Basic Principles of Cardiac Electrophysiology

Cardiac System during the Aging Process

The aging process is accompanied by a continuous decline of the cardiac system, disrupting the homeostatic regulation of cells, organs, and systems. Aging increases the prevalence of cardiovascular diseases, thus heart failure and mortality. Understanding the cardiac aging process is of pivotal importance once it allows us to design strategies to prevent age-related cardiac events and increasing the quality of live in the elderly. In this review we provide an overview of the cardiac aging process focus on the following topics: cardiac structural and functional modifications; cellular mechanisms of cardiac dysfunction in the aging; genetics and epigenetics in the development of cardiac diseases; and aging heart and response to the exercise.

Early life exercise training and inhibition of apoLpp mRNA expression to improve age-related arrhythmias and prolong the average lifespan in Drosophila melanogaster

Cardiovascular disease (CVD) places a heavy burden on older patients and the global healthcare system. A large body of evidence suggests that exercise training is essential in preventing and treating cardiovascular disease, but the underlying mechanisms are not well understood. Here, we used the Drosophila melanogaster animal model to study the effects of early-life exercise training (Exercise) on the aging heart and lifespan. We found in flies that age-induced arrhythmias are conserved across different genetic backgrounds. The fat body is the primary source of circulating lipoproteins in flies. Inhibition of fat body apoLpp (Drosophila apoB homolog) demonstrated that low expression of apoLpp reduced the development of arrhythmias in aged flies but did not affect average lifespan. At the same time, exercise can also reduce the expression of apoLpp mRNA in aged flies and have a protective effect on the heart, which is similar to the inhibition of apoLpp mRNA. Although treatment of UAS-apoLpp^RNAi and exercise alone had no significant effect on lifespan, the combination of UAS-apoLpp^RNAi and exercise extended the average lifespan of flies. Therefore, we conclude that UAS-apoLpp^RNAi and exercise are sufficient to resist age-induced arrhythmias, which may be related to the decreased expression of apoLpp mRNA, and that UAS-apoLpp^RNAi and exercise have a combined effect on prolonging the average lifespan.

Molecular mechanism of atrial remodeling in patients with aging atrial fibrillation under the expression of microRNA-1 and microRNA-21

We investigated the expression levels of microRNA-1 (miRNA-1) and microRNA-21 (miRNA-21) in the atrial tissues of patients with atrial fibrillation (AF) and the molecular mechanism of action in atrial remodeling. Patients with valvular heart disease were selected as the subjects. The ultrastructure, degree of myocardial fibrosis, apoptosis index (AI), expression of microRNA-1, expression of microRNA-21, and mRNA of TIMP-1, MMP-9, BCL-2, and Bax of patients were compared and analyzed in each group. The results showed that the degree of myocardial fibrosis and AI in patients with AF of the same age were extremely higher than those of patients with sinus rhythm (SR) (P < 0.01). Patients with AF showed much higher messenger RNA (mRNA) levels of mini-mental Parkinson 9 (MMP9) and Bax and obvious lover mRNA levels of tissue inhibitors of metalloproteinase 1 (TIMP-1) and Bcl-2 compared with patients with sinus rhythm (SR) (P < 0.05). It indicated that the expression of miRNA-1 in the AF patients was markedly down-regulated, and that miRNA-21 was up-regulated. This showed that microRNA-1 and microRNA-21 were involved in the molecular remodeling of aging AF through the regulation of primers, which would provide a critical basis for diagnosis and treatment of aging AF.

Mapping electric bulk conductivity in the human heart

PURPOSE

To explore the technical feasibility of mapping the electric bulk conductivity in the human heart, and to determine quantitative conductivity values of myocardium and blood from a small group of volunteers.

METHODS

Using a 3T MR system, 6 healthy male volunteers were measured. For all volunteers, a time-resolved 2D sequence over the cardiac cycle was applied (electrocardiogram [ECG]-triggered SSFP acquired in breath-hold). From these data, a dedicated, so-called "2D conductivity" has been derived in the framework of electrical properties tomography (EPT). To validate the concept of 2D conductivity, a static 3D sequence (ECG-triggered and respiratory-gated SSFP 3D whole heart acquisition, allowing the full 3D reconstruction of conductivity) as well as a Q-flow sequence (for investigating the relation between flow and reconstruction errors of the conductivity) have been applied for one of the volunteers.

RESULTS

For both, blood and myocardium, quantitative values of obtained 2D conductivity were approximately two-thirds of the obtained 3D conductivity, as expected from Maxwell's equations. Furthermore, the quantitative conductivity values agreed with corresponding literature values. Conductivity of left-ventricular blood volume showed characteristic over- and under-shooting at specific time points during the cardiac cycle for all volunteers investigated. This over- and under-shooting correlated with the phase pattern caused by blood flow into/out of the ventricle.

CONCLUSION

The study demonstrated the technical feasibility of cardiac conductivity measurements using standard MR systems and standard MR sequences, and therefore, may open new options for MR-based cardiac diagnosis.

Photoplethysmography behind the Ear Outperforms Electrocardiogram for Cardiovascular Monitoring in Dynamic Environments

An increasing proportion of occupational mishaps in dynamic, high-risk operational environments have been attributed to human error, yet there are currently no devices to routinely provide accurate physiological data for insights into underlying contributing factors. This is most commonly due to limitations of commercial and clinical devices for collecting physiological data in environments of high motion. Herein, a novel Photoplethysmography (PPG) sensor device was tested, called SPYDR (Standalone Performance Yielding Deliberate Risk), reading from a behind-the-ear location, specifically designed for high-fidelity data collection in highly dynamic high-motion, high-pressure, low-oxygen, and high-G-force environments. For this study, SPYDR was installed as a functional ear-cup replacement in flight helmets worn by rated US Navy aircrew. Subjects were exposed to reduced atmospheric pressure using a hypobaric chamber to simulated altitudes of 25,000 feet and high G-forces in a human-rated centrifuge up to 9 G acceleration. Data were compared to control devices, finger and forehead PPG sensors, and a chest-mounted 12-lead ECG. SPYDR produced high-fidelity data compared to controls with little motion-artifact controls in the no-motion environment of the hypobaric chamber. However, in the high-motion, high-force environment of the centrifuge, SPYDR recorded consistent, accurate data, whereas PPG controls and ECG data were unusable due to a high-degree-motion artifacts. The data demonstrate that SPYDR provides an accurate and reliable system for continuous physiological monitoring in high-motion, high-risk environments, yielding a novel method for collecting low-artifact cardiovascular assessment data important for investigating currently inaccessible parameters of human physiology.

Intelligent Diagnosis Method Based on 2DECG Model

Electrophysiological signals can effectively reflect various physiological states of human body, and provide favorable basis for medical diagnosis. However, the correct analysis of electrophysiological signals requires professional medical diagnosis experience. With the rapid development of artificial intelligence, intelligent diagnosis methods based on deep learning are gradually applied in the medical field in order to reduce the dependence of diagnosis results on medical experience. Deep learning has made remarkable achievements in the field of image processing, through which deeper information can be extracted than through time-series signals. Therefore, this paper proposes a method of 2DECG diagnosis based on Faster R-CNN (Faster Region-based Convolutional Neural Network). First, the time-series ECG signal is transformed into two-dimensional curve. Then, the Faster R-CNN model based on beat is obtained by using dataset training. Finally, three kinds of ECG diseases are diagnosed by the Faster R-CNN model. The test results show that compared with the effect of one-dimensional CNN, the method proposed in this paper has high diagnosis accuracy and can help doctors to diagnose diseases more intuitively.

The area under the waveform of electromyography for monitoring the external branches of the superior laryngeal nerve during thyroid surgery

Background

Injuries to the external branches of the superior laryngeal nerve (EBSLN) are difficult to identify during thyroidectomy. Monitoring the low amplitudes of the EBSLN during surgery has proven to be complicated. Therefore a new parameter, the area under the waveform (AUW), was designed to improve monitoring efficiency. The aim of this study was to determine the effectiveness of using AUW to monitor the EBSLN during thyroidectomy.

Methods

A total of 927 patients and 927 recurrent laryngeal nerves (RLN) and EBSLNs who underwent monitored unilateral thyroidectomy were included. Standardized intraoperative neuromonitoring procedures were followed. RLN injuries were confirmed using stroboscopic laryngoscopy after surgery. EBSLN injuries were identified by means of observing changes in cricothyroid muscle (CTM) twitches when stimulated. Amplitude and AUW changes were assessed using statistical analysis. The correlations between AUW and amplitude were verified using the ratio of the two parameters to determine any decreases that were observed in the number of nerve injury cases. The receiver operating characteristic (ROC) curve was used to estimate the prediction of nerve injury.

Results

The overall injury rates of the RLN and EBSLN were 3.56% and 2.05%, respectively. The AUW for the RLN and EBSLN presented linear correlations with amplitude. In the RLN injury cases, no significant difference was observed between the two parameters (P>0.05). In the cases with EBSLN injuries, the AUW decreased 64.5%±14.1%, on average, which was a greater decrease compared to that observed for amplitude 49.7%±22.2% (P<0.0001). The summary of the EBSLN injury prediction included, amplitude vs. AUW, AUC: 0.918 vs. 0.994; P<0.0001, and Youden's index: 31.54% vs. 49.58%.

Conclusions

The AUW demonstrated consistency with the change in amplitude, and the observed changes were significant. The use of the AUW allowed successful predictions for both RLN and EBSLN nerve injuries. Also, the sensitivity of AUW was greater than amplitude for predicting EBSLN injuries.

Conduction Disorders: The Value of Surface ECG

PURPOSE OF REVIEW

The purpose of the current mini-review is to describe the importance of surface ECG for the diagnosis of conduction disorder.

METHODS

The MEDLINE/PubMed database was used, with the keywords "ECG" and "conduction disorders"; over the past 10 years. Other documents were included because of their relevance.

MAIN FINDINGS

Data on the anatomy and function of the cardiac electrical system have been described. Conduction disorders including sinus node dysfunction, atrioventricular blocks, intraventricular conduction disorders are exposed as to their epidemiology, etiology, presentation, anatomical site of impaired conduction of the electrical stimulus. The importance of ECG in patients with a cardiac implantable electronic device was also discussed, in addition to future perspectives.

CONCLUSION

Surface ECG allows the diagnosis of atrioventricular and intraventricular conduction disorder and its anatomical block site most of the time, without the need for invasive tests such as electrophysiological study. Dysfunctions of cardiac implantable electronic devices can be diagnosed by ECG, as well as the prediction of response to cardiac resynchronization therapy.