Mechanism of syncope in patients with bundle branch block and negative electrophysiological test.

BACKGROUND: In patients with syncope and bundle branch block (BBB), syncope is suspected to be attributable to a paroxysmal atrioventricular (AV) block, but little is known of its mechanism when electrophysiological study is negative. METHODS AND RESULTS: We applied an implantable loop recorder in 52 patients with BBB and negative conventional workup. During a follow-up of 3 to 15 months, syncope recurred in 22 patients (42%), the event being documented in 19 patients after a median of 48 days. The most frequent finding, recorded in 17 patients, was one or more prolonged asystolic pause mainly attributable to AV block; the remaining 2 patients had normal sinus rhythm or sinus tachycardia. The onset of the bradycardic episodes was always sudden but was sometimes preceded by ventricular premature beats. The median duration of the arrhythmic event was 47 seconds. An additional 3 patients developed nonsyncopal persistent III-degree AV block, and 2 patients had presyncope attributable to AV block with asystole. No patients suffered injury attributable to syncopal relapse. CONCLUSIONS: In patients with BBB and negative electrophysiological study, most syncopal recurrences have a homogeneous mechanism that is characterized by prolonged asystolic pauses, mainly attributable to sudden-onset paroxysmal AV block.

Effects of long-term vasodilator therapy in patients with carotid sinus hypersensitivity.

BACKGROUND: In patients affected by carotid sinus hypersensitivity, long-term vasodilator therapy might increase the risk of syncopal episodes by reducing systolic blood pressure and venous return to the heart. METHODS AND RESULTS: Thirty-two patients (mean age 73 +/- 9 years; 20 men) who met all the following criteria were included: (1) one or more episodes of syncope occurring during long-term (>6 months) treatment with angiotensin-converting enzyme inhibitors, long-acting nitrates, calcium antagonists, or a combination of these; (2) a positive response to carotid sinus massage, defined as the reproduction of spontaneous syncope in the presence of ventricular asystole > or =3 seconds or a fall in systolic blood pressure > or =50 mm Hg; (3) negative workup for other causes of syncope. The patients were randomly assigned to continue or to discontinue use of vasodilators; carotid sinus massage was repeated 2 weeks after randomization. By the end of the study period, the baseline values of systolic blood pressure were significantly different between the 2 groups of patients both in supine (P=.01) and upright (P=.03) positions. Syncope had been induced by carotid sinus massage in 81% of patients in the "on-vasodilator" group and in 62% of patients in the "off-vasodilator" group (P=.21). The cardioinhibitory reflex was of similar magnitude in the 2 groups, being found in 50% of the patients in each group, with a maximum ventricular pause of 7.1 +/- 2.7 and 6.7 +/- 1.8 seconds, respectively. The percentage decrease of blood pressure did not differ between the 2 groups, even if, in absolute values, the baseline difference of blood pressure roughly persisted for the duration of the test. In consequence of that, the rise of blood pressure to similar values was delayed approximately 30 seconds in the "on-vasodilator" group and took more than 2 minutes to return to baseline values. CONCLUSIONS: In patients affected by carotid sinus hypersensitivity, chronic vasodilator therapy does not have a direct effect on carotid sinus reflexivity, although the delayed recovery of pretest blood pressure values could indirectly potentiate the severity of the clinical manifestations of the syndrome. The persistence of hypotension for a longer time after the end of the massage suggests that vasodilators cause an impairment of compensatory mechanisms.

[The re-evaluation of the vasodepressive component in the carotid sinus syndrome]. / Rivalutazione della componente vasodepressiva nella sindrome del seno carotideo.

BACKGROUND: The evaluation of the vasodepressor (VD) reflex of the carotid sinus syndrome is usually inaccurate, due to the difficulty in blood pressure measurement. AIM: To study the VD reflex with a beat-to-beat not invasive technique. METHODS: We investigated 68 patients (49 males, 19 females; mean age 70 +/- 11 years) affected by carotid sinus syndrome: cardioinhibitory (CI) form was present in 47 patients, mixed (M) form in 10 patients and VD form in 11 patients. The control group consisted of 9 patients (6 male, mean age 71 +/- 8 years) affected by third degree atrioventricular block who had received the implant of a permanent pacemaker and were pacemaker-dependent with a prolonged asystole at time of temporary inhibition of the pacemaker itself. The study of the VD reflex was performed in the supine position; beat-to-beat arterial systolic pressure was monitored by a photoplethysmographic method using a finger cuff (Finapres technique). RESULTS: In all the patients the carotid sinus massage caused a marked fall in systolic blood pressure which was greatest at the end of the massage: from 143 +/- 25 mm Hg to 74 +/- 20 mm Hg in the patients with CI form, from 144 +/- 14 mm Hg to 76 +/- 18 mm Hg in those with M form and from 125 +/- 26 mm Hg to 65 +/- 13 mm Hg in those with VD form. A decrease in systolic blood pressure > or = 50 mm Hg occurred in 84% of cases. Afterwards, the patients with CI form had a progressive increase of systolic blood pressure that reached the initial value after a mean of 27 seconds. In the patients with VD form systolic blood pressure was significantly (p < or = 0.5) lower than that observed in all the other groups, beginning from the third second after the end of the massage; mean systolic blood pressure value remained significantly lower than the initial value for more than 27 seconds. The patients with M form showed an intermediate pattern. Also control group patients showed a fall in systolic blood pressure immediately after pacemaker inhibition (from 152 +/- 29 mm Hg to 87 +/- 25 mm Hg) that was of similar extent than that observed in carotid sinus syndrome patients, but pressure returned to initial value within 9 seconds. CONCLUSIONS: An important VD reflex is present in most patients with carotid sinus syndrome. It lasts more than the CI reflex and it persists for several seconds after the end of the massage. The initial fall of systolic blood pressure is of similar extent in all the forms of carotid sinus syndrome, but the patients with the VD form are characterized by a longer duration and greater entity of the decrease. These results point out the importance of the VD reflex in patients with the carotid sinus syndrome.

[Progression to 2d and 3d grade atrioventricular block in patients after electrostimulation for bundle-branch block and syncope: a long-term study]. / La progressione a blocco atrioventricolare di II e III grado nei pazienti elettrostimolati per blocco di branca e sincope: uno studio a lungo termine.

BACKGROUND: Patients with bundle branch block and syncope, especially those with abnormal electrophysiologic study, are at high risk of progression to second-or third-degree atrioventricular block and therefore they often receive a permanent back-up pacemaker. The aim of this study was to evaluate of the incidence of bundle branch block progression to second or third-degree atrioventricular block during long-term follow-up. METHODS: A retrospective study was performed on 60 patients (49 males, age 77 +/- 9 years) with bundle branch block and permanent back-up pacemaker. The patients were subdivided into 3 groups: 13 patients, at pre-implant electrophysiologic study had HV interval > or = 100 msec and/or second- or third-degree atrioventricular block induced by ajmaline i.v. administration (Group 1); 20 patients with HV interval of 70-100 msec and/or HV > or = 120 msec after ajmaline administration (Group 2); 27 patients who had received a permanent pacemaker because of carotid sinus syndrome or sick sinus syndrome (22 patients) or because of recurrent syncopes and negative electrophysiologic study (5 patients) (Group 3). RESULTS: During a mean follow-up of 62 +/- 41 months, 17/60 patients (28%) had progression to second- (n = 4) or third-degree (n = 13) atrioventricular block: atrioventricular block occurred in 54% of Group 1 patients in 25% of Group 2 patients and in 19% of Group 3 patients. The actuarial rate of progression to atrioventricular block for the overall population was, at 5 and 10 years, 25% and 58% respectively; in Group 1 it was 46% and 62%; in Group 2 it was 22% and 55% and in Group 3 it was 21% and 59% (p = 0.06). The patients with right bundle branch block and left anterior hemiblock were at higher risk of progression to atrioventricular block than those with right bundle branch block or left bundle branch block (risk 42% vs 14%, p = 0.06). The presence of an abnormal electrophysiologic study did not increase the progression rate either in the patients with right bundle branch block and left anterior hemiblock (risk of 43%), nor did it in those patients with other types of bundle branch block (risk of 18%). Moreover, the induction of second- or third-degree atrioventricular block during ajmaline administration was associated with a higher risk of block during the follow-up (60% vs 25%, p = 0.06). CONCLUSIONS: Patients treated with pacemaker because of symptomatic bundle branch block have a high risk of progression to second- or third-degree atrioventricular block in the long-term follow-up. The results argue against the practical usefulness of electrophysiological study since a risk stratification could be obtained by the simpler surface electrocardiogram; moreover, risk of block was also present in the patients affected by carotid sinus syndrome or sick sinus syndrome, and in those affected by unexplained syncope with negative electrophysiologic study.

Role of autonomic reflexes in syncope associated with paroxysmal atrial fibrillation.

OBJECTIVES: The purpose of this study was to evaluate the role of autonomic reflexes in the genesis of syncope associated with the onset of paroxysmal atrial fibrillation. BACKGROUND: Syncope associated with paroxysmal atrial fibrillation has been interpreted as an ominous finding predictive of rapid ventricular rates. However, various mechanisms may be involved when heart rate is not particularly high. METHODS: Forty patients (age 60 +/- 14 years, 20 men, 20 women) with syncope and atrial fibrillation were compared with atrial fibrillation without syncope. Carotid sinus massage and head-up tilt testing (at 60 degrees for 60 min at baseline and during isoproterenol infusion) were performed during sinus rhythm. A positive response was defined as the induction of syncope. Atrial fibrillation was also induced on a tilt table at 60 degrees by means of short bursts of atrial pacing. RESULTS: Results of carotid sinus massage were positive in 15 (37%) of 40 patients but in no control subjects (p = 0.002). Head-up tilt test findings were positive in 25 (66%) of 38 patients and in 2 (12%) of 16 control subjects (p = 0.0004). The induction of atrial fibrillation in the upright position elicited syncope in 16 (42%) of 38 patients but in none of 16 control subjects (p = 0.001). At the beginning of atrial fibrillation, systolic blood pressure was lower in patients than in control subjects (88 +/- 32 vs. 127 +/- 32 mm Hg), whereas mean heart rate was similar (142 +/- 35 vs. 134 +/- 25 beats/min). The correlation between heart rate and systolic blood pressure was weak (r = 0.35), and in five patients syncope occurred at a heart rate < or = 130 beats/min. At the time of syncope, heart rate decreased (-12 +/- 21 beats/min) in patients with induced syncope, whereas it remained unchanged in patients without induced syncope (+1 +/- 17 beats/min, p = 0.04) or slightly increased in control subjects (+9 +/- 21 beats/min, p = 0.009). CONCLUSIONS: Patients with syncope associated with paroxysmal atrial fibrillation are predisposed to an abnormal neural response during both sinus rhythm and arrhythmia. In some patients the onset of atrial fibrillation triggers vasovagal syncope.