Influence of residual myocardial ischaemia on induced ventricular arrhythmias following a first acute myocardial infarction

Value of CMR and PET in Predicting Ventricular Arrhythmias in Ischemic Cardiomyopathy Patients Eligible for ICD

OBJECTIVES

This study presents a head-to-head comparison of the value of cardiac magnetic resonance (CMR)-derived left-ventricular (LV) function and scar burden and positron emission tomography (PET)-derived perfusion and innervation in predicting ventricular arrhythmias (VAs).

BACKGROUND

Improved risk stratification of VA is important to identify patients who should benefit of prophylactic implantable cardioverter-defibrillator (ICD) implantation. Perfusion abnormalities, sympathetic denervation, and scar burden have all been linked to VA, although comparative studies are lacking.

METHODS

Seventy-four patients with ischemic cardiomyopathy and left-ventricular ejection fraction (LVEF) ≤35%, referred for primary prevention ICD placement were enrolled prospectively. Late gadolinium-enhanced (LGE) CMR was performed to assess LV function and scar characteristics. [¹⁵O]H₂O and [¹¹C]hydroxyephedrine positron emission tomography (PET) were performed to quantify resting and hyperemic myocardial blood flow (MBF), coronary flow reserve (CFR), and sympathetic innervation. During follow-up of 5.4 ± 1.9 years, the occurrence of sustained VA, appropriate ICD therapy, and mortality were evaluated.

RESULTS

In total, 20 (26%) patients experienced VA. CMR and PET parameters showed considerable overlap between patients with VA and patients without VA, caused by substantial heterogeneity within groups. Univariable analyses showed that lower LVEF (hazard ratio [HR]: 0.92; p = 0.03), higher left-ventricular end-diastolic volume index (LVEDVi) (HR 1.02; p < 0.01), and larger scar border zone (HR 1.11; p = 0.03) were related to VA. Scar core size, resting MBF, hyperemic MBF, perfusion defect size, innervation defect size, and the innervation-perfusion mismatch were not found to be associated with VA.

CONCLUSIONS

In patients with ischemic cardiomyopathy, lower LVEF, higher LVEDVi, and larger scar border zone were related to VA. PET-derived perfusion and sympathetic innervation, as well as CMR-derived scar core size were not associated with VA. These results suggest that improved prediction of VA by advanced imaging remains challenging for the individual patient.

Myocardial Scar But Not Ischemia Is Associated With Defibrillator Shocks and Sudden Cardiac Death in Stable Patients With Reduced Left Ventricular Ejection Fraction

OBJECTIVES

This study sought to investigate the association of myocardial scar and ischemia with major arrhythmic events (MAEs) in patients with left ventricular ejection fraction (LVEF) ≤35%.

BACKGROUND

Although myocardial scar is a known substrate for ventricular arrhythmias, the association of myocardial ischemia with ventricular arrhythmias in stable patients with left ventricular dysfunction is less clear.

METHODS

A total of 439 consecutive patients (median age, 70 years; 78% male; 55% with implantable cardioverter defibrillator [ICD]) referred for stress/rest positron emission tomography (PET) and resting LVEF ≤35% were included. Primary outcome was time-to-first MAE defined as sudden cardiac death, resuscitated sudden cardiac death, or appropriate ICD shocks for ventricular tachyarrhythmias ascertained by blinded adjudication of hospital records, Social Security Administration's Death Masterfile, National Death Index, and ICD vendor databases.

RESULTS

Ninety-one MAEs including 20 sudden cardiac deaths occurred in 75 (17%) patients during a median follow-up of 3.2 years. Transmural myocardial scar was strongly associated with MAEs beyond age, sex, cardiovascular risk factors, beta-blocker therapy, and resting LVEF (adjusted hazard ratio per 10% increase in scar, 1.48 [95% confidence interval: 1.22 to 1.80]; p < 0.001). However, non transmural scar/hibernation or markers of myocardial ischemia on PET including global or peri-infarct ischemia, coronary flow reserve, and resting or hyperemic myocardial blood flows were not associated with MAEs in univariable or multivariable analysis. These findings remained robust in subgroup analyses of patients with ICD (n = 223), with ischemic cardiomyopathy (n = 287), and in patients without revascularization after the PET scan (n = 365).

CONCLUSIONS

Myocardial scar but not ischemia was associated with appropriate ICD shocks and sudden cardiac death in patients with LVEF ≤35%. These findings have implications for risk-stratification of patients with left ventricular dysfunction who may benefit from ICD therapy.

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.

Principles and techniques of imaging in identifying the substrate of ventricular arrhythmia

Life-threatening ventricular arrhythmias (VA) are a major cause of death in patients with cardiomyopathy. To date, impaired left ventricular ejection fraction remains the primary criterion for implantable cardioverter-defibrillator therapy to prevent sudden cardiac death. In recent years, however, advanced imaging techniques such as nuclear imaging, cardiac magnetic resonance imaging, and computed tomography have allowed for a more detailed evaluation of the underlying substrate of VA. These imaging modalities have emerged as a promising approach to assess the risk of sudden cardiac death. In addition, non-invasive identification of the critical sites of arrhythmias may guide ablation therapy. Typical anatomical substrates that can be evaluated by multiple advanced imaging techniques include perfusion abnormalities, scar and its border zone, and sympathetic denervation. Understanding the principles and techniques of different imaging modalities is essential to gain more insight in their role in identifying the arrhythmic substrate. The current review describes the principles of currently available imaging techniques to identify the substrate of VA.

Non-invasive imaging to identify susceptibility for ventricular arrhythmias in ischaemic left ventricular dysfunction

OBJECTIVE

Non-invasive imaging of myocardial perfusion, sympathetic denervation and scar size contribute to enhanced risk prediction of ventricular arrhythmias (VA). Some of these imaging parameters, however, may be intertwined as they are based on similar pathophysiology. The aim of this study was to assess the predictive role of myocardial perfusion, sympathetic denervation and scar size on the inducibility of VA in patients with ischaemic cardiomyopathy in a head-to-head fashion.

METHODS

52 patients with ischaemic heart disease and left ventricular ejection fraction (LVEF) ≤35%, referred for primary prevention implantable cardioverter-defibrillator (ICD) implantation, were included. Late gadolinium-enhanced cardiovascular MRI was performed to assess LV volumes, function and scar size. Using [(15)O]H2O and [(11)C]hydroxyephedrine positron emission tomography, both resting and hyperaemic myocardial blood flow (MBF), and sympathetic innervation were assessed. After ICD implantation, an electrophysiological study (EPS) was performed and was considered positive in case of sustained VA.

RESULTS

Patients with a positive EPS (n=25) showed more severely impaired global hyperaemic MBF (p=0.003), larger sympathetic denervation size (p=0.048) and tended to have larger scar size (p=0.07) and perfusion defect size (p=0.06) compared with EPS-negative patients (n=27). No differences were observed in LV volumes, LVEF and innervation-perfusion mismatch size. Multivariable analysis revealed that impaired hyperaemic MBF was the single best independent predictor for VA inducibility (OR 0.78, 95% CI 0.65 to 0.94, p=0.007). A combination of risk markers did not yield incremental predictive value over hyperaemic MBF alone.

CONCLUSIONS

Of all previously validated approaches to evaluate the arrhythmic substrate, global impaired hyperaemic MBF was the only independent predictor of VA inducibility. Moreover, a combined approach of different imaging variables did not have incremental value.

Impaired Hyperemic Myocardial Blood Flow Is Associated With Inducibility of Ventricular Arrhythmia in Ischemic Cardiomyopathy

Background—

Risk stratification for ventricular arrhythmias (VAs) is important to refine selection criteria for primary prevention implantable cardioverter defibrillator therapy. Impaired hyperemic myocardial blood flow (MBF) is associated with increased mortality rate in ischemic and nonischemic cardiomyopathy, which may be attributed to electric instability inducing VAs. The aim of this pilot study was to assess whether hyperemic MBF impairment may be related with VA inducibility in patients with ischemic cardiomyopathy.

Methods and Results—

Thirty patients with ischemic cardiomyopathy referred for primary prevention implantable cardioverter defibrillator implantation were prospectively included (26 men; 65±8 years old; left ventricular ejection fraction, 29±6%). [ 15 O]H 2 O positron-emission tomography was performed to quantify resting MBF, hyperemic MBF, and coronary flow reserve. Left ventricular dimensions, function, and scar burden were assessed with cardiovascular magnetic resonance imaging. An electrophysiological study was performed to test VA inducibility. Positive electrophysiological study patients (n=12) showed reduced hyperemic MBF (1.25±0.30 versus 1.66±0.38 mL·min −1 ·g −1 ; P <0.01) and coronary flow reserve (1.59±0.49 versus 2.12±0.48; P <0.01) compared with electrophysiological study negative patients (n=18). In electrophysiological study positive patients, the number of scar segments >75% transmurality was higher ( P <0.05), although scar size and border zone did not differ. Receiver-operating characteristic curve analysis indicated that impaired hyperemic MBF (area under the curve, 0.84; 95% confidence intervals [0.69–0.99]) and coronary flow reserve (area under the curve, 0.77; 95% confidence intervals [0.57–0.96]) were associated with VA inducibility.

Conclusions—

In this pilot study, impaired hyperemic MBF and coronary flow reserve were associated with VA inducibility in patients with ischemic cardiomyopathy. These results are hypothesis generating for a potential role of quantitative positron-emission tomography perfusion imaging in risk stratification for VAs.

Long-term prognostic value of inducible and resting perfusion defects detected by single-photon emission computed tomography in the era of wide availability of coronary revascularization

PURPOSE

To assess the long-term prognostic value of various types of perfusion defects detected by single-photon emission computed tomography (SPECT) in patients with stable angina.

METHODS

Seven hundred and thirty two patients (299 men, mean age 57 ± 9 years) with suspected or known stable coronary artery disease underwent rest/exercise SPECT protocol using 99mTc-methoxyisobutylisonitrile (MIBI). All patients completed clinical follow-up regarding cardiac events (cardiac death, sudden cardiac death, acute coronary syndrome, revascularization, cardiac hospitalization) for a mean period of 58 ± 8 months. Event rates were analysed in subgroups defined according to the presence of fixed or inducible myocardial perfusion defects.

RESULTS

During the follow-up, 15 cardiac deaths were recorded, 13 of which were qualified as a sudden cardiac death, 59 acute coronary syndromes, 65 revascularizations and 209 cardiac hospitalizations. The presence of inducible perfusion defects on SPECT was associated with a high risk for occurrence of all analysed end points: sudden cardiac death (HR = 3·96, P = 0·01), cardiac hospitalization (HR = 1·5, P = 0·004), coronary syndrome (HR = 2·33, P = 0·001) and coronary revascularization (HR = 2·76, P = 0·0002), except for the cardiac death (P = 0·27). Resting perfusion defects were highly predictive for cardiac death (HR = 7·45; P = 0·001), but not for other cardiac events (P = NS). The presence of any (inducible or resting) perfusion defects was associated with a high risk of all cardiovascular complications.

CONCLUSIONS

In long-term follow-up, SPECT proved highly predictive of cardiac events in patients with suspected or known CAD. In the revascularization era, cardiac death is most accurately related to the presence of resting perfusion defects, but all other cardiac events were better predicted by inducible perfusion defects.

Single-photon emission computed tomography myocardial perfusion imaging and the risk of sudden cardiac death in patients with coronary disease and left ventricular ejection fraction>35%

OBJECTIVES

The aim of this study was to determine whether single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is an effective method of risk stratification for sudden cardiac death (SCD) in patients with coronary artery disease (CAD) and left ventricular ejection fraction (LVEF)>35%.

BACKGROUND

Most victims of SCD have an LVEF>35%.

METHODS

The study population included 4,865 patients with CAD and LVEF>35% who underwent gated SPECT MPI. We used Cox proportional hazard modeling to examine the relationship between patient characteristics and SCD.

RESULTS

The median age of the population was 63 years (25th, 75th percentile: 54, 71 years), and the median LVEF was 56% (25th, 75th percentile: 50%, 64%). The median follow-up for all patients was 6.5 years (25th, 75th percentile: 3.6, 9.3 years). During follow-up, there were 161 SCDs (3.3%). After multivariable adjustment, LVEF, the Charlson index, hypertension, smoking, antiarrhythmic drug therapy, and the summed stress score (SSS) were associated with SCD (all p<0.05). For each 3-U increase in the SSS, the hazard ratio for SCD was 1.13 (95% confidence interval: 1.04 to 1.23). The addition of perfusion data to the clinical history and LVEF was associated with increased discrimination for SCD events (c-index 0.728). Risk stratification with a derived SPECT nomogram did not result in statistically significant net reclassification improvement (p=0.26) or integrated discrimination improvement (p=0.38).

CONCLUSIONS

Among patients with CAD and LVEF>35%, the extent of stress MPI perfusion defects is associated with an increased risk of SCD. Future large prospective studies should address the role of perfusion imaging in the identification of high-risk patients with LVEF>35% who might benefit from ICD implantation.

Quantitative tissue characterization of infarct core and border zone in patients with ischemic cardiomyopathy by magnetic resonance is associated with future cardiovascular events

OBJECTIVES

This study evaluates how characterization of tissue heterogeneity of myocardial infarction by cardiovascular magnetic resonance (CMR) is associated with cardiovascular events (CVE) in patients with ischemic cardiomyopathy (ICM).

BACKGROUND

Prior studies demonstrated that the quantification of myocardial scar volume by CMR is superior to left ventricular end-diastolic volume, left ventricular end-systolic volume, and left ventricular ejection fraction (LVEF) in predicting future CVE in ICM patients. Evaluation of infarct heterogeneity by measuring infarct core and border zones through CMR might have a higher association with CVE.

METHODS

Seventy patients (mean LVEF: 25 +/- 11%) considered for revascularization or medical management +/- implantable cardiac defibrillator were enrolled. A 1.5-T GE MRI (Signa, GE Healthcare, Milwaukee, Wisconsin) was used to acquire cine and delayed enhancement images. The patients' core and border zones of infarcted myocardium were analyzed and followed for CVE.

RESULTS

Larger infarct border zone and its percentage of myocardium were found in the 29 patients (41%) who had CVE (median 13.3 g [interquartile range (IQR) 8.4 to 25.1 g] vs. 8.0 g [IQR 3.0 to 14.5 g], p = 0.02 and 7.8% [IQR 4.9% to 17.0%] vs. 4.1% [IQR 1.9% to 9.3%], p = 0.02, respectively). The core infarct zone and its percentage of myocardium, left ventricular end-diastolic volume, left ventricular end-systolic volume, and LVEF were not statistically significant. Sub-analysis of the medical management and revascularization patients with CVE demonstrated that the medically managed patients had a larger border zone, whereas there was no difference between border and core zones in the revascularization group (p < 0.05).

CONCLUSIONS

Quantification of core and border zones and their percentages of myocardium through CMR is associated with future CVE and might assist in the management of patients with ICM.

[How to evaluate sudden cardiac death risk after myocardial infarction?]

Sudden cardiac death is the mode of death of more than half of coronary heart disease patients. Preventing sudden cardiac death involves prevention of ventricular arrhythmias occurrence as well as the treatment by an implantable cardioverter defibrillator. The evaluation of sudden cardiac death risk should consider the underlying cardiopathy, the associated coronary risk factors and all pharmacological treatment efficient to reduce ventricular remodeling and myocardial ischemia. Only significant low ejection fraction and positive ventricular testing in some cases are now considered are now considered by the current French recommendations for cardioverter defibrillator implantation in primary prevention. However, other noninvasive markers such as heart rate variability and T wave alternans are of interest in sudden cardiac death risk stratification after myocardial infarction.

Single-photon emission computed tomography myocardial perfusion defects are associated with an increased risk of all-cause death, cardiovascular death, and sudden cardiac death

BACKGROUND

Single-photon emission computed tomography myocardial perfusion imaging defects are associated with increased all-cause mortality and cardiovascular death. However, it is unknown whether single-photon emission computed tomography myocardial perfusion imaging can identify patients at increased risk of sudden cardiac death (SCD).

METHODS AND RESULTS

We analyzed a cohort of 6383 patients with angiographically documented coronary artery disease who underwent single-photon emission computed tomography imaging. Cox proportional hazards modeling was used to examine the relationship between patient characteristics and SCD. Among patients who died, the median time to SCD was 2.7 years (25(th), 75(th) percentiles 0.9, 4.9, respectively). The incidence of SCD was 3.4% (n=215) over 6.1 years (25(th), 75(th) percentiles 3.7, 9.2, respectively) of follow-up. Patients with SCD had more severe heart failure symptoms, greater comorbidity (Charlson index), and higher summed stress perfusion scores (all P<0.001). After adjusting for left ventricular ejection fraction and other clinical factors in the multivariable model, the summed stress perfusion score (fixed plus reversible defects) remained significantly associated with the occurrence of SCD: summed stress perfusion score (hazard ratios per 3 U: 1.16 [95% CI, 1.08 to 1.25], P<0.001), left ventricular ejection fraction (hazard ratios per 5 U: 0.90 [95% CI, 0.85 to 0.95], P<0.001), and Charlson index (hazard ratios 1.35 [95% CI, 1.23 to 1.49], P<0.001).

CONCLUSIONS

Myocardial perfusion imaging is a significant predictor of SCD and provides information independent of clinical history and left ventricular ejection fraction. Gated single-photon emission computed tomography imaging, which evaluates both myocardial perfusion and function, may represent a more effective means of risk stratification than solitary left ventricular ejection fraction determination and should be evaluated in prospective trials.

Quantitative characterization of myocardial infarction by cardiovascular magnetic resonance predicts future cardiovascular events in patients with ischemic cardiomyopathy

BACKGROUND

Cardiovascular magnetic resonance (CMR) can provide quantitative data of the myocardial tissue utilizing high spatial and temporal resolution along with exquisite tissue contrast. Previous studies have correlated myocardial scar tissue with the occurrence of ventricular arrhythmia. This study was conducted to evaluate whether characterization of myocardial infarction by CMR can predict cardiovascular events in patients with ischemic cardiomyopathy (ICM).

RESULTS

We consecutively studied 86 patients with ICM (LVEF < 50%, mean LVEF: 26 +/- 12%) with CMR before revascularization or medication therapy +/- implantable cardiac defibrillator, determined the amount of myocardial scar, and followed for development of cardiovascular events. Thirty-three patients (38%) had cardiovascular events (mean follow-up: 20 +/- 16 months). Patients who developed cardiovascular events had larger scar volume and scar percentage of the myocardium than those who did not develop cardiovascular events (16.8 +/- 12.4 cm3 vs. 11.7 +/- 12.6 cm3, p = 0.023 and 10.2 +/- 6.9% vs. 7.2 +/- 6.7%, p = 0.037, respectively). There were no significant differences in LVEDV, LVESV and LVEF between the patients with and without cardiovascular events (231 +/- 76 ml vs. 230 +/- 88 ml; 180 +/- 73 ml vs. 175 +/- 90 ml; and 25 +/- 10% vs. 27 +/- 13%, respectively).

CONCLUSION

Quantification of the scar volume and scar percentage by CMR is superior to LVEDV, LVESV, and LVEF in prognosticating the future likelihood of the development of cardiovascular events in patients with ICM.

Influence of the Dialysis Membrane on Markers of Tissue Ischemia

BACKGROUND

Hemodialysis (HD) is often accompanied by adverse effects, such as tissue ischemia. We have already observed an increase in plasma adenosine (ADO) levels during HD sessions, which may be the result of tissue ischemia. Here we evaluate the influence of the dialysis membrane on two sensitive and early markers of ischemia: ADO and ischemia-modified albumin (IMA).

METHODS

We included in the study 50 patients with end-stage renal failure, 39 hemodialyzed (mean age 61+/-24 years; 24 male; membranes: 23 synthetic and 16 cellulose based) and 11 undialyzed (mean age 55+/-12 years; 6 male), and 10 healthy subjects (mean age 47+/-11 years; 4 male). We compensated for hemoconcentration during HD by measuring either the IMA to albumin (Alb) or the ADO to Alb ratio.

RESULTS

Under basal conditions, the IMA to Alb ratio was not significantly different in patients and controls and HD did not significantly modify this ratio. Conversely, the ADO to Alb ratio (mean+/-SD in micromol/g) was higher in patients before HD compared with either undialyzed patients or controls (before HD: 0.077+/-0.02; undialyzed patients: 0.026+/-0.11; controls: 0.022+/-0.01). During HD, there was a significant increase in the ADO to Alb ratio (before HD: 0.077+/-0.02; after HD: 0.09+/-0.029; p<.01). We found no significant difference in the IMA to Alb or ADO to Alb ratio using either synthetic or cellulose-based membranes.

CONCLUSIONS

We concluded that ADO is a more sensitive marker of ischemia than IMA and that, under our HD conditions, the ischemia caused by HD was very weak, independent of the dialysis membrane.

[Risk stratification after acute myocardial infarction]

In recent years, the characteristics of patients who suffer acute myocardial infarction without complications during hospitalization have changed. In addition, the range of non-invasive studies available for evaluating left ventricular systolic function, residual myocardial ischemia, and myocardial viability in these patients has improved. Left ventricular systolic function and residual ischemia should be evaluated in all patients before release. The non-invasive technique used (exercise test, echocardiography, nuclear cardiology, magnetic resonance imaging) depends on availability, experience, and results at each institution. Coronary arteriography should be performed in patients with significant ischemia or severe left ventricular systolic dysfunction in non-invasive studies. In these cases coronary angiography must be performed to determine if coronary arteries are suitable for revascularization before performing a test of myocardial viability.