SAN FRANCISCO, April 21 -- Q-wave electrocardiography, the traditional method for retrospectively diagnosing chronic cardiac damage from an unrecognized heart attack, missed three-fourths of cases, researchers said.
Q-waves were present in only 8% of patients presenting for angiography because of suspected heart disease, Han W. Kim, M.D., of Duke University in Durham, N.C., and colleagues reported online in PLoS Medicine.
By comparison, 27% had previously undetected myocardial damage seen on delayed-enhancement cardiovascular magnetic resonance (DE-CMR) without Q-wave enhancement.
Although the magnitude may be surprising, the discrepancy shouldn't be, Dr. Kim said.
Even during acute, overt MI, Q-waves don't appear on the electrocardiogram for at least half of patients, and in others they may show up initially and then disappear, he noted.
Action Points
- Explain to interested patients that a heart attack can leave long-term damage in the heart even if the initial symptoms are missed.
- Note that the study included only a cohort with suspected coronary artery disease and may not generalize to the general population or entirely asymptomatic patients.
Large population-based studies suggest that 40% to 60% of all MIs go unrecognized, the researchers noted. Identifying these can have important implications for patients, they found.
Non-Q-wave unrecognized MI predicted 11.4-fold excess all-cause mortality (95% confidence interval 2.5 to 51.1) and 17.4-times higher cardiac mortality (95% CI 2.2 to 137.4) than no MI during two years of follow-up, even after accounting for New York Heart Association class and left ventricular ejection fraction.
But the researchers cautioned that it's too early to suggest screening with delayed-enhancement cardiac MRI since optimal medical treatment for unrecognized heart attack and the prognostic effect of early diagnosis remain unclear.
The diagnosis of non-Q-wave unrecognized MI is difficult because, "by definition, these patients either do not present during the acute phase of infarction or, even if they do present, MI is not suspected and cardiac biomarkers, such as troponins, are not drawn," they wrote.
Later cardiac assessment once the infarct is chronic will reveal normal troponin levels and nondiagnostic electrocardiograms.
"In these circumstances, noninvasive imaging may be helpful," Dr. Kim's group noted.
Given high sensitivity for chronic MI in a recent study, the researchers examined use of delayed-enhancement cardiovascular MR for unrecognized MI.
Their prospective study included 185 patients scheduled for invasive coronary angiography for suspected coronary artery disease but who had no history of MI.
Patients got cardiac MRI for research purposes only. The scans were not used to guide coronary revascularization or other clinical decision-making.
Overall prevalence of non-Q-wave unrecognized MI was 3.3-fold higher than Q-wave unrecognized MI (27% versus 8%).
Obstructive coronary artery disease on angiography was more common with non-Q-wave unrecognized MI than with Q-wave unrecognized MI, or no MI (96%, 73%, and 44%, respectively).
Both types of unrecognized MI were linked to greater extent and severity of coronary artery disease (both PP
Of the two, though, non-Q-wave unrecognized MI had a stronger relationship with coronary artery disease.
Prevalence in patients with triple vessel disease was 53% compared with 15% for Q-wave unrecognized MI prevalence. Likewise, "silent" MI without Q-wave enhancement was present among 64% of those with maximal stenosis greater than 90% compared with 17% for Q-wave unrecognized MI.
In the multivariable analysis, risk of non-Q-wave unrecognized MI rose 1.6-fold with each decade of age (P=0.01), 2.4-fold with diabetes (P=0.03), and 1.4-fold for every 10-percentage point decrease in left ventricular ejection fraction (P=0.0003).
The researchers pointed out that the patients studied were those scheduled for X-ray coronary angiography, and symptoms such as chest pain (62%) and dyspnea (30%) were fairly common.
They cautioned, therefore, that their findings may not be applicable to the general population or to those who are entirely asymptomatic.
Dr. Kim also noted that, while delayed-enhancement cardiovascular MRI uses standard cardiac MRI equipment, not all centers have the software to do these scans or the expertise to read them.
| The study was supported by the National Institutes of Health.
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Primary Source
PLoS Medicine
Kim HW, et al "Unrecognized non-Q-wave myocardial infarction: prevalence and prognostic significance in patients with suspected coronary disease" PLoS Med 2009.