/71 mmHg may appear normal but could represent relative hypertension in a post-Fontan or single-ventricle physiology patient, while the low ETCO2 of 21 mmHg suggests hyperventilation from respiratory distress or metabolic compensation. 1

High-Priority Differential Diagnoses

Acute heart failure with preserved blood pressure:

• Post-operative HLHS patients are at significant risk for acute heart failure, which can present with dyspnea and weakness even when blood pressure appears adequate 1
• The combination of dyspnea and weakness in a complex congenital heart disease patient warrants immediate evaluation for cardiac decompensation 1

Myocardial ischemia:

• Pediatric patients with congenital heart disease, particularly those who have undergone multiple operations, are at risk for ischemic mechanisms including intraoperative hypoxia during repair of congenital defects 1
• The headache with "spotty vision" (visual disturbances) could represent cerebral hypoperfusion from reduced cardiac output 1
• Children with documented MI can present with atypical symptoms; ST-segment elevation ≥2 mm has been shown valuable in making the diagnosis in pediatric patients 1

Symptomatic arrhythmia:

• While the EKG shows sinus rhythm with known LBBB, symptomatic arrhythmias including non-sustained ventricular tachycardia or atrial arrhythmias can occur intermittently in post-operative congenital heart disease patients 1
• The known LBBB itself is concerning in this population, as LBBB in heart failure patients is associated with increased risk of cardiac complications and mortality 2

Critical Pitfall: "Normal" Vital Signs Can Be Misleading

The SpO2 of 99% and blood pressure of 128/71 do not exclude serious cardiac pathology in this patient. 1

• Post-Fontan or single-ventricle patients may maintain adequate oxygen saturation despite significant cardiac dysfunction 1
• The ETCO2 of 21 mmHg is abnormally low and indicates either hyperventilation from respiratory distress or metabolic acidosis with respiratory compensation 1
• Blood pressure may be maintained by compensatory mechanisms even as cardiac output falls 1

Immediate Diagnostic Workload

Obtain immediately:

• 12-lead EKG to assess for acute ischemic changes (though interpretation is difficult with LBBB, look for ST elevation ≥2 mm which has diagnostic value in pediatric MI) 1
• Troponin and BNP/NT-proBNP to evaluate for myocardial injury and heart failure 1
• Echocardiography to assess ventricular function, valve function, and identify any acute mechanical complications 1
• Arterial blood gas to explain the low ETCO2 and assess for metabolic acidosis 1
• Continuous cardiac monitoring for arrhythmia detection, though ST-segment monitoring has limited utility with LBBB due to baseline ST-T wave abnormalities 1

Important Limitation of LBBB in This Context

The known LBBB significantly complicates both monitoring and diagnosis:

• Patients with LBBB have markedly deviated ST-T waves that make ST-segment monitoring unreliable and prone to false alarms 1
• LBBB causes immediate electrical and mechanical dyssynchrony that reduces left ventricular ejection fraction, even in otherwise normal hearts 3
• In the context of pre-existing structural heart disease (HLHS), LBBB compounds the mechanical inefficiency and can accelerate heart failure progression 3, 2

Neurological Symptoms Require Explanation

The headache with "spotty vision" is particularly concerning and suggests:

• Cerebral hypoperfusion from reduced cardiac output—the brain is exquisitely sensitive to decreased perfusion 1
• Possible thromboembolic event (though less likely given the acute presentation with other cardiac symptoms) 1
• Hypertensive emergency (though BP of 128/71 makes this less likely unless this represents significant elevation for this patient) 1

The visual disturbances combined with cardiac symptoms strongly suggest inadequate cerebral perfusion from cardiac dysfunction rather than a primary neurological process. 1

Immediate Management Approach

This patient requires urgent cardiology consultation and likely admission for:

• Continuous cardiac monitoring in an intensive care setting 1
• Serial troponins and echocardiography to assess for ischemia and ventricular function 1
• Consideration of diuretic therapy if heart failure is confirmed (though use cautiously given complex physiology) 1
• Avoidance of vasodilators if systolic blood pressure drops below 110 mmHg 1

Do not dismiss this presentation based on "normal" vital signs—post-operative congenital heart disease patients can decompensate rapidly, and the combination of dyspnea, weakness, and neurological symptoms demands aggressive evaluation. 1