SNM: SPECT may detect ischemic heart disease in diabetics

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In diabetic patients, fatty acid metabolism or perfusion mismatch obtained from dual SPECT using I-123 beta-methyl iodophenyl pentadecanoic acid (BMIPP)-TL, a medical isotope bound with an agent that is metabolized by the heart to image the fatty acid uptake of heart muscle cells, is a useful prognostic tool for adverse cardiac events, according to a study presented this week at the SNM’s annual meeting in San Antonio, Texas.

Ischemia of the myocardium can signal diminished oxygenation of the heart tissue and trigger a heart attack if left untreated. "Diabetes is a serious risk factor for ischemic heart disease," said Kenji Fukushima, MD, PhD, of the Tokyo Women's Medical University in Tokyo. "Most diabetic patients do not exhibit signs of myocardial ischemia and may be on course toward major cardiac events without any red alert. Molecular imaging could potentially provide an effective screening tool for at-risk diabetic patients suspected of having ischemic heart disease."

The researchers enrolled 191 diabetic patients (average age: 68 years, 123 men) without any history of heart disease who underwent rest ECG-gated BMIPP-TL dual SPECT. They obtained summed defect score for both SPECT (BMDS, TLDS) and mismatch score (TLDS-BMDS) from visual assessment with a myocardial 17-segment model. Left ventricular ejection fraction and end-diastolic volume were calculated from gated TL-SPECT. Other conventional risk factors including hypertension, dyslipidemia, renal dysfunction and hemodialysis were added to the analysis. 

The composite endpoint was a hard event of cardiac death and myocardial infarction and a soft event of late coronary intervention (three months), fatal arrhythmia and hospitalization for heart failure. The follow-up was 1,058 days.

During the follow-up, the study revealed 13 major and 25 minor events, proving that I-123 BMIPP is safe and beneficial for predicting the likelihood of cardiac events in diabetic patients suspected of having myocardial ischemia. 

Coxhazard univariate analysis showed BMDS, TLDS and mismatch score were significantly predictive for total event (p=0.001, 0.025 and 0.001, respectively), the researchers reported. These scores were no longer predictive from analysis for hard event. Multivariate analysis revealed mismatch score or BMDS for total event (p=0.001) and hemodialysis for hard event (p=0.008) were independent prognostic indicators. Also, a Kaplan-Meier analysis revealed patients with a mismatch score of at least six had a significantly higher rate for total event than those without.

“This is the first study of its kind detecting ischemic heart disease in diabetic patients without any history of myocardial disease,” Fukushima and colleagues noted. “If moved into clinical use, imaging both cell metabolism and blood flow through the heart could help physicians detect myocardial ischemia and make clinical decisions that could save lives.”