Cardiac 123I-MIBG scintigraphy and arrhythmic risk in left ventricular noncompaction

Left ventricular noncompaction is an unusual but increasingly recognized cardiomyopathy, the etiology of which is still not definitely established. Clinical presentation includes a wide spectrum of scenarios, including heart failure, thromboembolism and malignant arrhythmias, with half of deaths occurring suddenly. Early detection of LVNC is therefore essential to prevent sudden cardiac death. To our knowledge, this is the first report of the presence of cardiac sympathetic nervous dysfunction, assessed by 123iodine-metaiodobenzylguanidine myocardial scintigraphy, in a patient with LVNC, preserved left ventricular systolic function and exercise-induced nonsustained ventricular tachycardia. This finding may be related to the increased arrhythmic risk observed in this cardiomyopathy, giving a new insight into the pathophysiology of LVNC.     

Cardiac sympathetic innervation and cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) is a disease modifying, device-driven treatment that can reduce morbidity and mortality in patients with heart failure. According to the current guidelines, the indication for CRT is only based on QRS duration and functional class of heart failure. However, a substantial amount of patients do not respond to therapy. In addition, CRT is accompanied by significant cost and potential morbidity. It is therefore vital to improve patient selection for CRT to improve patient outcome and minimize therapy-related complications. In this regard, cardiac sympathetic innervation may be of interest. This review addresses the currently available literature, 9 studies with a total number of 225 patients, on CRT and cardiac innervation scintigraphy with ¹²³I-metaiodobenzylguanidine.     

Cardiac sympathetic dysfunction in an athlete's heart detected by 123I-metaiodobenzylguanidine scintigraphy

The athlete's heart is commonly characterized by an increase in left ventricular mass because of an increase in the left ventricular diastolic cavity dimensions or wall thickness or both. Endurance exercise also induces numerous cardiovascular adaptations, including increased vagal tone. However, the sympathetic function has not yet been precisely elucidated, so the present study evaluated cardiac sympathetic nerve function from metaiodobenzylguanidine (MIBG) images obtained 15 and 180 min after the injection of 123I-MIBG at a dose of 111 MBq. The ratio of heart/mediastinum count (H/M) and the washout rates of 123I-MIBG (WR) were calculated in 25 consecutive patients who were athletes (aged 52+/-13 years) and 23 normal subjects. There was a significant difference in the H/M between the athletic and normal hearts (2.3+/-0.3 vs 2.6+/-0.3, p<0.01, Scheffe's test). An increased WR was observed in the athletes group when compared with the normal group (34+/-4 vs 28+/-3, p<0.01), and there was a significant correlation between WR and the left ventricular mass index (r=0.578, p<0.01). Prolonged exercise training may alter cardiac sympathetic nerve function, which can be detected by MIBG imaging.     

Cardiac sympathetic activity as measured by myocardial 123-I-metaiodobenzylguanidine uptake and heart rate variability in idiopathic dilated cardiomyopathy.

In patients with idiopathic dilated cardiomyopathy (IDC) the increased sympathetic activity owing to chronic congestive heart failure leads to an imbalance of cardiac autonomic tone, as reflected by decreased heart rate variability (HRV). Iodine-123-metaiodobenzylguanidine (123-I-MIBG), which has the same affinity for sympathetic nerve endings as norepinephrine, can be used to assess the integrity and function of the cardiac sympathetic nervous system. The aim of the present study was to measure cardiac sympathetic activity by assessing 123-I-MIBG uptake compared with HRV in patients with IDC. In 12 patients with IDC and mild to moderate heart failure, myocardial MIBG uptake was calculated from the myocardial (M) to left ventricular cavity (C) voxel values density ratio and the 123-I activity in a blood sample as a reference (= M/C ratio) using a double radionuclide study with 123-I-MIBG and technetium-99m-MIBI. To investigate the relation between myocardial MIBG uptake and HRV in time domain, the linear regression between the M/C ratio, a new scintigraphic parameter, and the mean RR interval or the HRV triangular index, respectively, was determined. A significant correlation between the M/C ratio and mean RR interval (r = 0.52; p = 0.016) or M/C ratio and HRV triangular index (r = 0.76; p = 0.003), respectively, was found. Thus, the significant correlation between the M/C ratio and HRV indicate that they are both suitable noninvasive methods for evaluating cardiac sympathetic activity in patients with IDC and, furthermore, favor the view that there is evidence of a relation between HRV and the disorder of the cardiac presynaptic sympathetic nerve endings as demonstrated by a reduced M/C ratio.     

Cardiac sympathetic innervation in patients with ventricular arrhythmias: an assessment by 123I-metaiodobenzylguanidine scintigraphy

The aim of this study was to determine the state of sympathetic innervation in patients with ventricular arrhythmias (VA) using 123I-metaiodobenzylguanidine 123I -MIBG) scintigraphy. Fifty six patients (26 men and 30 women, mean age 37.4+/-11,6) underwent single-photon emission computed tomography (SPECT) imaging and planner scintigraphy after injection of 123I-MIBG (activity 148 MBq). They form three groups. Thirty patients with idiopathic VA (IVA) were included in group I: 14 patients with ventricular extrasystoles (VE) and 16 - with ventricular tachycardias (VT). Group II was formed by 17 patients (with dilated cardiomyopathy, n=7 and chronic myocarditis, n=10), 6 of them had VE and 11 - VT. The control group III was formed by 9 healthy subjects with structurally normal heart without VA. We analyzed early (30 minutes) and delayed (4 hours) images after 123I-MIBG administration. The global sympathetic activity (SA) was assessed by heart/mediastinum ratio and washout rate. Regional SA was assessed by extent and severity of defect. In group I 25 of 30 patients (83.3%) had regional SA abnormalities significantly different from controls (p<0.001). At the same time global uptake of 123I-MIBG in this group was not affected. In group II regional SA abnormalities were revealed in all patients (100%) and global reduction of 123I-MIBG uptake - in 14 patients (82.4%). Regional and global SA abnormalities in group II were different from controls (p<0.0001) and patients with IVA (p<0.001). There was no difference in SA abnormalities between patients with VE and VT. Our results suggest that patients with different VA have abnormalities of sympathetic innervation, including patients with structurally normal heart.     

Hypoadiponectinemia in type 2 diabetes mellitus in men is associated with sympathetic overactivity as evaluated by cardiac 123I-metaiodobenzylguanidine scintigraphy

Hypoadiponectinemia is associated with insulin resistance. However, there is very limited information about the relationship between plasma adiponectin and cardiac autonomic nervous function. We tested the hypothesis that hypoadiponectinemia is associated with cardiac sympathetic overactivity in patients with type 2 diabetes mellitus. Thirty-three male type 2 diabetic patients not on insulin treatment were classified into a hypoadiponectinemia group (plasma adiponectin concentration, <4.0 microg/mL; age, 58.6 +/- 8.6 years [mean +/- SD]; n = 14) and an age-matched normoadiponectinemia group (serum adiponectin concentration, >/=4.0 microg/mL; age, 58.2 +/- 8.1 years; n = 19). In each patient, baroreflex sensitivity, heart rate variability, plasma norepinephrine concentration, and cardiac (123)I-metaiodobenzylguanidine (MIBG) scintigraphic findings were assessed. Compared with the normoadiponectinemia group, the hypoadiponectinemia group had a higher body mass index (P < .01), higher plasma concentrations of glucose and insulin (P < .05 and P < .01, respectively), higher homeostasis model assessment of insulin resistance (HOMA-IR) values (P < .005), higher plasma triglyceride levels (P < .05), and lower plasma high-density lipoprotein cholesterol levels (P < .05). In the hypoadiponectinemia group, the autonomic function measurements included a lower baroreflex sensitivity (P< .05) and a lower delayed myocardial uptake of (123)I-MIBG (P < .01) with a higher washout rate (P < .05). Multiple regression analysis revealed that the plasma adiponectin level was independently associated with HOMA-IR (F = 9.916) and the percent washout rate of (123)I-MIBG (F = 5.985). Our results suggest that in middle-aged men with type 2 diabetes mellitus, hypoadiponectinemia is associated with cardiac sympathetic overactivity as determined by (123)I-MIBG scintigraphy.     

Cardiac resynchronization therapy in heart failure.

Cardiac resynchronization therapy (CRT) is a new therapeutic approach for a selected group of patients with symptomatic heart failure (NYHA functional class III-IV) despite optimal medical therapy, due to dilated cardiomyopathy of any etiology (left ventricular ejection fraction < or = 35% and left ventricular end-diastolic diameter > or = 55 mm), who present with electromechanical dyssynchrony (QRS > or = 130 ms). Safety and effectiveness of CRT have been demonstrated by several clinical trials, with patients achieving significant improvement in both clinical symptoms as well as functional status and exercise capacity. Furthermore, CRT has reduced morbidity of heart failure patients, while its impact in improving survival still remains to be clarified. Whether or not heart failure patients candidate to CRT should receive a defibrillator back-up remains debatable, although growing evidence is pointing to extensive use of a defibrillator in such a population.     

Cardiac resynchronization therapy optimization by finger plethysmography

OBJECTIVES: We tested a simple noninvasive method for cardiac resynchronization therapy (CRT) optimization using standard finger photoplethysmography (FPPG). BACKGROUND: CRT can increase left ventricular cardiac output in patients with heart failure and ventricular conduction delay. Optimal therapy delivery depends on an appropriate AV delay. Multiple invasive and noninvasive methods have been attempted to identify patients and the best AV delay for CRT, but all suffer from a combination of high patient risk, cost, complexity, and low reproducibility. METHODS: FPPG and invasive aortic pressure data were simultaneously collected from 57 heart failure patients during intrinsic rhythm alternating with very brief periods of pacing at 4 to 5 AV delays. After correcting data for artifacts, the median percentage responses for each AV delay were classified as positive, negative, or neutral compared to baseline (Wilcoxon rank test). RESULTS: FPPG correctly identified positive aortic pulse pressure responses with 71% sensitivity (95% CI: 60-80%) and 90% specificity (95% CI: 84-94%) and negative aortic pulse pressure responses with 57% sensitivity (95% CI: 44-69%) and 96% specificity (95% CI: 91-98%). The magnitude of FPPG changes were strongly correlated with positive aortic pulse pressure changes (R(2) = 0.73, P < .0001) but less well correlated with negative aortic pulse pressure changes (R(2) = 0.43, P < .0001). FPPG selected 78% of the patients having positive aortic pulse pressure changes to CRT and identified the AV delay giving maximum aortic pulse pressure change in all selected patients. CONCLUSIONS: FPPG can provide a simple noninvasive method for identifying significant changes in aortic pulse pressure with high specificity, including identifying patients in whom aortic pulse pressure increases with CRT and the AV delay giving the maximum aortic pulse pressure.     

131碘-间位碘代苄胍心肌显像探测急性心肌梗死后心脏交感神经分布和活力的变化

目的通过心脏交感神经受体显像探测急性心肌梗死(AMI)后心脏交感神经的分布和活力。方法 AMI组12例,男性11例,女性1例,年龄42～68岁,平均年龄(48±9)岁。对照组6名,男性4名,女性2名,年龄40～66岁,平均年龄(47±6)岁,为健康受试者。AMI组在AMI后2周、3个月及6个月时均行~(131)碘-间位碘代苄胍(~(131I-MIBG)受体显像及~(99m)锝-甲氧基异丁基异腈(~(99m)Tc-MIBI)心肌灌注显像(MPI),对照组在1周内完成~(131)I-MIBG受体显像及~(99m)Tc-MIBI MPI。分析~(131)I-MIBG及~(99m)TC-MIBI显像相同部位心肌节段的放射性分布,并利用感兴趣区(ROI)技术测定心肌与纵隔放射性比值(H/M)及MIBG的洗脱率(WR)。结果 (1)AMI组~(131)I-MIBG显像的放射性稀疏-缺损节段数为32个,而~(99m)Tc-MIBI显像的仪为24个。(2)AMI组在AMI后2周、3个月及6个月和对照组的~(131)I-MIBG显像H/M比值为(1.45±0.20)、(1.65±0.16)、(1.70±0.17)和(2.70±0.32),WR为32%、19%、15%和9.5%。AMI组各时间点的H/M和WR与对照组比较差异均有统计学意义(均为P0.05);AMI组2周分别与3个月和6个月比较,差异均有统计学意义(均为P0.05)。结论 AMI后交感神经受损区域明显大于MPI所显示的受损区域。AMI后心肌交感神经受体下调,表现为MIBG摄取减低;体内交感神经紧张度增高,表现为MIBG滞留时间短、洗脱率高。AMI后3～6个月内交感神经有不同程度的恢复。     

心脏再同步治疗与室性心律失常

心脏再同步治疗(CRT)是慢性心力衰竭治疗的重要进展,大量临床研究证实,对于符合适应证的慢性心力衰竭患者,CRT能够逆转心肌重构,改善心功能,提高生活质量,降低死亡率[1-4].     

Cardiac resynchronization therapy and ventricular tachyarrhythmia burden

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