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Exercise (rate) responsive pacemakers benefit patients by providing increased cardiac output when needed and permitting lower rate during rest. This paper briefly reviews trends in reported studies on rate responsive pacemakers. For patients with reliable atrial rhythms, atrial-triggered pacemakers (DDD) provide physiological ventricular rates unless complications arise. At low rates, A-V synchrony benefits patients with refractory cardiac decompensation; however, in patients with healthy myocardiums, achieving higher pacing rates is more significant than maintaining synchrony. If atrial rhythms are unreliable, an alternative sensor for determining pacing rate is indicated. Pacemakers that respond to changes in right ventricular blood temperature, respiratory rate, QT interval, body vibration (motion), and pH have been implanted in humans. Clinical evaluations have shown that increased pacing rate leads to increased exercise tolerance and cardiac output when needed, independent of the sensor type (DDD, QT, respiratory rate, etc.). The effectiveness of any sensor type to increase pacing rate appropriately requires reliable sensors that respond specifically to the need for increased pacing rate. Sensors for stroke volume, venous oxygen saturation, right atrial or ventricular pressure and catecholamines are also under preclinical investigation. The availability of a reliable, long-term sensor is a key limitation to several techniques including pH, stroke volume, oxygen saturation, pressure, and catecholamines. Sensor technology and clinical effectiveness are the keys to rate responsive pacing. |
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