16 Pacemakers and Implantable Cardioverter Defibrillators Fast Easy
16 Pacemakers and Implantable Cardioverter Defibrillators Fast & Easy ECGs, 2 nd E – A Self Paced Learning Program Fast & Easy ECGs, 2 E 1 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Artificial Pacemakers • Medical devices used to generate and deliver electrical impulses to the myocardium to stimulate a normal heartbeat • Some are external to the body and provide temporary treatment, others are permanently implanted in the chest Fast & Easy ECGs, 2 E 2 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Artificial Pacemakers • One type of temporary pacemaker is the transcutaneous pacemaker – It delivers electrical impulses through lead wires to electrode pads that are applied to the surface of the patient’s chest • Permanent pacemakers are implanted in a surgically created pocket beneath the skin in the patient’s chest wall just below the clavicle Fast & Easy ECGs, 2 E 3 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Permanent Pacemakers • Consist of: – A generator – One or more lead wires – A power source (often a lithium battery) – Logic circuits that detect cardiac electrical activity and determine the appropriate response I Fast & Easy ECGs, 2 E 4 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Permanent Pacemakers • May be used to: – Symptomatic bradycardia – Sick sinus syndrome – Atrial fibrillation with bradycardia – 3 rd degree (complete) AV heart block – Symptomatic 2 nd degree AV heart block, particularly type II – The sudden development of various combinations of AV heart block and bundle branch block in patients experiencing acute MI – Recurrent tachycardias that can be overdriven and thereby terminated by pacemaker activity – Synchronization of the heart beat in heart failure (cardiac resynchronization therapy) Fast & Easy ECGs, 2 E 5 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacemaker Electrodes • Are either positioned in the atrium or ventricle alone (single chamber pacemakers) or, more often, in both chambers (dual chamber pacemakers or AV sequential pacemakers) Fast & Easy ECGs, 2 E 6 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Permanent Pacemakers • Are programmable – Receive and transmit data/programming instructions through the skin using electromagnetic waves • Adjustments can be made to: – Output – Sensitivity – Refractory period – Rate adaption Fast & Easy ECGs, 2 E 7 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacing Modes • Single chamber – One pacing lead is inserted into either the right atrium or right ventricle but not both • Dual chamber – Electrodes are placed into two chambers of the heart – One lead paces the atrium while the other paces the ventricle – By assisting the heart in coordinating the function between the atria and ventricles, this type of pacemaker acts similarly to how the heart naturally paces itself – Also referred to as an AV sequential pacemaker – Most can be programmed to a single chamber mode, which can be useful if the atrial lead wire fails Fast & Easy ECGs, 2 E 8 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacing Modes • Fixed rate – Paces the heart at a single, preset rate • Rate responsive – Has sensors that identify increases or decreases in the patient’s physical activity and automatically adjusts base pacing rate to meet the body’s metabolic needs – Can boost the heart rate in response to motion or increased respirations for those patients whose body cannot appropriately increase the heart rate during activity Fast & Easy ECGs, 2 E 9 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacing Modes • Demand – Most common type used – Fires only when the patient’s intrinsic heart rate falls below a given threshold level • i. e. , if the pacemaker is set at 60 beats per minute it remains inactive until there is a pause between beats that translates into a rate below 60, then the pacemaker fires Fast & Easy ECGs, 2 E 10 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System • Pacemaker mode and function described by a five letter coding system – in practice, only three to four are commonly used Fast & Easy ECGs, 2 E 11 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System • First letter represents the heart chamber being paced. This letter may be – – O = none A = atrium V = ventricle D = dual (ventricle and atrium) • Second letter represents the chamber of the heart being sensed by the pacemaker. This letter may be – – O = none A = atrium V = ventricle D = dual (ventricle and atrium) Fast & Easy ECGs, 2 E 12 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System • Third letter indicates how the pacemaker generator responds to sensing. This letter may be – O = none – T = triggers pacing – I = inhibits pacing – D = dual (triggers and inhibits pacing) • Fourth letter has to do with adjustment of the pacing rate in response to exercise – If pacemaker is rate responsive, it is denoted with the letter “R” – If there is none, it is denoted as “O” Fast & Easy ECGs, 2 E 13 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System • The fifth letter indicates multisite pacing. This letter may be – O = none – A = atrium – V = ventricle – D = dual (ventricle and atrium) Fast & Easy ECGs, 2 E 14 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System Examples • VOO – In this mode, the ventricle is paced and there is no sensing function • AAI – Pacemaker paces and senses in the atrium – When it senses atrial activity, pac ing isinhibited • VVI – Ventricle is paced and sensed – If spontaneous cardiac output is detected, then the device is inhibited Fast & Easy ECGs, 2 E 15 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System Examples • VDD – Here the pacemaker paces the ventricle and senses both the atrium and ventricle – On sens ing intrinsic atrial activity, the pacemaker triggers ventricular pac ing; on sensing ventricular activity, the pacemaker inhibits pacing – It is also known as a P-synchronous pacer Fast & Easy ECGs, 2 E 16 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Coding System Examples • DVI – Pacemaker can pace in the atrium, the ventricle, or both – Sensing takes place only in the ventricle – When the pacemaker senses intrinsic ventricular activity, it inhibits pacing • DDD – Pacemaker paces and senses in the atrium, the ventricle, or both – On sensing ac tivity in either chamber, the pace maker inhibits pacing in that chamber – Or, on sensing atrial ac tivity, the pacemaker may trigger ventricular pacing Fast & Easy ECGs, 2 E 17 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Cardiac Resynchronization Therapy (CRT) • Used to resynchronize a heart that does not beat in synchrony, a common problem in patients with heart failure • Employs three leads: – one is placed in right atrium – one is located in right ventricle – last one is inserted through the coronary sinus to pace the free wall of the left ventricle – These three wires are connected to a CRT generator and programmed so that the two ventricular wires are activated simultaneously I Fast & Easy ECGs, 2 E 18 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Unipolar and Bipolar Systems • Unipolar – positive electrode is positioned in the heart tissue and the negative electrode is connected to the pulse generator – produces tall pacing spikes on the ECG • In a bipolar system, – electrodes are only millimeters apart in the cardiac tissue – produces short pacemaker spikes Fast & Easy ECGs, 2 E I 19 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
ECG Features of a Pacemaker • Depending on how many chambers are paced, the firing of a pacemaker produces one or two narrow pacemaker spikes on the ECG Fast & Easy ECGs, 2 E 20 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
ECG Features of a Pacemaker • A paced ECG complex shows two features: (a) a narrow “pacing spike, ” which reflects the impulse depolarizing the paced chamber and (b) a P wave or QRS complex that immediately follows the pacing spike I Fast & Easy ECGs, 2 E 21 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure • Pacemakers may not work properly for a number of reasons, including a failure to capture, a failure to pace, a failure to sense, oversensing, and pacemaker mediated tachycardia Fast & Easy ECGs, 2 E 22 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure • Failure to capture is seen as the presence of pacemaker spikes that are not followed by a P wave or broad QRS complex Fast & Easy ECGs, 2 E 23 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure • Failure of the pacemaker to sense is seen as the presence of ECG pacemaker spikes that fall where they shouldn’t Fast & Easy ECGs, 2 E 24 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure • Oversensing is seen as an absence of pacemaker spikes in the presence of a heart rate that is slower than the rate set for the pacemaker Fast & Easy ECGs, 2 E 25 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Pacemaker Failure • Pacemaker mediated tachycardia is seen as a fast heart rate with a pacemaker spike preceding each QRS complex on EGG. Fast & Easy ECGs, 2 E 26 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Implantable Cardioverter Defibrillator (ICD) • Is implanted in patients who are at risk of sudden cardiac death due to ventricular fibrillation and ventricular tachycardia Fast & Easy ECGs, 2 E 27 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Implantable Cardioverter Defibrillator • Is programmed to detect cardiac dysrhythmias and correct them by delivering paced beats, cardioversion, or defibrillation Fast & Easy ECGs, 2 E 28 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Therapies Provided by the ICD Fast & Easy ECGs, 2 E 29 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect • Analyze this ECG tracing I Fast & Easy ECGs, 2 E 30 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect • Analyze this ECG tracing I Fast & Easy ECGs, 2 E 31 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect • Analyze this ECG tracing I Fast & Easy ECGs, 2 E 32 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
Practice Makes Perfect • Analyze this ECG tracing I Fast & Easy ECGs, 2 E 33 © 2013 The Mc. Graw-Hill Companies, Inc. All rights reserved.
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