General Overview of Modern Cardiac Pacemakers

Editor's Notes

• #2: Survival of Adam-Stokes from < 50% to 85%
• #4: In 1804, Aldini successfully stimulated the hearts of decapitated criminals. He was In the nephew of Luigi Aldini The works in reanimation inspired the story of Frankenstein
• #5: Australian anaesthesiologist Used it resuscitate a stillborn neonate One pole was applied to a skin pad soaked in strong salt solution,” while the other pole “consisted of a needle insulated except at its point, and was plunged into the appropriate cardiac chamber.
• #6: An American physiologist An electro-mechanical instrument. Hyman coined the term ‘artificial pacemaker’, Pace the heart and lead it like an artificial maestro!
• #7: External cutaneous electrodes and a large PG Used to treat CHB patients It was the only type available when OPS started in the 1950. It kept some cardiac surgical patients alive until sinus rhythm returned. Painful, excoriations and skeletal contractions worsened as days passed. Surgeons would provoke Stokes-Adams to see if sinus rhythm or an adequate idioventricular rhythm had returned
• #8: Clarence Lillehei enlisted Earl Bakken A television engineer and later founder of Medtronics Corporation. Developing a small portable pacemaker Epicardial leads - Reduced the discomfort of patients Increased risk of ascending infection
• #9: Abou the size of a Walkman Increased risk of ascending infection.
• #10: It became possible by invention of transistors during the 1950s. Elmqvist was a medical graduate who became an engineer. He designed a portable ECG machine and ink jet printer. A transistor – semiconductor > gen, amplify or control flow of current .
• #12: Designing pacemaker that could sense – mid 1960’s Change of battery from mercury-zinc to lithium cell Programming of rate and stimulus duration Casing/housing of pacemakers Non-invasive assessments of pacemaker function and adjustment of pacemakers via radio or telephonic transmission
• #13: The heart is a muscle that contract in response to electrical impulse. That impulse is generated and transmitted by the conduction system. Conduction system – nodal tissue and conducting fibres Nodal tissue – generates impulses Conducting fibres - transmits Impulses propagated by the cardiac muscle cells. SA - deep to the epicardium (junction of SVC and RA) It is supplied by a SA node artery (RCA in 60% and LCA in 40% ) A-V node post wall of the RA (just behind TV) AV – junction between membranous and muscular part of IVS AV node artery of posterior IV artery of the RCA (80%)
• #14: The His bundle - only bridge between the atrium and ventricle. AV node through the fibrous skeleton of the heart Right and left bundle ramify into Purkinje fibres Pacemaker system SA node – 70 to 80bpm AV node - 40 to 60 bpm Purkinje - 15 to 40 bpm Delays SA to AV is 0.03sec Delay within AV 0.09sec Delay along His-Purkinje – 0.04sec
• #15: PR interval – delay in transmission QT interval – Contraction of vent
• #16: Abnormal rhythmicity of the pacemaker Shift of the pacemaker from the sinus node Blocks along normal conduction pathway Abnormal pathways of impulse transmission through the heart Spontaneous generation of impulses in almost any part of the heart
• #17: Junctional rhythm – absent p wave. Causes Congenital Iatrogenic (surgery) – node or artery (Fontan and Atrial switch) Myocardial infarction Myocarditis Electrolyte imbalances Well trained athletes
• #19: the action potential is sometimes strong enough to pass through the bundle into the ventricles and sometimes not strong enough to do so
• #20: Progressive prolongation of the P-R interval until a ventricular beat is dropped and is then followed by resetting of the P-R interval and repeating of the abnormal cycle In type II block, there is usually a fixed number of non-conducted P waves for every QRS complex. For example, a 2:1 block implies that there are two P waves for every QRS complex. At other times, rhythms of 3:2 or 3:1 may develop.
• #21: Intermittent (sec, min to weeks) or persistent. Escape bcos it has escaped the influence of SA Each time AV conduction ceases, the ventricles don’t start immediately Delays for about 5 to 30 sec because of overdrive suppression. Brain can remain active for 4 to 7 sec without blood - syncope Once the ventricle takes over – ventricular escape Syncope is relieved (40bpm is enough for brain perfusion) Stokes-Adams ventricular standstill at the onset of complete block is so long that it becomes detrimental to the patient’s health or even causes death
• #22: Current flows oppos
• #25: Despite advances the basic components are similar Battery source Circuitry (output, sensing, telemetry, microprocessor and memory) Metal shell Ceramic feedthrough – a piece of wire surrounded by glass or sapphire (port for leads) – The PG can take up to 3 leads Sensors Telemetry is the process of recording and transmitting the readings of an instrument.
• #26: Ideal energy density Predictable and gradual decrease in battery life. Initial voltage outage is app 2.8V When it reaches 2.0 – 2.4 V elective replacement indicator is triggered which change settings
• #27: Lead is direct connection between the PG and the endocardium It is made up of conducting cables and lead-tip electrode separated by an insulator
• #29: The pacing leads with
• #30: Unipolar leads – usually has a cathode (neg) and the anode is incorporated into the PG. Bipolar the difference in potential sensed or created is over a few mm Unipolar lead spans the distance between the lead the PG across the chest
• #31: (ICDs should not be used in conjunction with unipolar leads), and In addition, most generators are compatible with unipolar pacing through a bipolar lead if needed as a result of lead damage or high pacing thresholds.
• #33: Passive fixation leads acquire stability by becoming entrapped in myocardial trabeculations. Active-fixation leads have distal screws that are deployed and penetrate the myocardial wall. Active mechanism carry a lower risk of dislodge and provides versatility in the choice of implantation site (because their stability does not depend on presence of trabeculations) active-fixation leads generate a more extensive inflammatory response – increases the threshold after implantation. Electrodes implanted in myocardium elicit a strong foreign body granulomatous reaction that results in the formation of a local fibrous capsule at the lead tip Steroid-eluting leads Such leads have a reservoir of steroid near the electrode that flows through the porous electrode into the myocardium, thereby reducing the inflammatory response and the rise in pacing threshold
• #34: active pacing box (or generator) programmed to pace in VVI mode
• #35: Sensing occurs when filtered signal exceeds the set sensing threshold. atrial and ventricular leads are 1.5 to 5 mV and 5 to 25 mV, The lead has a recording electrode and indifferent electrode. As a wave approaches the recording electrode and then proceeds aways from it - it creates an intrinsic deflection. Intrinsic deflection is the transition from the approaching to the receding deflection. an amplifier that increases the signal from the recording electrode and a band pass filter to delete signals with frequencies too high or too low to represent an intrinsic deflection.
• #36: Pulse width is the time duration over which the impulse was delivered. These two parameters need to be optimized to enhance battery life. They can be reprogrammed to prevent extracardiac (e.g. phrenic stim) by lowering the pacing voltage to min far-field capture and increasing the pulse width to ensure cardiac stimulation. Impedance increases in insulating fracture Impedance increases in conductor fractures 50% of the current drain from the battery is used for pacing, Whereas the other one-half is used for sensing and housekeeping functions It is the flow of current that drains the battery and not the voltage. The voltage in the difference in electrical potential. Thus if you create a pathway for the flow of current to flow the potential begins to diminish as electrons move to establish an equilibrium. The more conducting the pathway established the faster the drain of the battery. The more resistive the pathway the slower the flow of current. Pacing lead are designed such that the resistance is high enough to avoid complete drainage of the battery within a short period but With good conductance enough to deliver the necessary current needed to stimulate the heart Just like gravitational potential the high you are the higher the potential but the lower you are the lower the potential.
• #37: T - a sensed event leads to delivery of a pacing stimulus It is used to prevent inappropriate inhibition by incorrectly sensed events such as skeletal muscles myopotential. This is life saving in patients who are pacemaker dependent. I – inhibition of pacemaker stimulus delivery in designated chamber (a new timing cycle is initiated) The presence of an intrinsic dep above pacing rate inhibits pacing D – Triggered and inhibited – sensing of intrinsic atrial activity leads to inhibition of an atrial pacing stimulus. An AV clock is then started (a programmed AV delay). A sensed vent impulse – leads to inhibited pacing No sensed vent impulse – trigger but it results in triggering of a ventricular pacing stimulus after the programmed AV delay. Pacing in the ventricle or atrium does not occur for a programmable time after intrinsic vent activity is sensed
• #38: Simple programmable - programmability of the pacemaker is limited to certain parameters; Multiprogrammable - able to program a large number of parameters. The communicating function refers to the ability to exchange signals between the pacemaker and a pacemaker programming device. Rate modulation is the capability of the pacemaker to adjust the pacing rate according to a sensor device. A variety of sensors that attempt to match the individual’s physical activity or metabolic demands by responding to different sources, such as motion, temperature, and chest wall impedance (as an estimate of minute ventilation).
• #39: AAI – requires normal AV conduction and functioning pathway to AV node It is seldom used because most patients require vent pacing VVI Used in patients with CHB or adv 2nd degree; esp if they have Atrial fibrillation. AV synchrony is not preserved – used mainly with elderly patients with sedentary lifestyle VOO Old generation of pacemakers Asynchronous pacing Failure to sensing any electrical impulse (from the heart or interferences) Incurrent practice, these modes are only used temporarily to prevent oversensing DDD Also called universal pacing because of its universal application Prserved AV synchrony Sinus node dysfunction and AV blocks Dual stimulation reduces battery life NB= If used in atrial tavhyarrhytmias – it can lead to ventricular tachycardia Because the atrial events are tracked in the ventricle VDD In all pacing modes, a lower rate limit indicates the rate below which pacing occurs (this is the slowest heart rate that should be present)
• #41:  presence of ≥2 consecutive, non-conducted P waves The ventricular arrhythmias presumed to be due to AV block Other medical conditions requiring drugs that result in symptomatic bradycardia. AF and bradycardia with 1 or more pauses of at least 5sec.
• #42: When type II second-degree AV block occurs with a wide QRS, including isolated right bundle branch block, pacing becomes a C Pacing induced infra-His block that is not physiological Alternating bundle branch block Incidental prolonged HV interval ≥ 100ms on electrophysiological study.
• #43: Neurocardiogenic syncope, also known as vasovagal syncope, is a sudden loss of rugada syndrome (BrS) is a genetic disorder in which the electrical activity of the heart is abnormal due to channelopathy consciousness that occurs when the body overreacts to a trigger. Brugada syndrome despite a normal heart rhythm, because of a sudden drop in blood pressure, known as vasovagal syncope
• #44: Temporary placement of a standard (screw-in) pacemaker lead is suggested. This serves as a bridge to implantation of a permanent pacemaker.
• #46: If one is to use a passive fixation – avoid site for PPI If for active fixation – Permanent sites
• #48: Injury or radiation therapy – potential abnormal venous drainage. On table venograpgy may be done to assess for abnormal drainage.
• #49: LA should be administered to the pectoral region Oblique incision along the deltopectoral groove Blunt dissection until a fatty pad between the pectoralis or deltoid muscles. Dissection of the cephalic vein free from surrounding tissues. Silk 0 sutures placed around the vein proximally and distally around the vein. The cephalic vein is incised and lead introduced through with a vein lifter.
• #51: Avoid the RV free wall due risk of ectopy and decreased lead stability, While a lead is being placed through the sheath, the patient should be instructed to transiently refrain from talking or breathing to avoid complication by air embolus through the introducer sheath The lead and guidewire introduced gently to avoid injury to the heart or vessels There should be some slack to the lead to avoid dislodgements
• #52: Soft stylets give more leverage in manipulating a lead to the desired position (e.g. mid septal pacing) and stiff stylets help maintain stability until fixation (e.g. ICD leads, tricky positions)
• #53: AP, 40° LAO, 30° RAO and left lateral fluoroscopic images showing lead tip at apical septum in a patient with dual-chamber pacemaker
• #55: Determine the impedance, sensing and pacing threshold. An R wave of 5 mV Pacing threshold of 1 mA or less are adequate Impedance < 1000ohms
• #57: Anchoring sleeve of the lead is plicated to the pectoralis muscle and fascia. Final sensing and pacing threshold Subcutaneous pocket is created medial to the delto-pectoral groove to house the PG
• #58: The leads are coiled under the generator, and the entire system is implanted into the pocket Subcutaneous tissues and skin are closed with absorbable sutures Skin is closed in a subcuticular manner
• #59: In some centres – patients are placed in a sling for 24hrs. After 24hrs patients can use limbs but cannot lift objects that are 2.5-5kg or raise arms above the shoulder for 6weeks X-ray to detect some of the complicatiosn
• #61: Constrerictive pericarditis It could involve an immune-mediated inflammatory response to initial cardiac injury - Dressler's syndrome. It could involve direct irritation of the pericardium by minimally protruding electrodes Tricuspid regurgitation Lead-leaflet interaction: The pacemaker lead can mechanically interfere with the tricuspid valve leaflets, causing them to become scarred, restricted, or perforated Inflammatory response: The lead can stimulate an inflammatory response that causes fibrosis and adhesions between the valve and the lead Asynchronized activation: The pacemaker can cause the right ventricle to activate out of sync
• #64: When including only a clear perforation, the sensitivity of chest radiography was 27.7
• #68: In this system, the pulse generator is placed within a pocket created between the fourth and fifth intercostal spaces at the midaxillary line. An electrode is positioned through two subcutaneous tunnels, extending from the pocket to a small xiphoid incision and from the xiphoid to a superior sternal incision.
• #72: Retrograde ventriculoatrial (VA) conduction – atrial sensing which then triggers ventricular pacing Circuituous pacemaker-mediated tachycardia Treatment – magnet Algorithms that extend the post-vent atrial refractory period Absence of rate response to physiologic need