Mechanisms of Tachycardia -

Mechanisms of Tachycardia -

The Electrical Management of Cardiac Rhythm Disorders Tachycardia Mechanisms of Tachycardia Unique Properties of Cardiac Tissue Selective permeability Only certain molecules or ions can pass through the cell

membrane at certain times Excitability Sequential depolarization and repolarization Communication with nearby cells Propagation of electrical signals Conductivity Transmitting an electrical impulse from one cell to the next Automaticity Ability of myocardium to depolarize spontaneously

Ions Ions are charged particles (positive or negative) They travel in and out of cardiac cells in response to stimuli Sudden movement of ions across the cell

membrane will cause a change in electrical potential that can actually be measured Action Potential and Ion Action Action Potential by Cardiac Region

Mechanisms of Arrhythmias Enhanced automaticity Abnormal acceleration of phase 4 Cellular or metabolic causes Ischemia Acid-base imbalances Drug toxicity Defibrillation is often ineffective in such patients

(cardiac tissue is refractory for longer periods of time, so defibrillation cannot work) Mechanisms of Arrhythmias Triggered automaticity Affects phase 4 Triggered by Pause-dependent arrhythmias

Catecholamine-dependent arrhythmias Premature beats Has many features in common with reentry tachycardias Torsades-de-pointes Mechanisms of Arrhythmias Reentry Most common form of ventricular tachyarrhythmias

Requires certain pre-existing conditions A conduction pathway with two limbs with different conduction times Unidirectional block A triggering event Patients must have the above conditions but do not necessarily have to have acute illness or chronic heart disease Can be atrial, supraventricular, or ventricular

Defibrillation was designed to treat these specific arrhythmias Supraventricular Tachycardias (SVTs) SVTs originate above the ventricles But may involve rapid ventricular response Types of SVTs Atrial fibrillation (AF) Atrial flutter

Intra-atrial reentry tachycardia Sinoatrial node reentry tachycardia AV nodal reentry tachycardia (AVNRT) AV reciprocating tachycardia (Wolff-Parkinson-White syndrome) Macro-Reentry versus Micro-Reentry Macro-reentry involves a large reentry circuit (can encompass both atria and ventricles)

Micro-reentry involves a small reentry circuit (within one chamber) Atrial flutter is a macro-reentry atrial tachycardia Reentry Triggered Reentry Not Triggered AVNRT

AV Nodal Reentry Tachycardia (AVNRT) is a common form of SVT Micro-reentry Reentry circuit is entirely within the AV node Atria and ventricles are activated as bystanders AVNRT will show up on an ECG as rapid atrial and rapid ventricular activity AVNRT on IEGM


Macro-reentry SVT Atrial and ventricular participation Concealed WPW Atrial Fibrillation (AF)

AF is a common form of SVT Can be extremely challenging to treat Appears chaotic Is associated with increased risk of stroke

Three main types Paroxysmal Resolves without treatment, often asymptomatic Persistent Requires treatment to convert, typically causes symptoms Permanent Medically refractory, symptomatic (can be severe)

AF with Irregular Ventricular Response How to Treat AF Many approaches to AF, but not all are right for every patient Pharmacological therapy Cardioversion Chemical

Electric Radiofrequency (RF) ablation Surgical approaches For device patients, the AF Suppression algorithm Ventricular Tachycardia Automatic VT Acute illness Metabolic cause

Abnormal phase 4 acceleration Reversible if underlying cause is corrected Triggered automatic VT Rarest form of VT Caused by an underlying chemical disturbance which leads to an electrical disturbance ICDs have not been proven effective for these types of VTs

Ventricular Tachycardia Reentry VT Most common form of VT ICDs were designed to treat this type of VT Often involves an area of fibrosis on the heart (possibly from prior heart attack or ischemia) Disrupted electrical pathways Areas of slow conduction Scar tissue can be ablated but ablation may just leave new

scar tissue! Monomorphic VT (from one source or focus) Polymorphic VT (from multiple foci) Monomorphic VT Polymorphic VT

Ventricular Fibrillation (VF) VF is a disorganized and potentially life-threatening arrhythmia VF rates are so high that cardiac output drops to zero QRS complexes cannot be clearly identified on ECG Hemodynamic collapse ICDs were designed to treat VF VF can be lethal in minutes

Ventricular Fibrillation Treating Ventricular Tachyarrhythmias Pharmacological therapy (works on action potential) Ablation Can be curative in some cases Most effective in early stages of disease Device-based options Combination therapy

Drugs to control tachycardia and reduce ambient arrhythmias Defibrillation for any potentially dangerous ventricular tachyarrhythmias that might break through Conclusion There are three main mechanisms of tachyarrhythmias Automaticity Triggered automaticity

Reentry Reentry is the most common form and it is the type of tachyarrhythmia that ICDs are designed to treat Ventricular tachycardia Ventricular fibrillation Arrhythmias are named for the place in the heart where they originate Supraventricular tachyarrhythmias Ventricular tachyarrhythmias

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