Physiological versus pathological cardiac electrical remodelling: potential basis and relevance to clinical management

The Influence of Special Military Training on Left Ventricular Adaptation to Exercise in Elite Air Force Soldiers

Purpose

The purpose of this study was to observe the influence of level physical training intensity on left ventricular (LV) adaptation in elite air force soldiers compared to regular basic military training.

Methods

The LV adaptation of special military physical training for elite air force soldiers was compared with basic military training for regular troops. A group of the nonmilitary subject was also evaluated as a control group. The presence of LV adaptation was evaluated using some echocardiography parameters, including LV mass index (LVMI), LV ejection fraction (LVEF), global longitudinal strain (GLS), and myocardial work index. The parameters of the myocardial work index include global constructive work (GCW), global wasted work (GWW), global work index (GWI), and global work efficiency (GWE).

Results

Forty-three elite air force soldiers underwent special military training, 43 regular troops underwent basic military training, and 23 nonmilitary subjects as a control group. Age, heart rate, blood pressure, and Cooper test results significantly differed among the three groups. Multivariate analysis among all groups showed that the level of physical training was associated with the LVMI (coefficient β = 6.061; 95% confidence interval [CI] = 1.91-10.22; P = 0.005), LVEF (coefficient β = -1.409; 95% CI = -2.41-[-0.41]; P = 0.006), LVGLS (coefficient β = 1.726; 95% CI = 1.20-2.25; P < 0.001), GWW (coefficient β = -13.875; 95% CI = -20.88-[-6.87]; P < 0.001), GWE (coefficient β = 0.954; 95% CI = 0.62-1.26; P < 0.001), GCW (coefficient β = 176.128; 95% CI = 121.16-231.10; P < 0.001), and GWI (coefficient β = 196.494; 95% CI = 144.61-248.38; P < 0.001).

Conclusions

Higher intensity of physical training observed in a special military training is associated with higher LV GLS, GWE, GCW, GWI, and lower GWW value suggesting greater physiological adaptation than the lower intensity training.

Casein Kinase-2 Interacting Protein-1 Regulates Physiological Cardiac Hypertrophy via Inhibition of Histone Deacetylase 4 Phosphorylation

Different kinds of mechanical stimuli acting on the heart lead to different myocardial phenotypes. Physiological stress, such as exercise, leads to adaptive cardiac hypertrophy, which is characterized by a normal cardiac structure and improved cardiac function. Pathological stress, such as sustained cardiac pressure overload, causes maladaptive cardiac remodeling and, eventually, heart failure. Casein kinase-2 interacting protein-1 (CKIP-1) is an important regulator of pathological cardiac remodeling. However, the role of CKIP-1 in physiological cardiac hypertrophy is unknown. We subjected wild-type (WT) mice to a swimming exercise program for 21 days, which caused an increase in myocardial CKIP-1 protein and mRNA expression. We then subjected CKIP-1 knockout (KO) mice and myocardial-specific CKIP-1-overexpressing mice to the 21-day swimming exercise program. Histological and echocardiography analyses revealed that CKIP-1 KO mice underwent pathological cardiac remodeling after swimming, whereas the CKIP-1-overexpressing mice had a similar cardiac phenotype to the WT controls. Histone deacetylase 4 (HDAC4) is a key molecule in the signaling cascade associated with pathological hypertrophy; the phosphorylation levels of HDAC4 were markedly higher in CKIP-1 KO mouse hearts after the swimming exercise program. The phosphorylation levels of HDAC4 did not change after swimming in the hearts of CKIP-1-overexpressing or WT mice. Our results indicate that swimming, a mechanical stress that leads to physiological hypertrophy, triggers pathological cardiac remodeling in CKIP-1 KO mice. CKIP-1 is necessary for physiological cardiac hypertrophy in vivo, and for modulating the phosphorylation level of HDAC4 after physiological stress. Genetically engineering CKIP-1 expression affected heart health in response to exercise.

Radionuclide imaging of cardiac sympathetic innervation in heart failure: unlocking untapped potential

Heart failure (HF) is associated with sympathetic overactivity, which contributes to disease progression and arrhythmia development. Cardiac sympathetic innervation imaging can be performed using radiotracers that are taken up in the presynaptic nerve terminal of sympathetic nerves. The commonly used radiotracers are (123)I-metaiodobenzylguanidine ((123)I-mIBG) for planar and single-photon emission computed tomography imaging, and (11)C-hydroxyephedrine for positron emission tomography imaging. Sympathetic innervation imaging has been used in assessing prognosis, response to treatment, risk of ventricular arrhythmias and sudden death and prediction of response to cardiac resynchronization therapy in patients with HF. Other potential applications of these techniques are in patients with chemotherapy-induced cardiomyopathy, predicting myocardial recovery in patients with left ventricular assist devices, and assessing reinnervation following cardiac transplantation. There is a lack of standardization with respect to technique of (123)I-mIBG imaging that needs to be overcome for the imaging modality to gain popularity in clinical practice.

I -123 metaiodobenzylguanidine imaging for predicting ventricular arrhythmia in heart failure patients

Compared to antiarrhythmic drugs, implantable cardioverter defibrillator (ICD) leads to a more significant improvement in preventing ventricular arrhythmia in heart failure patients. However, an important question has been raised that how to select appropriate patients for ICD therapy. I-123 metaiodobenzylguanidine (MIBG) planar and SPECT imaging have shown great potentials to predict ventricular arrhythmia in heart failure patients by assessing the abnormalities of the sympathetic nervous system. Clinical trials demonstrated that several parameters measured from I-123 MIBG planar and SPECT imaging, such as heart-to-mediastinum ratio, washout rate, defect score, and innervation/perfusion mismatch, predicted ventricular arrhythmias in heart failure patients. This paper introduces the current practice of ICD therapy and reviews the technical background of I-123 MIBG planar and SPECT imaging and their clinical data in predicting ventricular arrhythmia.

Use of cardiac radionuclide imaging to identify patients at risk for arrhythmic sudden cardiac death

Sudden cardiac death (SCD) accounts for about ½ of all cardiovascular deaths, in most cases the result of a lethal ventricular arrhythmia. Patients considered at risk are often treated with an implantable cardiac defibrillator (ICD), but current criteria for device use, based largely on left ventricular ejection fraction (LVEF), leads to many patients receiving ICDs that they do not use, and many others not receiving ICDs but who suffer SCD. Thus, better methods of identifying patients at risk for SCD are needed, and radionuclide imaging offers much potential. Recent work has focused on imaging of cardiac autonomic innervation. (123)I-mIBG, a norepinephrine analog, is the tracer most studied, and a variety of positron emission tomographic tracers are also under investigation. Radionuclide autonomic imaging may identify at-risk patients with ischemic coronary artery disease, particularly following myocardial infarction and in the setting of hibernating myocardium. Most studies have been done in the setting of congestive heart failure (CHF), with a recent large multicenter study of patients with advanced disease, typically at high risk of SCD, showing that (123)I-mIBG can identify a low risk subgroup with an extremely low incidence of lethal ventricular arrhythmias and cardiac death, therefore, perhaps not requiring an ICD. Cardiac neuronal imaging has been shown to be better predictive of lethal arrhythmias/cardiac death than LVEF and New York Heart Association class, as well as various ECG parameters. Autonomic imaging will likely play an important role in the advancement of cardiac molecular imaging.