Characterization of Circulating Endothelial Cells in Acute Myocardial Infarction

Features of endothelial cells in blood samples may eventually permit prediction of atherosclerotic plaque rupture events. Tell-Tale Cells In Edgar Allan Poe’s short story The Tell-Tale Heart, the narrator murders an old man and hides the body under the floorboards. The guilty murderer imagines that he hears the beating of the dead man’s heart emanating from the corpse underfoot—unwanted evidence of his guilt. But what if the body could leak evidence of a fragile condition before suffering a heart attack? The tale told could be frightening, yes, but the information may allow intervention at a crucial time in the pathophysiological process of heart disease. Now, Damani et al. take crucial first steps toward defining a clinical measure that could predict a thus-far unpredictable, myocardial infarction (MI)–associated event: acute atherosclerotic plaque rupture. Many people tell a personal story of a friend or relative who had a normal stress test just weeks before suffering a heart attack as a result of plaque rupture. Indeed, diagnosis of stable coronary artery disease (CAD) is now possible using stress tests and coronary artery imaging. In contrast, there are no clinically useful tests that warn of impending cardiovascular maladies caused by atherosclerotic plaque rupture. Physicians thus require a noninvasive, clinically feasible assay for a macromolecule or cell in blood that can identify people at risk for this condition, which is increasing in incidence as the population ages and widens. Endothelial cells (ECs) are normally found lining the blood vessels, and leakage into the circulation is evidence of ongoing injury to arteries that occurs on the way to potentially lethal plaque rupture. Elevated amounts of circulating endothelial cells (CECs) were previously linked to acute arterial catastrophes, but these measures have not yet made it into the clinic. Using automated, clinically feasible, three-channel fluorescence microscopy technology that can detect and permit isolation of rare cells, the authors measured and characterized CECs in healthy subjects and in patients who had experienced a type of heart attack known to manifest after acute arterial plaque rupture. CECs were elevated significantly in patients, relative to controls, and this elevation was not correlated with other measures of heart tissue death. Damani et al. also found that acute MI patients specifically displayed multicellular, multinuclear EC clusters and ECs with larger cellular and nuclear areas, relative to age-matched controls and patients with peripheral vascular disease (narrowing of arteries in the legs and feet). Although the study must be conducted in more patients and validated in an independent cohort, the new work suggests that tell-tale CECs may be useful in the clinic as evidence of ongoing plaque rupture and as a warning of possible heart attack in the near future. Acute myocardial infarction (MI), which involves the rupture of existing atheromatous plaque, remains highly unpredictable despite recent advances in the diagnosis and treatment of coronary artery disease. Accordingly, a clinical measurement that can predict an impending MI is desperately needed. Here, we characterize circulating endothelial cells (CECs) using an automated and clinically feasible CEC three-channel fluorescence microscopy assay in 50 consecutive patients with ST-segment elevation MI and 44 consecutive healthy controls. CEC counts were significantly elevated in MI cases versus controls, with median numbers of 19 and 4 cells/ml, respectively (P = 1.1 × 10−10). A receiver-operating characteristic (ROC) curve analysis demonstrated an area under the ROC curve of 0.95, suggesting near-dichotomization of MI cases versus controls. We observed no correlation between CECs and typical markers of myocardial necrosis (ρ = 0.02, creatine kinase–myocardial band; ρ = −0.03, troponin). Morphological analysis of the microscopy images of CECs revealed a 2.5-fold increase (P < 0.0001) in cellular area and a twofold increase (P < 0.0001) in nuclear area of MI CECs versus healthy controls, age-matched CECs, as well as CECs obtained from patients with preexisting peripheral vascular disease. The distribution of CEC images that contained from 2 to 10 nuclei demonstrates that MI patients were the only subject group to contain more than 3 nuclei per image, indicating that multicellular and multinuclear clusters are specific for acute MI. These data indicate that CEC counts may serve as a promising clinical measure for the prediction of atherosclerotic plaque rupture events.