TY - JOUR
AU - Daubert, Jean-Claude
AB - Abstract This paper reviews the beginnings and the evolution of cardiac resynchronization therapy (CRT), which required technological innovation and manual dexterity for its application. The expectations of CRT and its problems today are analysed. The frequent need for CRT with defibrillation capacity is discussed. Future development of CRT is anticipated. Cardiac resynchronization therapy, Heart failure, Implantable cardioverter defibrillator Introduction Cardiac resynchronization therapy (CRT) was conceived in the mid-1990s. It offered not only atrioventricular (AV) synchronization as had previously been used in dual-chamber pacing but also synchronization of the two ventricles. By pacing the region of the left ventricle (LV) with the most delayed activation, it was possible both to improve interventricular synchrony and the synchrony of the LV itself. At the outset of CRT, many pacing problems had already been overcome. For example, rate modulation in the absence of normal sinus node behaviour, mode switching from DDD to VVI or DDI for atrial tachyarrhythmias, and algorithms to avoid pacemaker-mediated tachycardia were all standard and well understood in the dual-chamber device of the mid-1990s. Some inspired work anticipated the introduction of CRT. Most notable was that of the Rennes group in attempting to resynchronize the atria in interatrial conduction block1 and in Lausanne, where desynchronization of the LV by right ventricular (RV) apical pacing was employed to reduce LV outflow obstruction and treat hypertrophic obstructive cardiomyopathy.2 Dual-chamber pacing was initially thought to benefit heart failure patients3 but when more patients were studied, long-term improvement could not be consistently demonstrated.4–6 The investigations of Prinzen’s group served to underline the negative effects on coordination of LV contraction imposed by RV apical stimulation.7 The scene was then set for the logical step of resynchronizing the ventricles and in appropriate patients simultaneously resynchronizing the two atria at the same time. 1994, the first four-chamber cardiac resynchronization therapy implantation The first published patient8 was 54 years old: in New York Heart Association class IV, presenting non-ischaemic dilated cardiomyopathy, ejection fraction (EF) < 35%, QRS duration > 150 ms (left bundle branch block pattern), and prolonged interatrial conduction. The patient was receiving maximal drug therapy including intravenous positive inotropic agents and was not considered a candidate for cardiac transplantation due to chronic alcoholism. An invasive haemodynamic study was made comparing standard DDD pacing with the RV lead either in the apex or in the outflow tract and atrio-biventricular pacing under the same conditions. The biventricular approach demonstrated a dramatic and reproducible increase in cardiac output, decrease in pulmonary capillary pressure, and suppression of mitral regurgitation. This study prompted implantation of a long-term four-chamber device. An LV screw-in lead was placed epicardially by a thoracic surgeon, together with right atrial, left atrial, and RV leads. The two atrial leads were connected to the atrial port and the two ventricular leads were connected to the ventricular port of a conventional dual-chamber pacemaker (Chorus 2, Ela Medical, Le Plessis Robinson, France) via two Y-adaptors. The patient proved to be a CRT responder. During the first night after implantation, he had a huge diuresis, inotropic agents were discontinued 48 h later, and he was discharged from hospital 1 week after the implant. This experience was successfully extended to benefit other patients.9 The report of this series of patients9 commenced the era of CRT. However, the concept was not really new, as it had been propounded in 198310 as an adjunct to cardiac surgery, using an LV screw-in epicardial electrode. Fusion beats were obtained by adjustment of the AV delay, resulting in normalization of the LV activation sequence when studied by angio-scintigraphy with phase analysis. The need for epicardial lead placement was potentially hazardous in severely ill heart failure patients and there was an appreciable mortality of the procedure. Despite this negative aspect, many survivors received obvious benefit in terms of mobility, quality of life, and, seemingly, prolongation of life. Development and worldwide spread of the technique Previous work was instrumental in developing CRT. The resynchronization of the atria1 and the pacing lead designed to achieve it (Medtronic, Minneapolis, MN, USA; Model 2188) inspired insertion of this lead into a coronary vein draining the left lateral wall of the LV (Figure 1).11 In some patients, epicardial LV lead placement was, thereby, avoided. A better lead presented itself (Vitatron, Dieren, NL; Model ISP13); being thinner and more flexible, it was easier to achieve insertion in the target coronary vein but success rates remained low (55–60%). Further advances came with the use of introduction sheaths, coronary venography (Figure 3), and the Medtronic 2187 lead, which had a more favourable shape and flexibility. Results became sufficiently predictable to permit randomized controlled trials, MUSTIC,12 which ran simultaneously with PATH-CHF.13 These were the first attempts to acquire an evidence base for the revolutionary concept of CRT. These studies demonstrated the functional benefits of the biventricular technique and a huge reduction in re-hospitalization rates. Eighty-eight per cent of the LV leads were still functioning correctly after 1 year. The MIRACLE trial confirmed these results, using the same Medtronic lead as in MUSTIC in a much larger scale study, designed in parallel.14 Implanters then started performing coronary sinus angiograms, providing information about coronary sinus anatomy and by this means better defining the procedure. The next important step came from Guidant, St Paul, MN, USA, with the Easytrack lead, which was an over-the-wire design, requiring combined angioplasty and device implantation skills. A long catheter had to be introduced into the coronary sinus; then an angioplasty wire was passed to the targeted vein defined by angiography. The pacing lead was then slid along the wire to the desired pacing site. Those experienced in coronary angioplasty had a skill advantage at this stage, and the failure rate of LV leads fell below 10%. The coronary sinus route with specifically designed leads represented the key to CRT development worldwide. The most recent step was the demonstration that implantable cardioverter defibrillator (ICD) technology should be combined with resynchronization. The MADIT trials15,16 indicated that patients with previous myocardial infarction and low EF should receive an ICD. The SCDHeFT trial confirmed the benefit of systematic use of an ICD in a population of heart failure patients with low EF.17 The COMPANION trial,18 which compared three arms, CRT-pacing (CRT-P) or CRT-defibrillator (CRT-D) plus optimal therapy with optimal therapy alone in ischaemic and non-ischaemic patients, showed an all-cause mortality and all-cause hospitalization reduction in favour of CRT. These results were confirmed by CARE-HF,19 with no difference between CRT-P and CRT-D. However, CRT-D was better than CRT-P when the secondary end-point of risk of death from any cause was considered but the trial was not designed to permit this conclusion. Nevertheless, the electrophysiological community jumped to this conclusion and CRT-D technology has become widely implanted. Benefits of 13 years of left ventricular lead implantation Two types of lead are currently available (Figure 2). There are pre-shaped leads, the first to be developed, with various curves, which are advanced by the use of conventional stylets. They are stiff and of large diameter, making them suitable for large coronary veins with smooth take-off from the coronary sinus. Subsequently developed are thinner over-the-wire leads, which are often also pre-shaped, offering the possibility of catheterizing both large and thinner, tortuous veins and achieve stability in both types. Some tools are very frequently required:Despite these technological improvements, the present implant failure rate remains stable, although low, at about 5%. Recent study reports probably underestimate the real number of failures. The main reasons for failure today are phrenic nerve stimulation when no other suitable position is available, inability to capture the LV wherever the lead can be placed, and lack of stability of the lead. From the implanters' point of view, the main problem remaining is the duration of the procedure in many difficult cases, especially when upgrading a previous standard pacing system. long pre-shaped sheaths to catheterize the coronary sinus and provide back-up when attempting insertion of the lead into the targeted vein; various multipurpose angiographic or electrophysiological catheters are especially useful when the right atrium is greatly enlarged, when the coronary sinus ostium is high in the right atrium, or when the sinus itself is tortuous; balloon catheters for coronary sinus angiography (Figure 3); venoplasty equipment when target veins are too narrow or tortuous. Optimal LV lead implantation is obtained when:The most important remaining problem is the rate of non-response, despite implantation of functional leads, estimated at 30% in the MIRACLE and CARE-HF trials. Non-response probably relates to selection criteria, device programming, lead position or an insufficient number of leads. it is technically possible; with an acceptable stimulation threshold of <2 V; in a lateral position20; with adequate stability. Right heart leads The right atrial lead Heart failure patients, candidates for CRT, frequently present inter- or intra-atrial conduction disorders. Biatrial pacing as proposed in the 1980s and reported in the 1990s1 was an attempt to reduce interatrial delays to prevent atrial tachyarrhythmias mostly arising from the left atrium. Today, the possibility of left atrial ablation exists as an effective alternative. The pacing lead configuration of the first CRT recipient included dual-atrial leads, which was adopted in 25% of subsequent patients in our series.21 However, left atrial capture was not guaranteed in the long-term and two leads were required in the coronary sinus, which had to be connected to a four-port device. Septal atrial pacing from the right atrium, either the coronary sinus ostium or the high septum, has been proposed to minimize interatrial conduction delay. Whenever possible, either of these techniques is to be preferred over a separate lead for the stimulation of the left atrium. Haemodynamic benefit can be offered by providing the same AV delay for both sides of the heart. This concept was initially studied in hypertrophic obstructive cardiomyopathy. Patients who usually have a short PR interval and whose ventricles must be fully depolarized from the RV apex so as to achieve the desired desynchronization effect ameliorating LV outflow obstruction need very short-programmed AV delay. However, when interatrial conduction delay coexists in these patients, left atrial contraction is delayed with reduced LV filling, which may sharply decrease the beneficial effect of the reversed LV contraction pattern. Heart failure patients with prolonged interatrial conduction times present a similar situation. Correction of their inter- and intraventricular delay without attending to interatrial conduction risks inappropriate AV timing either on the right or the left side of the heart. Positioning the right atrial lead to reach the high atrial septum is straightforward. The lead should be inserted into the RV, then a stylet in the shape of a bishop’s staff is introduced to the tip of the lead. The lead is withdrawn to the right atrium smoothly across the superior aspect of the tricuspid valve, usually prompting some premature ventricular complexes (PVCs). The shape of the stylet guides the lead tip to the high septal site between the septum and the anterior wall of the right atrium. The right ventricular lead The literature provides evidence that RV pacing from the apex can be deleterious to haemodynamic performance in the long term. Alternative pacing sites have been attempted in the RV but proof that any other position should be preferred is lacking for all patients not least those who require CRT. One of the initial papers on CRT indicated, using acute haemodynamic parameters, that the optimal position of the RV lead was individual during biventricular pacing.22 Some patients will require an apical position, others a mid-septal, and others different sites. This may be explained by the pattern of heart disease, the location of fibrosis, the position of the LV lead, the size of the RV, and some additional, as yet, unknown features. The implanter’s skills also play a part, as there are no specific tools to guide the lead into various sites. Accessing the anterior septum from the pulmonary valve to the apex is not difficult. The lead should be introduced into the pulmonary artery. A straight stylet is then passed to the lead tip and is slowly withdrawn. The tip will follow the angle between the RV septum and the anterior wall, which is likely to be associated with runs of PVCs. Reaching real septal or anterior wall positions is more difficult but occasionally some patients may benefit from the use of such unconventional sites. After positioning the lead postero-anterior and left anterior, oblique views allow accurate determination of the final position. Some methods of RV lead placement are electrocardiographic and depend on the reduction of the delay between LV and RV local activation analogous to the method of pacing at the contracting segments with the most delay.23 This procedure raises a risk of stimulating at a fibrotic area, thus effectively delaying electrical propagation and failing to provide resynchronization. Other workers prefer a systematic approach placing the RV lead either at the apex or in the septum. The goal is for CRT to correct dyssynchrony, the best results occur if the stimulation sites compensate for the abnormalities identified prior to implantation24 and optimal lead placement should have a measurable impact on haemodynamics. Presently, the simplest, most reliable, and reproducible non-invasive technique for the assessment of benefit is echocardiography but there are many approaches to optimal parameters and their measurement.25–28 In our department, all dyssynchrony at atrial, AV, inter-, and intraventricular levels and only those within the LV are taken into account. Results are assessed by long-standing haemodynamic techniques.29,30 The pacing system, device, and leads are merely the electrical tools to achieve the mechanical objective, which prompts us to suspect that more than two ventricular leads will be necessary in the future in order to decrease the number of non-responders.31 Cardiac resynchronization therapy-defibrillator The aims of CRT-D devices are two-fold: both to provide atrial, AV, and ventricular resynchronization and, at the same time, to protect the patient against life-threatening ventricular arrhythmias. These two objectives are not always compatible. To have correct defibrillator lead placement, it is necessary to keep the whole RV defibrillating coil in the RV. The coil must not cross the tricuspid valve leaving a portion of it in the right atrium: inappropriate diagnosis of ventricular arrhythmias may occur during atrial tachyarrhythmias and defibrillation capacity may also be questionable. Overcoming this problem may not always be compatible with choosing an optimal RV pacing site, which, for example, may be the mid-septum or another non-apical position. As the septum often bulges into the RV due to huge LV dilatation, the coil may lie partly in the right atrium. The implanter is then forced to select a less optimal site from the haemodynamic point of view in order to achieve effective arrhythmia diagnosis and defibrillation. Thus, CRT-D, which is an attractive therapy over CRT-P in many heart failure patients, may not always be possible to deliver. The future To improve CRT, alternative approaches for LV leads are needed. Coronary veins are still occasionally inaccessible and, more importantly, may not be present at the optimal stimulation site. Two possibilities are envisaged:These risks and difficulties will be worth overcoming if further haemodynamic benefit can accrue and the number of non-responders be reduced. The trans-atrial septal approach has the advantage of free access to the endocardial LV in order to achieve the optimal lead position or positions, if several are needed, for providing maximal LV functional improvement. However, complications of mechanical interference between the lead or leads and the mitral valve apparatus will require careful evaluation, and long-term anticoagulation will almost certainly be mandatory. The trans-cutaneous epicardial approach offers the possibility of positioning the leads anywhere on the surface of the LV but difficulties exist with lead fixation and the physical relationship of the stimulation site to the epicardial coronary arteries To confirm acute haemodynamic benefit with these techniques, a simple, effective, and rapid means of assessment is required. At present, echocardiography during the implantation procedure is widely practised. Alternatives are LV dp/dt, which could be derived from an LV lead by means of a sensor, other parameters sensed by the device or another non-invasive technique. Whatever is ultimately chosen must be easy for the physician and patient, readily reproducible, and reliable. A solution to this problem, which is included in the device, is most attractive, as it may offer the added potential of the device, making its own adaptation to changing circumstances. The hand of the physician will probably be replaced by a robotic tool as applied already in a few centres equipped with the Stereotaxis system (Stereotaxis Inc., St Louis, MO, USA). Simpler and less costly systems will become available, which may permit reduced X-ray exposure for the implanter and patient. Conclusion Very much work remains. By the end of the second decade of CRT, there is no doubt that today’s implant procedures will appear obsolete. Technology will provide advances in robotics combined with better means of assessment of stimulation patterns in heart failure patients and the leads for different approaches to achieve more complete chamber resynchronization. Figure 1 View largeDownload slide Lateral X-ray view of the first fully transvenous cardiac resynchronization therapy system (courtesy of D.G. and J.-C.D., University Hospital of Rennes, August 1994). Figure 1 View largeDownload slide Lateral X-ray view of the first fully transvenous cardiac resynchronization therapy system (courtesy of D.G. and J.-C.D., University Hospital of Rennes, August 1994). Figure 2 View largeDownload slide Evolution of dedicated leads for catheterization of coronary sinus tributaries (coronary veins). Figure 2 View largeDownload slide Evolution of dedicated leads for catheterization of coronary sinus tributaries (coronary veins). Figure 3 View largeDownload slide Coronary sinus angiography has revolutionized cardiac resynchronization therapy implant procedures. Figure 3 View largeDownload slide Coronary sinus angiography has revolutionized cardiac resynchronization therapy implant procedures. Conflict of interest: none declared. References 1 Daubert JC, Mabo P, Berder D. Atrial tachyarrhythmias associated with high degree interatrial block: prevention by permanent atrial resynchronization. Eur J Cardiac Pacing Electrophysiol  ( 1994) 4: 35–44. 2 Kappenberger L, Linde C, Daubert C, McKenna W, Meisel E, Sadoul N, Chojnowska L, Guize L, Gras D, Jeanrenaud X, Rydén L. Pacing in hypertrophic obstructive cardiomyopathy: a randomized cross-over study. Eur Heart J  ( 1997) 18: 1249–1256. 3 Hochleitner M, Hörtnagl H, Ng CK, Hörtnagl H, Gschnitzer F, Zechmann W. Usefulness of physiologic dual-chamber pacing in drug-resistant idiopathic dilated cardiomyopathy. 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TI - Cardiac resynchronization therapy implantation: a blend of skill and technology
JF - European Heart Journal Supplements
DO - 10.1093/eurheartj/sum069
DA - 2007-12-01
UR - https://www.deepdyve.com/lp/oxford-university-press/cardiac-resynchronization-therapy-implantation-a-blend-of-skill-and-WNHshEHAS0
SP - I107
EP - I112
VL - 9
IS - suppl_I
DP - DeepDyve
ER -