Extra heart beats
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Understanding Extra Heart Beats: Mechanisms, Detection, and Implications
Introduction to Extra Heart Beats
Extra heart beats, also known as extrasystoles, are premature heartbeats originating from the atria or ventricles. These beats can be benign or indicative of underlying heart conditions. This article synthesizes recent research on the mechanisms, detection methods, and clinical implications of extra heart beats.
Mechanisms of Extra Heart Beats
Premature Ventricular and Atrial Beats
Premature beats can originate from different sites within the heart, such as the atria or ventricles. The point of origin influences the heart rate turbulence (HRT) parameters, specifically the turbulence onset (TO) and slope (TS). Research indicates that while the site of origin affects TO, it does not significantly influence TS, making HRT a reliable measure for assessing extra beats from Holter ECGs.
Excitation-Contraction Coupling
The relationship between beat-to-beat intervals and the strength of heart contractions is crucial in understanding extra heart beats. Studies show that the recovery of left ventricular mechanical function occurs approximately 800 milliseconds after a beat, and the potentiation of subsequent beats varies based on the interval of the extrasystole. This variation is more pronounced in patients with normal left ventricular function compared to those with abnormalities, suggesting a disturbance in excitation-contraction coupling mechanisms in the latter group.
Reentry Mechanisms
Reentry is a common mechanism for repetitive ventricular extra beats. Local cooling of myocardial foci in animal models has shown that premature stimuli near the refractory period can cause conduction delays, leading to nonstimulated extra beats due to reentry. This phenomenon is influenced by the size of the focus and the timing of the premature stimulus.
Detection Methods for Extra Heart Beats
Analytical Spectra Mutual Correlation
A novel method for detecting premature ventricular complexes (PVCs) and supraventricular premature beats (SPBs) involves multiscale correlation analysis. This technique, based on the analytical spectra of ECG signals, has proven effective in identifying extra beats in real ECG recordings from standard databases.
Artificial Neural Networks
Classification of normal and extrasystolic heart sounds using Mel-Frequency Cepstrum Coefficients (MFCC) and artificial neural networks has shown high accuracy. This method involves normalizing heart sounds, reducing noise with an elliptic filter, and then classifying the features using neural networks. The classification success rate for detecting extra systoles was reported to be 90%.
Heart Rate Variability (HRV) Artefact Correction
Heart rate variability measurements can be distorted by artefacts such as extra beats. A robust algorithm for artefact detection uses time-varying thresholds and a novel beat classification scheme to identify and correct these artefacts. This method has demonstrated high sensitivity and specificity in detecting ectopic beats, ensuring reliable HRV analysis.
Clinical Implications of Extra Heart Beats
Work Cost Measurement
Extra heart beats can be used as a measure of work cost in physical tasks. Studies comparing the extra heart beats generated by lifting different weights found that this method is easier and equally effective compared to measuring kcal/minute, making it a recommended approach for assessing both light and heavy work.
Prognostic Significance in Heart Disease
In patients with recurrent ventricular tachycardia, the incidence of repetitive ventricular beating in response to single ventricular extrastimuli is relatively low. This repetitive response does not significantly correlate with the incidence of sudden death, indicating that it is not a reliable prognostic indicator for vulnerability to ventricular tachycardia.
Calcium-Dependent Arrhythmias
In transgenic mice with heart failure, overexpression of TNF-alpha leads to ventricular arrhythmias triggered by single extra beats. These arrhythmias are associated with prolonged action potential durations and abnormal calcium handling. Lowering extracellular calcium levels can normalize conduction and prevent inducible arrhythmias, highlighting the role of calcium in the initiation and maintenance of these arrhythmias.
Conclusion
Extra heart beats are a complex phenomenon influenced by various physiological and pathological factors. Advances in detection methods and a deeper understanding of their mechanisms have significant implications for clinical practice, from assessing work cost to managing heart disease. Continued research is essential to further elucidate the role of extra heart beats in cardiovascular health.
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