As in vasovagal syncope, there usually are vasodepressor and cardioinhibitory components of this reflex. 33Īn uncommon cause of syncope is the hypersensitive carotid sinus syndrome, which is defined as syncope or presyncope resulting from an extreme response to carotid sinus stimulation. Asymptomatic spontaneous or provoked prolonged sinus pauses in this group of patients have an excellent prognosis even without pacing therapy. 32 Head-up tilt-table testing may be diagnostic in this condition and help the physician select patients who may benefit by pacing therapy.
#Mobitz type 2 trial
31 In a recent randomized trial of symptomatic patients with bradycardia, permanent pacing decreased the one-year recurrence rate of syncope to 19 percent in patients treated with a pacemaker, compared with 60 percent in control patients. Although some studies have shown significant reduction of syncopal episodes with pacing therapy, 30 others have reported that pacing did not prevent syncope any better than drug therapy. Another large subset have a mixed vasodepressor and cardioinhibitory response (i.e., sinus bradycardia, prolongation of the PR interval, or advanced AV block). 29 These patients would not benefit from pacing.
Approximately 25 percent of patients have a predominant vasodepressor response (loss of vascular tone and hypotension without significant bradycardia). Pacing therapy for patients with refractory neurocardiogenic syndromes associated with severe bradycardia or asystole is controversial. Clinical studies have shown that rate-responsive pacing clinically benefits patients by restoring physiologic heart rate during exercise. 18 Another form of sinus node dysfunction is “chronotropic incompetence,” defined as an inadequate sinus rate response to stress or exercise. In turn, atrial overdrive pacing (pacing at a rate higher than the native sinus rate) may reduce episodes of obstructive sleep apnea in these patients. In patients with sleep apnea, treatment of the apnea frequently will reduce the occurrence of pauses. The clinical significance of such pauses is uncertain. In the general population, monitoring during sleep may reveal sinus pauses of variable duration.
16, 17 These findings are caused by increased vagal tone and usually do not indicate the need for pacing. During sleep, these athletes may have a heart rate as low as 30 beats per minute with associated pauses or type I second-degree AV block resulting in asystole as long as 2.8 seconds. Trained athletes often manifest physiologic sinus bradycardia with resting heart rates as low as 40 to 50 beats per minute. Many studies have documented that pacemaker therapy can reduce symptoms, improve quality of life and, in certain patient populations, improve survival. Biventricular pacing (resynchronization therapy) recently has been shown to be an effective treatment for advanced heart failure in patients with major intraventricular conduction effects, predominately left bundle branch block. They also are effective in the prevention and treatment of certain tachyarrhythmias and forms of neurocardiogenic syncope. Permanent pacemakers are implanted in adults primarily for the treatment of sinus node dysfunction, acquired atrioventricular block, and certain fascicular blocks. In general, rate-responsive devices are preferred because they more closely simulate the physiologic function of the sinus node. In older patients, devices that maintain synchrony between atria and ventricles are preferred because they maintain the increased contribution of atrial contraction to ventricular filling necessary in this age group. Current pacemaker devices treat bradyarrhythmias and tachyarrhythmias and, in some cases, are combined with implantable defibrillators. Each year, pacemaker therapy is prescribed to approximately 900,000 persons worldwide.
0 kommentar(er)
