Observation Of The Effect Of Dual-chamber CLS Pacing In The Prevention Of Vasovagal Syncope

BackgroundSyncope refers to a syndrome of sudden,reversible, transient loss of consciousness. The main clinical features of syncope is sudden onset (a few of patients with prodrome), a short period of loss of consciousness (usually1-2min, rarely more than30min).Patients can not maintain the original position usually and then fall down, and wake up quickly in a short period with less of sequelae. Syncope is not an independent disease, but a clinical symptom caused by many diseases. The common pathogenesis of various types of syncope is hypoxic brain function interrupt, because of the state of consciousness is closely related to the blood supply of the brain. The metabolic activity of the human brain is very active and its energy supply comes mainly from the aerobic oxidation of glucose. But the glycogen storage of the brain tissue is rarely and the glucose required almost rely on blood transporting, only the very rich and stable blood supply in order to ensure glucose and oxygen which the brain required. The experiments show that, the cerebral blood flow of healthy people of every100g of brain tissue is50-60ml/min, which accounting for12%-15%of the blood volume of resting cardiac and the smallest oxygen demand for maintaining conscious is3.0-3.5ml/min per100g of brain tissue. Syncope will occur while the human brain is completely hypoxia for6-10s, and convulsions and coma can appear if it continues for10-20s.Therefore, any factors (such as decreased cardiac output, venous capacity decreased, vascular resistance adjustment disorder, increased cerebral vascular resistance, etc.)that affect brain perfusion, as well as factors that reduce the function of oxygen release can cause for insufficient blood supply to the brain or suddenly plungling into hypoxia from oxygen-rich state of brain. There often is amaurosis what people call "class syncope symptoms" before syncope, because of optic nerve is most sensitive to ischemia and hypoxia. There will be cortical inhibition and loss of consciousness if the blood supply to the brain is still not restored, often accompanied by the loss of skeletal muscle tension which to maintain the posture and independent body position and fall down, as well as incontinence of sphincter and urination because of relaxation of defecation.The etiology of syncope is very complex. According to the etiology of syncope it can be broadly divided into cardiogenic syncope, vascular reflex syncope, blood-borne syncope, cerebral syncope and drug-induced syncope, and the last four types are also known as non-cardiogenic syncope. Each type of syncope can be caused by various diseases, the cause of diseases are as follows:(1) cardiac syncope: ventricular outflow obstruction diseases, ventricular inflow obstruction diseases, arrhythmia, cardiac pump failure, acute cardiac tamponade.(2) the vascular reflex syncope:vasovagal syncope, orthostatic hypotension syncope, vagus reflex syncope, carotid sinus hypersensitivity syncope.(3) bloodborne syncope:hypoglycemic syncope, severe anaemic syncope, blood gas abnormal syncope.(4) brain-derived syncope:neurogenic syncope, psychopathic syncope.(5) pharmic syncope: cardiovascular drugs, antipsychotic drugs, and other drugs.Vasovagal syncope (VVS) is caused by the sudden enhancements of vagal activity which significantly slow down heart rate and(or) vasodilatation caused by sudden reduction of sympathetic activity. It can be divided into cardiac inhibition type, vascular suppression type and mixed type in clinical. It’s most common cause of syncope and accounting for58%to74%of syncope cases. WS is more common in weak constitutions female without organic heart disease and there often is obvious incentive. Common incentives include:emotional stress, fatigue, standing too long, hunger, and in the crowded, stuffy environment, etc. There often is the short prodrome before syncopal episodes, such as dizziness, nausea, sweating, abdominal discomfort, blurred vision, followed by loss of consciousness and fall down. Patients will reply consciousness between seconds to a few minutes with characteristics of waking up just after fell to the groud. The causes of WS are indefinite, and the main pathogenesis is Bezold-Jarisch reflex:A strong reaction of catecholamines produced when the cardiac preload of VVS patients reduced, and then stimulating the baroreceptor of posterior inferior wall of the left ventricular. Stimulus signal transmitts via unmyelinated nerve fibers (C fibers) to the vascular centre of medulla oblongata, then causing reflection of sympathetic nerve activity weakened and vagus nerve activity enhanced. It will cause the decrease of peripheral vascular resistance and (or) heart rate, and then causing the lack of blood supply to brain, leading to the occurrence of syncope caused by lack of oxygen. Some scholars believe that the media abnormalities involved in the pathogenesis of WS. The study found that plasma endothelin (ET) and nitric oxide (NO) levels were significantly increased while fainting episode of patients, suggesting that vascular endothelial dysregulation may be involved in the occurrence of WS. Another scholars consider that the inhibition of sympathetic efferent impulse caused by increase of central serotonin (5-HT) activity leading to hypotension and bradycardia. Some vasoactive substances such as neuropeptide-Y, β-endorphin may be an important role of its pathogenesis, but its mechanism is not very clear. Someone believes that abnormal regulation of cerebral blood flow, psychological stress, breathing mechanism involved in its pathogenesis.The pathogenesis of VVS is not clear, and may resulted from synergy of varietal factors of organism. Therefore it can not be treated for the cause, and there isn’t a effective treatment at home and abroad. The primary pharmacotherapy is beta-blockers, but the effect is not certain, the POST test results in2006showed that metoprolol can not bring more benefit compared with placebo. The therapeutic efficiency of other drugs such as disopyramide, scopolamine, clonidine,5-hydroxytryptamine inhibitor received mixed reviews. Some scholars believe that the tilt training can be effective in preventing the occurrence of syncope in VVS patients. It can be chosen as a treatment method, but each study varied, and most patients can not adhere to the long-term, especially be discharged from hospital without medical supervision, so that seriously affect its efficacy. The vasovagal syncope can be divided into cardiac inhibition, vascular suppression and hybrid. Blood pressure of vascular suppression patients decreased but heart rate showed no significant decrease when syncope episodes,so the role of pacemaker which elevates heart rate to increasing cardiac output to resist the decline of blood pressure is small. All the cardiac inhibition and mixed patients have obvious decline in heart rate while syncope occurring, and dual-chamber CLS can pace at a higher frequency before the decline in heart rate, so as to prevent the occurrence of syncope. While medication is ineffectual, often considered to pacing therapy for patients cardiac inhibition or mixed. The North American Vasovagal Pacemaker Study (VPS) and The Vasovagal Syncope International Study (VASIS) show that random implantation of heart responsive dual-chamber pacemaker frequency on suppressed patients with recurrent syncope can reduce the occurrence of syncope, but these studies do not double-blind design, so there is the deviation of the results of the evaluation and the placebo effect of consulting room. In the Second Vasovagal Pacemaker Study (V PS II), Connolly and his colleagues conducted a randomized, double-blind, pacemaker therapy research pointed out that the effect of pacemaker therapy in syncope was lack of evidence Occhetta reported the INVASY and Pre-INVASY study respectively in2003and2004, a total of92WS patients were implanted dual-chamber CLS pacemakers, showing that the rate of syncope recurrence was only2.9%after the longest follow-up of47.3months. However, the time of follow-up was relatively shorter. Recently, Occhetta and his colleagues Miriam Bortnik followed-up35patients for average of (61±35) months, including29patients with no recurrence of syncope, and the times of syncope significantly reduced in the remaining patients over the previous. The quality of life of all patients significantly improved than before, and also proved that it was effective in mixed syncope patients. Pietro Palmisano divided41refractory WS patients into two groups (25vs.16), and respectively implanted the CLS pacemaker and traditional pacemaker with rate drop response functions into the patients. The results showed that the syncope recurrence rate was significantly reduced in CLS the pacemaker group (4%vs.38%) after the follow-up (4.4±3.0) months. The diagnosis and treatment guidelines for syncope of ESC in2009recommended pacing therapy to the treatment of reflex syncope for Class Ha indications, and considered that dual-chamber pacing is superior to single chamber pacing. Head-up tilt table testing(HUTT) is recognized as the effective method for checking on WS, and the sensitivity of the diagnosis of W’S is30%to85%and specificity is80%to90%. It is think that WS is benign syncope and it’s prognosis is good at the present time, but many patients with syncope recurring can lead to trauma. It will seriously impact on the quality of life of patients and bring patients spiritual burden, so it’s vital to search for an effective treatment. In this study, patients with reiterant episodes of syncope who were confirmed diagnosis of VVS from tilt test were divided into2groups, and respectively received pacing therapy and pharmacotherapy. And then follow-up and compare its efficacy, to explore whether the dual-chamber CLS pacemaker is the effective treatment for vasovagal syncope.ObjectivesTo observer effect of dual-chamber CLS pacing in the prevention of vasovagal syncope.Methods40patients(22male,18female) with recurrent syncope episodes who were diagnosed as the VVS by HUTT from Cardiovascular Department of Nanfang Hospital were collected in September2010to December2011.Average age of them were (54±9) years, and all enrolled patients were heart suppressed type or mixed type excluding vascular suppression type. All patients with recurrent frequent episodes of syncope preceding hospitalization had more than3syncopal episodes recurrent episodes (>3times) and at least2recurrence of syncope within6months. All patients underwent thorough inquiry detailted history, physical examination, routine biochemical check, ECG, Holter monitoring, echocardiography, X-ray chest film, X-ray of cervical spine, neck vascular ultrasound, head CT and EEG. A part of them had underwent cardiac electrophysiological study, coronary angiography and head MRI. All were excluded angiocardiopathy,brain vascular organic diseases and hematogenous or drug-induced syncope.The patients were randomly divided into two groups:(1) pacemaker group:18(10men and8women), age (55±9) years;(2) pharmacotherapy group:22(12men,10women), age (54±10) years.All the patients received different treatment and followed up. Patients in pacemaker group were respectively implanted with a dual-chamber CLS pacemaker (Biotronic produced, the Cylos series pacemakers, parameters is default setting,CLS reaction set is moderately sensitive) and meanwhile given oral metoprolol sustained-release tablets (the same dose and usage to the drug group). Those in pharmacotherapy groups were given oral metoprolol sustained-release tablets (trade name:metoprolol sustained-release tablets, AstraZeneca pharmaceutical Co., Ltd.)23.75mg per day for1week, and then the dose was adjusted to47.5mg per day.3months after discharge All patients came back to the hospital for checking investigation of HUTT, and regular monthly clinic or telephone follow-up for6to21months and recorded recurrence syncope and relapse frequency.All analysis was performed with the use of SPSS software version13.0. The measurement data were expressed as mean±standard deviation. Classification count data used x2test or Fisher’s exact test. Groups were compared with t-test or approximate t-test. A value of P<0.05was considered statistically significant for all statistical determinations.ResultsBalancing test between two groups:There was no statistically significant difference between the two groups,such as gender, age, syncope type, the number of syncope in nearly six months, basal heart rate, basal blood pressure and average time of follow-up.Efficacy comparison between two groups:The experimental results showed that seroconversion rate of HUTT was significantly higher in pacemaker group than pharmacotherapy group (P<0.01).There was1patient with HUTT positive in the pacemaker group, and15patients in the pharmacotherapy group.Follow-up results:The follow-up time between the two groups was no statistically significant [pacemaker group (13±5) months vs. pharmacotherapy group (13±5) months].After a mean follow-up of6～21(13±5) months, there was no patient with recurrent syncope and2patients with presyncope but significantly reduction in symptoms in the pacemaker group, and9patients with recurrent syncope but less attacks than before in the pharmacotherapy group. The syncope recurrence rate was significantly lower in pacemaker group than the pharmacotherapy group (P <0.01).ConclutionDual-chamber CLS pacing can prevent the occurrence of syncope in patients with vasovagal syncope.