Impact of ischemia and scar on therapeutic benefit of myocardial revascularization

The question of how to optimally manage coronary artery disease (CAD) has been a challenge for the cardiology community. The results of early, large randomized clinical trials (RCTs) comparing strategies of medical therapy alone versus revascularization plus medical therapy in patients with stable CAD suggested a survival advantage for a revascularization strategy in the setting of more advanced, higher-risk CAD (left main, three-vessel CAD), but a superiority of medical therapy in patients with more limited, relatively lower-risk CAD (one vessel, limited two-vessel CAD). The results of the Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) and Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) trials redefined the management of CAD, supporting the concept that the impact of aggressively applied modern "medical therapy" on patient survival and patient-reported outcomes is not further improved by the addition of percutaneous intervention. On the other hand, RCTs incorporating fractional flow reserve have shown that this physiologic metric can help identify which patients will benefit from a revascularization strategy. This paradigm has been extended to the use of myocardial perfusion imaging-identified ischemia to determine which patients may have enhanced survival with early revascularization versus medical therapy. Although data from a series of observational studies suggest that inducible ischemia on myocardial perfusion scintigraphy can identify revascularization candidates, several studies, including substudies from major RCTs, do not support this idea. Until RCTs comparing revascularization with medical therapy strategies are performed, many questions remain open. The correct thresholds for treatment, the metric to guide treatment, and how revascularization should be performed are as yet undefined.

Gated SPECT in assessment of regional and global left ventricular function: an update

Gated myocardial perfusion SPECT (GSPECT) is a major clinical tool, widely used for performing myocardial perfusion imaging procedures. In this review, we have presented the fundamentals of GSPECT and the ways in which the functional measurements it provides have contributed to the emergence of myocardial perfusion SPECT in its important role as a major tool of modern cardiac imaging. GSPECT imaging has shown unique capability to provide accurate, reproducible and operator-independent quantitative data regarding myocardial perfusion, global and regional systolic and diastolic function, stress-induced regional wall-motion abnormalities, ancillary markers of severe and extensive disease, left ventricular geometry and mass, as well as the presence and extent of myocardial scar and viability. Adding functional data to perfusion provides an effective means of increasing both diagnostic accuracy and reader's confidence in the interpretation of the results of perfusion scans. Assessment of global and regional LV function has improved the prognostic power of myocardial perfusion SPECT and has been shown in a large registry to add to the perfusion assessment in predicting benefit from revascularization.

Lessons learned from MPI and physiologic testing in randomized trials of stable ischemic heart disease: COURAGE, BARI 2D, FAME, and ISCHEMIA

There is a preponderance of evidence that, in the setting of an acute coronary syndrome, an invasive approach using coronary revascularization has a morbidity and mortality benefit. However, recent stable ischemic heart disease (SIHD) randomized clinical trials testing whether the addition of coronary revascularization to guideline-directed medical therapy (GDMT) reduces death or major cardiovascular events have been negative. Based on the evidence from these trials, the primary role of GDMT as a front line medical management approach has been clearly defined in the recent SIHD clinical practice guideline; the role of prompt revascularization is less precisely defined. Based on data from observational studies, it has been hypothesized that there is a level of ischemia above which a revascularization strategy might result in benefit regarding cardiovascular events. However, eligibility for recent negative trials in SIHD has mandated at most minimal standards for ischemia. An ongoing randomized trial evaluating the effectiveness of randomization of patients to coronary angiography and revascularization as compared to no coronary angiography and GDMT in patients with moderate-severe ischemia will formally test this hypothesis. The current review will highlight the available evidence including a review of the published and ongoing SIHD trials.

Myocardial scar burden predicts survival benefit with implantable cardioverter defibrillator implantation in patients with severe ischaemic cardiomyopathy: influence of gender

Objective

We sought to assess the impact of myocardial scar burden (MSB) on the association between implantable cardioverter defibrillator (ICD) implantation and mortality in patients with ischaemic cardiomyopathy (ICM) and left ventricular EF ≤40%. In addition, we sought to determine the impact of gender on survival benefit with ICD implantation.

Design

Retrospective observational study.

Setting

Single US tertiary care centre.

Patients

Consecutive patients with significant ICM who underwent delayed hyperenhancement-MRI between 2002 and 2006.

Interventions

ICD implantation.

Main outcome measures

All-cause mortality and cardiac transplantation.

Results

Follow-up of 450 consecutive patients, over a mean of 5.8 years, identified 186 deaths. Cox proportional hazard modelling was used to evaluate associations among MSB, gender and ICD with respect to all-cause death as the primary endpoint. ICDs were implanted in 163 (36%) patients. On multivariable analysis, Scar% (χ² 28.21, p<0.001), Gender (χ² 12.39, p=0.015) and ICD (χ² 9.57, p=0.022) were independent predictors of mortality after adjusting for multiple parameters. An interaction between MSB×ICD (χ² 9.47, p=0.009) demonstrated significant differential survival with ICD based on MSB severity. Additionally, Scar%×ICD×Gender (χ² 6.18, p=0.048) suggested that men with larger MSB had significant survival benefit with ICD, but men with smaller MSB derived limited benefit with ICD implantation. However, the inverse relationship was found in women.

Conclusions

MSB is a powerful independent predictor of mortality in patients with and without ICD implantation. In addition, MSB may predict gender-based significant differences in survival benefit from ICDs in patients with severe ICM.

Appropriate test selection for single-photon emission computed tomography imaging: association with clinical risk, posttest management, and outcomes

BACKGROUND

Appropriate use criteria (AUC) for stress single-photon emission computed tomography (SPECT) are only one step in appropriate use of imaging. Other steps include pretest clinical risk evaluation and optimal management responses. We sought to understand the link between AUC, risk evaluation, management, and outcome.

METHODS

We used AUC to classify 1,199 consecutive patients (63.8 ± 12.5 years, 56% male) undergoing SPECT as inappropriate, uncertain, and appropriate. Framingham score for asymptomatic patients and Bethesda angina score for symptomatic patients were used to classify patients into high (≥5%/y), intermediate, and low (≤1%/y) risk. Subsequent patient management was defined as appropriate or inappropriate based on the concordance between management decisions and the SPECT result. Patients were followed up for a median of 4.8 years, and cause of death was obtained from the social security death registry.

RESULTS

Overall, 62% of SPECTs were appropriate, 18% inappropriate, and 20% uncertain (only 5 were unclassified). Of 324 low-risk studies, 108 (33%) were inappropriate, compared with 94 (15%) of 621 intermediate-risk and 1 (1%) of 160 high-risk studies (P < .001). There were 79 events, with outcomes of inappropriate patients better than uncertain and appropriate patients. Management was appropriate in 986 (89%), and appropriateness of patient management was unrelated to AUC (P = .65).

CONCLUSION

Pretest clinical risk evaluation may be helpful in appropriateness assessment because very few high-risk patients are inappropriate, but almost half of low-risk patients are inappropriate or uncertain. Appropriate patient management is independent of appropriateness of testing.

Abstract 293: Predictors Of Repeat Cardiovascular Testing In Patients Who Receive An Index Negative Stress Echocardiography

Background: Repeat cardiovascular imaging in most situations is of indeterminate appropriateness. We sought to identify baseline characteristics associated with repeat testing in patients who had an initial negative test result.

Methods: Medicare beneficiaries who had a negative index stress echo (SE) between 2002-2008 were linked to corresponding Medicare claim data. We identified the nature and date of claims for repeat cardiac testing (exercise stress test, SE, cardiac PET, cardiac SPECT, or angiography). Kaplan-Meier analysis and Cox proportional hazards (CPH) analysis were used to determine the association of baseline covariates on the risk of a repeat test. The pre-defined outcome endpoint included time to first repeat test.

Results: Of 3,113 Medicare beneficiaries with a negative SE (mean follow-up, 2.6 ± 1.9 years), 1553 (50%) received subsequent imaging [1411 (91%) white, 85 (5.5%) African-American, 55 (3.5%) Hispanic, Asian, or other origin]. Kaplan-Meier analysis stratified by race was associated with repeat cardiovascular imaging (p <0.0001). CPH analysis revealed that race, hyperlipidemia, CAD, T-wave changes after stress, resting diastolic blood pressure, maximum rate pressure product, percent peak maximum heart rate, and patients using aspirin and beta blockers were independently associated with repeat testing (χ 2 =242.3, P<0.0001). After risk-adjustment, African-American patients were half as likely to have a repeat test compared to white patients (HR 0.52 [0.40-0.70], p<.001) independent of other variables.

Conclusions: Although some repeat testing in patients with negative studies reflects risk level, the presence of racial differences suggests that nonmedical factors may have an important role.

Identification of therapeutic benefit from revascularization in patients with left ventricular systolic dysfunction: inducible ischemia versus hibernating myocardium

BACKGROUND

Although the recent surgical treatment of ischemic heart failure substudy reported that revascularization of viable myocardium did not improve survival, these results were limited by the viability imaging technique used and the lack of inducible ischemia information. We examined the relative impact of stress-rest rubidium-82/F-18 fluorodeoxyglucose positron emission tomography identified ischemia, scar, and hibernating myocardium on the survival benefit associated with revascularization in patients with systolic dysfunction.

METHODS AND RESULTS

The extent of perfusion defects and metabolism-perfusion mismatch was measured with an automated quantitative method in 648 consecutive patients (age, 65±12 years; 23% women; mean left ventricular ejection fraction, 31±12%) undergoing positron emission tomography. Follow-up time began at 92 days (to avoid waiting-time bias); deaths before 92 days were excluded from the analysis. During a mean follow-up of 2.8±1.2 years, 165 deaths (27.5%) occurred. Cox proportional hazards modeling was used to adjust for potential confounders, including a propensity score to adjust for nonrandomized treatment allocation. Early revascularization was performed within 92 days of positron emission tomography in 199 patients (33%). Hibernating myocardium, ischemic myocardium, and scarred myocardium were associated with all-cause death (P=0.0015, 0.0038, and 0.0010, respectively). An interaction between treatment and hibernating myocardium was present such that early revascularization in the setting of significant hibernating myocardium was associated with improved survival compared with medical therapy, especially when the extent of viability exceeded 10% of the myocardium.

CONCLUSIONS

Among patients with ischemic cardiomyopathy, hibernating, but not ischemic, myocardium identifies which patients may accrue a survival benefit with revascularization versus medical therapy.

Association of epicardial fat, hypertension, subclinical coronary artery disease, and metabolic syndrome with left ventricular diastolic dysfunction

Epicardial fat is a metabolically active fat depot that is strongly associated with obesity, metabolic syndrome, and coronary artery disease (CAD). The relation of epicardial fat to diastolic function is unknown. We sought to (1) understand the relation of epicardial fat volume (EFV) to diastolic function and (2) understand the role of EFV in relation to potential risk factors (hypertension, subclinical CAD, and metabolic syndrome) of diastolic dysfunction in apparently healthy subjects with preserved systolic function and no history of CAD. We studied 110 consecutive subjects (65% men, 55 ± 13 years old, mean body mass index 28 ± 5 kg/m(2)) who underwent cardiac computed tomography and transthoracic echocardiography within 6 months as part of a self-referred health screening program. Exclusion criteria included history of CAD, significant valvular disease, systolic dysfunction (left ventricular ejection fraction <50%). Diastolic function was defined according to American Society of Echocardiography guidelines. EFV was measured using validated cardiac computed tomographic software by 2 independent cardiologists blinded to clinical and echocardiographic data. Hypertension and metabolic syndrome were present in 60% and 45%, respectively. Subclinical CAD was identified in 20% of the cohort. Diastolic dysfunction was present in 45 patients. EFV was an independent predictor of diastolic dysfunction, mean peak early diastolic mitral annular velocity, and ratio of early diastolic filling to peak early diastolic mitral annular velocity (p = 0.01, <0.0001, and 0.001, respectively) with incremental contribution to other clinical factors. In conclusion, EFV is an independent predictor of impaired diastolic function in apparently healthy overweight patients even after accounting for associated co-morbidities such as metabolic syndrome, hypertension, and subclinical CAD.