What are the next best investigations for a patient with schizophrenia, experiencing recurrent episodes of shortness of breath (SOB) and dizziness, with normal electroencephalogram (EEG), chest X-ray (CXR), and electrocardiogram (ECG)?

Next Best Investigations for Recurrent SOB and Dizziness in Psychiatric Patient

Given the brief, episodic nature of symptoms (1-2 minutes) with random onset and normal initial cardiac workup, the next best investigation is 24-hour Holter monitoring or extended ambulatory ECG monitoring to capture paroxysmal arrhythmias, followed by echocardiography to assess for structural cardiac disease and evaluate for antipsychotic-related cardiotoxicity. 1, 2

Rationale for Cardiac Arrhythmia Evaluation

The symptom pattern strongly suggests a cardiac arrhythmic etiology:

• Brief, self-limiting episodes (1-2 minutes) with SOB and dizziness are classic for paroxysmal arrhythmias that may not be captured on a single resting ECG 1
• The European Society of Cardiology guidelines on syncope management emphasize that ECG monitoring is indicated when there is high pre-test probability of identifying an arrhythmia responsible for symptoms 1
• Patients with palpitations or dizziness associated with syncope-like symptoms require electrocardiographic monitoring and echocardiography as first evaluation steps 1

Specific Recommended Testing Sequence

1. Extended Ambulatory ECG Monitoring (Priority #1)

• Start with 24-48 hour Holter monitoring to capture frequent paroxysmal arrhythmias 1, 2
• The American Heart Association recommends serial ECGs for patients receiving antipsychotic medications, as these drugs may produce cardiac effects including QT prolongation and arrhythmias 1, 2
• If initial Holter is non-diagnostic but symptoms persist, consider external loop recorder or implantable loop recorder for longer-term monitoring 1

2. Echocardiography (Priority #2)

• Transthoracic echocardiography is appropriate for symptoms potentially due to suspected cardiac etiology, including dyspnea, shortness of breath, lightheadedness, and syncope 1
• Critical to evaluate for antipsychotic-induced cardiomyopathy, particularly if patient is on clozapine or other high-risk agents 3
• Assess for structural abnormalities, valvular dysfunction, and left ventricular systolic function 1

3. Exercise Stress Testing (Consider if above negative)

• Exercise ECG testing is recommended when symptoms occur during or after effort 1
• Can unmask exercise-induced arrhythmias or ischemia not apparent at rest 1

Critical Antipsychotic-Related Considerations

Antipsychotic medications, particularly phenothiazines and other psychotropic agents, are known to produce significant ECG changes including QT prolongation and arrhythmias: 1

• Clozapine specifically can cause cardiomyopathy and myocarditis, presenting with fatigue, SOB, and chest pain 3
• The American College of Cardiology/American Heart Association guidelines state that ECG recordings are appropriate after initiation of drug therapy, after changes in therapy, and after addition of other drugs that may interact and have cardiac effects 1, 2
• Serial monitoring is warranted in patients on antipsychotics to detect QT prolongation, which predisposes to ventricular arrhythmias 1

Additional Investigations to Consider

If Cardiac Workup Remains Negative:

• Psychiatric assessment may be warranted if cardiac evaluation is unrevealing, as panic attacks can present with similar brief episodes of SOB and dizziness 1
• However, do not attribute symptoms to psychiatric causes without thoroughly excluding organic cardiac disease, especially given antipsychotic use 4

Laboratory Screening:

• Electrolyte panel (particularly potassium, magnesium, calcium) as abnormalities can precipitate arrhythmias and may be exacerbated by antipsychotics 1
• Thyroid function tests if not recently checked 1

Common Pitfalls to Avoid

• Do not dismiss symptoms as anxiety-related without comprehensive cardiac evaluation in patients on antipsychotics, as these medications carry significant cardiac risk 1, 4, 3
• A single normal resting ECG does not exclude paroxysmal arrhythmias—extended monitoring is essential for episodic symptoms 1, 2
• Avoid assuming the EEG rules out all causes—while it excludes seizures, it does not evaluate cardiac rhythm 1
• Do not delay echocardiography in patients on long-term antipsychotics, as drug-induced cardiomyopathy can be insidious 3