Holter ECG monitoring was performed after the
Holter ECG monitoring was performed after the patient consumed 180mL of sake (alcohol) each night in both the DDD-R and DDD-CLS modes. The mean HR in the DDD-CLS mode (68bpm) was similar to that (71bpm) in the DDD-R mode, but during sleep, the atrial pacing ratio (43.2%) in DDD-CLS was significantly higher than that (7.4%) in the DDD-R mode (p<0.001). The patient\'s condition was checked in each of the DDD-CLS and DDD-R modes during early morning urination. In the DDD-CLS mode, increased atrial pacing rates maintained his HR at a higher rate during and after micturition, and he had no symptoms (Fig. 2A). In the DDD-R mode, he experienced a sense of cold perspiration and presyncope after micturition. His intrinsic HR changed to atrial pacing after micturition but soon decreased to the basal rate (50ppm) (Fig. 2B). Although we did not measure BP, we assume that, in the DDD-R mode, his BP and intrinsic HR might have decreased after micturition. Therefore, we implanted the DDD-CLS pacemaker. After implantation, the patient has not experienced syncope episodes for 40 months.
Discussion Micturition syncope is a daily excretion-related transient circulatory disorder and is classified as situational syncope. Sumiyoshi et al. showed that in the elderly, micturition syncope commonly occurred early in the morning or after alcohol consumption at midnight. They also showed that the rate of positive response to the head-up tilt test was low, and premonitory symptoms before syncope were rare [8,9]. No syncope was observed in our patient during the isoproterenol-infusion head-up tilt test. Syncope did not occur after micturition in either of the DDD-R and DDD-CLS modes during the day, but the patient experienced a sense of presyncope in the DDD-R mode after alcohol consumption and after micturition early in the morning. The left ventricular mechanoreceptors are activated when there is an increase in cardiac contractility and a decrease in left ventricular dimensions. If these activated mechanoreceptors override the baroreceptor reflex, then peripheral vasodilatation, hypotension, and bradycardia occur because of diminution of the vasomotor tone and enhancement of parasympathetic activity [1,2]. The CLS XMU-MP-1 can detect cardiac phenomena such as a decrease in right ventricular volume and an increase in myocardial contractility at an earlier stage. It produces a more prompt and sustained atrial pacing response to the associated bradycardia compared with other sensing algorithms such as rate-drop or rate-hysteresis responses. In our patient, the atrial pacing ratio and HR in the DDD-CLS mode increased more than that in the DDD-R mode, during urination in the day (Fig. 1) and early in the morning (Fig. 2A and B). Although he had a mild sinus node dysfunction, his increased atrial pacing ratio indicated that his left ventricular mechanoreceptor was activated, especially during and after micturition. In contrast, his intrinsic HR was more frequent in the DDD-R mode than in the DDD-CLS mode at midnight, indicating that, at midnight, his basic sympathetic tone was accelerated in the DDD-R mode. Increased sympathetic tone induces a more prominent vasovagal reflex, known as the Bezold–Jarisch reflex . Therefore, these conditions suggested that, in the DDD-R mode, the vasovagal response occurred more prominently with presyncope early in the morning. Urodynamic study results by Sakakibara et al. revealed that the sitting position in which the bladder is distended causes mild orthostatic hypotension and urinary bladder evacuation resulting in a drop in arterial pressure and a decrease in HR. These responses were similar to those described in vasovagal syncope . In many patients with recurrent NMS, a significant drop in BP precedes any appreciable decline in HR. An increase in myocardial contractility and a decrease in left ventricular end-systolic dimensions occurred 2–4min before the onset of syncope, and left ventricular hypercontractility played an important role in the pathogenesis of syncope induced by the head-up tilt test . Therefore, the CLS system, which can detect a decrease in right ventricular volume and an increase in myocardial contractility at an earlier stage, may partially prevent an excessive drop in BP caused by atrial pacing-associated increased HR even in micturition syncope, as well as having been effective in vasovagal syncope.