Normally, the entire mass of ventricular myocardium is depolarized in about 80 to 100 milliseconds. This requires highly synchronous electrical activation of the ventricular myocardium, which can be achieved only through the rapidly conducting His-Purkinje system (HPS). The term intraventricular conduction disturbances (IVCDs) refers to abnormalities in the intraventricular propagation of supraventricular impulses resulting in changes in the morphology and/or duration of the QRS complex. These…

Anatomy and physiology of the atrioventricular junction Internodal and interatrial conduction Evidence suggests the presence of preferential impulse propagation from the sinus node to the atrioventricular node (AVN)—that is, higher conduction velocity between the nodes in some parts of the atrium than in other parts. However, whether preferential internodal conduction is caused by fiber orientation, size, or geometry or by the presence of specialized preferentially conducting…

Anatomy and physiology of the sinus node Anatomy The sinus node is a crescent-shaped, subepicardial specialized muscular structure located posterolaterally in the right atrial (RA) free wall. The sinus node lies within the epicardial groove of the sulcus terminalis, at the junction of the anterior trabeculated RA appendage with the posterior smooth-walled venous component ( Fig. 9.1 ). The endocardial aspect of the sulcus terminalis is…

Radiofrequency ablation Biophysics of radiofrequency energy Radiofrequency (RF) refers to the portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current (AC) fed to an antenna. Electrosurgery (coagulation, cauterization, and ablation) currently uses hectomeric wavelengths found in band 6 (300–3000 kHz), which are similar to those used for broadcast radio. However, the RF energy is electrically conducted, not radiated, during catheter…

Conventional RF ablation has revolutionized the treatment of many supraventricular as well as ventricular arrhythmias. Success in stable arrhythmias with predictable anatomical locations or characteristics identifying endocardial electrograms, such as idiopathic ventricular tachycardia (VT), atrioventricular nodal reentrant tachycardia (AVNRT), atrioventricular reentrant tachycardia (AVRT), or typical atrial flutter (AFL), has approached 90% to 99%. However, as interest has turned to a broad array of more complex arrhythmias,…

Cardiac mapping refers to the process of identifying the temporal and spatial distributions of myocardial electrical potentials during a particular heart rhythm. Cardiac mapping is a broad term that covers several modes of mapping such as body surface, endocardial, and epicardial mapping, in order to characterize timing and/or amplitude (voltage) of signals relative to each other. Mapping during tachycardia aims at elucidation of the mechanism(s) of…

Indications Invasive electrophysiological (EP) testing involves recording a portion of cardiac electrical activity and programmed cardiac electrical stimulation via multipolar catheter electrodes positioned percutaneously strategically at various locations within the cardiac chambers. EP testing is used predominantly in patients with suspected or documented cardiac arrhythmias when the precise EP diagnosis is required for management decisions or when catheter ablation is planned. Additionally, EP testing is of…

The mechanisms responsible for cardiac arrhythmias are generally divided into categories of disorders of impulse formation (automaticity or triggered activity), disorders of impulse conduction (reentry), or combinations of both. Automaticity is the property of cardiac cells to initiate an impulse spontaneously, without the need for prior stimulation. Triggered activity is impulse initiation in cardiac fibers caused by depolarizing oscillations in membrane voltage (known as afterdepolarizations) that…

Ion channels are pore-forming membrane proteins that regulate the flow of ions passively down their electrochemical gradient across the membrane. Ion channels are present on all membranes of cells (plasma membrane) and intracellular organelles (nucleus, mitochondria, endoplasmic reticulum). There are more than 300 types of ion channels in a living cell. The channels are not randomly distributed in the membrane but tend to cluster at the…

Ionic equilibrium The lipid bilayer of the cell membrane is hydrophobic and impermeable to water-soluble substances such as ions. Hence, for the hydrophilic ions to be able to cross the membrane, they need hydrophilic paths that span the membrane (i.e., pores), which are provided by transmembrane proteins called ion channels. Once a hydrophilic pore is available, ions move passively (i.e., require no expenditure of energy) across…