What would happen if a patient with preferential perfusion performed high‑intensity interval training?

High-Intensity Interval Training in Patients with Preferential Perfusion

A patient with preferential perfusion (myocardial ischemia detected on stress imaging) should NOT perform HIIT without first undergoing comprehensive cardiac evaluation and risk stratification, as high-intensity exercise can provoke dangerous ischemia, arrhythmias, and acute coronary events in patients with significant coronary disease.

Understanding the Critical Safety Concern

Preferential perfusion refers to heterogeneous myocardial blood flow distribution detected on nuclear perfusion imaging, indicating underlying coronary artery disease with areas of ischemia. This is fundamentally different from a healthy heart and creates specific risks with high-intensity exercise:

• HIIT imposes extreme cardiovascular demands through bursts at 85-95% of peak heart rate, creating substantial myocardial oxygen demand that can exceed supply in ischemic territories 1, 2
• The American College of Cardiology warns that high-intensity exercise can trigger arrhythmias through sympathetic-vagal imbalance and increase cardiovascular strain, particularly in individuals with underlying coronary conditions 3, 2
• Exercise is contraindicated in patients with refractory/unstable angina and other high-risk cardiovascular conditions including high-grade arrhythmias 4

What Would Actually Happen During HIIT

Immediate Physiological Consequences

• Myocardial oxygen demand would spike dramatically during high-intensity intervals (85-95% HRmax), potentially exceeding the compromised blood supply to ischemic regions 1
• The ischemic areas would become more severely underperfused, potentially triggering angina, ST-segment depression, dangerous arrhythmias, or even acute myocardial infarction 4
• Rapid blood pressure fluctuations between work and recovery intervals could worsen hemodynamic instability and provoke cardiovascular events 2

Potential Adverse Events

The evidence shows serious risks in cardiac populations:

• Three vasovagal episodes occurred even in a supervised cardiac rehabilitation HIIT program with carefully selected patients 5
• Serious adverse events occurred in 25-39% of heart failure patients during exercise training trials, though not all were exercise-related 6
• The risk is substantially higher in patients with active ischemia who have not been properly evaluated and stabilized 4

The Correct Clinical Pathway

Step 1: Mandatory Pre-Exercise Cardiac Evaluation

Before ANY exercise beyond light activity, this patient requires:

• Exercise myocardial perfusion SPECT to identify the extent, severity, and location of ischemia in patients with baseline ECG abnormalities 4
• Assessment of the functional significance of coronary lesions (if intermediate 25-75% stenosis) 4
• Evaluation for high-risk features including left bundle branch block, electronically paced rhythm, or severe coronary calcification 4
• Cardiopulmonary exercise testing to objectively measure exercise capacity and detect exercise-induced ischemia or arrhythmias 1

Step 2: Risk Stratification and Treatment

Based on findings:

• If significant ischemia is present, the patient needs revascularization (PCI or CABG) before intensive exercise 4
• If stable with medical therapy, repeat perfusion imaging should be performed to assess efficacy before exercise progression 4
• The American Diabetes Association and American College of Cardiology recommend that HIIT should only be considered after cardiovascular conditions have been evaluated and controlled 2

Step 3: Exercise Prescription (Only After Stabilization)

If the patient is eventually cleared for exercise:

• Start with short periods of low-intensity exercise and slowly increase duration and intensity as tolerated, as recommended for patients with high cardiovascular risk 2
• Moderate-intensity continuous training is the most feasible and cost-effective aerobic training modality for patients with chronic coronary syndromes 4
• There is insufficient evidence to promote HIIT over moderate-intensity continuous training in coronary patients 4
• HIIT can be prescribed in selected patients for specific targets (e.g., to increase VO2 peak), but only after careful evaluation and under supervision 4

Critical Pitfalls to Avoid

• Never assume preferential perfusion is "mild" or "insignificant" – it represents real coronary disease requiring proper evaluation 4
• Do not rely on the patient being "asymptomatic" – many patients with significant ischemia have atypical or absent symptoms 2
• Avoid starting with HIIT as initial exercise therapy in any patient with known or suspected coronary disease 4, 2
• Do not prescribe exercise based solely on predicted heart rate formulas in patients with cardiac disease – objective testing is mandatory 1

When HIIT Might Eventually Be Appropriate

Only after the following conditions are met:

• Complete cardiac evaluation with stress imaging showing no significant residual ischemia 4
• Successful revascularization if indicated, with repeat testing at 3-5 years 4
• Supervised cardiac rehabilitation setting with continuous monitoring 5
• Individualized prescription using objective measures (VO2max, heart rate reserve, ventilatory thresholds) rather than predicted formulas 4, 1
• Medical monitoring as individuals intensify their exercise program to ensure safety 2

The bottom line: HIIT in a patient with diagnosed preferential perfusion without proper evaluation and stabilization is dangerous and could precipitate acute coronary syndrome, life-threatening arrhythmias, or sudden cardiac death. 4, 2