TỔNG QUAN Pacing Therapy for Bradyarrhythmias

Pacing Therapy for Bradyarrhythmias Introduction • Pacemaker was first implanted in 1958 • Since then, today’s pacemakers are very small and light compared to those of past years • Compared to the very first pacemakers paced only in the lower chamber, we’ve had pacemakers that function in both the upper and lower chambers of the heart (DDD/R pacemaker) • One of the most notable development was a type of pacemaker that can change its pacing rate because of sensor(s) inside the pacemaker The DDDR pacemaker What is a pacemaker? • A pacemaker is really a system that has two parts: a small metal titanium can containing the electronic circuitry and a long-lasting battery, called a pulse generator and an insulated wire, called a lead The Pulse Generator: • Contains a battery that provides the energy for sending electrical impulses to the heart • Houses the circuitry that Circuitry controls pacemaker operations Battery Leads Are Insulated Wires That: • Deliver electrical impulses from the pulse generator to the heart • Sense cardiac depolarization Lead Pacemaker Components Combine with Body Tissue to Form a Complete Circuit • Pulse generator: power source or battery Lead • Leads or wires • Cathode (negative electrode) • Anode (positive electrode) IPG Anode • Body tissue Cathode Types of Leads • Endocardial or transvenous leads • Myocardial/Epicardial leads Transvenous Leads Have Different “Fixation” Mechanisms • Passive fixation – The tines become lodged in the trabeculae (fibrous meshwork) of the heart Transvenous Leads • Active Fixation – The helix (or screw) extends into the endocardial tissue – Allows for lead positioning anywhere in the heart’s chamber Myocardial and Epicardial Leads • Leads applied directly to the heart – Fixation mechanisms include: • Epicardial stab-in • Myocardial screw-in • Suture-on Today Pacemakers Dual-Chamber Systems Have Two Leads: • One lead implanted in the atrium • One lead implanted in the ventricle Benefits of Dual Chamber Pacing • Provide AV Synchrony ventricular backup if A-to-V conduction is lost where a single chamber pacing system cannot • Provide Proven Benefits of Atrial Based Pacing Study Results Higano et al 1990 Improved cardiac index during low level exercise (where most patient activity occurs) Gallik et al 1994 Increase in LV filling Santini et al 1991 30% increase in resting cardiac output Rosenqvist et al 1991 Decrease in pulmonary wedge pressure Increase in resting cardiac output Sulke et al 1992 Increase in resting cardiac output, especially in patients with poor LV function Decreased incidence of mitral and tricuspid valve regurgitation Proven Benefits of Atrial Based Pacing Study Results Rosenquist 1988 Less atrial fibrillation (AF), less CHF, improved survival after years compared to VVI Santini 1990 Less AF, improved survival after years average Stangl 1990 Less AF, improved survival after years compared to VVI Suppression of atrial dysrhythmias Zanini 1990 Improved morbidity (less AF, CHF, embolic events) after plus uears, compared to VVI Most Pacemakers Perform Four Functions: • Stimulate cardiac depolarization • Sense intrinsic cardiac function • Respond to increased metabolic demand by providing rate responsive pacing • Provide diagnostic information stored by the pacemaker Rate Responsive Pacing Rate Response • Rate responsive (also called rate modulated) pacemakers provide patients with the ability to vary heart rate when the sinus node cannot provide the appropriate rate • Rate responsive pacing is indicated for: – Patients who are chronotropically incompetent (heart rate cannot reach appropriate levels during exercise or to meet other metabolic demands) – Patients in chronic atrial fibrillation with slow ventricular response Rate Responsive Pacing • Cardiac output (CO) is determined by the combination of stroke volume (SV) and heart rate (HR) • SV X HR = CO • Changes in cardiac output depend on the ability of the HR and SV to respond to metabolic requirements Rate Responsive Pacing • SV reserves can account for increases in cardiac output of up to 50% • HR reserves can nearly triple total cardiac output in response to metabolic demands Rate Responsive Pacing • When the need for oxygenated blood increases, the pacemaker ensures that the heart rate increases to provide additional cardiac output Adjusting Heart Rate to Activity Normal Heart Rate Rate Responsive Pacing Fixed-Rate Pacing Daily Activities A Variety of Rate Response Sensors Exist • Those most accepted in the market place are: – Activity sensors that detect physical movement and increase the rate according to the level of activity – Minute ventilation sensors that measure the change in respiration rate and tidal volume via transthoracic impedance readings Rate Responsive Pacing • Activity sensors employ a piezoelectric crystal that detects mechanical signals produced by movement • The crystal translates the mechanical signals into electrical signals that in turn increase the rate of the pacemaker Piezoelectric crystal Rate Responsive Pacing • Minute Ventilation (MV) is the volume of air introduced into the lungs per unit of time • MV has two components: – Tidal volume–the volume of air introduced into the lungs in a single respiration cycle – Respiration rate–the number of respiration cycles per minute Rate Responsive Pacing • Minute ventilation can be measured by measuring the changes in electrical impedance across the chest cavity to calculate changes in lung volume over time