Pacemaker overview Chennai Feb 2017 The Implantable Pacemaker

Pacemaker : overview Chennai: Feb 2017

The Implantable Pacemaker System • The Implantable Pulse Generator (IPG) : metal can (titanium) containing electronics/battery & an electrode or lead connector header • Lead : Electrical connection between the pacemaker & the heart

Unipolar & Bipolar Pacing Bipolar Unipolar Anode (+) Cathode (-)

A Bipolar Pacing System Contains a Lead with Two Electrodes Within the Heart. In This System, the Impulse: • Flows through the tip electrode located at the end of the lead wire • Stimulates the heart • Returns to the ring Anode Cathode electrode above the lead tip Tip electrode coil Indifferent electrode coil

Pacemaker Functions • Stimulation of Cardiac Tissue • Sensing of natural (intrinsic) cardiac depolarization or contraction • Diagnostic information

Voltage, Current, and Impedance Are Interdependent – Voltage represents the force with which. . . – Current (water) is delivered through. . . – A hose, or lead, where each component represents the total impedance: • The nozzle, representing the electrode • The tubing, representing the lead wire Ohm’s Law Voltage = Current X Resistance (V=IR) Current = Voltage/Resistance As voltage increases, current increases As resistance decreases, current increases

The Pacing Pulse Output Voltage Pacing Pulse V = Pulse Amplitude in Volts (V) (say 2. 5 V) t = Pulse Duration or Width in milliseconds (ms) (say 0. 5 ms) V t t Pulse Duration (Width) R = Impedance of Pacing Circuit (ohms) (say 500 ohms) I = V/R = Current through pacing circuit (m. A) = 2. 5 V/ 500 ohms = 0. 005 A = 5 m. A

Stimulation Threshold • Pacing Voltage Threshold – The minimum pacing voltage at any given pulse width required to consistently stimulate the heart causing it to contract

Capture – Loss of Capture VVI / 60 Non-Capture

NBG Code for Pacing I Chamber Paced II Chamber Sensed III Response to Sensing IV Programmable Functions/Rate Modulation V: Ventricle T: Triggered P: Simple programmable A: Atrium I: Inhibited M: Multiprogrammable D: Dual (A+V) D: Dual (T+I) C: Communicating O: None S: Single (A or V) O: None V Antitachy Function(s) P: Pace S: Shock D: Dual (P+S) R: Rate modulating O: None

Single Chamber Pacemakers Most basic type of pacemaker Works only on one chamber of the heart – usually the RV Paces the heart at a FIXED RATE programmed Inhibits pacing whenever a natural heartbeat is sensed by the pacemaker

Single Chamber Pacemakers Ventricular Single Chamber Pacing or VVI pacing Pacing Rate Pace Sense Pace

Single-Chamber System AAI VVI

Dual Chamber Pacemakers • DDD, DDDR – sense & pace both atrium and ventricle • VDD – Sense atrium, pace ventricle

The four faces of dual chamber pacing AV SEQUENTIAL PACING Atrial Pacing Rate – 60, AV Interval – 200 ms AV Synchronous Pacing : NATURAL ATRIAL CONTRACTION & VENTRICULAR PACING : VDD AV Interval = 150 ms Spontaneous Atrial Rate – 55 Spontaneous Atrial Rate – 110

The four faces of dual chamber pacing Atrial Pacing Rate = 70, Natural AV conduction NATURAL ATRIAL CONTRACTION WITH NORMAL AV CONDUCTION Spontanoeus Atrial Rate = 65, Spontaneous PR interval = 160 ms

#1 72 M with symptomatic bifasicular block with prolonged PR interval s/p DDD pacemaker 2 week ago, UTR 100/min Returns with history of atypical R sided chest pain and back pain SBP 70 mm Hg BP improved promptly with IV fluid and pt felt better

Typical values • LRL : 50 -60/mt • URL : 110 -130/mt • AV delay : 120 -200/ms • PVARP : 250 ms • VRP : 200 ms • Blanking periods : < 50 ms

Sensing of intrinsic heartbeats • Sensing is the ability of the pacemaker to “see” when a natural (intrinsic) depolarization is occurring – Pacemakers record the Intracardiac Electrogram (EGM) by constantly recording the potential difference between the cathode and anode Depolarization Wave Processed by Device

Undersensing • Pacemaker does not “see” the intrinsic beat, and therefore does not respond appropriately Intrinsic beat Scheduled pace delivered VVI / 60

Oversensing Marker channel shows intrinsic activity. . . though no activity is present VVI / 60 • An electrical signal other than the intended P or R wave is detected • Pacing is inhibited

Amplitude Threshold Testing Keeping pulse width stable, decrement voltage until loss of capture @ 0. 5 ms 1. 5 V 1. 0 V . 5 V

Intrinsic R wave Amplitude • Typical intrinsic R wave amplitude measured from pacing leads in the Right Ventricle are more than 5 m. V in amplitude Amplitude Intrinsic R wave in EGM The Intrinsic R wave amplitude is usually much greater than the T wave amplitude

Sensitivity Setting This is a value specified to the pacemaker in millivolts through programming. All ventricular electrogram deflections seen by the pacing lead that exceed the sensitivity setting will be identified by the pacemaker as intrinsic R waves The typical sensitivity setting that is programmed for Ventricular sensing is 2. 5 m. V

Sensitivity Setting 2. 5 1. 25 Time 5. 0 Amplitude (m. V) 5. 0 2. 5 1. 25 Time Sensitivity settings less than 2. 5 mv – High sensitivity – can lead to oversensing Sensitivity settings greater than 2. 5 m. V – Low sensitivity – can lead to undersensing

VVI Mode Lower Rate Interval • { Pacing inhibited with intrinsic activity VP Blanking/Refractory VVI / 60 VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI TIMING V VP VP VP VS VP

VVI @ 65/mt VVI VVI Fusion beat Sensed native R waves reset VVI timing

Presenting Rhythm and Rate Battery Status Lead Status Sensing Threshold Observation, Data, and Events Program 39 UC 200702005 EN Medtronic, Inc. USA September 2006

Diagnostic Information

Cardiac Compass® Management of atrial tachyarrhythmias May help with assessment of: • Rate-control therapy • Rhythm-control therapy • Risk for stroke 1 1 Glotzer TV, Hellkamp AS, Zimmerman J. et al. , Atrial high rate episodes detected by pacemaker diagnostics predict death and stroke: Report of the Atrial Diagnostics Ancillary Study of the Mode Selection Trial (MOST). Circulation 2003; 107: 1614 -1619.

Potential Problems with Pacemakers • Battery Depletion • Lead displacement or perforation – Loss of capture and/or sensing • Lead fracture or insulation break – Loss of capture and/or sensing • Increase in thresholds due to • Drugs • Electrolyte imbalance • Interference from external electromagnetic sources • Device malfunction

Pacemaker Follow-up • All the Information for Routine Follow-ups Operating Mode Last Interrogation Longevity A&V Pacing Thresholds A&V Pacing Lead Impedance P&R wave Amplitudes Arrhtymia Summary % Pace/Sense Histograms Alert of situations that may require further investigation

Magnet Operation • Varies across manufacturers and models • Medtronic Normal - VOO, DOO mode 85 ppm - No sensing, asynchronous pacing • Medtronic ERI – VOO, DOO mode 65 ppm

Special Precautions – EMI • General Principle – Avoid proximity to powerful electric or magnetic fields – Move away from the field if symptomatic – Keep safe distance – 6 inches for electrical appliances • Safe from Interference – Microwave, TV, Washing Machine, Fridge, Vacum cleaners etc. – Cordless phones – Computer, printer, scanner, photcopier • Possible interference – Items with large magnets, e. g. speakers, car ignition systems – Hand-held hair dryers – Radiotransmitters – Cellular Phones