Imaging techniques in cardiac resynchronization th

Authors: Maria Isabel Sá Albert de Roos Jos J M Westenberg Lucia J M Kroft

Publish Date: 2007/05/15

Volume: 24, Issue: 1, Pages: 89-105

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Abstract

Cardiac resynchronization therapy is a high cost therapeutic option with proven efficacy on improving symptoms of ventricular failure and for reducing both hospitalization and mortality However a significant number of patients do not respond to cardiac resynchronization therapy that is due to various reasons Identification of the optimal pacing site is crucial to obtain the best therapeutic result that necessitates careful patient selection Currently using echocardiography for mechanical dyssynchrony assessment performs patient selection MultiDetectorRow Computed Tomography MDCT and Magnetic Resonance Imaging MRI are new imaging techniques that may assist the cardiologist in patient selection These new imaging techniques have the potential to improve the success rate of cardiac resynchronization therapy due to preinterventional evaluation of the venous coronary anatomy to evaluation of the presence of scar tissue and to improved evaluation of mechanical dyssynchrony In conclusion clinical issues associated with heart failure in potential candidates for cardiac resynchronization therapy and the information regarding this therapy that can be provided by the imaging techniques echocardiography MDCT and MRI are reviewedCardiac resynchronization therapy CRT obtained by implanting a biventricular pacemaker is an established therapeutic option for patients with reduced left ventricular ejection fraction ≤35 prolonged QRS interval ≥120 ms and NYHA class III/IV systolic heart failure HF despite optimal medical therapy CRT improves symptoms and decreases both hospitalizations and mortality 1 CRT is effective by reversing left ventricular LV remodelling and increasing the ejection fraction EF while correcting the main cause of LV functional and morphologic disturbances named mechanical dyssynchrony which is basically an activation delay between cardiac chambers or LV segments LV reverse remodelling defined by a reduction in endsystolic and enddiastolic diameters and volumes has been referred as an indicator to CRT response However between 20 and 30 of patients do not respond to CRT 2 Suggested reasons include a prolonged QRS duration without mechanical dyssynchrony and therapeutic failure due to mismatch between the LV lead position and the most delayed myocardial region 2 3 4 It has been suggested that measuring mechanical dyssynchrony by echocardiography may better identify patients who are likely to respond to CRT 5 Currently echocardiography has been used in selection and followup of candidates to CRT namely in the evaluation of LVEF and LV remodelling and ventricular dyssynchrony MultiDetectorRow Computed Tomography MDCT and Magnetic Resonance Imaging MRI are increasingly used for cardiac evaluation MDCT and MRI allow depiction of cardiac anatomy with high spatial resolution as well as highly accurate measurements of cardiac function 6 7 8 In this review clinical issues concerning CRT as well as clinical applications of these three imaging modalities will be discussedHeart Failure HF and cardiomyopathy refer to a spectrum of diseases that encompass various clinical entities where inadequate function of one or both ventricles forms the basis of cardiac disease Chronic HF develops after injury or stress to the myocardium due to a variety of causes eg ischemia hypertension valvular disease myocarditis etc In compensatory response the heart remodels leading to changes in myocardial structure and neurohormonal milieu of the entire cardiovascular system Increased wall stress leads to alterations in the geometry of the heart with hypertrophy or dilatation of the ventricles 9 Increased LV size and decreased LVEF are associated with increased neurohormonal activation and predict prognosis Also when class III or IV symptoms and LVEF less than 30 are present LV dimension is considered a strong predictor of mortality 10 Moreover right ventricular RV dysfunction is also associated with increased mortality 11The effects of CRT can be divided into early and longterm effects Studies in the acute setting have demonstrated that CRT abruptly increases LVEF with improved energetic chamber efficiency 12 13 14 15 The main longterm CRT effect is the socalled “LV reverse remodelling” 2 5 A 10 reduction in LV endsystolic and enddiastolic volumes has been associated with increased LVEF 16 Even this relatively small amount of LV reverse remodelling has been shown to be a strong predictor for improved survival and decrease of HF events 2 15 16 17

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