Cardiac dyssynchrony

CRT is now recommended for patients with LVEF less than or equal to 35%, sinus rhythm, and NYHA functional class III or ambulatory class IV symptoms despite recommended, optimal medical therapy and who have cardiac dyssynchrony, which is currently defined as a QRS duration greater than 0.12 ms, unless contraindicated. To date, over 4,000 patients have been studied in randomized clinical trials of CRT. A recent evaluation of complications from those studies suggest a risk of implant mortality of 0.4%, failure to implant a functioning LV lead in 10%, lead malfunction or dislodgement in 8.5%, and pacemaker infection in 1.4% [123]. 

Cazeau S, Bordachar P, Jauvert G, et al. Echocardio-graphic modeling of cardiac dyssynchrony before and during multisite stimulation a prospective study. Pacing Clin. Electrophysiol. 2003 26 137 3. 

Fruhwald FM, Fahrleitner-Pammer A, Berger R, et al. Early and sustained effects of cardiac resynchronization therapy on N-terminal pro-B-type natriuretic peptide in patients with moderate to severe heart failure and cardiac dyssynchrony. Eur Heart J 2007 28 1592-7. 

Hehn RH, Leclercq C, Paris OP, Ozturk C, McVeigh E, Lardo AC, Kass DA. Cardiac dyssynchrony analysis using circumferential versus longitudinal strain implications for assessing cardiac resynchronization. Circulation 2005 111 2760-7. 

The Cardiac Resynchronization in Heart Failure (CARE-HF) evaluated 813 patients with New York Heart Association Functional Class III or TV heart failure due to left ventricular systolic dysfunction and cardiac dyssynchrony (QRS interval > 120 ms) who were receiving standard pharmacologic therapy. Patients were randomly assigned to receive medical therapy alone or with cardiac resynchronization. The primary end point (time to death from any cause or an unplanned hospitalization for a major cardiovascular event) was reached by 159 patients in the cardiac-resynchronization group, as compared with 224 patients in the medical-therapy group (39 versus. 55% hazard ratio = 0.63 95% Cl 0.51-0.77 p < 0.001). There were 82 deaths in the cardiac-resynchronization group, as compared with 120 in the medical-therapy group (20 versus 30% hazard ratio = 0.64 95% Cl 0.48-0.85 P < 0.002) (194,195). 

In patients with heart failure and cardiac dyssynchrony, CRT improves symptoms and the quality of life and reduces complications and the risk of death. These benefits are in addition to those afforded by standard pharmacologic therapy. 

These conduction disturbances typically worsen overall cardiac function. The AV delay seen with first degree heart block can lead to suboptimal contribution of atrial systole, less filling time for the LV, and worsened mitral regurgitation (4,5). The intraventricular conduction abnormality can lead to regional LV wall motion delay, which is termed LV dyssynchrony. In LBBB, the LV lateral wall typically depolarizes late and therefore, contracts late. This delayed contraction of the LV lateral wall occurs when the septum is already in its relaxation phase. On echo, it can be seen that the relaxed septum moves paradoxically away from the lateral wall late in systole. This is inefficient contraction since the septum and lateral walls are not moving in unison to... 

The CARE-HF (Cardiac Resynchronization-Heart Failure) study was designed specifically to evaluate the effects of CRT on morbidity and mortality (1). This trial was started in January 2001 and was published in April 2005. Eight hundred nineteen patients with EF <35% and evidence dyssyn-chrony were randomized to optimal medical therapy or CRT. Dyssynchrony was defined as either a QRS duration > 150 ms or a QRS duration of 120-149 ms with echocardiographic evidence of dyssynchrony. In the CRT group, there was a 37% risk reduction (p < 0.001) in the primary endpoint, which was a composite of death from any canse or unplanned hospitalization for a major cardiac event (Fig. 11.3). In terms of all-cause mortality (secondary endpoint), there was a 36% risk reduction (p < 0.002) in the CRT group compared to optimal medical therapy. This study went beyond COMPANION by showing that CRT alone, even without the defibrillator, could improve survival. 

Fig. 11.8 Stepwise algorithm for management of heart failure patients who are nonresponders to CRT. AV = atrioventricular CXR = chest X-ray EKG = electrocardiogram Htx = heart transplant LV = left ventricular LVAD = left ventricular assist device MR = mitral regurgitation RV = right ventricular VV = interventricular. Cardiac ischemia is evaluated in patients with ischemic cardiomyopathy. Evidence of dyssynchrony includes septal to posterior wall motion delay > 130ms, intraventricular mechanical delay >40ms, and tissue Doppler imaging > 65 ms. (Reproduced witih permission from Aranda JM, Woo GW, Schofield RS, et al. J Am Coll Cardiol 2005 46 2193-8.)...

Bax JJ, Bleeker GB, Marwick TH, Molhoek SG, Boersma E, Steendijk P, van der Wall EE, SchaUj MJ. Left ventricular dyssynchrony predicts response and prognosis after cardiac resynchronization therapy. J Am CoU Cardiol 2004 44 1834-40. 

Badhwar N, Viswanathan M, O Connell JW, De Marco T, Schreck C, Lee BK, Tseng ZH, Lee RL, Olgin JE, Botviniek EH. Novel scintigraphic parameters to assess left ventricular dyssynchrony predict clinical response in heart failure patients requiring cardiac resynchronization therapy (abstract). J Nuc Med. 2006 47 (Supplement 1) 1P. 

Disordered electrical and mechanical ventricular activation can compromise cardiac function. Pacing technology has been nsed to att pt to correct the inter- and intraventricular conduction in an effort to optimize cardiac performance. The earliest attempts were performed during surgery when epicardial leads were placed over the lateral left ventricle free wall. Later, the coronary sinus was utilized to activate the left ventricle. Cardiac-resynchronization therapy (CRT) for treatment of patients with congestive heart failure and ventricular dyssynchrony can have a remarkable beneficial effect. Use of this technology continues to evolve. 

Management of a Biventricular Device. It has been estimated that up to 38% of patients with moderate to severe congestive heart failure due to left ventricular systolic dysfunction have intraventricular conduction delays with wide QRS complexes and ventricular dyssynchrony (79). Cardiac resynchronization therapy using a biventricular pacemaker is now a Class I indication therapy for systolic heart failure in patients with a QRS complex > 120 ms and left ventricular ejection fraction < 35% (80). Although cardiac resynchronization therapy decreases heart failure hospitalizations (81,82), as the overall number of patients with biventricular pacemakers and ICDs increase, more critical care patients will present with implanted biventricular devices, and familiarity with the management of these devices will become increasingly important. 

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