Most Likely Diagnosis: Acute Coronary Syndrome (Non-ST Elevation Myocardial Infarction)
This patient is experiencing an acute coronary syndrome, most likely NSTEMI, based on the combination of severe chest pain, high-risk ECG findings (ST depression and Q waves), tachycardia, hypertension, and a recent syncopal episode in the context of significant cardiac risk factors. The RSR' pattern represents a right bundle branch block that is likely chronic given his history of ASD, not the primary pathology 1.
Critical High-Risk Features Present
This patient demonstrates multiple high-risk indicators for acute coronary syndrome:
Severe prolonged chest pain (9/10 for one hour) meets criteria for high-risk ACS, as pain lasting >20 minutes at rest is a defining feature of unstable angina/NSTEMI 2.
ST-segment depression on ECG is one of the most reliable electrocardiographic indicators of unstable coronary disease and highly suggestive of acute coronary syndrome 2. ST-segment depression >1 mm in two or more contiguous leads carries high risk for death or nonfatal MI 2.
Q waves (pathological) indicate prior myocardial infarction and are highly suggestive of significant coronary atherosclerosis, though they don't necessarily imply current instability alone 2. However, when combined with acute symptoms and ST depression, they indicate high-risk ACS 2.
Recent syncope in a patient with chest pain suggests hemodynamic compromise and places him in the high-risk category 2.
Tachycardia (HR 108) and hypertension (148/96) reflect autonomic activation typical of acute MI 2.
Why Not the Other Diagnoses
The RBBB (RSR' pattern) is likely chronic, not acute:
The RSR' or rSr' pattern in patients with ASD is typically a manifestation of right ventricular volume overload rather than true conduction delay in the right bundle branch 1.
His ECG was normal two months ago, but "normal" in ASD patients often still shows the characteristic RSR' pattern that clinicians may not report as abnormal 1.
New or presumed new bundle branch block can indicate high-risk presentation and may serve as a STEMI-equivalent requiring immediate catheterization 2. However, the dominant pathology here is the ST depression and Q waves indicating acute ischemia, not the bundle branch block itself.
Restrictive or dilated cardiomyopathy with reduced ejection fraction:
While heart failure can present with elevated troponins and chest discomfort, the acute presentation with severe chest pain, ST depression, and Q waves points directly to ACS 2.
The tachycardia and hypertension are more consistent with acute ischemia than decompensated heart failure, which typically presents with hypotension or narrow pulse pressure 2.
Immediate Management Algorithm
Activate the cardiac catheterization laboratory immediately for high-risk NSTEMI 2:
Administer aspirin (if not already given) 2.
Obtain serial troponins immediately and at 3-6 hours 2.
Start dual antiplatelet therapy and anticoagulation per ACS protocols 2.
Perform invasive coronary angiography within 24-48 hours, as this reduces mortality from 6.5% to 4.9% in high-risk NSTE-ACS patients 3.
Key Clinical Pitfalls
Do not be distracted by the RBBB pattern - while bundle branch blocks can mask underlying ischemia, the ST depression and Q waves are visible despite the RBBB and indicate acute ischemia 2.
Do not wait for troponin results to initiate treatment - blood sampling should be done routinely but treatment decisions for high-risk patients should not be delayed 2.
The history of ASD increases complexity but does not change acute management - his chronic structural heart disease may have contributed to his baseline ECG pattern, but the acute presentation with ST changes demands immediate ACS evaluation 2.
Recurrent dizziness and syncope in this context suggest either arrhythmia or hemodynamic compromise from ischemia - both require urgent evaluation and continuous cardiac monitoring 2.