Modulation of Cardiac Potassium Current by Neural Tone and Ischemia

Autonomic modulation of ventricular electrical activity: recent developments and clinical implications

PURPOSE

This review aimed to provide a complete overview of the current stance and recent developments in antiarrhythmic neuromodulatory interventions, focusing on lifethreatening vetricular arrhythmias.

METHODS

Both preclinical studies and clinical studies were assessed to highlight the gaps in knowledge that remain to be answered and the necessary steps required to properly translate these strategies to the clinical setting.

RESULTS

Cardiac autonomic imbalance, characterized by chronic sympathoexcitation and parasympathetic withdrawal, destabilizes cardiac electrophysiology and promotes ventricular arrhythmogenesis. Therefore, neuromodulatory interventions that target the sympatho-vagal imbalance have emerged as promising antiarrhythmic strategies. These strategies are aimed at different parts of the cardiac neuraxis and directly or indirectly restore cardiac autonomic tone. These interventions include pharmacological blockade of sympathetic neurotransmitters and neuropeptides, cardiac sympathetic denervation, thoracic epidural anesthesia, and spinal cord and vagal nerve stimulation.

CONCLUSION

Neuromodulatory strategies have repeatedly been demonstrated to be highly effective and very promising anti-arrhythmic therapies. Nevertheless, there is still much room to gain in our understanding of neurocardiac physiology, refining the current neuromodulatory strategic options and elucidating the chronic effects of many of these strategic options.

Prevalence and significance of notched T-waves in elite professional cyclists

OBJECTIVES

To identify the frequency and significance of notched T-waves (NTW) in elite endurance athletes.

METHODS

Professional cyclists were followed for 4 years with a clinical, electrocardiographic and echocardiographic assessment. Electrocardiograms were classified according to the presence or absence of NTWs; clinical and echocardiographic correlates were assessed.

RESULTS

42 Caucasian male cyclists were included. NTW were detected in 8 (19%) cyclists who showed significantly longer QT (461 ± 15 vs 422 ± 33 ms, p < 0.01) and QTc intervals (434 ± 19 vs 383 ± 21 ms, p < 0.01), a larger left ventricular end-diastolic volume (163 ± 27 vs 137 ± 23 mL, p = 0.014), end-diastolic volume index (84 ± 13 vs 73 ± 11 mL, p = 0.037) and end-diastolic apex-to-base length (9.9 ± 0.7 vs 9.3 ± 0.5 mm. p = 0.035). There were no detected arrhythmic events, and echocardiography did not reveal any abnormalities.

CONCLUSIONS

This is to our knowledge the first study reporting a high prevalence of NTW in athletes. In our small cohort of cyclists NTW were associated with QT interval prolongation and left ventricular changes. This may be indicative of underlying inhomogeneity of repolarisation. Expanding on this research could reveal a role for NTW in identifying ventricular morphological changes.

The effect of myocardial action potential duration on cardiac pumping efficacy: a computational study

BACKGROUND AND AIMS

Although studies on the relation between arrhythmias and the action potential duration (APD) have been carried out, most of them are based only on electrophysiological factors of the heart and lack experiments that consider cardiac mechanical and electromechanical characteristics. Therefore, we conducted this study to clarify the relevance of the shortening of APD of a cell in relation to the mechanical contraction activity of the heart and the associated risk of arrhythmia.

METHODS

The human ventricular model used in this study has two dynamic characteristics: electrophysiological conduction and mechanical contraction. The model simulating electrophysiological characteristics was consisted of lumped parameter circuit that can mimic the phenomenon of ion exchange through the cell membrane of myocyte and consisted of 214,319 tetrahedral finite elements. In contrast, the model simulating mechanical contraction characteristics was constructed to mimic cardiac contraction by means of the crossbridge of a myofilament and consisted of 14,720 hermite-based finite elements to represent a natural 3D curve of the cardiac surface. First, we performed a single cell simulation and the electrophysiological simulation according to the change of the APD by changing the electrical conductivity of the I Ks channel. Thus, we confirmed the correlation between APD and intracellular Ca2+ concentration. Then, we compared mechanical response through mechanical simulation using Ca2+ data from electrical simulation.

RESULTS

The APD and the sum of the intracellular Ca2+ concentrations showed a positive correlation. The shortened APD reduced the conduction wavelength of ventricular cells by shortening the plateau and early repolarization in myocardial cells. The decrease in APD reduced ventricular pumping efficiency by more than 60% as compared with the normal group (normal conditions). This change is caused by the decline of ventricular output owing to reduced ATP consumption during the crossbridge of myofilaments and decreased tension.

CONCLUSION

The shortening of APD owing to increased electrical conductivity of a protein channel on myocardial cells likely decreases the wavelength and the pumping efficiency of the ventricles. Additionally, it may increase tissue sensitivity to ventricular fibrillation, including reentry, and cause symptoms such as dyspnea and dizziness.