Week 10 Pacemakers and Internal Defibrillators PDF

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Warning This material has been produced and communicated to you by or on behalf of Charles Sturt University in accordance with section 113P of the copyright act (Act). The material in this communication may by subject to copyright under the act. Any further reproduction or communication of this material by you may be the subject of copyright protection under this act. Do not remove this notice Week 10 Pacemakers and internal defibrillators Ehrman Chapter 18 SUBMIT ASSESSMENT 1 (part A and B) to EASTS BEFORE 11:59PM this Friday May 3th 2 Learning Outcomes On successful completion of this subject, you should: be able to explain the pathophysiology, characteristics and diagnosis of common rhythm disorders requiring cardiac device implant intervention, be able to describe the types and function of common pacemakers and implantable cardioverter-defibrillators, be able to outline the risk factors, complications and co-morbidities that must be accounted for when applying exercise interventions to individuals with cardiac device implants; and, be able to demonstrate the ability to conduct exercise tests and exercise prescription as a therapeutic modality for individuals with cardiac device implants. 3  Introduction Implantable cardiac devices (PM & ICD) Regulate HR Synchronise chambers (in heart failure) Defibrillate the heart in life-threatening arrythmias (VF & VT) Once fitted most return to ‘their’ normal ADL’s and exercise Increasing number of patients attending CR have a PM or ICD CR allows for: optimising medical treatment Increasing exercise capacity Improve clinical conditions Assess the device is functioning correctly 4  Cardiac Electrical Pathophysiology A growing subset of cardiac rehab programs have a cardiac rhythm device Pacemaker (PM) Implantable cardioverter-defibrillator (ICD) An artificial pacemaker is designed to maintain a normal HR when the intrinsic electrical circuitry of the heart fails HR too slow due to SA node dysfunction Conduction block in the AV node Pacing systems are used to normalise conduction and resynchronise ventricles in patients with CHF, myocardial conduction slowing (as seen in LBBB) – Known as biventricular pacing: uses an additional pacing lead that is programmed to restore synchrony and mechanical activation Defibrillators shock the heart in times of life-threatening arrhythmias like ventricular fibrillation and tachycardia, increased number of participants in CR 5  Prevalence Approx 85% of people who require a pacemaker are over 65 years Equal distribution between men and women According to ACC, implanted pacemakers increased by 56% from 1993 to 2009 in the US Bradshaw et al. (2014) reported 9782 pacemakers were inserted during 1995- 2009 in Western Australia alone Prevalence rose throughout the study period to 1 in 50 in people aged >75 years Prevalence of dual chamber and triple chamber pacing also increased over the study period 40% were women Likely to continue to rise with an ageing population 6  Pathophysiology Sick sinus syndrome: term used for rhythm disorders that involve the SA node Include the inability to generate a heartbeat or increase HR in response to changing circulatory demands. SA node dysfunction symptoms include Fatigue Light headedness Exercise intolerance Syncope AV conduction failure (AV block) is when the impulses are blocked by the AV node and ventricular activation is dependent on activation below the block. Known an escape rhythm and are unreliable Pre-syncope Syncope Death AV-synchrony; sequence or timing of the atria and ventricles 7  Pathophysiology Depending on the condition a pacemaker may: Replace the SA node signals that are slowed or blocked Maintain normal timing between upper and lower chambers 8  Pacing System - Pacemaker Consists of separate but integrated components that stimulate the heart with precise timing Pulse generator (pacemaker) is located in a small metal case that also contains controlling circuitry Designed to control cardiac rhythm continuously while others are for backup and fires when SA node fails to produce an appropriate rate or fails to transmit impulses Each lead has at least one electrode that can deliver energy from pacemaker to the heart and sense information (1, 2 or 3 lead) Miniature and Leadless Temporary or permanent 9  Types of Pacemakers 1. Single chamber pacemaker – typically has one lead to and from the right atrium or the right ventricle Used when SA node sends signals too slowly, but conduction pathway is intact Slow ventricular rate 2. Dual chamber pacemaker – two leads, placed in the right atrium and right ventricle Monitor and deliver impulses to either or both chambers Used when conduction pathway to lower chamber is partly or completely blocked Dual chamber pacemaker 10 Figure 18.2 (a) Coding for a ventricular demand pacemaker that is also rate responsive. B) VVI operation during atrial fibrillation. Ventricular pacing (V) occurs at the programmed lower rate limit of 60 b. min -1. when the intrinsic ventricular activity falls below that level. Intrinsic ventricular activity at a faster rate inhibits ventricular pacing. Figure 18.2 (a) Coding for a ventricular demand pacemaker that is also rate responsive. B) DDD operation. Atrial pacing (A) occurs at the programmed lower rate limit of 75 b. min-1. Because of complete heart block, the pacemaker tracks the atrial rate to pace the ventricle (V) at the same rate after programmed AV delay Considerations Substantial increase in Q during maximal exercise compared to rest O2 uptake = Q x aVO2-diff O2 uptake can increase by 700-1200% aVO2 diff increase by 200-400% Q increase by 200-400% SV increase by 15-20% HR increase by 200-300% HR is the most important component for increasing Q 15  Physiological Pacing Physiological pacing = maintenance of the normal sequence and timing of contractions of both the atrium and ventricles AV synchrony = producing higher Q without increasing myocardial O2 uptake Dual chamber pacemakers Send impulse to ventricle following appropriate AV timing when there is a complete block Improves efficiency Set AV interval based on heart rate Augment ventricular filling and Q, improve venous return; all of which improves valve closure Improve hemodynamic responses (narrower aVO2 difference and lower La- concentrations) 16 Figure 18.3 The relative contribution of atrioventricular (AV) synchrony, stroke volume (contractility), and heart rate to cardiac output at rest and during exercise. Heart rate is the most important contributor to cardiac output during exercise. Figure 18.4 Synchronous pacing (VDD) results in less metabolism at a given level of work compared with nonsynchronous pacing (VVI).  Further considerations Patients with SA node dysfunction and AV block develop atrial arrhythmia (fibrillation most common) Mode switching controls the ventricular rate rather than tracking or matching every atrial impulse Maximal tracking rate = maximal arterial rate that will trigger ventricular pacing Once too high, will ignore the atrial impulses, resulting in dropped ventricular beats Revert to a 2:1 AV conduction (every second atrial beat results in a ventricular contraction), and returns to 1:1 when below max tracking rate again Rate-responsive pacing (aka. rate adaptive or rate modulated) = used when native SA node cannot increase HR to meet metabolic needs (e.g. Exercise) Can sense body’s need for increased Q Max sensor rate = highest rate the pacemaker will pace the ventricle in response to a sensor-driven rate 19  Rate-responsive pacing during exercise Rate-modulated pacing limits exercise capacity due to limits on HR responses Sensors in the pacemaker sense exercise-induced changes and generate impulses to pace the heart Vibration of movement, anterior and posterior acceleration Create issues with stair climbing and decent Use of blended sensors (respiration and motion) measure workload through respiration and motion = more physiological rate response Closed-loop stimulation monitors/ processes myocardial contraction dynamics on a beat-to- beat basis Controlled by the autonomic nervous system and works better than accelerometer and no rate sensors in those requiring ≥80% pacing Benefits = better performance on ADL’s, a reduced orthostatic hypotension, improved chronotropic response closer to a normal heart rate 20  Implantable Cardioverter Defibrillators Designed to detect and terminate lethal arrhythmias with an electrical shock Life threatening ventricular arrhythmias and/or managing CHF symptoms Combined pacemaker implementation and ICD therapy can reduce mortality by 40% vs a pacemaker alone (15%) Exercise with an ICD has received less attention compared to pacemakers General guidelines follow those with any CV disease Training 20 beats below ICD activation threshold 21  Loop recorders Loop monitors Implanted diagnostic tool to monitor for cardiac arrhythmias NO therapy or intervention. Mostly use to investigate unexplained syncope and occasionally heart palpitations. Emerging indication that atrial fibrillation is linked to cryptogenic stroke (a stroke with no definite cause) Reprinted from APGL VOL. 47,NO 5, 2018 23 Exercise Testing and Prescription 25 Exercise Testing Clients will pacemakers should undergo exercise testing to provide appropriate rate responses Pacemaker settings can be adjusted to optimise responses during testing Including sensitivity, responsiveness to physiological changes, rate at which heart rate changes, minimum rate at rest and maximal Testing then informs settings to improve exercise capacity and reduce symptoms Establishing an upper rate limit Angina threshold (if applicable) Ischemic threshold (if applicable) 26  Testing can be with or without real-time ECG monitoring and optimal rate-responsive parameters Dependent on type of pacemaker, facilities, experience Informal testing Walking at a self-determined ‘casual’ pace followed by a brisk pace for 3 min each More appropriate for inactive clients ECG to determine sensor-driven cardiac rate Casual pace = 10-20 beats/min above lower rate limit Brisk pace = 20-50 beats/min above lower rate limit The 6MWT = good predictor of maximum O2 uptake thus a good alternative to formal testing protocols 27  Formal exercise testing More appropriate for active clients likely to reach the programmed maximum sensor rate Programming upper-rate improves exercise performance and exertional symptoms during low and high workloads Bruce and Naughton are limited in optimal programming for rate-responsive pacemakers Chronotropic assessment exercise protocol (more appropriate) 28  Exercise Prescription for Clients with Pacemakers The sensor-driven HR increase rate follows pacemaker algorithms Key parameters: slope of the HR increase/ decline; sensor sensitivity The pacemaker will follow the sinus rate up to a maximal tracking rate during exercise. The activity sensor can be programmed to allow a further increase in the paced rate to the maximal sensor rate in response to physical activity. If intensity continues, the pacemaker may reach maximal tracking rate or maximum sensor rate; where the heart rate will not increase further. If the native sinus rate continues to increase, the pacemaker will switch to an AV block mode. 1st to a Wenckebach-type block (allow gradual slowing of ventricles) Then if higher intensities = 2:1 block (mindful of sudden drop in HR) 30 DDDR pacing and physical activity Figure 18.6 DDDR pacing and physical activity. The pacemaker follows the sinus rate to a maximal tracking rate. In response to physical activity, the sensor driven response can drive the rate to the maximum sensor rate. The paced rate increases in response to programmed slope and threshold settings. 31  Sudden drops in HR need to be communicated with client’s GP/cardiologist Some aerobic modalities have challenges when increases in work are associated with increases in gradient rather than speed Minimal detection of changes in vibration Stationary cycling and stair climbing machines – increased feelings of fatigue compared to walking Figure 18.7 Figure 18.8 32 Type of pacemaker is important Fixed-rate pacemaker – Q and arterial pressure are increased by SV Target HR cannot be used RPE more suitable Monitor BP responses Intensity to be below angina/ischemic thresholds (if applicable) Rate-responsive pacemakers – mediate HR responses to exercise Type of sensor is important – affect the mode chosen RPE and MET equivalents applicable 33 Mode While HR is not used to set intensities, monitor to assess that the pacemaker is responding appropriately Aerobic exercise poses the greatest benefit Rate-responsive pacemakers – check that HR responses are appropriate for the workload Mindful of stationary cycle ergos and increasing slope rather than speed in treadmill Unusual SOB and fatigue may indicate rate-responsive pacing is not responding appropriately. Resistance training is safe provided no bars/weights come in contact with the pacemaker Avoid activities that have direct contact with the pacemaker (contact sports) 34 Frequency Will vary depending on goals of the client and intensity of exercise, however typically perform aerobic exercise 3-5 day/week → progression to daily Intensity Recommended range 40-85% VO2peak Primarily dependent on co-morbidities (i.e angina or CHF) Upper limits programmed Client’s with fixed-rate pacemaker should not exceed intensity in which BP begins to plateau with increased workload; use RPE and METs Rate-responsive = HR can used, but use with RPE and METs 35 Duration Follows general guidelines for health promotion: 20 – 60 min May be intermittent rather than continuous > 1000 kcal/wk Special Considerations If client experiences a second degree type I (Wenckebach) block during exercise it is likely due to the sinus rate exceeding the pacemaker’s maximal tracking or sensor rate. Reduce exercise intensity Sudden drops in HR = notify the doctor/cardiologist so it can be evaluated 36  Aerobic Training Following CHF guidelines; intensities ranging between 40-75% VO2peak (50-80% HRR; 11-14 RPE) Stable CHF = 3-5days/week May need to start with interval training (intermittent) Resistance Training RPE 12-15 12-25 reps (muscle endurance) with work to rest ration 1:2 Avoid upper body RT for a couple of months following implementation of pacemaker Implantable Cardioverter Defibrillators Exercise guidelines need to be set by the cardiologist Prescription should be age, health and functional capacity-specific (similar to those with CVD) Commence under supervision with HR monitoring To avoid unintended shocks, employ 20-30 beat below ICD activation limits 38  Week 10 SUBMIT ASSESSMENT 2 to EASTS BEFORE 11:59PM this Friday 3rd MAY WATCH ✓ Week 10 Lecture READ ✓ Online reading ✓ Ehrman chapter 18 ENGAGE ✓ Tutorial Thursday – exercise prescription and case studies 39