I-37 CARDIAC RESYNCHRONISATION THERAPY IN HEART FAILURE ATRIO-BIVENTRIKULARNA ELEKTROSTIMULACIJA SRCA PRI SRČNEM POPUŠČANJU Cecilia Fantoni, Angelo Auricchio Division of Cardiology, University Hospital Magdeburg, Germany Arrived 2005-04-27, accepted 2005-04-30; Zdrav Vestn 2005; 74: Supl. I: 37–40 Key words: chronic heart failure; cardiac resynchronisation therapy; electro-mechanical dyssynchrony; defibrillator; left bundle branch block; ventricular conduction disturbance; cardiac resynchronisation therapy Abstract – Cardiac resynchronisation therapy (CRT) is a new therapeutic approach for a selected group of patients with symptomatic heart failure (NYHA III-IV) despite optimal medical therapy, due to dilated cardiomyopathy of any etiology (LVEF≤ 35%, and LVEDD≥ 55 mm), who present with electro-mechanical dyssynchrony (QRS≥ 120 msec). Safety and effectiveness of CRT have been demonstrated by several clinical trials, with patients achieving significant improve- ment in both clinical symptoms as well as functional status and exercise capacity. Furthermore, CRT has reduced morbidity and mortality of heart failure patients. Whether or not heart failure patients candidate to CRT should receive a defibrillator (ICD) back-up remains debatable, although growing evidence is pointing to extensive use of a defibrilla- tor in such a population. Ključne besede: kronično srčno popuščanje; atrio-biventri- kularna elektrostimulacija srca; elektromehanična dissinhro- nija; levokračni blok; kardioverter defibrilator Izvleček – Atrio-biventrikularna elektrostimulacija srca (CRT) je nov način zdravljenja nekaterih bolnikov z izraže- nim srčnim popuščanjem (NYHA III-IV), ki se pojavi kljub ustre- znemu zdravljenju z zdravili. Vzrok dilatacijske kardiomio- patije ni pomemben (LVEF≤ 35%, in LVEDD≥ 55 mm), pač pa je pomembna elektromehanična dissinhronija (QRS ≥ 120 ms). Varnost in učinkovitost CRT so pokazale številne klinič- ne raziskave, kjer so ugotavljali izboljšanje kliničnih simpto- mov, fizikalnih parametrov kot tudi telesne zmogljivosti. Ugo- tovitve kažejo, da CRT zmanjšuje obolevnost in umrljivost pri bolnikih s srčnim popuščanjem. Ni še povsem jasno, ali naj bi bolniki, ki so kandidati za CRT, hkrati prejeli tudi kardiover- ter defibrilator (ICD), narašča pa število dokazov, ki nedvo- mno podpirajo široko uporabo ICD v tej populaciji bolnikov. Introduction Despite striking advances in medical therapy of heart failure (HF) (1, 2), morbidity and mortality of HF patients remain high (3). Heart transplantation and ventricular assist devices offer an effective, but limited alternative therapy due to shortage of organ availability and elevated costs. Cardiac resynchroni- sation therapy (CRT) has emerged as an effective option in selected HF patients with electro-mechanical dyssynchrony. Its safety and clinical efficacy have been proved in several prospective, randomised, controlled trials (4–7). Furthermore, CRT has been proved able to reduce morbidity and mortality of HF patients (8–10), especially when combined with a de- fibrillator back-up (7). Mechanical consequences of electrical delays »… Obviously the shorter the distance that must be transversed in order to reach the Purkinje conducting system, the smaller the fractionate contraction element derived from fiber to fiber excitation and the greater the number of fractions excited over the natural pathways, with the result that more vigorous beats occur…« Wiggers. Am J Physiol 1925; 73: 346–78. Wiggers first recognised the acute effects of a non-physiologi- cal activation sequence on left ventricular function. The strict relationship between conduction delays and abnormal mechanical function has been later confirmed in many other animal models (11) and in human beings (12). HF patients often present with conduction delays located at various levels of the conduction system, which may depress cardiac performance. Spontaneous or pharmacologically induced sinus node incompetence may contribute to further reduce the already impaired functional capacity of HF patients (13). About 50% of HF patients show different degree of atrio- ventricular block, being the most frequent one a prolonged atrio-ventricular conduction time. Prolongation of atrio- ventricular time delays ventricular contraction (and conse- quently relaxation of the ventricle), so that early passive filling overlaps the active one, with reduced atrial booster con- tribution to ventricular filling. Finally, loss of atrio-ventricular synchrony may determine a ventriculo-atrial tele-diastolic gradient with early re-opening of the mitral valve leading to significant so called »pre-systolic or diastolic« mitral regurgi- tation (14). All together these phenomena lead to impaired ventricular pre-load. A significant prolongation of QRS complex of more than 120 ms may be found in approximately 30% of HF patients. The negative prognostic value related to QRS widening, indepen- dently of QRS morphology, has been shown in several studies (15, 16). At our best understanding, prolongation of QRS du- ration is the result of electrical asynchrony at the inter-ventri- ZDRAV VESTN 2005; 74: I-37–40 I-38 ZDRAV VESTN 2005; 74: SUPPL I cular, intra-ventricular and intramural level (17). Prolongation of QRS duration may result in mechanical ventricular dyssyn- chrony which, at the present time, has only been identified at the inter-ventricular and intra-ventricular level. Inter-ventricu- lar delay is defined as the time difference between the onset of pulmonary artery flow and the onset of aortic flow with respect to the beginning of the QRS complex. A delay longer than 40 ms is usually considered indicative of significant inter-ventri- cular dyssynchrony. Nevertheless, many studies have questio- ned the real importance of such delay in impairing systolic func- tion compared to intra-ventricular electrical delay (18). Left bundle branch block is the most common intra-ventricu- lar conduction disturbance occurring in patients with depres- sed ventricular function. Recent electrophysiological findings have demonstrated that left bundle branch block is a rather complex and heterogeneous electrical disease (19–21). There is increasing evidence that disarray of myocardial layers may partly account for this heterogeneity (20). In patients with left bundle branch block, the region of earliest ventricular activa- tion (usually the inter-ventricular septum) contracts while the remaining ventricular myocardium is still in a non-activated phase. Thus, consistent part of contraction energy is wasted as no effective intra-ventricular pressure can develop. At the same time, the latest activated regions of the left ventricle (usually the lateral and postero-lateral walls) are passively stretched with increasing wall tension at this site and further waste of energy. By the time that the latest depolarised ventricular regions contract, the septum starts to relax and is no more able to withstand the increasing pressure develop- ment, and is pushed toward the right ventricle (paradoxical septal motion). In this way, pressure is generated asynchroni- cally by different regions of the left ventricle without effecti- ve ejection and with higher waste of energy. Furthermore, the delayed depolarisation of the lateral wall causes a delayed and slow contraction of the postero-lateral papillary muscle. This event, in the presence of a dilated cham- ber and abnormal ventricular geometry, contributes to signifi- cant worsening of mitral regurgitation. Finally, the heteroge- neous electrical and mechanical ventricular activation may further impair systolic ventricular function by delaying relax- ation phase and reducing ventricular filling time. Structural changes related to electromechanical dyssynchrony In different heart models (22–24), it has been demonstrated that the abnormal loading and work distribution caused by electro-mechanical dyssynchrony may induce regional alterations of myocardial metabolism, gene expression and protein synthesis (23). It may be postulated that these changes could lead to rearrangement of both contractile and non-contractile cells, fibrosis and apoptosis. Experimentally- induced left bundle branch block causes eccentric hyper- trophy (25) with an apico-basal and septo-lateral oriented gradient and determines altered synthesis of stress kinases and calcium-handling proteins in the high stress areas (23). Furthermore, it has been demonstrated that mechanical dyssynchrony causes a redistribution of regional flows (26) with consequent chronic hypoperfusion of unloaded regions. The meaning of such complex interactions between changes in regional loading conditions, myocardial metabolism, gene expression, protein synthesis and blood flow distribution induced by an abnormal activation sequence is not fully understood. All together it appears that mechanical dyssyn- chrony arising from conduction disturbances favours mal- adaptive structural remodeling process. Thus, it is conceiv- able that dyysnchrony represents a newly appreciated pathophysiological process which directly depresses ventri- cular function and ultimately leads to further ventricular dila- tation and progression of HF. Cardiac resynchronisation therapy CRT improves cardiac performance at reduced myocardial metabolism cost through different mechanisms (27). Pre- excitation of the left ventricular lateral wall with atrial-synchro- nous left or biventricular pacing restores a normal atrio- ventricular timing, resynchronises right and left ventricular activation as well as septum and lateral wall contraction. In addition to an improved coordination of the septal and lateral wall contraction, reduction of mitral regurgitation and improvement of ventricular filling (28, 29), recent data pos- sibly suggest that CRT may improve cardiac efficiency by slo- wing the heart rate (30). This may have a beneficial effect on diastolic times and on myocardial oxygen demand. Clinical and structural effects of CRT Several prospective, randomised, controlled trials (4–6, 10, 31), conducted in patients with functional NYHA class III-IV, due to dilated cardiomyopathy of any etiology, presenting with electro-mechanical dyssynchrony, have proven the safety and clinical effectiveness of CRT. All these studies demonstrated a significant improvement of quality of life, NYHA functional class, exercise tolerance, and a significant reduction in the hospitalisations for HF. Furthermore, there was a consistent report of significant improvement of left ventricular ejection fraction and partial reversal of maladaptive remodeling process (28, 6). CRT also showed a favourable effect on sympa- thetic-parasympathetic activity with a reduction of plasma norepinephrine levels and increase of heart rate variability (30). Finally, the recently concluded CARE-HF Study (Cardiac Resynchronisation in Heart Failure) (10), demonstrated a clear survival benefit in HF patients given by CRT in addition to optimal medical therapy compared to optimal medical therapy alone. Based on these evidences, CRT is currently indicated (Class IIa ACC/AHA/NASPE Guidelines, see Table 1) for patients with symptomatic HF (NYHA III-IV) despite optimal medical the- rapy, due to dilated cardiomyopathy of any etiology (LVEF≤ 35%, and LVEDD≥ 55 mm), who present with ventricular elec- trical dyssynchrony (QRS ≥ 130 msec) for the improvement of symptoms, functional status and exercise capacity (32). It has been reported that a small proportion of patients treated with CRT remain symptomatic. These individuals are usually considered as non-responder patients to CRT. All randomised clinical CRT trials have used statistical techniques to define the response of groups of patients to CRT. No stan- dardised criteria are available to predict reliably the clinical response of a given individual. The large clinical improvement that is observed in some individuals after CRT has created the perception that patients who do not exhibit such improve- ment are not responding positively to CRT. However many patients who do not show overt improvement may neverthe- less benefit from a slowing of disease progression by living longer and not undergoing hospitalisations. Although major efforts have been made for identifying such patients, there are still several unresolved issues in the definition of non- responders and in how to best identify and then treat these patients. Effects on morbidity and mortality The COMPANION trial (Comparison of Medical therapy, Pa- cing, And Defibrillation in chronic heart failure) (7), has shown I-39 marked reduction in combined measures of morbidity and mortality with both CRT alone and with CRT plus defibrillator back-up (CRT-D) with a similar 1-year event-free survival rate. Nevertheless, in contrast to CRT alone which demonstra- ted a relative risk reduction in all-cause mortality of about 24% (p = 0.060), CRT-D provided a larger (36%) and signifi- cant relative risk reduction in all-cause-mortality compared to optimal drug therapy (p = 0.003). These results are con- sistent with data of a recent meta-analysis showing that CRT alone may be able to reduce all-cause mortality by about 21% (8). Based on these data, the number of patients who needed to be treated to save 1 life is about 25 for CRT alone and 14 when CRT combined to ICD is given. These numbers are comparable with many pharmacological trials which enrolled similarly sick HF patients. The recently concluded CARE-HF trial (10) that randomised 813 advanced HF patients to optimal medical therapy alone or in combination with a CRT device showed a 36% reduction in the relative risk of all cause mortality with CRT compared with medical therapy alone. Nevertheless, 32% and 35% of deaths occurred among patients randomised to medical therapy and to CRT respectively were sudden deaths that could have been avoided by associating a defibrillator back-up. Finally, results of the CARE-HF and COMPANION trials and those from another important meta-analysis (9) were consi- stent in showing a similar risk reduction for the combined end-point – hospitalisations and death – in patients treated with CRT. This finding may suggest a substantial reduction of medical resources. Implantation issues The implantation technique is similar to a standard dual cham- ber sequential pacemaker or implantable cardioverter-de- fibrillator. The most challenging aspect for achieving resyn- chronisation therapy is placing a permanent left ventricular lead. A transvenous or thoracotomic approach can be used. The transvenous approach requires the retrograde cannulation of the coronary sinus, a selective angiography of the coro- nary sinus and his tributaries which delineates the venous ana- tomy and the final placement of a specifically designed pacing lead into a coronary vein lying over the surface of the left ventricle. Several reports have demonstrated the impor- tance of targeting the latest activated wall which requires implantation of a pacing lead into a lateral or postero-lateral vein (1). The transvenous approach may be a difficult and time-consuming technique. The major limitation is that options for lead placement are governed largely by the patient’s venous anatomy which shows considerable inter- individual variability. In about 10% to 15% of cases, it is not possible to achieve a satisfactory left ventricular pacing posi- tion or left phrenic nerve stimulation may occur, so that a thoracotomic approach becomes necessary. Selection of patients Duration of QRS complex has so far been used as the most practical and readily available criteria to select patients can- didate to CRT. Indeed, QRS duration is one of the simplest ways to measure electrical abnormalities that may have a me- chanical correlate. Baseline QRS duration has been shown to be associated with degree of mechanical dyssynchrony and with short-term clinical improvement obtained from CRT. Nevertheless there are increasing data (34) suggesting that a considerable proportion of HF patients presenting with narrow QRS complex (< 120 ms) may present echocardio- graphically-assessed mechanical dyssynchrony of similar mag- nitude as patients with prolonged QRS duration (> 120 ms). Recently introduced tissue Doppler imaging (TDI) techniques permit precise evaluation of regional systolic and diastolic synchrony by comparing the time to peak systolic contrac- tion and early diastolic relaxation of multiple segments. TDI appears to offer a comprehensive assessment of cardiac mechanical synchrony. A number of parameters based on TDI have been proposed to evaluate intra-ventricular dyssynchro- ny but the validity of TDI and other echocardiographic para- meters in selecting patients with both narrow and wide QRS who can benefit from CRT need to be confirmed in prospec- tive, randomised long-term studies. Open questions CRT is not currently indicated in patients with NYHA class II, even though there are increasing data suggesting that appli- cation of CRT in mildly symptomatic HF patients could pre- vent or slow HF progression. Furthermore, the increasing indications to ICD implantation, based on results of recent big trials (MADIT, MADIT II, SCD-HeFT ) rise the problem of considering implementation of the ICD-devices with a CRT back-up in less symptomatic (NYHA II) pts. Not enough data are so far available about CRT in patients with atrial fibrillation, although preliminary results support its efficacy in this clinical setting (35). Furthermore, there are increasing evidences that the implantation of a CRT device instead of a standard single- or dual-chamber pacemaker may be appropriate for HF patients who undergo His-bundle ablation. The question of whether HF patients with a standard pace- maker indication for bradycardia benefit from CRT is still unanswered. Nevertheless, data of DAVID trial (36) encoura- ges implantation of a CRT device in patients with impaired ventricular systolic function candidate to chronic pacing. Recent data suggest that also patients with narrow QRS (< 120 ms), but with echocardiographic evidence of mecha- nical dyssynchrony may benefit from CRT. Nevertheless, CRT should not be extended to this group before results of prospective randomised trials will be available. The important issue raised by the COMPANION study (7) is whether all HF patients candidate to CRT should be treated with an additional ICD back-up. The recently concluded trial, the Sudden Cardiac Death – Heart Failure Trial (SCD-HeFT) (37), has provided further evidence that implantation of a defibrillator in addition to best pharmacological therapy is the most effective long-term (5 year) treatment compared to conventional optimal therapy alone or with the adding of amiodarone, to prolong life in HF patients. Therefore, despite the fact that CRT-D devices have larger initial costs, and may require more extensive follow-up than CRT alone, this strategy may be more cost-effective particularly when mea- sured in terms of quality-adjusted life-years gain. Summary Cardiac resynchronisation therapy is an effective, adjunctive treatment to pharmacological therapy for a selected group of HF patients who remain symptomatic despite optimal medical therapy, and who present with electro-mechanical dyssynchrony. Safety and effectiveness of CRT have been demonstrated by many clinical trials, with patients achieving significant improvement in symptoms, functional status and exercise capacity. Furthermore, CRT promotes reverse re- modeling and reduces morbidity and mortality of HF patients. Thus, CRT should not be considered an alternative to medical therapy but a synergistic therapy. 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