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Dr. B Vidal
Assessing mechanical cardiac asynchrony by echography could enable a better use of cardiac resynchronisation therapy in patients with advanced heart failure.
Mechanical cardiac asynchrony worsens prognosis and CRT helps to correct it. Electrical asynchrony is not a good response predictor to CRT while the presence of mecanical asyncrony is. However, current guidelines indicate CRT in electrical asynchrony, with no mention of mechanical asynchrony. Mechanical asynchrony can be found with echography at the atrioventricular, interventricular and intraventricular level, but there is no consensus yet on what the best marker for it is, if any. An individualised optimisation of both atrio-ventricular and VV intervals could potentially contribute to increase the benefit obtained from CRT.
Indeed, echocardiography is the preferred technique for studying cardiac mechanical synchrony. In this analysis, the main clinical application is cardiac resynchronisation therapy (CRT). Although current guidelines indicate CRT only if there is electric asynchrony (wide QRS in the ECG), the echocardiographic demonstration of cardiac asynchrony can be useful to identify patients who would also benefit from CRT yet who do not have conductance disturbances as well as to help in individualising CRT device programming.
Mechanical cardiac asynchrony is defined as the presence of a delayed contraction of certain myocardial segments. It usually appears at the end stage of a number of different cardiac diseases, together with left ventricular (LV) dilatation and systolic dysfunction. Mechanical cardiac asynchrony may or may not be associated with electrical asynchrony which is present in up to 30% of patients with heart failure, expressed mainly as a left bundle branch block (LBBB) in the surface ECG. The presence of mechanical intraventricular asynchrony contributes to aggravating LV hemodynamics , favors the apparition of functional mitral regurgitation and consequently, worsens the patient’s prognosis.
Due to its huge availability, high temporal resolution and low-cost, echocardiography has been the most widely used imaging technique to study the presence of mechanical asynchrony. Some studies based on echocardiographic data have shown that up to 30% of patients with a wide QRS (electrical asynchrony) do not have mechanical asynchrony (1) whereas the same proportion - around 30% of patients with narrow QRS-, have mechanical asynchrony (2). This data is interesting, because identifying these patients, - with advanced heart failure and a normal surface ECG- , can extend the indication of CRT seeing that some studies have already demonstrated the benefit of CRT in patients with narrow QRS if mechanical asynchrony can be demonstrated. Furthermore, most studies agree that the absence of mechanical asynchrony has an important role in a non-response to CRT (3,4) . This data could be useful to improve the selection of patients undergoing CRT if an easy echocardiographic marker to define the presence or absence of mechanical synchrony could be determined, and for this reason, CRT indication continues if electrical asynchrony is present, regardless of the presence or not of mechanical asynchrony.
Most CRT trials have shown the benefit of CRT that uses devices with simultaneous biventricular pacing (5), however all of the studies have systematically shown around 30% of non-responders. In order to improve these results, CRT devices are now equipped with sequential pacing capability, in other words, devices that permit the stimulation of both ventricles either simultaneously or sequentially, with a specific delay (VV interval). Given that one specific electrical pattern does not always entail the same specific mechanical delay, LV stimulation is currently performed from the epicardium while the right ventricle is stimulated from the endocardium, lead positioning may also affect the transmission of the stimulus and the ventricular activation sequence, causing interventricular and intraventricular delays.
It is reasonable to think that an individualised optimisation of both atrio-ventricular and VV intervals would potentially contribute to increasing the benefit obtained from CRT, as some studies have begun to suggest (6). Echocardiography has an important role in this field since it allows for the non-invasive measurement of all these delays thus permitting, at the same time, the evaluation of the acute hemodynamic effect of different programming.
Mechanical asynchrony can be found at the following three levels: atrioventricular, interventricular and intraventricular level. They can coexist and may be measured by echography.
Atrioventricular, interventricular and intraventricular asynchrony can be measured with different echo techniques and this is particularly true for determining LV intraventricular synchrony. Although this knowledge would be useful to select patients, to extend CRT indications and to help in CRT programming optimisation, no consensus exists regarding which parameters are the best ones to use. This is the reason why patients continue to be selected by demonstrating the presence of electrical asynchrony.
Atrioventricular asynchrony assessment. DFT: diastolic filling time measured with PW - Doppler in the 4-chamber apical view as the time passed from the beginning of the E wave to the end of the A wave. Atrioventricular asynchrony is described if the DFT is < 40% of the cardiac cycle.
Interventricular asynchrony is assessed with PW - Doppler applied at the aortic and pulmonary valves measuring the difference between the aortic pre-ejection time and the pulmonary pre-ejection time defined as the time passed from the beginning of the QRS complex to the beginning of the pulmonary or aortic ejection.
Intraventricular asynchrony determined by M-mode scans in the long axis paraesternal view calculating the time from the septum peak contraction to the posterior wall peak contraction. A delay > 130 ms is diagnostic of LV intraventricular asynchrony.
Septum to lateral wall delay measured as the time difference between the time interval from the QRS beginning to the peak of the systolic contraction of the basal septal and lateral segments in the 4 chambers apical view as Bax et al described. A maximum delay to peak systolic tissue velocity > 60 ms is considered as a criterion of LV intraventricular asynchrony.
The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.
1. Curtis AB. Cardiac resynchronization therapy 101: if it's not late, pacing it early won't help. J Am Coll Cardiol. Jan 4 2005;45(1):70-71. 2. Ghio S, Constantin C, Klersy C, Serio A, Fontana A, Campana C, et al. Interventricular and intraventricular dyssynchrony are common in heart failure patients, regardless of QRS duration. Eur Heart J. Apr 2004;25(7):571-578. 3. Yu CM, Zhang Q, Fung JW, Chan HC, Chan YS, Yip GW, et al. A novel tool to assess systolic asynchrony and identify responders of cardiac resynchronization therapy by tissue synchronization imaging. J Am Coll Cardiol. Mar 1 2005;45(5):677-684. 4. Bax JJ, Bleeker GB, Marwick TH, Molhoek SG, Boersma E, Steendijk P, et al. Left ventricular dyssynchrony predicts response and prognosis after cardiac resynchronization therapy. J Am Coll Cardiol. Nov 2 2004;44(9):1834-1840. 5. Abraham WT, Fisher WG, Smith AL, Delurgio DB, Leon AR, Loh E, et al. Cardiac resynchronization in chronic heart failure. N Engl J Med. Jun 13 2002;346(24):1845-1853. 6. Vidal B, Sitges M, Marigliano A, Delgado V, Diaz-Infante E, Azqueta M, et al. Optimizing the Programation of Cardiac Resynchronization Therapy Devices in Patients With Heart Failure and Left Bundle Branch Block. Am J Cardiol. Sep 15 2007;100(6):1002-1006.
Dr. B. Vidal and *Dr J. Brugada Thorax Institute, Hospital Clínic de Barcelona. *Chairman of the European Heart Rhythm Association
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