Prevalence of myocardial ischemia during mechanical ventilation and weaning and its effects on weaning success.

BACKGROUND: Myocardial ischemia may be considered both a consequence of weaning from ventilation and a potential cause of weaning failure. A limited number of investigations have evaluated myocardial ischemia during mechanical ventilation and weaning and its effect on weaning success. The purpose of this pilot investigation was to determine the prevalence of myocardial ischemia in a diverse group of medical intensive care unit (MICU) patients during baseline mechanical ventilation, during weaning using continuous positive airway pressure, and up to 24 hours after extubation and to evaluate the relationship between ischemia and weaning failure.
METHODS: This study was a prospective, repeated-measure, descriptive investigation that studied 43 ventilated MICU patients. Slightly more than half of participants were male (53%), and participants had a mean age of 51.1 +/- 14.6 years and were ventilated an average of 11.7 +/- 11.3 days. Myocardial ischemia was evaluated by examination of plasma cardiac troponin I, creatine phosphokinase-myocardial band (CK-MB), and ST-segment changes on electrocardiogram. Continuous electrocardiographic data were obtained by a calibrated, frequency-modulated, continuous 3-channel electrocardiographic recorder using leads I, II, and V2.
RESULTS: Seventy percent of these participants (n = 30) exhibited ST-segment deviation at some point during data collection (baseline mechanical ventilation, during weaning, after extubation). Twenty-four participants exhibited ST-segment deviation at baseline, 7 during weaning, and 8 after extubation. Nine participants exhibited ST-segment deviation at >1 data collection time point. None had ST-segment deviation at all 3 time points. Cardiac enzyme concentrations were highly variable; five participants demonstrated clinically important increases in either CK-MB and/or troponin I. Thirty-five percent of participants required >1 weaning trial. Participants who exhibited ST-segment deviation during baseline ventilation were 60% more likely to fail their initial weaning trial. There were no significant differences in CK-MB or troponin I levels between those participants who were successfully weaned with 1 trial and those who failed to wean during that first trial.
CONCLUSIONS: Silent myocardial ischemia was a common occurrence in this diverse group of MICU patients, although only 21% had previously diagnosed coronary disease. Clinicians must be aware of the potential for silent ischemia, monitor and evaluate their patients for such, and intervene to promote optimal cardiovascular function, particularly during the stress of ventilator weaning.