Validation of a Method for Choice of Pacing Mode in Carotid Sinus Syndrome With or Without Sinus Bradycardia

A new method for selection of the pacing mode in 60 consecutive patients with severe cardie-inhibitory or mixed carotid sinus syndrome was prospectively validated. ODD pacing was preferred for 26 patients with: (1) the cardioinhibitory form and who had symptomatic pacemaker effect; (2) mixed type I form, (cardioinhibitory and vasodepressor) with symptomatic pacemaker effect, ventriculoatrial conduction or orthostatic hypotension; (3) mixed type II; or (4) severe bradycardia. VVI pacing was seiected in the remaining 34 patients without these symptoms. During a 32 ± 10 month follow-up period syncope and severe dizziness persisted in five patients in the VVI group (15%) and in three patients in the ODD group (12%). Symptomatic relief occurred in 87% (52/60) of patients. Minor symptoms persisted in 47% of the VVI group and 42% of the DDD group. No patient developed cardiac insufficiency or intolerance to pacing. During a 2-month duration a single-blind, randomized, cross-over study compared VVI and DDD pacing, 69% of the patients programmed from DDD to VVI suffered more frequent, severe, and intolerable symptoms. (1) Thirty four of 60 patients (57% of the entire group) in whom VVI pacing was satisfactory were identified prior to pacemaker implant. In the remainder, VVI pacing was contraindicated as it produced frequent side effects. (2) The preimplant predictive value that VVI pacing would be successful was 85% for those eventually receiving VVI pacemakers and the preimplant predictive value that VVI pacing would fail was 69% for those who underwent DDD implant.     

Natural and Unnatural History of Patients with Severe Carotid Sinus Hypersensitivity: A Preliminary Study

Natural history of patients with symptomatic severe carotid sinus hypersensitivity is not clearly known. In order to evaluate the effectiveness of pacing therapy in these patients we performed a randomized treatment/no-treatment prospective study in 35 patients. They were randomly assigned to two groups: 19 patients received no therapy, 16 patients received a VVI (# 11) or DDD (#) pacemaker implant. During the 8.4 ± 4.3 month follow-up period patients receiving no therapy had recurrence of syncope in 9 cases (47%) and minor symptoms in 13 (68%); at the 16th month, actuarial curve showed absence of syncope in 36% of patients and of any symptoms in 30%. During the 7.2 ±4.1 month follow-up period, the patients receiving the pacemaker implant had no recurence of syncope, minor symptoms in three (19%); at the 16th month, actuarial curve showed absence of syncope in 100% of patients and of any symptoms in 78%. During follow-up, 12 patients in no-treatment group received a pacemaker implant because of the recurrence of severe symptoms; successively they had a strong reduction of symptoms. In conclusion, this study definitively demonstrates that patients with severe symptomatic carotid sinus hypersensitivity had a high rate of recurrence of spontaneous symptoms and that in these patients cardiac pacing is a useful therapy.     

Carotid Sinus Hypersensitivity: Diagnosis of Vasodepressor Type in the Presence of Cardioinhibitory Type

The diagnosis of carotid sinus syncope may sometimes be difficult because its symptoms are not specific, especially in the older age group where carotid sinus hypersensitivity and syncope are not uncommon events. Of major diagnostic importance is the screening of the vasodepressor type of carotid sinus syncope in the presence of the cardioinhihitory type, as this diagnosis has important therapeutic applications. This work is based on the electrophysiological studies performed on seven men with a mean age of 61.9 years who had syncope of unknown cause and hypersensitive carotid sinus reflex. The studies revealed no evidence of sinus node dysfunction or high degree atrioventricular block that would explain the neurological symptoms. The studies also included carotid sinus stimulation with simultaneous interarterial pressure recordings with and without atrial or A-V sequential pacing. The pacing assured the maintenance of normal heart rate during carotid sinus stimulation. The results of these studies revealed that five patients suffered from cardioinhibitory type and two from a combined form of cardioinhibitory and vasodepressor type (mixed form) of carotid sinus syncope. A permanent cardiac pacemaker was implanted in the five patients with the isolated cardioinhibitory type and in one patient with the mixed type of carotid sinus syncope.     

CAROTID SINUS HYPERSENSITIVITY IN PATIENTS REFERRED WITH POSSIBLE EPILEPSY

SUMMARY Four patients with recurrent transient loss of consciousness, all of whom had previously undergone extensive non-invasive cardiological investigations, were referred for neurological opinion. All were found to exhibit a resting bradycardia and a cardioinhibitory response to carotid sinus stimulation. All were referred for cardiological opinion but only two patients were considered by their respective cardiologists to warrant pacemaker implantation. Those who did not receive a pacemaker continue to suffer from their symptoms. The clinical management of these patients highlights an apparent divergence of opinion amongst cardiologists on the treatment of carotid sinus hypersensitivity and emphasises that, unless the ECG and blood pressure responses to carotid sinus stimulation are observed in patients with histories of unexplained episodes of altered consciousness, carotid sinus hypersensitivity will be missed as a possible cause of symptoms. The presence of unexplained bradycardia may suggest carotid sinus hypersensitivity.     

Carotid Sinus Hypersensitivity and Syndrome in Patients with Chronic Atrial Fibrillation

Carotid sinus hypersensitivity (CSH) has been studied in subjects in sinus rhythm, but it has never been studied in patients with chronic atrial fibrillation (AF). After a finding of CSH in a patient with chronic AF and syncope, we studied the effects of carotid sinus stimulation in a group of patients with AF. Ten patients with chronic AF and normal ventricular rates who complained of dizziness or loss of consciousness underwent right and left carotid sinus massage (CSM) during ECG monitoring. A control group of ten patients with AF but without neurological symptoms was likewise investigated. CSH was present in eight symptomatic patients (5 patients presented right CSH, 1 left and 2 bilateral CSH), but only in three of the control patients. The mean duration of asystole induced by right CSM was 5.94 ± 2.10 seconds; the mean asystolic interval induced by left CSM lasted 8.58 ± 1.42 seconds. Six patients in the symptomatic group had a recurrence of spontaneous symptomatology during CSM, so that a diagnosis of carotid sinus syndrome was established. All symptomatic patients (8 patients with CSH, 2 patients with ventricular standstills but without CSH) received a permanent ventricular pacemaker. Following pacing, all patients, except for one with a significant drop of systolic blood pressure during CSM. became completely asymptomatic. In elder patients with chronic AF, CSH can induce prolonged ventricular asystole, which may be responsible for neurological symptoms such as dizziness, presyncope, or syncope, as observed in patients in sinus rhythm with carotid sinus syndrome. Abnormal sensitivity of the carotid sinus could, therefore, be one of the causes of increased morbidity and mortality in patients with chronic AF. Permanent ventricular pacing may help reduce these complications.     

Ventricular and Dual Chamber Pacing for Treatment of Carotid Sinus Syndrome

Thirty-nine consecutive patients with recurrent syncope and either cardioinhibitory or mixed type carotid sinus syndrome were studied to determine the efficacy of ventricular (VVI) pacing in 16, and dual chamber (DDD/DVI) in 23 patients. Only those patients affected by the isolated vasodepressor form were excluded. Follow-up lasted 12 ± 5 months. Symptoms were totally eliminated in 67% of patients and ameliorated with persistence of minor symptoms in 33%. All patients underwent an initial 2-month follow-up in the VVI mode. Evaluation of the 19 patients who remained symptomatic and the 20 who became asymptomatic with VVI pacing demonstrated that factors observed prior to pacemaker implant were related to failure of the VVI mode. These included symptomatic pacemaker effect (42% vs 0%), mixed carotid sinus syndrome (95% vs 65%), orthostatic hypotension (47% vs 15%), or ventriculoatrial conduction (68% vs 38%). In the 23 patients with dual chamber pacing, random 2 month comparisons were performed between VVI and DVI/DDD pacing. The dual chamber mode was preferred by 14 patients, none preferred the VVI mode and nine noted no difference. Comparison of the two groups found that the factors linked to DVI/DDD preference were symptomatic pacemaker effect (50% vs 0%), ventriculoatrial conduction (78% vs 44%), or orthostatic hypotension (50% vs 11 %). VVI pacing is efficacious in a high proportion of patients affected by cardioinhibitory or mixed carotid sinus syndrome. The identification of causes of VVI pacing failure allows determination of those who will benefit from VVI pacing and those who should have DVI/DDD. VVI pacing is suggested for the cardioinhihitory type with no symptomatic pacemaker effect and for the mixed type with no symptomatic pacemaker effect or orthostatic hypotension or ventriculoatrial conduction. Dual chamber pacing should be used in all other instances.     

Ventricular Pacing as the Preferable Mode for Long-Term Pacing in Patients with Carotid Sinus Syncope of the Cardioinhibitory Type

This study was designed to determine the efficacy of long-term VVI pacing in patients having the isolated cardioinhibitory type of carotid sinus syncope. The study included 20 patients suffering from repeated syncopal attacks; all were proven by electrophysiological studies to have isolated forms of cardioinhibitory type carotid sinus syncope. Long-term pacing by the VVI mode was carried out in all patients by programming the pacemaker rate well below the patient's sinus rate. The follow-up period after pacemaker implantation, which ranged from 2 to 54 months (average, 20 months), revealed that none of the patients had any recurrence of syncopal attack. Repeated Holter monitoring showed that ten had permanent sinus rhythm without any artificial pacing activity, while in the other ten, pacemaker activity was recorded--predominant in two patients and rare in the other eight. During Holter monitoring, attacks of weakness were reported by four patients; however, they were not related to pacemaker activity. This report indicates the importance of electrophysiological studies in patients suffering from carotid sinus syncope. These studies make possible the diagnosis of the isolated form of cardioinhibitory type syncope for which VVI pacing offers complete relief of symptomatology, thus rendering AV sequential pacing superfluous.     

Is DDD Superior to VVI Pacing in Mixed Carotid Sinus Syndrome? An Acute and Medium-Term Study

The aim of this study was to evaluate fhe importance of atrial synchronism for pacing therapy of patients with mixed carotid sinus syndrome. In 23 patients (21 m, two f: mean age 69 ± 8 years) affected by symptomatic mixed carotid sinus syndrome we performed: (1) Research of ventriculo-atrial conduction, orthostatic hypotension and pacemaker effect; and [2] Carotid sinus massage in the standing position during VVI and DVI temporary pacing. Next, ail patients received a permanent DDD pacemaker and entered a 2 month two period single-blind, randomized, cross-over study on DVI/DDD versus VVI mode. During the DVI/DDD period, no syncope occurred in any patients, minor symptoms persisted in 11 (48%) of them; during VVI period syncopes recurred in three patients, symptoms requiring the withdrawal of VVI pacing and premature DVI/DDD reprogramming in eight patients, minor symptoms in 17 (74%). A comparison between 14 patients, who preferred DVI/DDD period (Group A), and the remaining nine patients who noted no preference between DVI/DDD and VVI period (Group B) was performed on the basis of the preimplant evaluation. Group A patients had a greater pacemaker effect (-34 ± 16 mmHg vs -16 ± 14 mmHg) and a higher prevalence of symptomatic pacemaker effect (50% vs 0%), of ventriculo-atrial conduction (78% vs 44%) and of orthostatic hypotension (50% vs 11%), while the entity of the systolic pressure fall caused by carotid sinus massage was similar in the two groups either during VVI mode (Group A-51 ± 16 mmHg vs Group B-56 ± 27 mmHg) or DVI mode (Group A-38 ± 17 mmHg vs Group 3–45 ± 17 mmHg). Thus, we conclude that vasodepressor reflex of carotid sinus syndrome is not prevented by DVI/DDD pacing even if the loss of atrial synchronism resulting from WI pacing, by adding an important pacemaker effect, causes a more severe hemodynamic consequence. DVI/DDD pacing is more effective than VVI in 61% of patients. When pacemaker effect, ventriculoatrial conduction and orthostatic hypotension are present, VVI failure is possible, therefore DVI/DDD stimulation is indicated; on the contrary the evaluation of the vasodepressor reflex during WJ or DVI temporary pacing is of little value in the choice of the mode of pacing.     

Pacing for Carotid Sinus Syndrome and Sick Sinus Syndrome

BRIGNOLE, M., ET AL: Pacing for Carotid Sinus Syndrome and Sick Sinus Syndrome. The real incidence of pacemaker implants for carotid sinus syndrome (CSS) and the relation between CSS and sick sinus syndrome (SSS) is not precisely known. Patients who needed pacing therapy because of atrial bradyarrhythmias were investigated by means of carotid sinus massage, dynamic ECG, and invasive electrophysiological sinus node evaluation. Of 298 consecutive patients receiving a pacemaker implant, 36 (12%) had a severe cardioinhibitory carotid sinus reflex with reproducible spontaneous symptoms (CSS), 33 (11%) had sinus bradycardia < 50 beat/min or an abnormal electrophysiological evaluation (SSS) and 24 (8%) had both (CSS + SSS). The annual incidence was 40, 37, and 26, respectively, implants per year/million of inhabitants (total incidence 325). Patients affected by CSS, if compared with those affected by SSS, showed: a higher prevalence of syncope (97% vs 42%); more syncopal, episodes per patient (2.9 ± 2 vs 1.8 ± 0.9); a lower prevalence of associated cardiac diseases (53% vs 100%); cardiac enlargement (36% vs 88%); heart failure (6% vs 36%) and paroxysmal atrial fibrillation (0% vs 42%); and a more frequent indication for VVI pacing (75% vs 3%). In patients with CSS + SSS, intermediate characteristics were present. In conclusion, CSS is as frequent an indication to cardiac pacing as SSS; clinical differences justify a distinction between them, even if they are associated in 26% of cases.     

Diagnosis and treatment of sick sinus syndrome

Sick sinus syndrome comprises a variety of conditions involving sinus node dysfunction and commonly affects elderly persons. While the syndrome can have many causes, it usually is idiopathic. Patients may experience syncope, pre-syncope, palpitations, or dizziness; however, they often are asymptomatic or have subtle or nonspecific symptoms. Sick sinus syndrome has multiple manifestations on electrocardiogram, including sinus bradycardia, sinus arrest, sinoatrial block, and alternating patterns of bradycardia and tachycardia (bradycardia-tachycardia syndrome). Diagnosis of sick sinus syndrome can be difficult because of its nonspecific symptoms and elusive findings on electrocardiogram or Holter monitor. The mainstay of treatment is atrial or dual-chamber pacemaker placement, which generally provides effective relief of symptoms and lowers the incidence of atrial fibrillation, thromboembolic events, heart failure, and mortality, compared with ventricular pacemakers.     

Hypersensitive Carotid Sinus Syndrome Manifested as Cough Syncope

We describe a patient with cough syncope who was found to have carotid sinus hypersensitivity with mixed cardioinhibitory and vasodepressor responses. Symptoms were ameliorated by denervation of the more hypersensitive carotid sinus. Spontaneous atypical Wenckebach cycles in this patient were caused by the combined hypersensitive cardioinhibitory and vasodepressor responses. This report stresses the importance of checking blood pressure as well as heart rate in all pa-tients in whom carotid sinus syndrome is suspected.     

Sinus node dysfunction in pediatric and young adult patients: treatment by implantation of a permanent pacemaker in 39 cases

To examine the clinical course of sinus node dysfunction that necessitates permanent pacing in the pediatric and young adult populations, we studied the records of the 39 patients 40 years of age or younger (mean age, 23 years) who underwent implantation of a permanent pacemaker for treatment of this disorder at our medical center between 1960 and 1983. The tachycardia-bradycardia syndrome was the most common rhythm disturbance, and syncope was the most frequent initial symptom. All symptomatic patients noted resolution of symptoms after pacemaker implantation. Twenty-five of the 39 patients (64%) had associated cardiovascular disease, most commonly transposition of the great arteries. In each of the 11 patients with this anomaly, sinus node dysfunction developed after a surgical procedure for correction of the defect. Of the total patient population, 20 patients (51%) had previously undergone a cardiac operation. The mean interval between pacemaker implantation and the previous operation was 105 months. After a mean follow-up of 50.5 months, the patients with no obvious underlying heart disease have done well. Each of the eight patients who have died had underlying cardiovascular disease. None of the deaths was thought to be pacemaker related. Sinus node dysfunction should be considered in the differential diagnosis of young patients with syncope or dizziness, especially if they have undergone a reparative cardiac surgical procedure. If symptomatic sinus node dysfunction is confirmed, permanent pacing is an effective therapeutic modality. In the absence of associated heart disease, the prognosis seems to be excellent.     

Hemodynamic and symptomatic consequences of ventricular pacing

After implantation of a ventricular demand pacemaker (VVI), occasional patients continue to have dizziness, syncope, or near syncope ("pacemaker syndrome"). To identify patients in whom VVI pacing may have deleterious effects, we compared cuff blood pressure responses to VVI pacing with blood pressure responses to atrioventricular sequential pacing (DVI) or sinus rhythm in 50 consecutive patients. Patients with intact ventriculoatrial conduction had a much greater decrease in systolic blood pressure with VVI pacing (24 +/- 11 mm Hg) than those with ventriculoatrial dissociation (-4 +/- 15 mm Hg) (P less than 0.005). Patients who were in heart failure had a lesser decrease in blood pressure with VVI pacing than did those without failure (P less than 0.05); 13 of the 14 heart failure patients lacked ventriculoatrial conduction. Ten patients had symptomatic dizziness after VVI pacing; the incidence of symptoms was higher in patients with ventriculoatrial conduction (9 of 23) than in those without ventriculoatrial conduction (1 of 27) (P less than 0.003). We conclude that the presence of intact ventriculoatrial conduction appears to be a crucial determinant of the hemodynamic response to VVI pacing, and its presence may identify patients who are at risk for "pacemaker syndrome."     

Evaluation of Sinus and Atrioventricular Nodes Function in Patients with Vasovagal Syncope

Aim: Evaluation of sinus and atrioventricular nodes function as a potential factor responsible for prolonged bradycardia, asystole, or both in patients with cardioinhibitory and non-cardioinhibitory vasovagal syncope (VVS). The study included 258 patients (mean age = 47.7 ± 17.2 years; range 18–62; 147 females) with a history of VVS. They were divided among four groups, according to results of head-up tilt test (HUTT).
Methods: All patients underwent standard HUTT, carotid sinus massage (CSM), and rapid transesophageal atrial pacing for evaluation of total sinus node recovery time (SNRT), and corrected sinus node recovery time (CNRT), resting and intrinsic heart rate (IHR), and Wenckebach point (WP). Values of SNRT > 1,500 ms, CNRT > 525 ms, WP < 130 bpm, and CSM-induced pause >3 seconds were considered abnormal.
Results: SNRT, CNRT, and WP before and after pharmacological blockade, resting heart rate, and IHR did not differ significantly among the study groups. The prevalence of mild sinus node dysfunction (SND), decreased value of WP, and cardioinhibitory carotid sinus hypersensitivity was similar among all study groups.
Conclusions: The prevalence of mild SND, abnormal atrioventricular conduction, and carotid sinus hypersensitivity (CSH) was similar among patients with VVS regardless of the type of vasovagal reaction. SND and CSH do not seem to play an important role in the pathogenesis of cardioinhibitory vasovagal reaction.     

起搏治疗对病窦综合征患者预后的影响

目的：观察不同起搏方式对病窦综合征预后的影响。方法：136例病窦综合征患者安装了永久人工心脏起搏器，其中VVI54例，DDD70例，AAI12例，分别随访了2～7．5年，观察房颤，充血性心力衰竭和起搏器综合征的发生率及病死率。结果：DDD，AAI与VVI起搏相比，房颤、充血性心力衰竭和起搏器综合征的发生率及病死率明显降低。结论：对病窦综合征患者起搏治疗应选择DDD和AAI起搏方式。     

Intermittent Ventricular Standstill During Chronic Atrial Fibrillation in Patients with Dizziness or Syncope

Thirty-two patients with atrial fibrillation and normal ventricular rates who complained of dizziness or loss of consciousness underwent 24-hour ambulatory electrocardiographic monitoring. A control group of 25 patients in atrial fibrillation but without symptoms of dizziness or loss of consciousness was likewise investigated. All patients remained in atrial fibrillation; periods of ventricular standstill (mean, 2.9; range, 1.8-8.0) were present in 31 symptomatic patients but in only three of the control patients (mean, 1.9 s; range, 1.7-2.4). Twenty-three symptomatic patients with pauses greater than or equal to 2.0 s received a demand pacemaker. Following pacing, nineteen became completely asymptomatic; four patients continued to have dizziness but three of these, who also experienced syncope, no longer did so (mean follow-up, 13 months; range, 6-30). It is suggested that ventricular standstill may commonly occur in patients with controlled atrial fibrillation who complain of dizziness or syncope and that the majority will benefit from permanent cardiac pacing.     

Natural History of Severe Sinus Bradycardia Discovered by 24 Hour Holter Monitoring

This study follows patients with severe sinus bradycardia (40 beats per minute for 6 seconds or greater) in order to evaluate mortality and the effectiveness of permanent pacemaker insertion. Severe sinus bradycardia was noted on a 24-hour Holter in 95 patients. There were 64 males and 31 females with a mean age of 69 +/- 10 years. All were available for follow-up at 26 +/- 13 months. Twenty-eight required a permanent pacemaker at an average of 2 +/- 3 months after the Holter. Of this group 12 had the Holter for arrhythmia, 11 for cerebral symptoms, 4 for palpitations and 1 for chest pain. Only 1 was taking digitalis and no patients were taking Inderal. Six (21%) died at a mean interval of 21 +/- 15 months following pacemaker insertion. Sixty-seven did not require pacemaker insertion. The indications for Holter monitoring were arrhythmia in 16, palpitations in 19, cerebral symptoms in 20 and chest pain in 12. Four of these patients were on digitalis, 8 on Inderal, and 4 on both. Eleven (16%) died at a mean interval of 12 +/- 7 months after the initial Holter recording. Dizziness and/or syncope reoccurred in 22. Five had these symptoms even after pacemaker insertion. We conclude that severe sinus bradycardia is associated with a significant mortality. Insertion of a permanent pacemaker may decrease recurrent symptoms and slightly increase time of survival, but does not appear to influence the overall survival rate.     

The Use of Serotonin Reuptake Inhibitors for the Treatment of Recurrent Syncope Due to Carotid Sinus Hypersensitivity Unresponsive to Dual Chamber Cardiac Pacing

Carotid sinus hypersensitivity can be a cause of recurrent unexplained syncope in the older patient. Dual chamber cardiac pacing may relieve the bradycardia, but may not affect the vasodilatory component of this disorder. We report on two patients with carotid sinus hypersensitivity with a predominant vasodilatory component who experienced recurrent syncope following permanent pacemaker implantation. Both patients were treated with serotonin reuptake inhibitors and after 4–6 weeks of therapy had complete resolution of symptoms. We conclude that serotonin reuptake inhibitors may be useful in the treatment of recurrent syncope due to carotid sinus hypersensitivity resistant to dual chamber cardiac pacing.     

Course of Symptoms and Spontaneous ECG in Pacemaker Patients: A 5-Year Follow-up Study

We investigated the course of symptoms and the spontaneous ECG retrospectively in 308 patients who had received a pacemaker because of atrioventricular (AV) block (n = 115), sick sinus syndrome (SSS, n = 107), bradyarrhythmic atrial fibrillation (bradyarrhythmia, n = 51), carotid sinus syndrome (CSS, n = 16), complete bifascicular block associated with 1st degree AV block (n = 13) and with other indications (n = 6). The mean implantation time was 63 months. The clinical state of 93% of all patients improved after pacemaker implantation; their symptoms decreased markedly. Persisting syncopy in some patients with SSS, however, supports a restricted implantation policy. We rarely saw improved AV conduction in patients with AV block (11%). Furthermore, in patients with SSS, atrial fibrillation occurred significantly more often (35%) than in those with AV block (17%; P less than 0.01). Only 3% of patients with SSS developed 2nd and 3rd degree AV block within the observation period. In all patients with initial bifascicular block and additional 1st degree AV block, pacing prevented further syncopal attacks; four of them showed 3rd degree AV block at control, indicating that pacemaker implantation is mandatory in symptomatic patients with bifascicular disease and 1st degree AV block.     

Recurrent Symptoms after Ventricular Pacing in Unexplained Syncope

We report clinical and hemodynamic data in two cases of recurrent syncope. Both patients received permanent demand ventricular pacing (VVI) for unexplained syncope. Both patients experienced recurrent syncope after pacemaker implantation. They later underwent 60 degrees head-up tilt testing, initially noninvasively and then with hemodynamic profile. A vasovagal response to tilt occurred with bradycardia and was complicated by the onset of ventricular pacing and retrograde atrioventricular conduction (RAVC) with hemodynamic deterioration and rapid reproduction of syncope. Limited intracardiac electrophysiological study (EPS) excluded atrioventricular (AV) conduction disease, sinus node disease, and carotid sinus syndrome, and confirmed RAVC. Both patients were upgraded to dual chamber pacing, DDI mode, with 50/80 rate hysteresis. One patient was asymptomatic at repeat tilt testing; the other experienced continued symptoms due to the vasodepressor component of vasovagal syncope. Cardiac pacing alone is ineffective treatment for this phenomenon, and no proven therapy is presently available. Ventricular pacing applied to patients with unexplained syncope may lead to an increase in or continuation of symptoms rather than an amelioration. There is a need for full investigation of such patients, which must include tilt testing, to allow for the most accurate diagnosis possible and guide the most appropriate therapy.