Myocardial 123I-MIBG scintigraphy predicts an impairment in myocardial functional reserve during dobutamine stress in patients with idiopathic dilated cardiomyopathy

Myocardial innervation imaging: MIBG in clinical practice

123I-metaiodobenzylguanidine (MIBG) is a radiolabeled norepinephrine analog that can be used to investigate myocardial sympathetic innervation. 123I MIBG scintigraphy has been investigated with interest in many disease settings. In patients with systolic heart failure (HF), 123I MIBG scintigraphy can capture functional impairment and rarefaction of sympathetic terminals (which manifest as reduced early and late heart-to-mediastinum [H/M] ratio on planar scintigraphy), and increased sympathetic outflow (which can be visualized as high washout rate). These findings have been consistently associated with a worse outcome: most notably, a phase 3 trial found that patients with a late H/M 1.60 have a higher incidence of all-cause and cardiovascular mortality and life-threatening arrhythmias over a follow-up of less than 2 years. Despite these promising findings, 123I MIBG scintigraphy has not yet been recommended by major HF guidelines as a tool for additive risk stratification, and has then never entered the stage of widespread adoption into current clinical practice. 123I MIBG scintigraphy has been evaluated also in patients with myocardial infarction, genetic disorders characterized by an increased susceptibility to ventricular arrhythmias, and several other conditions characterized by impaired sympathetic myocardial innervation. In the present chapter we will summarize the state-of-the-art on cardiac 123I MIBG scintigraphy, the current unresolved issues, and the possible directions of future research.

Late gadolinium enhancement on cardiac magnetic resonance combined with 123I- metaiodobenzylguanidine scintigraphy strongly predicts long-term clinical outcome in patients with dilated cardiomyopathy

Late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) is limited in its ability to detect diffuse interstitial fibrosis, which is commonly found in idiopathic dilated cardiomyopathy (DCM). On the other hand, Washout rate (WR) by cardiac ¹²³I- metaiodobenzylguanidine (¹²³I-MIBG) scintigraphy which evaluates cardiac sympathetic nervous function, is a useful tool for predicting the prognosis in DCM. We investigated the predictive value of the combination of two different types of examinations, LGE on CMR and WR by ¹²³I-MIBG scintigraphy for outcomes in DCM compared with LGE alone. One-hundred forty-eight DCM patients underwent CMR and ¹²³I-MIBG scintigraphy. Patients were divided into 4 groups according to the presence or absence of LGE and WR cut-off value of 45% for predicting prognosis based on receiver operating characteristic curve analysis. Cardiac deaths, re-hospitalization for heart failure, implantation of a left ventricular assist device, and life-threatening ventricular arrhythmias were defined as clinical events. Forty-two DCM patients reached the clinical events during the median follow-up for 9.1 years (interquartile range, 8.0–9.2 years).Multivariable Cox regression analysis identified WR≥45%+LGE positive group as an independent predictor of cardiac events (HR 3.18, 95%CI 1.36–7.45, p = 0.008). Notably, there was no significance in the cardiac event-free survival rate between the WR<45%+LGE positive and WR≥45%+LGE negative groups (p = 0.89). The combination of WR by ¹²³I-MIBG scintigraphy and LGE on CMR, which evaluate different type of cardiac deterioration, serves as a stronger predictor of long-term outcomes in DCM patients than LGE alone.

Myocardial contractile reserve predicts left ventricular reverse remodeling and cardiac events in dilated cardiomyopathy

BACKGROUND

Catecholamine sensitivity estimated using a dobutamine stress test (DST) is recognized as a measure of the beta-adrenergic myocardial contractile reserve, which is involved with left ventricular reverse remodeling (LV-RR). We investigated whether the prognostic ability of the DST for LV-RR could predict cardiac events.

METHODS

There was a total of 192 enrolled patients with dilated cardiomyopathy (DCM). DCM was defined as a LV ejection fraction (LV-EF) ≤45% and LV end-diastolic dimension (LVDd) ≥55mm. One hundred patients were subjected to micromanometer-based measurement of the maximal first derivative of LV pressure (LVdP/dt_max), an index of LV contractility, at baseline and following the infusion of dobutamine (10μg/kg/min) via a pigtail catheter. Percentage changes in LVdP/dt_max from the baseline to peak values under dobutamine stress (ΔLVdP/dt_max) were also calculated. After excluding 17 patients who received cardiac resynchronization therapy within 3 months of undergoing DST (n=15) and who did not receive follow-up echocardiography (n=2), 83 patients were enrolled (52.5±12.3 years).

RESULTS

During the follow-up period (4.7±2.6 years), LV-RR was recognized in 49 of 83 patients (59.0%). A multivariate logistic regression analysis revealed that ΔLVdP/dt_max (hazard ratio: 1.024, p=0.007) and the symptom duration (hazard ratio: 0.977, p=0.003) were independent predictors of LV-RR. A receiver operating characteristic curve analysis revealed a ΔLVdP/dt_max cut-off value of 75.1% for LV-RR and a significantly lower cardiac event rate in the ΔLVdP/dt_max≥75.1% group (p=0.045).

CONCLUSIONS

ΔLVdP/dt_max estimated using DST was a useful predictor of LV-RR and cardiac events in patients with DCM.

Left ventricular deformation at rest predicts exercise-induced elevation in pulmonary artery wedge pressure in patients with unexplained dyspnoea

AIMS

Impaired left ventricular (LV) deformation despite preserved LV ejection fraction (LVEF) is common and predicts outcomes in heart failure with preserved LVEF. We hypothesized that impaired LV deformation at rest is a marker of impaired cardiac systolic and diastolic reserve, and aimed to determine whether resting longitudinal (LS) and circumferential strain (CS) are associated with invasively measured haemodynamic response to exercise in patients with dyspnoea and a normal LVEF.

METHODS AND RESULTS

We studied 85 patients with LVEF ≥50% and free of significant valvular disease who were referred for evaluation of dyspnoea. All patients underwent rest echocardiography followed by right heart catheterization and cardiopulmonary exercise testing with concomitant invasive haemodynamic monitoring. The LS, CS and CS/LS ratio were measured by two-dimensional speckle-tracking echocardiography at rest. Lower absolute LS at rest was associated with greater increase in pulmonary arterial wedge pressure (PAWP) from rest to peak exercise (r = 0.23, P = 0.034). In contrast, higher absolute CS at rest predicted a greater increase in PAWP (r = - 0.27, P = 0.032) and greater stroke volume augmentation with exercise (r = - 0.26, P = 0.021). Higher CS/LS ratio was most predictive of elevation in PAWP with exercise (r = 0.30, P = 0.015). Of the measures of LV systolic and diastolic function assessed, the CS/LS ratio resulted in the highest area under the curve and specificity for the presence of rest- or exercise-induced pulmonary venous hypertension.

CONCLUSION

Left ventricular deformation at rest predicts exercise-induced rise in PAWP among patients with dyspnoea and a preserved LVEF. A pattern of rest deformation characterized by worse LS and exaggerated CS is most strongly associated with exercise-induced rise in PAWP.

Prognostic Value of Cardiac Sympathetic Nerve Imaging Using Long-Term Follow-up Data - Ischemic vs. Non-Ischemic Heart Failure Etiology

BACKGROUND

Although there are several known prognostic determinants in heart failure (HF), individual risk profiles can vary, in particular between ischemic and non-ischemic HF background. This study investigated the difference in prognostic efficacy of cardiac (123)I-meta-iodobenzylguanidine (MIBG) imaging between the 2 etiologies.

METHODS AND RESULTS

All 1,322 patients with HF were enrolled and followed up at most after 10 years. The HF patients were divided into 2 groups: an ischemic group (n=362) and non-ischemic group (n=960), and Cox proportional hazards model was used for data analysis. During 10 years of follow-up, 296 (22.4%) of 1,322 patients died; the mortality rates were 21.8% and 22.6% for the ischemic and non-ischemic groups, respectively. The ischemic group had greater prevalence of sudden death and lethal acute myocardial infarction, and the non-ischemic group had a higher rate of pump failure death. On multivariate Cox proportional hazards analysis using categorized variables, in the ischemic group, delayed heart-to-mediastinum ratio (HMR; P<0.0001), age (P=0.0002) and LVEF (P=0.03) were the independent significant predictors of lethal events. In the non-ischemic group, delayed HMR (P<0.0001), NYHA class (P<0.0001) and age (P<0.0001) were significant determinants of lethal outcome.

CONCLUSIONS

Cardiac MIBG imaging has nearly identical prognostic value in both ischemic and non-ischemic HF, independent of cause of cardiac death.