Risk stratification of patients with prior myocardial infarction and advanced left ventricular dysfunction by gated myocardial perfusion SPECT imaging

Advanced imaging for risk stratification for ventricular arrhythmias and sudden cardiac death

Sudden cardiac death (SCD) is a leading cause of mortality, comprising approximately half of all deaths from cardiovascular disease. In the US, the majority of SCD (85%) occurs in patients with ischemic cardiomyopathy (ICM) and a subset in patients with non-ischemic cardiomyopathy (NICM), who tend to be younger and whose risk of mortality is less clearly delineated than in ischemic cardiomyopathies. The conventional means of SCD risk stratification has been the determination of the ejection fraction (EF), typically via echocardiography, which is currently a means of determining candidacy for primary prevention in the form of implantable cardiac defibrillators (ICDs). Advanced cardiac imaging methods such as cardiac magnetic resonance imaging (CMR), single-photon emission computerized tomography (SPECT) and positron emission tomography (PET), and computed tomography (CT) have emerged as promising and non-invasive means of risk stratification for sudden death through their characterization of the underlying myocardial substrate that predisposes to SCD. Late gadolinium enhancement (LGE) on CMR detects myocardial scar, which can inform ICD decision-making. Overall scar burden, region-specific scar burden, and scar heterogeneity have all been studied in risk stratification. PET and SPECT are nuclear methods that determine myocardial viability and innervation, as well as inflammation. CT can be used for assessment of myocardial fat and its association with reentrant circuits. Emerging methodologies include the development of "virtual hearts" using complex electrophysiologic modeling derived from CMR to attempt to predict arrhythmic susceptibility. Recent developments have paired novel machine learning (ML) algorithms with established imaging techniques to improve predictive performance. The use of advanced imaging to augment risk stratification for sudden death is increasingly well-established and may soon have an expanded role in clinical decision-making. ML could help shift this paradigm further by advancing variable discovery and data analysis.

Evaluating the role of left ventricle global longitudinal strain in myocardial perfusion defect assessment

Myocardial perfusion defect, assessed with single photon emission computed tomography (SPECT), is useful for patient management and risk stratification. Left ventricle Global Longitudinal Strain (LV GLS) has gained interest for observing subclinical LV dysfunction. We aimed to investigate the utility of LV GLS in evaluating myocardial perfusion defect. A retrospective study of all patients who underwent SPECT and LV GLS at Tel Aviv Sourasky medical center. Overall, 86 patients were included. LV GLS and SPECT correlated in the base and apex sections for infraction, and in the apex only for ischemia. Adjusted analysis showed a significant correlation between LV GLS of both the mid and apical section and infarction by SPECT, but no association with ischemia. No associations were found by arterial supply territory. A sub-analysis of patients without left bundle branch block (LBBB) strengthened the correlations, with a 58-70% higher chance of both fixed and reversible defects for every 1-unit decrease LV GLS in the mid and apical sections. LV GLS effectively evaluated the presence of infarction by SPECT in the mid and apical sections, particularly in patients without LBBB. Due to its high availability, LV GLS may have a role in evaluating myocardial perfusion defect.

Evaluation of Need for Implantable Cardioverter-Defibrillator by Thallium-201 Scintigraphy Among Japanese Patients With Prior Myocardial Infarction

BACKGROUND

Identifying who among current Japanese patients with prior myocardial infarction (MI) would benefit from an implantable cardioverter-defibrillator (ICD) is imperative. Accordingly, this study seeks to determine whether single-photon emission computed tomography (SPECT) can help identify such patients. Methods and Results: This retrospective study enrolled 60 consecutive patients with prior MI who underwent stress thallium-201 SPECT and ICD implantation from February 2000 to October 2014. Occurrence of arrhythmic death and/or or appropriate ICD therapy, defined as shock or antitachycardia pacing for ventricular fibrillation or tachycardia, was identified until November 2016. During the median follow-up interval of 6.6 years, 18 (30%) patients experienced arrhythmic death and/or appropriate ICD therapy. Multivariate Cox proportional hazard regression analysis revealed that the summed stress score (SSS) [hazard ratio (HR)=1.14; P=0.005] and left ventricular ejection fraction (LVEF) at rest (HR=0.92; P=0.038) were significantly associated with the occurrence of arrhythmic events. Patients with SSS ≥21 and LVEF ≤30%, which were determined to be the best cutoff points, had significantly higher incidence of the arrhythmic events than the other patients (64% vs. 11%; HR=7.18; log-rank P=0.001).

CONCLUSIONS

SSS using stress thallium-201 SPECT in combination with LVEF can help determine the need for ICD therapy among current Japanese patients with prior MI.

Mortality outcome and predictive risk factors for death in patients with heart failure and reduced ejection fraction who declined implantable cardioverter defibrillator implantation in Singapore

BACKGROUND

There have been conflicting data regarding the risk of sudden cardiac death (SCD) in Asian population with reduced left ventricular ejection fraction (LVEF). We aim to study mortality outcome and its risk predictors in patients with reduced LVEF who declined an implantable cardioverter defibrillator (ICD) implantation and assess whether current ICD guidelines for primary prevention are applicable to the population in Singapore.

METHODS

This prospective observational study involved 240 consecutive patients who fulfilled the ACC/AHA/HRS criteria for ICD implantation for primary prevention of SCD but declined ICD implantation. Baseline characteristics and mortality outcomes through May 2017 were collected via case-note review after a mean follow-up of 44.8 ± 16.6 months.

RESULTS

Majority of our patients were Chinese (71.3%), followed by Malays (16.2%) and Indians (10.8%). Mean age (±SD) was 61 ± 10 years, and 84% were male. Majority were in New York Heart Association (NYHA) functional classes I (46.7%) and II (46.3%). Over a mean follow-up of 44.8 ± 16.6 months, all-cause mortality rate was 34.6%. Diabetes mellitus (HR = 1.57; 95% CI, 1.01-2.44; P = 0.047) and chronic kidney disease (CKD; HR = 1.95; 95% CI, 1.17-3.23; P = 0.010) were independent predictors of mortality. Patients in NYHA classes II (HR = 2.15; 95% CI, 1.32-3.50; P = 0.002) and III (HR = 2.82; 95% CI, 1.34-5.96; P = 0.007) showed higher risk of death.

CONCLUSION

The mortality rate was comparable with major primary prevention trials. ICD guideline recommendations for primary prevention may thus be applicable to our local population. Patients with diabetes, CKD, and poorer NYHA status exhibited higher mortality rates.

NUCLEAR IMAGING IN SUDDEN CARDIAC DEATH RISK ASSESSMENT

Sudden cardiac death is a cause of fatal outcomes in large proportion of cardiovascular patients. Left ventricle ejection fraction at the moment is the main criteria for sudden cardiac death risk stratification, however the parameter is not enough reliable. Nuclear imaging methods make it to visualize finer pathophysiological processes representing the probability of the life threatening ventricular arrhythmias development. The review is focused on recent data on nuclear imaging for cellular perfusion assessment, transient ischemia, vitality of myocardium and myocardial blood flow, metabolic disorders and sympathetic innervation.

Cardiac Imaging in Patients With Ventricular Tachycardia

Ventricular tachycardia (VT) is a major cause of sudden cardiac death. The majority of malignant VTs occur in patients with structural heart disease. Multimodality imaging techniques play an integral role in determining the underlying etiology and prognostic significance of VT. In recent years, advances in imaging technology have enabled characterization of the structural arrhythmogenic substrate in patients with VT with increasing precision. In parallel with these advances, the role of cardiac imaging has expanded from a largely diagnostic tool to an adjunctive tool to guide interventional approaches for treatment of VT. Invasive and noninvasive imaging techniques, often used in combination, have made it possible to integrate structural and electrophysiological information during VT ablation procedures. An important area of current development is the use of noninvasive imaging techniques based on body surface electrocardiographic mapping to elucidate the mechanisms of VT. In the future, these techniques may provide a priori information on mechanisms of VT in patients undergoing interventional procedures. This review provides an overview of the role of cardiac imaging in patients with VT.

Impact of basal inferolateral scar burden determined by automatic analysis of 99mTc-MIBI myocardial perfusion SPECT on the long-term prognosis of cardiac resynchronization therapy

AIMS

Left-ventricular (LV) scarring may be associated with a poor response to cardiac resynchronization therapy (CRT). The automatic analysis of myocardial perfusion single-photon emission computed tomography (MP-SPECT) may provide objective quantification of LV scarring. We investigated the impact of LV scarring determined by an automatic analysis of MP-SPECT on short-term LV volume response as well as long-term outcome.

METHODS AND RESULTS

We studied consecutive 51 patients who were eligible to undergo 99mTc-MIBI MP-SPECT both at baseline and 6 months after CRT (ischaemic cardiomyopathies 31%). Quantitative perfusion SPECT was used to evaluate the defect extent (an index of global scarring) and the LV 17-segment regional uptake ratio (an inverse index of regional scar burden). The primary outcome was the composite of overall mortality or first hospitalization for worsening heart failure. A high global scar burden and a low mid/basal inferolateral regional uptake ratio were associated with volume non-responders to CRT at 6 months. The basal inferolateral regional uptake ratio remained as a predictor of volume non-response after adjusting for the type of cardiomyopathy. During a median follow-up of 36.1 months, the outcome occurred in 28 patients. The patients with a low basal inferolateral regional uptake ratio with a cutoff value of 57% showed poor prognosis (log-rank P= 0.006).

CONCLUSION

The scarring determined by automatic analysis of MP-SPECT images may predict a poor response to CRT regardless of the pathogenesis of cardiomyopathy. The basal inferolateral scar burden in particular may have an adverse impact on long-term prognosis.

The Role of Cardiovascular Magnetic Resonance in Cardiac Resynchronization Therapy

Randomized, controlled trials have shown that cardiac resynchronization therapy (CRT) is beneficial in patients with heart failure, impaired left ventricular (LV) systolic function, and a wide QRS complex. Other studies have shown that targeting the LV pacing site can also improve patient outcomes. Cardiovascular magnetic resonance (CMR) is a radiation-free imaging modality that provides unparalleled spatial resolution. In addition, emerging data suggest that targeted LV lead deployment over viable myocardium improves the outcome of patients undergoing CRT. This review explores the role of CMR in the preoperative workup of patients undergoing CRT.

Life-Threatening Ventricular Arrhythmias: Current Role of Imaging in Diagnosis and Risk Assessment

Sudden cardiac arrest continues to be a major cause of death from cardiovascular disease but our ability to predict patients at the highest risk of developing lethal ventricular arrhythmias remains limited. Left ventricular ejection fraction is inversely related to the risk of sudden death but has a low sensitivity and specificity for the population at risk. Nevertheless, it continues to be the main variable considered in identifying patients most likely to benefit from implantable defibrillators to prevent sudden death. Imaging myocardial sympathetic innervation with PET and SPECT as well as imaging characteristics of myocardial infarcts using gadolinium-enhanced cardiac magnetic resonance are emerging as imaging modalities that may further refine patient selection beyond ejection fraction. This review will primarily focus on employing advanced imaging approaches to identify patients with left ventricular dysfunction that are most likely to develop lethal arrhythmias and benefit from inserting a primary prevention implantable cardiac defibrillator. While not yet tested in prospective studies, we will review risk prediction models incorporating quantitative imaging and biomarkers that have been developed that appear promising to identify those at highest risk of sudden death.

The role of nuclear cardiac imaging in risk stratification of sudden cardiac death

Sudden cardiac death (SCD) represents a significant portion of all cardiac deaths. Current guidelines focus mainly on left ventricular ejection fraction (LVEF) as the main criterion for SCD risk stratification and management. However, LVEF alone lacks both sensitivity and specificity in stratifying patients. Recent research has provided interesting data which supports a greater role for advanced cardiac imaging in risk stratification and patient management. In this article, we will focus on nuclear cardiac imaging, including left ventricular function assessment, myocardial perfusion imaging, myocardial blood flow quantification, metabolic imaging, and neurohormonal imaging. We will discuss how these can be used to better understand SCD and better stratify patient with both ischemic and non-ischemic cardiomyopathy.

The Role of Cardiovascular Magnetic Resonance in Cardiac Resynchronization Therapy

Randomized, controlled trials have shown that cardiac resynchronization therapy (CRT) is beneficial in patients with heart failure, impaired left ventricular (LV) systolic function, and a wide QRS complex. Other studies have shown that targeting the LV pacing site can also improve patient outcomes. Cardiovascular magnetic resonance (CMR) is a radiation-free imaging modality that provides unparalleled spatial resolution. In addition, emerging data suggest that targeted LV lead deployment over viable myocardium improves the outcome of patients undergoing CRT. This review explores the role of CMR in the preoperative workup of patients undergoing CRT.

Role of nuclear cardiology for guiding device therapy in patients with heart failure

Heart failure is a dynamic condition with high morbidity and mortality and its prognosis should be reassessed frequently, particularly in patients for whom critical treatment decisions may depend on the results of prognostication. In patients with heart failure, nuclear cardiology techniques are useful to establish the etiology and the severity of the disease, while fewer studies have explored the potential capability of nuclear cardiology to guide cardiac resynchronization therapy (CRT) and to select patients for implantable cardioverter defibrillators (ICD). Left ventricular synchrony may be assessed by radionuclide angiography or gated single-photon emission computed tomography myocardial perfusion scintigraphy. These modalities have shown promise as predictors of CRT outcome using phase analysis. Combined assessment of myocardial viability and left ventricular dyssynchrony is feasible using positron emission tomography and could improve conventional response prediction criteria for CRT. Preliminary data also exists on integrated positron emission tomography/computed tomography approach for assessing myocardial viability, identifying the location of biventricular pacemaker leads, and obtaining left ventricular functional data, including contractile phase analysis. Finally, cardiac imaging with autonomic radiotracers may be useful in predicting CRT response and for identifying patients at risk for sudden cardiac death, therefore potentially offering a way to select patients for both CRT and ICD therapy. Prospective trials where imaging is combined with image-test driven therapy are needed to better define the role of nuclear cardiology for guiding device therapy in patients with heart failure.

Risk stratification of ventricular arrhythmias in patients with systolic heart failure

PURPOSE OF REVIEW

Sudden cardiac death (SCD) accounts for an estimated 310 000 deaths in the United States each year. Implantable cardioverter defibrillator (ICD) implantation has revolutionized SCD prevention in heart failure patients, but only a minority of patients with ICDs receive appropriate therapy for ventricular arrhythmias. At present, the selection of patients for ICD is based largely on left ventricular ejection fraction and heart failure, but further risk stratification is still needed to determine which patients will derive the greatest benefit.

RECENT FINDINGS

Multicenter studies have failed to confirm the utility of microvolt T-wave alternans to predict ventricular arrhythmias in patients with ICDs. Additional risk stratification tools including resting ECG characteristics, nonsustained ventricular tachycardia, tests of autonomic function, and cardiac MRI demonstrate predictive value but have limited clinical applicability at present.

SUMMARY

Depressed ejection fraction with symptomatic heart failure remains the most powerful predictor of SCD and is the primary method currently used in patient care decisions. Progress continues in evaluation of additional risk factors and risk stratification tools, but no one test or combination of tests is definitive for prediction of arrhythmic events.

Predictors of post-stress LVEF drop 6 months after reperfused myocardial infarction: a gated myocardial perfusion SPECT study

OBJECTIVE

To identify the predictive factors of myocardial stunning as assessed by the drop in post-stress Left Ventricular Ejection Fraction (LVEF) in patients with a recent history of myocardial infarction (MI).

METHODS

We prospectively included 215 consecutive patients admitted for acute MI who underwent percutaneous coronary intervention with a greater than or equal to grade-3 TIMI flow in the culprit vessel. Six months after discharge, a post-stress/rest 99mTc-sestamibi gated SPECT was performed. The perfusion score was evaluated visually using a 17-segment model. The LVEF drop was considered significant if the post-stress LVEF was ≥ 5% below the rest LVEF (QGS® software).

RESULTS

A post-stress LVEF drop was observed in 51 (24%) patients. Patients with an LVEF drop were more likely than patients with a stable post-stress LVEF to have diabetes (22% vs. 10%, p = 0.048), significant ischemia (SDS > 2) (51% vs. 28% p = 0.003) and higher rest LVEF [62% (56-69) vs. 56% (49-63) p < 0.001]. In contrast, summed rest score, related to infarct size, did not differ between the groups. Multivariate logistic regression analysis identified SDS > 2 (OR 3.78, 95% CI 1.8-7.92, p < 0.001), diabetes (OR 3.35, 95% CI 1.33-8.49; p = 0.011) and rest LVEF (OR 1.08, 95% CI 1.04-1.12, p < 0.001) as independent explanatory variables of an LVEF drop.

CONCLUSION

In patients with recent MI and post-procedural grade-3 TIMI flow, ischemia and diabetes were independent predictive factors of myocardial stunning. The higher incidence of reversible perfusion abnormalities validates the model of myocardial stunning in the post-MI period, and excludes the potential involvement of myocardial necrosis.

Right ventricular stimulation threshold at ICD implant predicts device therapy in primary prevention patients with ischaemic heart disease

AIMS

Myocardial excitability is known (amongst other reasons) to be related to the degree of ischaemia, contractile dysfunction and heart failure. It was hypothesized that the right ventricular (RV) stimulation threshold has prognostic value with respect to the occurrence of ventricular arrhythmias (VAs) and patient survival in recipients of an implantable cardioverter defibrillator (ICD).

METHODS AND RESULTS

Ischaemic heart disease patients receiving an ICD at Leiden University Medical Center as primary prevention for sudden cardiac death were included in this study. Right ventricular thresholds were determined at ICD implant. Data were collected on VAs triggering ICD therapy and on all-cause mortality. A total of 689 consecutive patients were included (87% male, age 63 ± 11 years, left ventricular ejection fraction (LVEF) 29 ± 11%) and followed for a median of 28 months. Post-implant RV-threshold was 0.7 ± 0.5 volt (V) at 0.5 ms pulse duration. Best dichotomous separation was reached at a cut-off of 1 V. During follow-up, 167 (24%) patients received appropriate ICD therapy, 88 (13%) had appropriate shocks and 134 (19%) died. Cumulative appropriate shock incidence for patients with RV threshold ≥ 1 V (n = 166) was 16% at 1 year, 24% at 3 years and 34% at 5 years compared with 4, 11 and 17% for patients with an RV-threshold < 1 V (n = 523). Adjusted hazard ratio of RV threshold ≥ 1 V was 2.0 (95% CI: 1.4-2.9) for appropriate therapy, 3.3 (95% CI: 2.0-5.4) for appropriate shocks and 1.6 (95% CI: 1.1-2.5) for mortality.

CONCLUSION

The RV stimulation threshold at ICD implant has a strong independent prognostic value for the occurrence of VAs triggering appropriate ICD therapy, appropriate shocks and mortality.

Will imaging assist in the selection of patients with heart failure for an ICD?

Sudden cardiac death remains the leading cause of death in the U.S. A left ventricular ejection fraction (LVEF)<30% to 35% identifies a population of patients at increased risk for sudden cardiac death. Once identified, an implantable cardioverter-defibrillator (ICD) is effective in reducing the occurrence of sudden cardiac death. Yet in a substantial proportion of patients who receive an ICD based on reduced LVEF, the device never delivers therapy. Furthermore, the majority of patients who die suddenly do not qualify for ICD placement under current LVEF-based criteria in the guidelines. This review considers the potential role of cardiac imaging in improving the selection of patients most likely to benefit from an ICD. The presence of myocardial scar and/or unrevascularized myocardial ischemia provides an important substrate for the occurrence of potentially fatal ventricular arrhythmias. The presence of clinical heart failure further increases the risk of ventricular arrhythmia. The sympathetic nervous system provides an important trigger for major arrhythmic events, both through global overactivity and through regional heterogeneity of sympathetic activity. A mismatch of myocardial perfusion and innervation may pose a particularly great risk. Imaging modalities provide unique opportunities to investigate the anatomic and pathophysiologic substrates, as well as the triggering effects of cardiac sympathetic innervation. Combining imaging and electrophysiologic modalities offers promise for improved accuracy in future selection of patients with heart failure for ICD placement.

Structured care for patients after acute myocardial infarction: sudden cardiac death prevention--data from the Leiden MISSION! AMI study

AIMS

To assess the number of patients in daily clinical practice that meets criteria for implantation of an implantable cardioverter defibrillator (ICD) following acute myocardial infarction (AMI) when treated according to an aggressive treatment protocol.

METHODS AND RESULTS

Patients were treated according to the MISSION! protocol. The protocol encompasses pre-hospital, in-hospital, and outpatient clinical framework for the acute and chronic treatment of AMI patients and the decision making regarding primary prevention of sudden cardiac death (SCD). A total of 676 consecutive AMI patients (78% male, mean age 59 +/- 12 years) treated according to the MISSION! protocol were included in this analysis. Left ventricular ejection fraction at 3 months was 54 +/- 10%. Only 39 (6%) patients met criteria for implantation of an ICD <1 year post-MI. These patients suffered more extensive infarctions as indicated by higher peak troponin T values (mean 14.5 +/- 8.3 vs. 6.5 +/- 14.7 microg/L; P < 0.001) and had more left anterior descending artery related infarctions (79 vs. 46%; P < 0.001). Cumulative first appropriate therapy rate was 15% at 3 years follow-up. No SCD was observed in the study population.

CONCLUSION

Aggressive treatment of AMI patients and close monitoring after the index event according to a standardized protocol, results in only a small number of patients becoming candidate for prophylactic ICD implantation. An easy-to-use protocol combining aggressive reperfusion, optimal medication, and a risk stratification algorithm tailored to fit within routine practice may help to maintain ICD implantation rates within manageable proportions.

Ischemic cardiomyopathy: a clinical nuclear cardiology perspective

Ischemic cardiomyopathy results from severe extensive coronary artery disease, which is associated with left ventricular dysfunction and also, in many cases, with significant left ventricular dilatation. Mortality is high, especially in patients who satisfy myocardial viability criteria but who have not undergone revascularization. Although age, exercise capacity and comorbidity influence survival, the most important prognostic factors are the extent of the ischemia, myocardial viability and left ventricular remodeling, all of which can be successfully evaluated by gated myocardial perfusion single-photon emission computed tomography (SPECT).