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Noninvasive Diagnosis Using Sounds Originating from within the Body
Published in Robert B. Northrop, Non-Invasive Instrumentation and Measurement in Medical Diagnosis, 2017
Another cardiac defect that can be diagnosed by hearing the S2 sound “split” is a left or right bundle branch block. The synchronization of the contraction of the muscle of the left and right ventricles is accomplished by the wave of electrical depolarization that propagates from the AV node, down the bundle of His, which bifurcates into the left and right bundle branches which run down on each side of the ventricular septum. Near the apex of the heart, the bundle branches branch extensively into the Purkinje fibers which invade the inner ventricular cardiac muscle syncytium, carrying the electrical activity that triggers ventricular contraction. See Figure 3.7 for a schematic, cut-away view of the heart, and Figure 3.8 for a time-domain schematic of where certain heart sounds occur in the cardiac cycle.
Cardiovascular System:
Published in Michel R. Labrosse, Cardiovascular Mechanics, 2018
Once the action potential is initiated in the S-A node, it spreads quickly across the atria via the intermodal pathway towards the A-V node and via the intra-atrial pathway and gap junctions to the left atrium (this takes about 30 ms). This ensures that all the atrial cells are depolarized at the same time and the resulting atrial contraction is unified. The impulse experiences a delay of approximately 100 ms at the A-V node. This delay ensures that the atria have fully contracted and ejected their blood into the ventricles before the ventricles begin their contraction. The impulse spreads from the A-V node through the bundle of His and into the left and right bundle branches before spreading out through the Purkinje fibers and gap junctions to depolarize the ventricles simultaneously (again, about 30 ms). The electrical activity can be recorded externally as an electrocardiogram (ECG) (Figure 1.5). There are typically three waveforms recorded on an ECG—the P wave (which represents atrial depolarization and triggers atrial contraction), the QRS complex (which represents ventricular depolarization and triggers ventricular contraction), and the T wave (which represents ventricular repolarization and triggers ventricular relaxation). Abnormalities in the ECG waveforms can help diagnose arrhythmias such as heart block, atrial flutter, and atrial fibrillation, as well as myopathic conditions such as myocardial ischemia and infarction (commonly called a heart attack). If the coordination of the electrical impulses is lost and the myocardial cells are no longer contracting as a unit, the result is known as fibrillation. Ventricular fibrillation, which results in no significant ejection of blood, is life-threatening and requires electrical defibrillation for survival.
Spatiotemporal regularization for inverse ECG modeling
Published in IISE Transactions on Healthcare Systems Engineering, 2020
Cardiac electrical signal is initiated by the sinoatrial (SA) node, i.e. the pacemaker of the heart, and then propagates through the right and left atria toward the atrioventricular node (AVN). The electric impulse further travels through the bundle of His and Purkinje fibers, and enter the left and right ventricles, which completes the cardiac cycle. As shown in Figure 2, the forward ECG problem denotes the prediction of electric potentials on the body surface based on the excitation and propagation of space-time electrodynamics in the heart. The objective of the inverse ECG problem is to estimate cardiac electrical sources from electrical signals (e.g. BSPMs) measured on the body surface.
How does new-onset left bundle branch block affect the outcomes of transcatheter aortic valve repair?
Published in Expert Review of Medical Devices, 2019
Guillem Muntané-Carol, Leonardo Guimaraes, Alfredo Nunes Ferreira-Neto, Jerôme Wintzer-Wehekind, Lucia Junquera, David del Val, Laurent Faroux, François Philippon, Josep Rodés-Cabau
In the TAVR field, a wider QRS duration after TAVR with LBBB pattern can indicate a more proximal mechanical interruption of the left bundle branch, with a theoretical risk of extension to the bundle of His leading to complete heart block (CHB). Additionally, patients with aortic stenosis usually have a chronically overloaded and already remodelled ventricle. Therefore, the response to new-onset LBBB in TAVR recipients may differ from that observed in patients with dilated cardiomyopathies. Finally, both the occurrence of AV block and the chronic effects of new-onset LBBB may influence the clinical outcomes after TAVR.