ΤΟ ΗΚΓ ΣΤΟΝ ΒΗΜΑΤΟΔΟΤΟΥΜΕΝΟ ΑΣΘΕΝΗ ΤΖΩΡΤΖ ΔΑΔΟΥΣ ΕΠΙΚΟΥΡΟΣ ΚΑΘΗΓΗΤΗΣ Α.Π.Θ. ΜΑΡΙΑ ΚΑΡΑΛΙΟΛΙΟΥ ΕΙΔΙΚΕΥΟΜΕΝΗ ΙΑΤΡΟΣ ΚΑΡΔΙΟΛΟΓΟΣ Β ΚΑΡΔΙΟΛΟΓΙΚΗ ΚΛΙΝΙΚΗ Α.Π.Θ. ΙΠΠΟΚΡΑΤΕΙΟ Γ.Ν.Θ.
5 Why a Pacemaker is Implanted A pacemaker is implanted to: Provide a heart rate to meet metabolic needs In order to pace the heart, it must capture the myocardium In order to pace the heart, it must know when to pace, i.e., it must be able to sense Today s pacemakers also: Provide diagnostic information About the pacing system About the patient We ll discuss how a pacemaker performs these functions in upcoming CorePace modules.
The Diseased Heart May: Prevent, or delay, impulse generation in the SA node Prevent, or delay, impulse conduction via the AV node SA node Inhibit impulse conduction via the bundle branches AV node
Intrinsic Pacemaker The heart generates electrical impulses that travel along a specialized conduction pathway Typically, the sinus node (SA node) generates the impulses Conduction paths include: Bachman s Bundle AV node Bundle of HIS Bundle Branches Purkinje Network This pattern of conduction makes it possible for the heart to pump blood efficiently
Cardiac Conduction Review SA node Atria Ventricles AV node Bundle branches
Implantable Pacemaker System Lead wire(s) Implantable pulse generator (IPG) Myocardial tissue
Implantable Pacemaker Circuit Implantable pulse generator (IPG): Battery Lead Circuitry Connector(s) Leads or wires Cathode (negative electrode) Anode (positive electrode) Body tissue IPG Anode Cathode
The Pulse Generator Contains a battery to provide energy for sending electrical impulses to the heart Houses the circuitry that controls pacemaker operations Includes a connector to join the pulse generator to the lead(s) Connector Block Circuitry Battery
Leads are Insulated Wires Deliver electrical impulses from the pulse generator to the heart Sense cardiac depolarization Lead
Lead Characterization Position within the heart Endocardial or transvenous leads Epicardial leads Fixation mechanism Active/Screw-in Passive/Tined Polarity Unipolar Bipolar Insulator Silicone Polyurethane Shape Straight J-shaped used in the atrium
Endocardial Passive Fixation Leads The tines become lodged in the trabeculae, a fibrous meshwork, of the heart Inserted via a cut-down or transvenous sheath Tines
Transvenous Active Fixation Leads The helix, or screw, extends into the endocardial tissue Allows for lead positioning anywhere in the heart s chamber The helix is extended using an included tool Inserted via a cut-down or transvenous sheath
Epicardial Leads Leads applied directly to the surface of the heart Fixation mechanisms include: Epicardial stab-in Myocardial screw-in Suture-on Applied via sternotomy or laproscopy
Lead Polarity Unipolar leads May have a smaller diameter lead body than bipolar leads Usually exhibit larger pacing artifacts on the surface ECG Bipolar leads Usually less susceptible to oversensing of non-cardiac signals (i.e., myopotentials, EMI, etc.) Unipolar lead Bipolar coaxial lead To tip (cathode)
20 Unipolar Pacing System The lead has only one electrode the cathode at the tip The pacemaker can is the anode Anode + When pacing, the impulse: Flows through the tip electrode (cathode) Stimulates the heart Returns through body fluid and tissue to the IPG can (anode) Cathode -
Bipolar Pacing System The lead has both an anode and cathode The pacing impulse: Flows through the tip electrode located at the end of the lead wire Stimulates the heart Returns to the ring electrode, the anode, above the lead tip Anode + Anode Cathode - Cathode
Lead Insulators Silicone insulated leads Inert Biocompatible Biostable Repairable with medical adhesive Historically very reliable Polyurethane Silicone Polyurethane insulated leads Biocompatible High tear strength Low friction coefficient Smaller lead diameter Newer bipolar lead insulation
24 Rate and Interval Review Calculated on the horizontal axis At 25 mm/s speed Each small box = 40 ms Each bold box = 200 ms How do you convert intervals to rate? 60,000 / (Interval in ms) = Rate in bpm Click for Answer
Single Chamber and Dual Chamber Pacing Systems
27 Single Chamber System The pacing lead is implanted in the atrium or ventricle, depending on the chamber to be paced and sensed How else can you describe this system? Click for answer Ventricular pacemaker with a bipolar lead
Paced Rhythm Recognition Atrial pacing at a rate of 60 ppm
Paced Rhythm Recognition Ventricular pacing at a rate of 60 ppm The spike is an artifact created by the pacemaker s output
30 Paced Rhythm Recognition On the ECG, note the difference between the paced and intrinsic beats. Why do you think this is? Click for answer Because the paced beat originates and is conducted differently than the intrinsic beat.
Advantages/Disadvantages of Single Chamber Pacing Systems Advantages Disadvantages Implant only one lead Pacemaker itself usually smaller Single ventricular lead does not provide AV synchrony Ventricular based pacing linked to AF and HF hospitalizations Single atrial lead does not provide ventricular backup if A-V conduction is lost
33 VVI Mode Chamber paced: Ventricle Chamber sensed: Ventricle Response to sensing: Inhibited A ventricular sense: Inhibits the next scheduled ventricular pace
38 VVI Example Chamber paced: Ventricle Chamber sensed: Ventricle Response to sensing: Inhibition VVI 60 = Lower Rate timer of 1000 ms Pacing every 1 second if not inhibited Lower Rate Timer 1000 ms Lower Rate Timer 1000 ms Lower Rate Timer. V P V P V P
39 VVI Example VVI 60 Chamber paced: Ventricle VVI 60 = Lower Rate timer of 1000 ms Pacing every 1 second if not inhibited Chamber sensed: Ventricle Response to sensing: Inhibition A ventricular sense interrupts the pacing interval, resets the lower rate timer, and inhibits the next scheduled paced (x) Lower rate timer 1000 ms Lower rate timer 1000 ms x V P V P V S V P
40 VOO Mode VOO 60 The intrinsic ventricular event cannot be sensed, and thus, does not interrupt the pacing interval. 1000 ms 1000 ms 1000 ms V P V P V P V P Chamber paced: Ventricle Chamber sensed: None Response to sensing: None VOO results in fixed-rate pacing in the ventricle. Placing a magnet over the pacemaker usually results in this behavior at known rates, for example, 85 ppm.
Dual Chamber System Two leads One lead implanted in the atrium One lead implanted in the ventricle These systems can be unipolar or bipolar Are these leads in the picture active or passive fixation? Click for answer Passive fixation. Note, the tines look like small grappling hooks, but are actually soft silicone.
Paced Rhythm Recognition Dual chamber pacing at a rate of 60 ppm The spike followed closely by the P- or R-wave is how we tell if the pacemaker has captured the myocardium
44 DDD Mode Chamber paced: Atrium & ventricle Chamber sensed: Atrium & ventricle Response to sensing: Triggered & inhibited An atrial sense: Inhibits the next scheduled atrial pace Re-starts the lower rate timer Triggers an AV interval (called a Sensed AV Interval or SAV) An atrial pace: Re-starts the lower rate timer Triggers an AV delay timer (the Paced AV or PAV) A ventricular sense: Inhibits the next scheduled ventricular pace
46 DDD Examples The Four Faces of DDD Atrial and ventricular pacing A P V P A P V P Atrial pace re-starts the lower rate timer and triggers an AV delay timer (PAV) The PAV expires without being inhibited by a ventricular sense, resulting in a ventricular pace
47 DDD Examples The Four Faces of DDD Atrial pacing and ventricular sensing A P V S A P V S Atrial pace restarts the lower rate timer and triggers an AV delay timer (PAV) Before the PAV can expire, it is inhibited by an intrinsic ventricular event (R-wave)
48 DDD Examples The Four Faces of DDD Atrial sensing, ventricular pacing A S V P A S V P The intrinsic atrial event (P-wave) inhibits the lower rate timer and triggers an AV delay timer (SAV) The SAV expires without being inhibited by an intrinsic ventricular event, resulting in a ventricular pace
49 DDD Examples The Four Faces of DDD Atrial and ventricular sensing A S V S A S V S The intrinsic atrial event (P-wave) inhibits the lower rate timer and triggers an AV delay timer (SAV) Before the SAV can expire, it is inhibited by an intrinsic ventricular event (R-wave)
50 Dual Response to Sensing DDD The pacemaker can: Inhibit and trigger A P-wave inhibits atrial pacing and triggers an SAV interval An atrial pace triggers a PAV interval An R-wave inhibits ventricular pacing We ll see later how a PVC can affect atrial timing
54 DDI Mode Chamber paced: Atrium & ventricle Chamber sensed: Atrium & ventricle Response to sensing: Inhibited An atrial sense: Inhibits the next scheduled atrial pace Re-starts the lower rate timer An atrial pace: Re-starts the lower rate timer Starts an AV delay timer (the Paced AV or PAV) A ventricular sense: Inhibits the next scheduled ventricular pace
55 DDI Example Why would we want a dual chamber pacing mode that does not trigger an SAV? P P P P P P P P P P P P What rhythm is this? Click for Hint The underlying rhythm is an atrial tachycardia.
56 DDI Example Why would we want to use DDI? To control pacemaker timing during atrial tachycardias Avoids a fast paced ventricular response to AT/AF DDD tracking the AF May limit patient symptoms during AT/AF DDI Not tracking the AF Click to change 540ms = 110bpm This function has come to be called Mode Switching
65 Nuggets Note that in both the single and dual chamber examples: When the device paces for the purposes of timing capture is assumed Some newer devices have algorithms to check for capture Sensing is critical to timing If the device fails to sense, undersensing, it will usually pace If it oversenses, e.g., senses myopotentials, it will inhibit pacing
66 Remember This Strip? Intermittent loss of capture (LOC) Note how the underlying timing is unaffected by the failure to capture For timing purposes, pace = capture Click for Answer DD D Review question: Name some possible causes for this condition. Incomplete fracture, insulation failure, lead dislodgement, poor connection in header, programming error, change in pacing thresholds
72 Diagnose This Strip Undersensing, the device fails to reliably see P-waves How do we know this is undersensing? Click for Answer DD D Because: The atrial lower rate timer is not inhibited there are atrial pacing spikes The intrinsic P-waves do not start an SAV
85 Status Check Identify the most likely pacemaker that resulted in this strip Click for answer Atrial pacemaker Ventricular pacemaker Dual chamber pacemaker
86 Status Check Which pacemaker modes could be operating on this strip? Assume normal pacemaker operation Click for Answer A. DDD B. VVI C. AAI D. DOO A. DDD Yes, the intrinsic rate could be faster than the lower rate, and the PAV/SAV is longer than the P-R interval. B. VVI Yes, the ventricular rate is faster than the lower rate, thus inhibiting the IPG. C. AAI Yes, the atrial rate is faster than the lower rate, thus inhibiting the IPG. D. DOO No, DOO results in fixed rate pacing. No sensing is possible, no inhibition is possible.
87 Status Check Which pacemaker modes could be operating on this strip? Assume normal pacemaker operation Click for Answer A. DDD B. VVI C.AAI D.DOO A. DDD Yes, this is very likely the DDD mode. B. VVI Yes, it could be, but the consistent A-V relationship should make us suspicious. C. AAI No, not possible. Cannot have ventricular pacing in the AAI mode. D. DOO No, DOO results in fixed rate pacing. No sensing is possible, no inhibition is possible. We would see atrial and ventricular pacing if this was DOO.
88 Status Check Which pacemaker modes could be operating on this strip? Assume normal pacemaker operation Click for Answer A. DDD Yes, this is very likely the DDD mode. This is sometimes called tracking, as the ventricle is tracking the atrium. A. DDD B. DDI C.VOO D.DOO B. DDI Not possible. The consistent AV intervals suggest the P-wave is triggering an SAV. DDI inhibits only, triggering not possible. C. VOO Not likely because of the consistent AV intervals. Unable to diagnose until we see the IPG response to an intrinsic ventricular event (evidence of sensing). D. DOO No, DOO results in fixed rate pacing. No sensing is possible, no inhibition is possible. We would see atrial and ventricular pacing if this was DOO.
ΕΥΧΑΡΙΣΤΩ
97 Status Check Provide an explanation for why the pacemaker did not capture (think of the electrical concepts)? Click for answer Lead fracture, failing battery, improper programming, insulation failure any or all might explain this. We ll discuss how to determine the cause in Evaluation and Troubleshooting.
98 Status Check Identify the most likely pacemaker that resulted in this strip Click for answer Atrial pacemaker Ventricular pacemaker Dual chamber pacemaker