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Respiratory Support in Critical Care

Demand Myocardial Ischemia: Application of 12 lead ECG Monitoring

Kathy Booker, RN, PhD, CCRN
Dean, School of Nursing
Millikin University, Decatur, IL USA

The article also available in PDF: 45 KB

See the author giving the Clinical Window presentation at the 23rd ISICEM congressin in Brussels (March 2003).

 

Demand myocardial ischemia develops in patients with conditions that greatly increase the demand for cardiac output or perfusion when myocardial supply may be marginal or inadequate.

Pathophysiology of demand ischemia:

  • Transient ST depression associated with demand conditions is believed to reflect subendocardial ischemia
  • Increased demand ischemia may be caused by microvascular endothelial dysfunction
  • Transient demand ischemia is usually reversible but likely does represent a current of injury & may progress to infarction

Classically delineated by exercise stress testing, demand ischemia may now be detected in hospitalized patients or those undergoing diagnostic testing via the use of continuous 12 lead ECG monitoring.

Table: Role of 12-lead monitoring

  • 12 lead monitoring allows for multiple lead surveillance of ST segment changes
  • System algorithms analyze baseline ST segment measurements compared to real time
  • Problems: artifact, false positive changes of ST segments (positional changes, tachycardia-induced ST changes)

Primarily demonstrated as ST segment depression or T wave inversion, demand ischemia differs from classic supply-sided ischemia in a number of ways.

The case for multiple lead monitoring

  • Recent studies: V5 best lead for demand ischemia - but may miss up to 50% of events
  • Complexity: Monitoring systems must allow for rapid identification of ST changes in more than one lead
  • Quality tracings: To decrease false positives, good skin prep and proper placement crucial!
  • Demand ischemia is transient and may be found in non-contiguous leads. Most are silent!

Case studies involving postoperative patients and patients undergoing polysomnography for severe obstructive sleep apnea will be presented. The benefits and barriers of 12 lead ECG monitoring will also be examined in the presentation. (See the presentation slides)

Selected References

  1. Drew, B. J., & Krucoff, M. W. for the ST-segment monitoring practice guideline international working group. (1999). Multilead ST-segment monitoring in patients with acute coronary syndromes: A consensus statement for healthcare professionals. American Journal of Critical Care, 8, 372-388.
  2. Mehta, D., Curwin, J., Gomes, J. A. & Fuster, V. (1997). Sudden death in coronary artery disease: Acute ischemia versus myocardial substrate. Circulation, 96, 3215-3223
  3. Vincent, M., Abildskov, J. A., & Burgess, M. J. (1977). Mechanisms of ischemic ST-segment displacement. Circulation, 56, 559-566.
  4. Wagner, G. S. (2001) Marriott’s Practical Electrocardiography, (10th ed.). Philadelphia: Lippincott Williams & Wilkins.
  5. Zeiher, A.M., Krause, T., Schachinger, V., Minners, J., & Moser, E. (1995). Impaired endothelium-dependent vasodilation of coronary resistant vessels is associated with exercise-induced myocardial ischemia. Circulation, 91, 2345-2352.

[Editor’s note: The slides of Professor Booker’s presentation at the 2003 ICU Congress in Brussels can be reviewed in this issue of the Clinical Window Web Journal.]


Last updated: 1 March 2003Created
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Kathy Booker:
Demand Myocardial Ischemia
ppt presentation

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Weaning With Indirect Calorimetry ppt presentation

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Non-invasive ventilation in intensive care
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