ABSTRACT
BACKGROUND: Although atrial ventricular (AV) intervals are often optimized at rest in patients receiving cardiac resynchronization therapy (CRT), there are limited data on the impact of exercise on optimal AV interval. METHODS: In 15 patients with CRT, AV intervals were serially programmed while patients were supine and at rest, and during exercise with heart rates that averaged 20 and 40 beats per minute above their resting rates. Echocardiographic Doppler images were acquired at each programmed AV interval and each rate. Three independent echocardiographic criteria were retrospectively used to determine each patient's optimal AV interval as a function of exercise-induced increased heart rates: the duration of left ventricular filling, stroke volume, and a clinical assessment of left ventricular function. RESULTS: A negative correlation between the optimal AV interval and heart rate was observed across all patients using all three independent criterion: the maximum left ventricular filling time (slope =-0.77, intercept = 151.9, r = 0.55, P < 0.001), maximum stroke volume (slope =-0.93, intercept = 183.3, r = 0.50, P = 0.002), or the subjective clinical assessment (slope =-1.06, intercept = 182.0, r = 0.72, P < 0.001). Consistent trends were observed between all three parameters for 12 out of the 15 patients. CONCLUSIONS: These results suggest that in patients indicated for CRT, rate-adaptive functions may be useful to shorten AV intervals with increased rate, in order to maximize left ventricular filling, stroke volume, and clinical left ventricular function. Further studies are necessary to determine the clinical impact of these rate-adaptive algorithms.
Subject(s)
Cardiac Pacing, Artificial/methods , Echocardiography , Exercise Test , Heart Failure/diagnostic imaging , Heart Failure/prevention & control , Therapy, Computer-Assisted/methods , Ventricular Dysfunction, Left/diagnostic imaging , Ventricular Dysfunction, Left/prevention & control , Female , Humans , Male , Middle Aged , Treatment OutcomeABSTRACT
Cardiac resynchronization therapy improves hemodynamics in selected patients with heart failure. Mechanic asynchrony parameters that may guide patient selection or therapy optimization are still being investigated. A biventricular (BiV) pacemaker was implanted in 34 patients with dilated ischemic, idiopathic, or valvular cardiomyopathy, and a QRS duration of > or =130 milliseconds. Two-dimensional standard and Doppler tissue echocardiography was performed during right ventricular (RV), left ventricular (LV), BiV, and no pacing in a random and blinded manner. LV and BiV pacing increased stroke volume (P <.02 for both) and ejection fraction (P <.001 for both). Regional contractility assessed by displacement, strain rate, and peak systolic strain was improved in some segments (P <.05) during LV and BiV pacing. A homogenization of segmental contractions was observed during LV and BiV pacing as evaluated by net systolic displacement and segmental myocardial performance index. LV and BiV pacing provides benefits that can be quantified by echocardiography.
Subject(s)
Cardiac Pacing, Artificial/methods , Cardiomyopathies/diagnostic imaging , Cardiomyopathies/therapy , Echocardiography, Doppler , Ventricular Dysfunction, Left/diagnostic imaging , Ventricular Dysfunction, Left/therapy , Analysis of Variance , Blood Flow Velocity , Cardiomyopathies/physiopathology , Female , Hemodynamics , Humans , Image Processing, Computer-Assisted , Male , Middle Aged , Ventricular Dysfunction, Left/physiopathologyABSTRACT
INTRODUCTION: Although invasive studies have shown that cardiac resynchronization therapy by biventricular pacing improves left ventricular (LV) function in selected heart failure patients, it is impractical to apply such techniques in the clinical setting. The aim of this study was to assess the acute effects of cardiac resynchronization therapy by noninvasive techniques. METHODS AND RESULTS: Twenty-two patients enrolled in the InSync trial (age 64 +/- 9 years, 18 men and 4 women; all with ejection fraction < 35% and QRS > 130 msec) were studied 1 to 12 months after pacemaker implantation during pacing, and while ventricular pacing was inhibited. Regional myocardial strains of the interventricular septum, LV free wall, and right ventricular free wall were derived from color Doppler tissue echocardiography. Peak power index was calculated as a product of simultaneously recorded noninvasive blood pressure and pulse-wave (PW) Doppler velocity of the LV outflow tract. The Z ratio (sum of LV ejection and filling times divided by RR interval) and tei index were calculated from PW Doppler data. During pacing, overall regional strain improved (P = 0.01), while the LV strain coefficient of variation decreased from 2.7 +/- 2.4 to 1.3 +/- 0.7 (P = 0.009). Additionally, peak power index improved from 84 +/- 24 to 94 +/- 27 cm x mmHg/sec (P = 0.004). The Z ratio increased from 0.71 +/- 0.08 to 0.78 +/- 0.07 (P = 0.0005), while the tei index decreased from 0.86 +/- 0.33 to 0.59 +/- 0.16 (P = 0.0002). CONCLUSION: Using novel noninvasive indices, we demonstrated that cardiac resynchronization therapy improves LV performance.
