The Australian and New Zealand Cardiac Implantable Electronic Device Survey, Calendar Year 2021: 50-Year Anniversary.

BACKGROUND: A cardiac implantable electronic device (CIED) survey was undertaken in Australia and New Zealand for calendar year 2021. The survey involved pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs). The survey was conducted on the 50th anniversary of the first survey for both Australia and New Zealand in 1972; that initial survey being conducted by two of the current authors. RESULTS AND CONCLUSIONS: For 2021, there were 19,410 PMs (17,971 in 2017) sold in Australia for new implants and 2,282 (1,811 in 2017) sold in New Zealand. The number of new PM implants per million population was 755 for Australia (745 in 2017) and 446 for New Zealand (384 in 2017). Unlike previous recent surveys, the percentage of PM replacements compared to total sales in both Australia and New Zealand rose. Pulse generator types implanted were predominantly dual chamber; Australia 77% (73% in 2017) and New Zealand 70% (68% in 2017). There were 1,509 biventricular PMs implanted in Australia (1,247 in 2017) and 172 in New Zealand (118 in 2017). Transvenous pacing leads were >90% active fixation in the atrium and ventricle. There was an increase in ICD usage with Australia 4,519 new implants (4,212 in 2017) and New Zealand 449 (396 in 2017). New ICD implants per million population were 187 for Australia (175 in 2017) and 88 for New Zealand (90 in 2017). For the first time the survey included implantable event monitors with 6,933 being implanted in Australia. However, for proprietary reasons, survey figures for subcutaneous implantable defibrillators, leadless pacemakers and conduction system pacing have not been included. Both Australia and New Zealand have high PM and ICD implant numbers compared to the rest of the Asia Pacific region.

Aberrant Ventricular Conduction: Revisiting an Old Concept.

The well-defined concept of aberrant ventricular conduction was introduced over 100 years ago and, despite advances in cardiac physiology and electrophysiologic testing, it is still widely misunderstood. Aberrant ventricular conduction is due to physiologic refractoriness of the His-Purkinje system and in most cases does not reflect underlying conduction system disease. Electrophysiologically, aberrant ventricular conduction can manifest with premature atrial ectopics, the Ashman phenomenon with atrial tachyarrhythmias, concealed conduction, echo beats and with the sinus mechanism including rate dependent bundle branch block, bradycardia dependent bundle branch block and early sinus beats. It is important to recognise aberrant ventricular conduction in the context of a broad complex tachycardia, as the differentiation between supraventricular tachyarrhythmias with aberrant ventricular conduction and ventricular tachyarrhythmias carry different therapeutic and prognostic implications. This review will define the ECG footprints of aberrant ventricular conduction to allow accurate ECG interpretation.

The Development of Pacemaker Programming: Memories From a Bygone Era.

Programmability is a stable, reversible change in the operating parameters of a cardiac implantable electronic device. The era of non-invasive programming began in 1972, with the development of a dedicated hand-held battery-operated device. Prior to this, there had been crude attempts, involving invasive procedures or a magnet, to change the pacemaker operating parameters. A non-invasive programming system requires an implanted pulse generator and an external programmer, communicating via an energy link. This was initially a pulsed magnetic field allowing opening and closing of a reed switch in the pulse generator in synchrony with the pulses. Soon after, radiofrequency communication was introduced and involved transmission of pulsing on-off radiofrequency bursts, which allowed complex encoding, that recognised the implanted hardware, prevented mis-programming, had security features and confirmed successful programming. As programming became more complex and sophisticated, programmers evolved into desktop models with programming wands and printers. By 1978, multiprogrammable programmers with bidirectional telemetry were introduced and became a driving force in the development of new cardiac implantable technologies and devices.

The Footprints of Pacing Lead Position Using the 12-Lead Electrocardiograph.

The 12-lead resting electrocardiograph (ECG) of a patient with an implanted cardiac pacemaker is a snapshot of cardiac electrical activity at the time of recording and may provide valuable information on both pacemaker function and malfunction, as well as identifying the position of pacing leads in the heart. The traditional site for atrial pacing is within or adjacent to the right atrial appendage and paced P waves on the ECG have a normal frontal plane axis, whereas the traditional site for ventricular pacing is at the right ventricular apex with the ECG demonstrating a left bundle branch block configuration and a left axis. More recently, ventricular leads and to a lesser extent, atrial leads have been positioned in alternate non-traditional sites resulting in 12-lead ECG appearances which have characteristic features, that are generally poorly recognised. Left ventricular pacing results in a right bundle branch block configuration and an axis dependent on the position of the lead in the ventricle. This review will describe the ECG patterns of pacing lead positions in the right atrium and ventricle as well as positions in the left ventricle, whether intentional or unintentional.

Rate Adaptive Pacing: Memories From a Bygone Era.

With the recognised physiologic value of dual chamber pacing, there was, at the commencement of the 1980s, an intense search for sensors to enable ventricular pacemakers to alter the pulse repetition rate in response to physiologic demand. Manufacturers fell into two main groups; those who chose highly physiologic sensors often requiring special pacing leads and those whose sensors allowed a standard pacing lead. Thirteen (13) sensors for rate adaptive pacing progressed at least to human investigational studies. Eventually the activity sensor, which responded quickly to exercise, but not to emotional stimuli or pyrexia and used a standard lead would predominate, with all manufacturers eventually accepting what was the least physiologic sensor investigated. The activity-based rate response was not dependent on cardiac or pulmonary disease, which could nullify the response with many of the other sensors. Three (3) other sensors survived that period and are still available today; minute ventilation, closed loop stimulation and central venous temperature, with the first two incorporated with activity as dual sensor systems. This review will outline the development of all the sensors used for rate adaptive pacing.

The Cardiac Pacemaker Clinic: Memories From a Bygone Era.

In 1963, soon after the first ventricular pacemakers were implanted at the Royal Melbourne Hospital, attempts were made to identify impending pacing failure, thus preventing sudden death in these very vulnerable patients. By 1970, patient numbers had increased, a formal regular pacemaker clinic was established, and guidelines and protocols developed. The clinic was staffed by a physician, a biomedical engineer and cardiac technicians. The unipolar, asynchronous, non-programmable pulse generators were powered by mercuric oxide/zinc batteries and implanted in the abdomen, using either transvenous or epimyocardial leads. Although, pulse generators were electively replaced at 3 years, most had already been replaced because of power source depletion, electronic failure or lead issues. Testing in all patients involved an electrocardiographic rhythm strip and electronic analysis of the stimulus artefact using a calibrated high-speed storage oscilloscope. Results were compared to previous studies and significant changes were interpreted as impending power source depletion. As a result of this testing, 97% of cases of impending power source depletion were detected prior to failure. These findings allowed testing each 4 months and for pulse generator life to be extended beyond three years. With ventricular triggered pulse generators, new testing procedures were designed. With time, visiting regional centres and clinical evaluation of new products became important functions of the clinic.

The Electrocardiographic Footprints of Ventricular Ectopy.

Ventricular ectopics, also known as ventricular extrasystoles, premature ventricular contractions or complexes (PVC) and ventricular premature depolarisations (VPD) are beats arising from within the ventricles. When they occur in groupings such as bigeminy, trigeminy, couplets and triplets they are referred to as ventricular ectopy. The electrocardiographic (ECG) footprints of a ventricular ectopic include a broad (>110 ms), premature, ventricular complex (QRS deflection); no evidence of pure atrioventricular (AV) conduction; a full, more than, or less than compensatory pause; and discordant QRS and T wave axis. Ventricular ectopy is a very common finding on Holter monitoring at all ages, but particularly in the elderly. In the otherwise normal heart, ventricular ectopy is generally infrequent and a benign finding, but in patients with heart disease, they may be a harbinger to more serious ventricular tachyarrhythmias. In this review, the range and manifestations of ventricular ectopy will be explored in detail with ECG examples.

Interpreting the Normal Pacemaker Electrocardiograph.

Modern cardiac pacing systems have sophisticated software to document, evaluate and record intrinsic and paced rhythms as well as correct pacing abnormalities and rhythm disturbances by applying algorithms, which are generally company specific. To the cardiologist and technologist, these algorithms may be difficult to interpret on both the 12-lead electrocardiograph (ECG) and Holter ambulatory monitoring recordings, which are usually performed because of patient symptoms or physician concern. The tracings may appear bewildering and mimic pacemaker malfunction, thus leading to unnecessary tests or even surgery. This review will define the common programmed pacemaker modes and describe a range of ECG appearances of normal pacemaker function during the application of testing, correcting or therapy algorithms.

The Australian and New Zealand Cardiac Implantable Electronic Device Survey: Calendar Year 2017.

BACKGROUND: A cardiac implantable electronic device (CIED) survey was undertaken in Australia and New Zealand for calendar year 2017 and involved pacemakers (PMs) and implantable cardioverter-defibrillators (ICDs). RESULTS AND CONCLUSIONS: For 2017, there were 17,971 (15,203 in 2013) new PMs sold in Australia and 1,811 (1,641 in 2013) implanted in New Zealand. The number of new PM implants per million population was 745 for Australia (652 in 2013) and 384 for New Zealand (367 in 2013). In both Australia and New Zealand, the number of PM replacements fell as a result of improved power source service life. Pulse generator types implanted were predominantly dual chamber; Australia 73% (74% in 2013) and New Zealand 68% (59% in 2013). There were 1,247 biventricular PMs implanted in Australia (661 in 2013) and 118 in New Zealand (83 in 2013). Transvenous pacing leads were overwhelmingly active fixation in both the atrium and ventricle. In Australia there was an increase in ICD usage with 4,212 new implants (3,904 in 2013), but a small fall in New Zealand to 396 (423 in 2013). The new ICD implants per million population were 175 for Australia (167 in 2013) and 90 for New Zealand (95 in 2013). There was a small reduction in biventricular ICDs in both Australia (2,195) and New Zealand (111).

The Footprints of Electrocardiographic Interference: Fact or Artefact.

Corporeal and particularly extra-corporeal interference is a very common problem encountered with both resting electrocardiograph (ECG) tracings and ambulatory recordings. The interference may be either electrical or mechanical and if severe, may affect the interpretation of the tracings. The interference, seen as artefact, can be divided into obvious, subtle or complicated. Obvious artefact may result from poor electrode attachment or body motion, whereas electrical interference is predominantly 50 or 60 Hz alternating current or radiofrequency waves from power lines, electrical equipment, mobile phones, fluorescent lights and electrical diathermy. Careful attention to the application of electrodes and finding the best environment for performing a 12-lead ECG will eradicate most interference. When subtle, the artefact can mimic cardiac arrhythmias, leading to incorrect interpretation of the tracings. There is also a complicated interference group, usually due to implanted cardiac electronic pacing devices and neurostimulators. These create persistent artefact, which may result in repeated unsuccessful attempts at procuring an artefact free tracing. This manuscript will describe the genesis of interference, how an ECG machine or monitor deals with interference and will discuss the common causes of interference. The characteristic patterns will be described and clues provided on how to differentiate subtle artefact from cardiac arrhythmias.

The Electrocardiographic Footprints of Atrial Ectopy.

Atrial ectopics, also known as a premature atrial complexes (PAC) or atrial premature depolarisations (APD), are supraventricular beats arising from a focus other than the sinus node. Because the various foci provide an array of electrocardiographic (ECG) appearances, an extensive, but confusing nomenclature has developed. Atrial ectopics are a very common finding on Holter ECG monitoring at all ages, the incidence increasing in frequency with age. In the otherwise normal heart, they are generally infrequent and an innocent finding, but in patients with heart disease, they may be a harbinger to more serious atrial tachyarrhythmias. In this review, the ECG footprints of atrial ectopy will be defined. These footprints include prematurity and P wave morphology. The associated features of variable atrioventricular (AV) conduction, variable post-ectopic pauses and variable QRS morphology due to aberrancy will also be discussed. Each of these features will be explained in detail with ECG examples.

The Spectrum of Ambulatory Electrocardiographic Monitoring.

Since its introduction as a clinical investigative tool, the 12-lead electrocardiograph (ECG) has been the gold standard for recognition of cardiac arrhythmias. The resting 12-lead ECG, however, gives only a rhythm snapshot in time, whereas arrhythmias maybe short-lived, paroxysmal and even asymptomatic making documentation in many patients very difficult. To overcome this, ambulatory ECG monitoring has been developed as a means of recording the ECG in patients over a set period of time, whether it be short-, medium- or long-term. With the miniaturisation of recording devices and advances in solid state technology, there has been a recent revolution in hardware design, so that the boundaries between these time-dependent devices have become blurred. Not surprisingly, the indications for monitoring have broadened as the quality and range of monitoring devices have become available. In this review, the indications for ambulatory ECG monitoring with emphasis on non-arrhythmic indications such as ST segment analysis, heart rate variability, signal averaged ECGs, diurnal QT and QTc analysis, obstructive sleep apnoea and vectorcardiography will be discussed. Also, the types of electrode systems used, lead placement, monitoring hardware, data collection, analysis and presentation as well as cost effectiveness of the investigation will be covered.

The Electrocardiographic Footprints of Wenckebach Block.

In 1899, Karel Frederik Wenckebach described a cardiac arrhythmia with periodic dropped beats now referred to as a Wenckebach sequence. This was later shown to be due to a block in the atrioventricular node, but today, we identify Wenckebach sequences throughout the heart with most being recognised on the surface electrocardiograph as characteristic footprints. This manuscript will revisit Wenckebach atrioventricular block, the typical features of which only occur in about 15% of cases, with the remainder atypical. Earlier reports regarded Wenckebach atrioventricular sequences as rare as they are only occasionally seen on the surface 12-lead electrocardiograph. Today, however, with the increased use of ambulatory Holter monitoring, Wenckebach atrioventricular sequences occur in 4-6% of all traces and are particularly common at night in the young. Most, but not all cases are benign and the clinical spectrum will be reviewed. Atypical Wenckebach atrioventricular sequences are a complex group which will be analysed in detail with a broad range of illustrations. Outside the atrioventricular conducting system, such as in the sinus node, Wenckebach sequences may not be obvious as they are partially hidden from the electrocardiographic tracing. However, by understanding the sequence footprints, clues are available in interpreting tracing with periodic pauses. Dual chamber paced rhythms may show Wenckebach sequences due to electronic control of the atrioventricular delay. Rarely exit blocks at the cellular level in the atrium, ventricle or at the pacing electrode-tissue interface can demonstrate Wenckebach sequences recognised on the surface electrocardiograph.

Twisted Leads: The Footprints of Malpositioned Electrocardiographic Leads.

BACKGROUND: Malposition of electrocardiograph (ECG) leads is poorly recognised even by cardiologists who report tracings. When ECG tracings are regularly performed by doctors, nurses or technicians, lead malposition is very uncommon particularly if the operator can also interpret the findings. However, a significant proportion of 12-lead ECG tracings are today performed in a doctor's surgery or by private pathology services, often in haste without sufficient attention to correct lead positioning. As a result, a variety of malposition combinations occur, which in turn may confuse the interpreter of the ECG tracing, leading to incorrect diagnoses. OBJECTIVES: To investigate various combinations of ECG lead malposition and determine if characteristic findings can be summarised into identifiable footprints. METHODS: In 10 normal subjects, 12-lead ECGs were performed with normal lead positioning as well as six limb lead malpositions and reversal of chest leads. RESULTS: In all subjects, there was consistency in the ECGs performed allowing the creation of five characteristic and easily identifiable footprints. CONCLUSIONS: A summary of the footprints of ECG lead malposition should be readily available for those who perform ECGs, those who interpret the tracings and those responsible for clinical care.

Injury to the coronary arteries and related structures by implantation of cardiac implantable electronic devices.

Damage to the coronary arteries and related structures from pacemaker and implantable cardioverter-defibrillator lead implantation is a rarely reported complication that can lead to myocardial infarction and pericardial tamponade that may occur acutely or even years later. We summarize the reported cases of injury to coronary arteries and related structures and review the causes of troponin elevation in the setting of cardiac implantable electronic device implantation.

The Australian and New Zealand cardiac pacemaker and implantable cardioverter-defibrillator survey: calendar year 2013.

BACKGROUND: A pacemaker (PM) and implantable cardioverter-defibrillator (ICD) survey was undertaken in Australia and New Zealand for calendar year 2013. RESULTS AND CONCLUSIONS: For 2013, PMs sold as new implants in Australia was 15,203 (12,523 in 2009) and implanted in New Zealand were 1,641 (1,277 in 2009). The number of new PM implants per million population 652 for Australia (565 were in 2009) and 367 for New Zealand (299 in 2009). Although PM replacements rose in New Zealand, there was a fall in Australia as a result of improved power source service life. Pulse generator types sold in Australia were predominantly dual chamber 74% (71% in 2009) and implanted in New Zealand 59% (54% in 2009). There were 661 biventricular PMs implanted in Australia (446 in 2009) and 83 in New Zealand (45 in 2009). Transvenous pacing leads were overwhelmingly bipolar with preferences for active fixation leads, although, since 2009, there has been a minor resurgence in Australia of passive fixation lead usage in the atrium from 20 to ∼24%. There was also a marked increase in the ICD implants with 3904 new implants in Australia (3555 in 2009) and 423 in New Zealand (329 in 2009). The new ICD implants per million population were 167 for Australia (160 in 2009) and 95 for New Zealand (77 in 2009). Biventricular ICD implants increased significantly in both Australia (2211) and New Zealand (118).

The cardiac implantable electronic device power source: evolution and revolution.

Although the first power source for an implantable pacemaker was a rechargeable nickel-cadmium battery, it was rapidly replaced by an unreliable short-life zinc-mercury cell. This sustained the small pacemaker industry until the early 1970s, when the lithium-iodine cell became the dominant power source for low voltage, microampere current, single- and dual-chamber pacemakers. By the early 2000s, a number of significant advances were occurring with pacemaker technology which necessitated that the power source should now provide milliampere current for data logging, telemetric communication, and programming, as well as powering more complicated pacing devices such as biventricular pacemakers, treatment or prevention of atrial tachyarrhythmias, and the integration of innovative physiologic sensors. Because the current delivery of the lithium-iodine battery was inadequate for these functions, other lithium anode chemistries that can provide medium power were introduced. These include lithium-carbon monofluoride, lithium-manganese dioxide, and lithium-silver vanadium oxide/carbon mono-fluoride hybrids. In the early 1980s, the first implantable defibrillators for high voltage therapy used a lithium-vanadium pentoxide battery. With the introduction of the implantable cardioverter defibrillator, the reliable lithium-silver vanadium oxide became the power source. More recently, because of the demands of biventricular pacing, data logging, and telemetry, lithium-manganese dioxide and the hybrid lithium-silver vanadium oxide/carbon mono-fluoride laminate have also been used. Today all cardiac implantable electronic devices are powered by lithium anode batteries.

Capturing the His-Purkinje system is not possible from conventional right ventricular apical and nonapical pacing sites.

INTRODUCTION: Direct His bundle capture may negate ventricular electrical dyssynchrony induced by right ventricular (RV) apical pacing. We sought to evaluate if direct His bundle pacing is possible with conventional pacemaker lead implantation at various sites in the RV. METHODS: Consecutive patients underwent RV pacing using standard implantable active fixation pacing leads in a random order in the RV outflow tract, middle RV, and RV apex at stimulation threshold and at increasing voltages of 2.5, 5, 7.5, and 10 volts (V). At each location, QRS width and morphology on 12-lead electrocardiograph (ECG) were compared in sinus and paced rhythm at the different voltages. RESULTS: Twelve patients underwent a total of 2,160 paced QRS measurements. Progressive increases in stimulation voltage did not change QRS morphology or duration regardless of site of pacing (RV outflow tract, middle RV, and RV apex) in any of the 12 ECG leads. In addition, apart from the stimulation threshold between the RV outflow tract and RV apex, there was no statistically significant difference in QRS duration between the three pacing sites. CONCLUSION: In patients with a baseline normal QRS duration, none of the three conventional RV pacing sites were able to produce QRS narrowing and capture the His-Purkinje system. Furthermore, based on paced QRS duration as an indirect surrogate of electrical LV dyssynchrony, there was no clear advantage of one pacing site over another.