Left Ventricular Mechanics and Myocardial Blood Flow: Materials and Methods

This study included patients who were being observed in the pacing clinic and had been referred for coronary angiography because of chest pain. The inclusion criteria were as follows: (1) dual-chamber pacing with optimal AV delay for at least 1 year for sick sinus syndrome; (2) normal intraventricular conduction before pacemaker implantation and throughout the study (QRS, < 110 ms); and (3) a prolonged PR interval allowing complete ventricular pacing capture at rest and during exercise (ie, to a QRS duration similar to that during VVI pacing, as established by 12-lead resting ECG and Holter ECG recordings).
The optimal AV delay was defined, using ultrasound measurements of transmitral flow, as that which provided the longest diastolic filling time without interruption of the A wave. This is the usual procedure in our pacing clinic for the programming of DDD pacemakers in patients with a prolonged PR interval. At the time of initial pacemaker programming, the patients in this study had a particularly prolonged mean (± SD) spike-R interval during AAI pacing (ie, 270 ± 15 ms) due to a long intrinsic PR interval and the drugs they were taking (ie, P-blockers, Ca+ + antagonists, and propafenone).

The exclusion criteria were as follows: (1) known history of coronary artery disease (myocardial infarction); (2) coronary arteries with stenosis of > 50% of the lumen; (3) impaired LV systolic performance (ie, LV ejection fraction [LVEF], < 50% [estimated during a transthoracic echocardiogram]); and (4) aortic valve stenosis or presence of a prosthetic cardiac valve.
To examine the possible alterations in LV function, we analyzed LV pressure-volume loops using a conductance catheter with a micromanometer on its tip. Additionally, we calculated the coronary flow by means of a Doppler guidewire to estimate the influence of the restoration of a normal ventricular activation sequence on the coronary circulation.

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