Myocardial Ischemia: Oxygen Supply vs Demand
Does normal blood pressure rule out myocardial ischemia?
Normal blood pressure does not establish adequate myocardial oxygen supply. Coronary blood flow, arterial oxygen content, heart rate and the heart’s workload all matter. Ischemia occurs when supply cannot meet demand; an ECG change or a pressure value is one finding within that larger assessment, not a complete diagnosis.
Key takeaways
- Arterial pressure does not directly measure myocardial oxygen delivery.
- A faster rate can increase demand while shortening diastolic time.
- ECG territory clues do not independently prove a culprit artery or infarction.
In this video
- Opening: normal blood pressure and oxygen supply
- Where the heart muscle gets its oxygen
- How much oxygen the heart pulls out
- The pressure that pushes blood in
- Where the demand comes from
- Wall stress and the thick ventricle
- What the ECG suggests
- Which leads go with which wall
- Lead two and V five
- Working a case
- Two patients, one preload drop
- Interview question
- Quick check
What determines myocardial oxygen supply?
Oxygen delivery to myocardium depends on coronary flow and the oxygen content of the blood reaching it. Hemoglobin and oxygenation therefore matter alongside the circulation. A pressure that looks reassuring does not measure all of those quantities.
The heart’s demand also changes with rate and workload. Tachycardia can increase demand while shortening diastolic time, so the same arterial pressure can accompany very different supply-demand conditions.
Why are pressure gradients only part of the explanation?
Aortic diastolic pressure relative to left-ventricular filling pressure can help explain a driving gradient for left-ventricular subendocardial perfusion. That simplified relationship is not a complete measurement of coronary flow or a universal rule for the right ventricle.
Changing loading conditions can alter both sides of a gradient. A lower ventricular pressure is not automatically beneficial if arterial pressure also falls. Interpret the change as a relationship rather than treating one reduced number as proof of better perfusion.
What can the ECG establish?
ST, T-wave and Q-wave findings supply information that must be read with the rest of the tracing and the patient. A lead-location association does not identify every culprit lesion or prove that a change represents acute infarction.
This page explains physiology rather than an acute coronary treatment plan. It does not select a vasodilator, fluid, transfusion threshold or other intervention from one pressure or ECG feature.
