What's the Price to be Paid for Rate Response: AV Sequential Versus Ventricular Pacing?

The purpose of this study was to compare the effects of atrioventricular (AV) sequential and ventricular pacing at rest and during exercise on parameters of left ventricular performance. Twenty-five patients were studied by means of first pass radionuclide angiography. Pacing rates increased significantly (P less than 0.001) during exercise in both pacing modes, resulting in a significant increase in the cardiac index (P less than 0.001). Pulmonary transit times decreased significantly (P less than 0.001) during exercise in both pacing modes with a significantly shorter pulmonary transit time for AV sequential pacing at rest (P less than 0.01) and during exercise (P less than 0.05), indicating impaired left ventricular function in ventricular pacing. Regional left ventricular wall movement deteriorated significantly during exercise in both pacing modes (P less than 0.02), with a significantly worse performance during ventricular pacing at rest (P less than 0.05) and during exercise (P less than 0.05). Therefore, the price to be paid for rate response is a deterioration of regional wall movement. An additional loss of AV synchrony worsens the situation. It is concluded that rate modulated pacing requires preservation of AV coordination to optimize left ventricular performance.