Introductory Chapter: Modern Methods and Devices for Cardiac Rhythm Management

1. Introduction

Cardiovascular disease (CVD), which refers to interdependently related heart and blood vessel problems, is currently known to be one of the leading causes of death in the world. The World Health Organization (WHO) reported that CVD is responsible for one-third of all deaths globally. The annual cost of CVD to the economy is estimated about £25 billion in the UK and over $500 billion in the USA. The prevalence and cost of CVD raise an urgent need for solutions to elevate standards of care and improve patient outcomes.

A significant proportion of CVD is associated with heart rhythm problems, which means that the rhythm responds poorly or not at all to the physiological needs of the body. There are both an excessively slow rhythm (bradycardia) and an excessively high rhythm (tachycardia) or an unstable rhythm (arrhythmia, rhythm disturbances). All these incorrect rhythm phenomena are life-threatening. Fortunately, many methods, techniques, and tools have been developed and successfully applied today to stabilize and control the heart rate (HR). Modern implantable devices and treatment methods, including minimally invasive surgery, have been developed for cardiac rhythm management and avoiding heart failure. These measures benefit many millions of people every year [1].

Not only electrical pacing [1, 2, 3], but also ablation is an effective minimally invasive surgical method for reducing and blocking arrhythmic phenomena [4, 5], both as an independent treatment method and in conjunction with pacing therapy. In the following, we will look at modern cardiac rhythm management methods and devices in more detail together with some important medical aspects of their use.

2. Making the devices smarter

2.1 Historical glimpse

The implementation of artificial pacing goes back more than 70 years [6]. The first electrical devices connected to a patient to provide electrical impulses to stimulate the heartbeat in bradycardia cases have been known since the 1950s. Thanks to the invention of silicon transistor in 1956, the 1958 was a remarkable milestone. In winter 1958, engineer Earl Bakken of Minneapolis, USA, co-founder of Medtronic company, produced the first wearable external pacemaker for a patient of C. Walton Lillehei. On October 8, 1958, the first electronic pacemaker was implanted by Senning and Elmqvist in Solna, Sweden. In 1958, Dr. William Chardack teamed up with engineer Wilson Greatbatch and Dr. Andrew Gage to implant an electrode in a dog attached to a pulse generator. They worked for the next two years to refine their design of a unit. They implanted the pacemaker into a man and commercialized the product in 1960.

All the early pacemakers maintain the same constant pulse rhythm for long periods of time. A pacemaker in demand also appeared in the 1960s, which only paced when stimulation was required (when natural pacing ceased). In addition, the dual-chamber pacemaker with synchronized pacing of both atrium and ventricle (known as physiological pacing) was first designed in 1960s [6]. In the end of this period are included also first attempts to use the variable pacing rhythm to adapt it to a physiological need, i.e., the metabolic requirement corresponding to body’s work known as rate-responsive pacing [7]. The medical use of rate-responsive pacing began in early 1980s [8].

2.2 Sensing and sensors for the adaptive and closed-loop control of pacing rate

The problem is: how to get information for the adjusting of pacing rate? Obviously, it is almost impossible to use the body’s natural sensing nodes for this purpose; the help of artificial means or sensors is required [7, 8]. Some of the proposed information sources for regulating the pacing rate are oxygen saturation level, venous pH, QT interval, activity of body motions, respiratory rate, minute volume (MV), stroke volume (SV), central venous temperature, peak endocardial acceleration, and electrical impedance changes of the right ventricle (reflects a stroke volume) during the whole cardiac cycle. QT interval (reflecting both physiological and mental status) and minute volume (MV) sensors based on the electrical bioimpedance measurement of a tidal volume (TV) of lungs and stroke volume (SV) and cardiac output (CO) sensors based on the measurement of the internal bioimpedance of the left ventricle have been lifted onto the shield. There is no single sensor giving adequate information for regulating the pacing rate. The carefully weighted resultant from multiple sensors can provide reliable information for setting the pacing rate. Artificial intelligence methods, the results of which are under strict supervisory inspection to avoid the possibility of fatal error, can be the direction for future developments [9, 10, 11].

2.3 Principles of bioimpedance sensing

For bioimpedance sensing, a low-level microamp (μA) range alternating current (AC) excitation of kilohertz range (kHz) is delivered from one electrode to another, and the caused voltage drop is measured. For example, these electrodes can be the pacing electrodes inside the right ventricle (in apex) and the case of implanted pacemaker [9]. Between these electrodes are situating both breathing lungs and contracting/relaxing myocardium of the beating heart [9, 10, 11, 12, 13]. As a result, we can measure the dynamic impedance of breathing lungs Z_L(t) and of working myocardium Z_M(t). The impedance Z_L(t) gives the bases for calculating the tidal volume (TV), respiration rate (RR), and minute volume MV = TV × RR in liters. It is well known how the minute volume (MV) of breathing correlates with the physical work W of patient’s organism, which, in turn, determines the need for a fresh oxygen-rich blood expressed through a stroke volume (SV) and cardiac output CO = SV × HR in liters. Heart rate (HR) is equal to pacing rate (PR) for pacemaker patients. Therefore, the pacing rate (PR) determines the amount of oxygen-rich blood (CO) directly. The described mechanism forms the pacing rate (PR) management principle in modern cardiac rhythm devices. However, because we do not know exactly the functional relationship between the required blood volume (CO) and PR, it becomes necessary to measure the effective CO and compare it with the desired comparison and negative feedback. With this, we achieve the automatic PR adjustment based on the feedback principle of closed-loop control [8, 14]. The feedback mechanism is provided determining the resulting stroke volume (SV) and cardiac output (CO) via measuring the electrical bioimpedance Z_V of the right ventricle, which is inversely proportional to stroke volume [13].

2.4 Supervisory control of pacing rate limits

For the benefit of the patient, it is reasonable not to rigidly fix the upper and lower pacing rate limits, but to leave them sliding within certain limits depending on the patient’s current medical condition. At the same time, however, both underpacing and overpacing must be strictly avoided. Both are dangerous for life, especially overpacing that can cause myocardial infarction, and must be strictly avoided [13, 14]. The principle is that the body demand for oxygen-rich blood must not exceed the ability of patient’s injured heart. Energy balance between the energy supply and energy consumption of myocardium must be fulfilled in every moment of heart work. The balance conditions and overpacing risk were derived from the measurement of myocardial impedance Z_M [12]. Underpacing risk was derived from the bioimpedance Z_V measurement of ventricular volume—too large volumes indicate underpacing danger for the myocardium [12, 13].

2.5 Traditional and novel methods for delivering the pacing pulses

2.5.1 Traditional single-chamber pacing

The most known location of the pacing electrode is the tip (apex cavity) of the right ventricle. This solution has been working well for many decades in cardiac pacemakers to prevent bradycardia since the invention of the portable/wearable pacemaker in the 1950s and the widespread use of the implantable device in the 1960s [6]. In addition, the most modern leadless pacemakers [15] use only the ventricular pacing. Many implantable cardioverter defibrillators (ICDs) use only the ventricular pacing to restore unstable or failed heart rate to its normal beating through timed electrical shock delivery.

2.5.2 Dual-chamber pacing

Later, in the mid-1970s, a dual-chamber pacing—one pacing electrode in the ventricular apex and another in the atrium of heart’s right side—has been introduced in medical practice [6]. The dual-chamber pacing most closely resembles the normal physiology of cardiac initiation, compared to other pacemaker modes. Therefore, this device is also called as a physiological pacemaker, which ensures atrium-ventricle timing (synchronization) and suppresses atrial fibrillation (AF), that is, reduces the risk of pacemaker syndrome, which represents the clinical consequences of atrioventricular dyssynchrony after pacemaker implantation. Dual-chamber implantable cardioverter defibrillators (ICDs) provide dual-chamber pacing to prevent both atrial fibrillation and supraventricular tachycardia not available in single-chamber ICDs [16]. Nowadays, most of the currently implanted ICD devices provide overdrive pacing to convert ventricular tachycardia (VT) or deliver electrical shocks to restore normal rhythm in the case of sustained ventricular tachycardia or ventricular fibrillation.

2.5.3 Biventricular pacing

Biventricular pacing, also called as cardiac resynchronization therapy (CRT), is for people with heart failure due to abnormal work of electrical systems in the heart. The CRT system consists of two components—the pulse generator, or device, and thin, insulated wires called leads. A CRT device delivers tiny amounts of electrical energy to the heart through these leads to restore the normal timing of heartbeats, causing both the ventricles to pump more efficiently. There are two types of CRT devices. One is a special kind of pacemaker called as a cardiac resynchronization therapy pacemaker (CRT-P) or “biventricular pacemaker” [17]. The other is one includes additionally a built-in implantable cardioverter defibrillator (ICD). This device is called a cardiac resynchronization therapy defibrillator (CRT-D), which is used to treat ventricular tachycardia and ventricular fibrillation and avoid sudden cardiac arrest.

The CRT-P device functions like a normal pacemaker to treat slow heart rhythms, as well as delivers small electrical impulses indirectly, however, to the left ventricle to help the both the ventricles contract at the same time.

The CRT-D device combines a dual-chamber pacemaker and a defibrillator. It has the same three leads as a CRT-P, but it can also deliver a high-energy shock to treat fast ventricular arrhythmias (VAs) such as ventricular tachycardia or ventricular fibrillation, which can cause sudden cardiac arrest.

2.5.4 Alternative pacing sites (septum pacing)

It expected that the right ventricular septal pacing is a valid alternative to apical pacing, which most mimics normal physiology. Whether the pacing of right ventricular outflow tract septum (RVOTS) is superior to right ventricular apex (RVA) pacing with respect to cardiac function is still not fully clear. Placing the pacing electrode on the mid-septum may be more challenging than the RVOTS case. Anyway, the septal pacing is of great interest [18]. There is no need to pass the tricuspid valve, but the outcome is similar to right ventricle pacing.

His bundle pacing in humans was first reported in 2000 [19]. Permanent His bundle pacing is an emerging technique to deliver a more physiological pattern of ventricular pacing and has the potential to mitigate the adverse consequences of chronic right ventricular pacing and promote atrioventricular and intraventricular synchrony. His bundle pacing is a technique that uses the native His-Purkinje system to maintain a physiological pattern of ventricular activation. It is a good alternative to RV and biventricular pacing. However, it is currently undergoing clinical trials to verify whether it has any clinical advantages over RVP or biventricular pacing.

3. Radiofrequency ablation to avoid arrhythmias

3.1 The role of ablation in suppressing arrhythmias

Though the electrical pacing enables the suppressing of suddenly appearing arrhythmic phenomena, the most effective outcome can be achieved by using ablation techniques and, sometimes, both ablation and pacing methods together.

Radiofrequency ablation (RFA) has revolutionized the treatment of both supraventricular and ventricular arrhythmias. However, conventional, X-ray-guided mapping techniques have a limited utility in the ablation of more complex arrhythmias, such as in atrial tachycardia, atrial fibrillation (AF), and ventricular tachycardia (VT). By using 3D technologies and catheters permitting faster acquisitions, in association with high-performance imaging techniques, the development of novel mapping systems has led to the overcoming of these limitations [4].

3.2 Atrial fibrillation

In terms of atrial fibrillation, the development of pulmonary vein (PV) electrical isolation has contributed to a significant reduction in the recurrence of AF, particularly in patients with paroxysmal AF. It has previously been shown that the empirical isolation of all four PVs produces better results than the focal ablation of triggers at the PV level or isolation of fewer PVs [4, 5]. Furthermore, in terms of PV isolation, high-power short-duration (HPSD) applications have been shown to be superior to low-power long-duration ablation [20]. In patients with persistent AF and significant remodeling of the left atrium, the use of substrate-based techniques in addition to PV isolation has shown better results [21]. Non-PV electrical activity originating at the level of the Marshall vein, the coronary sinus, and the superior vena cava is another source of AF in some patients; thus, both focal ablation and electrical isolation of these veins have been studied in selected patients [22].

Although previous research has shown an improvement in these patients’ ablation results, the long-term impact on outcomes is still unknown, and more research is needed to prove the efficacy of these techniques.

3.3 Ventricular arrhythmias

Ventricular arrhythmias (VAs) can occur on both the normal and abnormal structural hearts. Structural heart diseases are most frequent, and it is well known that cardiomyopathies lead to cardiac injury, which is clinically expressed by VAs. In contrast to ischemic dilated cardiomyopathies (DCMs), the substrate for VAs in nonischemic DCM is not well defined, and patients may present with any type of VAs, including premature ventricular complexes, monomorphic or polymorphic ventricular tachycardia (VT), and ventricular fibrillation [4, 23, 24].

The two main strategies in the ablation of VTs are represented by the detection of the critical isthmus of the VT circuit and the modification of the arrhythmogenic substrate. However, considering the distribution of the scar in patients with DCM, endocardial mapping alone is often insufficient. Previous research demonstrated that combined endocardial and epicardial ablation improved the procedures results, and the mid-term outcomes in patients with previously failed endocardial only ablation and also as a first-line strategy [25, 26].

3.4 Epicardial ablation and high-power short-duration ablations

Two new techniques used for the catheter ablation of cardiac arrhythmias are epicardial ablation and high-power short-duration ablation. The approach in epicardial ablations is similar to that in endocardial ablations, including activation mapping, entrainment mapping, pace mapping, and substrate mapping. However, the optimal access technique and the better prevention of complications remain a subject of future research.

Electrophysiologists should be well-versed in the indications and contraindications of the epicardial approach, as well as different puncture techniques and periprocedural complications. From the posterior approach, anterior approach, needle-in-needle approach, fluoroscopic method, and wire-guided puncture technique, interventionists can select the most appropriate strategy. The surgical method should be considered in the event of pericardial adhesions. Contrast-enhanced computed tomography may have additional benefits, primarily in terms of detecting abnormal anatomical, dynamic, and perfusion characteristics, but also in terms of distinguishing between epicardial fat and scar tissue.

High-power short-duration RFA is defined in a variety of ways, with power ranging from 40 to 90 W and lasting less than 15 seconds per lesion. PV isolation has been a standard strategy for the catheter ablation of AF since the pioneering work of Hassaguerre et al. in 1994 [27]. However, the long procedure times and high rates of PV reconnection that result have sparked interest in using high-power short-duration ablation. To determine the efficacy and safety profile of this novel technique, researchers looked at the particular biophysical ablation characteristics of HPSD ablation.

3.5 Conclusions on radiofrequency ablation

In conclusion, while RFA has demonstrated significant benefits in the treatment of arrhythmias, some issues remain debatable and long-term results are still needed.

4. Summary

Heart rate management and control continues to be a serious problem in medicine, requiring a variety of measures, including the development of implantable cardiac devices and, in particular, the methods and medical indications for their use in the interests of an ever-widening cohort of patients in their various life and health conditions.

Such situations as pacing after syncope, pacing following transcatheter aortic valve implantation, and cardiac resynchronization therapy for both heart failure and the prevention of pacing-induced cardiomyopathy have been of ongoing interest. Automatic pacing rate control responding to the metabolic demand of the organism and pacing in various diseases of the heart, including new diagnostic tools for semiautomatic decision-making on pacing, as well as pacing the His bundle and the left bundle branch, are of intensive recent research.

New techniques are introduced for the catheter ablation of cardiac arrhythmias: epicardial ablation and high-power short-duration radiofrequency ablation. Although both the methods have demonstrated significant benefits in the treatment of arrhythmias, some issues remain debatable and long-term results are still needed. The same goes for the application of both the methods of ablation and pacing, together, although it has been used in medical practice. The combined application of both the methods of ablation and pacing has been used in medical practice, and the effectiveness of the results requires continued research. The optimal access technique and the better prevention of complications remain a subject of future research [28, 29, 30, 31, 32].

Finally, the experienced authors of the chapters in the present book will certainly make a significant contribution to the progress of cardiac rhythm management. Moreover, IntechOpen has made substantial contributions to the publishing of scientific and practical results in the field, and a number of books have been issued during the last decade [33, 34, 35, 36].