Beat-to-Beat Analysis of Left Ventricular Pressure-Volume Relation and Stroke Volume by Conductance Catheter and Aortic Modelflow in Cardiomyoplasty Patients

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Abstract
Background Since the clinical introduction of dynamic cardiomyoplasty, a discrepancy has been observed between unchanged measurements of cardiac function and improved clinical outcome. Methods and Results We performed a beat-to-beat analysis of cardiac performance at rest in nine cardiomyoplasty patients 6 to 24 months after operation. Conductance and micromanometer catheters were placed in left ventricle and aorta and used for measurements over a 15-second period, during which the wrapped latissimus dorsi (LD) muscle was stimulated for 10 seconds in a 1:2 synchronization mode followed by a 5-second period without LD stimulation. The synchronization delay between start of the QRS complex and the LD contraction was changed from 4 up to 125 ms at the patient’s clinical stimulation strength and at an increased supramaximal amplitude. Comparing the LD assisted period to the unassisted period, at the clinical settings no significant changes in stroke volume (SV) as measured by the conductance technique and the aortic Modelflow technique were observed. A significant ( P <.05) rise in left ventricular end-diastolic pressure (LVEDP) was observed directly after the assisted 10-second period. The peak ejection rate (PER) of left ventricular volume increased ( P <.05), with a mean of 28±23% during the LD stimulated beats. At the patient’s individual best setting, SV of the stimulated beats increased ( P <.01) by a mean of 20±15%. Systolic aortic pressure increased ( P <.01) by a mean of 7 mm Hg, peak negative dP/dt increased ( P <.01), and PER increased, with a mean of 68±24% ( P <.01). LVEDP was similar in stimulated and unstimulated beats and increased ( P <.05) in the nonpaced 5-second period. The delay for the best setting ranged from 25 to 125 ms; the stimulus strength was 1.5 to 3 V higher than the clinical setting. At the patient’s individual worst setting, SV remained unchanged and PER was higher, with a mean of 30±25% ( P <.05). The worst setting was observed at the 1.5- to 3-V-higher stimulus strength; in six patients, it was at a short delay (4 to 25 ms) and in three patients, at the longest delay (100 to 125 ms). Conclusions By the left ventricular conductance catheter and aortic Modelflow methods, improvement in cardiac function by dynamic cardiomyoplasty was demonstrated in this patient group. The synchronization interval, stimulus strength, and stimulus duration appeared to be critical for obtaining optimal improvement.