Myocardial ischemia in patients awaiting coronary artery bypass grafting
A A Knight1, M Hollenberg, M J London
1Department of Anesthesiology, San Francisco Veterans Administration Medical Center 94121.
Insights
Patients undergoing coronary artery bypass grafting (CABG) surgery frequently experience silent myocardial ischemia. Most ischemic episodes occur without a heart rate increase, and painful episodes are shorter but more severe than silent ones.
Area of Science:
- Cardiology
- Clinical Medicine
- Diagnostic Monitoring
Background:
- Patients with severe coronary artery disease (CAD) often undergo elective Coronary Artery Bypass Grafting (CABG) surgery.
- Ambulatory electrocardiogram (ECG) monitoring is a key diagnostic tool for assessing cardiac ischemia.
- Characterizing ischemic episodes in this specific patient cohort is crucial for understanding disease progression and treatment efficacy.
Purpose of the Study:
- To characterize ambulatory ECG findings in men scheduled for elective CABG surgery.
- To quantify the frequency, duration, and characteristics of ischemic episodes, including silent versus symptomatic events.
- To investigate the role of heart rate changes in the occurrence of myocardial ischemia.
Main Methods:
- Fifty male patients undergoing elective CABG surgery were monitored using continuous ambulatory ECG for 48 hours.
- ST segment deviation was quantified for duration, maximum change, and area under the curve (AUC).
- Ischemic episodes were analyzed for their relationship to heart rate changes.
Main Results:
- 42% of patients experienced ischemic episodes, with 87% being silent.
- Symptomatic episodes showed greater ST segment deviation but were shorter than silent episodes.
- 75% of ischemic episodes were unrelated to an initial increase in heart rate.
Conclusions:
- Patients with severe CAD continue to experience frequent silent myocardial ischemia despite medical therapy.
- Painful ischemic episodes are more severe but shorter than silent ones.
- The majority of ischemic episodes occur independently of heart rate elevation, suggesting complex underlying mechanisms.
Abstract:
The results of ambulatory ECG monitoring are described in a group of patients that have not previously been characterized. Fifty men who were initially seen for elective CABG surgery underwent 48 hours of continuous ambulatory ECG monitoring. ST segment deviation from baseline, trended every 15 seconds, was quantified for duration, maximum ST segment change, area under the ST segment-time curve (AUC), and average ST segment change for the episode (AUC/duration). Ischemic episodes, 87% of which were silent, occurred in 42% of the patients. Symptomatic episodes had greater maximum ST segment change than silent episodes (-2.4 vs -1.9 mm; p less than 0.05) but were shorter in duration (11 vs 18 minutes; p less than 0.05). Episodes that were unrelated to heart rate, that is, episodes with less than 20% increase in heart rate over the baseline rate at the onset of ischemia, made up 75% of all ischemic events and occurred in 90% of patients (19 of 21). Heart rate-related and unrelated ischemic episodes did not differ in duration, maximum ST segment change, AUC, or average ST segment change. It was concluded that: (1) as with patients with unstable angina, patients with severe coronary artery disease continue to have frequent episodes of silent myocardial ischemia despite intensive medical therapy; (2) painful episodes have greater maximum ST segment change but are shorter than silent ones; (3) most ischemic episodes (75%) occur without an initial increase in heart rate; and (4) heart rate-related and unrelated episodes are quantitatively similar.
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