SPECT can predict cardiovascular mortality in elective aneurysm repair patients

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By Kimihiro Komori and Yosuke Inoue

Elective abdominal aortic aneurysm repair is a prophylactic operation to prevent aneurysm-related death. Patients must have an expectation of relatively long survival, taking into account the operative risk. After successful abdominal aortic aneurysm repair, independent of whether by open or endovascular repair (EVAR), relatively reduced survival with long-term follow-up remains unresolved. Furthermore, there have been very few studies reporting predictors of long-term outcomes after elective open abdominal aortic aneurysm repair or EVAR in a Japanese population. Therefore, clarification of the risks regarding long-term mortality after repair is necessary.

Stress myocardial perfusion single-photon emission computed tomography (SPECT) is an established tool not only for diagnosing coronary artery disease but also for predicting treatment outcomes. In particular, the use of the summed stress scores (SSS), representing the extent of myocardial perfusion abnormality, is effective in predicting future morbidity and mortality. Although many studies have shown that coronary artery disease is a risk factor after elective abdominal aortic aneurysm repair, the definitions of coronary artery disease have differed between studies. Furthermore, to the best of our knowledge, there is a lack of reports employing stress myocardial perfusion SPECT findings for predicting long-term cardiovascular mortality after elective abdominal aortic aneurysm repair. Therefore, the aim of the present study was to determine the risk factors for cardiovascular death in Japanese patients undergoing elective abdominal aortic aneurysm repair employing SSS evaluated on preoperative pharmacological stress myocardial perfusion SPECT.

The study followed consecutive patients who underwent successful elective infrarenal abdominal aortic aneurysm open repair or EVAR, between January 2007 and June 2011 at Nagoya University Hospital. In all patients, except for those with uncontrolled bronchial asthma, pharmacological stress myocardial perfusion SPECT was performed within two months prior to abdominal aortic aneurysm repair. The primary endpoint was cardiac death, defined as death from cardiovascular cause or sudden death. Follow-up of the patients lasted for up to three years. The database was developed prospectively and clinical data were analysed retrospectively. For stress, adenosine triphosphate disodium was used for all patients, a dose of 720μg/kg being injected over six minutes using an infusion pump. Thallium-201 was injected intravenously for three minutes after the start of adenosine infusion.

Scintigraphic images were acquired at 10 minutes and then four hours after tracer injection using a two-detector camera (Symbia-S, Siemens Japan or E CAM, Toshiba) equipped with a low-energy high-resolution parallel collimator. Energy discrimination was provided by a 20% window centred at 70 KeV. SPECT images were transferred to a computer with 64×64 matrix size and were reconstructed from data using a data processor (e soft, Toshiba) combined with a Butterworth filter and a ramp filter, without attenuation or scatter correction. SPECT slices were created relative to the anatomic axis of the left ventricle, and the vertical long axis, horizontal long-axis, and short-axis were generated.

The SSS from the 201Tl SPECT data using a 17-segment and five-point scoring system was calculated automatically using Heart Score View software (Nihon Medi-Physics). A previous report demonstrated that defect scores calculated by this software were similar to those attainted by visual assessments. The results were checked visually by two physicians blinded to the patient details. Thresholds of percentage tracer uptake required to produce scores by the software were determined as previously described. We stratified the severity of coronary artery disease in accordance with methods reported in the previous literature: normal, SSS <4; mildly abnormal, SSS 4–8; moderately abnormal, SSS 9–13; and severely abnormal, SSS ≥14.

Two hundred and eighty five patients were eligible for the present study. No major problems were encountered during preoperative pharmacological stress myocardial perfusion SPECT, although several patients experienced minor complications. Abnormal SPECT images were obtained for 83 patients (29%). The median follow-up duration was 925 days (541–1,095 days). During the follow-up period, 24 patients (8%) died of cardiovascular disease (sudden death, n=3; myocardial infarction, n=4; heart failure, n=6; stroke, n=4; others, n=7). Incidence of cardiac death was 6% in patients with normal SSSs (≤3), 9% in those with mildly abnormal SSSs (4–8), 25% in those with moderately abnormal SSSs (9–13), and 24% in those with severely abnormal SSSs (≥14; p=0.020). The incidence of cardiac death in patients with moderately abnormal SSSs (9–13) and that in patients with severely abnormal SSSs (≥14) was significantly higher than that in patients with normal SSS (≤3; p=0.042 and p=0.025, respectively).

The prevalence of diabetes and chronic kidney disease ≥ stage 3 in patients with cardiac death was significantly higher than in survivors (44, 17% vs.10, 42%, p=0.006; and 125, 48% vs. 17, 71%, p=0.034). Worse SSS was evident in patients suffering from cardiac death than in survivors (p=0.020). Kaplan-Meier analysis indicated that the cumulative three-year survival rate was significantly lower in patients with SSS ≥9 than in those with SSS

The present study concludes that preoperative pharmacological stress myocardial perfusion SPECT is not only safe, but is also a useful method to predict long-term cardiovascular mortality for patients undergoing elective abdominal aortic aneurysm repair. Patients with SSS ≥9, as well as diabetes or chronic kidney disease, are at high risk after elective aneurysm repair. Careful follow-up is required for such high-risk patients. Additionally, it was fortunate that, even in aneurysm patients with no past history of cardiac events, it was possible to discover abnormal pharmacological stress myocardial perfusion SPECT results. Thus, it is possible for such patients to receive treatment before surgery leading to better outcomes of aneurysm surgical treatment.

 


Kimihiro Komori, is professor and chairman, Division of Vascular Surgery, Department of Surgery, Nagoya University Graduates School of Medicine, Nagoya, Japan. Yosuke Inoue is with the Department of Cardiology, Nagoya University Graduate School of Medicine

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