[Cardioinhibitory carotid sinus hypersensitivity in subjects with symptomatic sinus dysfunction]

Cardioinhibitory carotid sinus hypersensitivity is present in about one third of patients affected by sinus dysfunction. Aim of the study was to evaluate whether carotid sinus hypersensitivity is related to a well defined (intrinsic or extrinsic) sinus node damage. Fifty-four patients with ecg signs of sinus dysfunction underwent an electrophysiological study and carotid sinus massage. Spontaneous heart rate and corrected sinus node recovery time were measured in basal condition, after adrenergic blockade (propranolol 0.2 mg/Kg i.v.) and after autonomic blockade (propranolol 0.2 mg/Kg i.v. plus atropine 0.04 mg/Kg i.v.). The association between sinus dysfunction and cardioinhibitory carotid sinus hypersensitivity was found in 18/54 pt. (16 men, 2 women; mean age +/- 1 SD 63.6 +/- 14.5 years). The remaining 36 patients (19 men, 17 women; mean age +/- 1 SD 65.8 +/- 9.8 years), affected by sinus dysfunction alone, were used as controls. No electrophysiological differences between the two groups were found; particularly, an abnormal intrinsic heart rate (according to Jose values) or an abnormal intrinsic corrected sinus node recovery time (greater than 385 msec.) were present in 83% of the patients in both groups. Among sinus dysfunction clinical features, heart rate, presence of spontaneous syncope, sino-atrial block or sinus arrest and organic heart disease were similar in the two groups while the percentage of patients with spontaneous atrial tachyarrhythmias (bradi-tachy syndrome) was significantly smaller (11% vs 44%; p less than 0.01) in carotid sinus hypersensitivity group. In conclusion, in sinus dysfunction patients, the presence of carotid sinus hypersensitivity cannot be used as a criterion to differentiate a subgroup with peculiar clinical and electrophysiological sinus node characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of atrial pacing to induce atrial fibrillation and flutter

We studied the clinical and electrophysiological significance of induction of atrial fibrillation or atrial flutter by atrial electrical stimulation. Our atrial fibrillation/flutter induction protocol included incremental atrial pacing up to a rate of 200 beats/min, ramp up to 250 and 300 beats/min, and bursts up to 600 beats/min. The end point was sustained atrial fibrillation/flutter induction (30 sec). We performed a provocative study on 72 subjects previously divided into three groups: the first was the control group; the second comprised patients with spontaneous paroxysmal atrial fibrillation/flutter; the third comprised patients without spontaneous atrial fibrillation/flutter, but with pathologies assumed to put them at risk for atrial fibrillation/flutter. We were unable to induce sustained atrial fibrillation/flutter in the control group, but were able to induce these arrhythmias in 95% of the subjects with spontaneous atrial fibrillation/flutter. Thus the methods have a sensitivity of 95% and a specificity of 100%. We were also able to induce atrial fibrillation/flutter in 57% of patients at risk for atrial fibrillation/flutter, that is a lower incidence than patients with spontaneous episodes. When sustained atrial fibrillation/flutter could be induced, it was well tolerated and stopped spontaneously in less than 24 hours without treatment. The technique thus involves no risk and demonstrates that antiarrhythmic therapy is usually superfluous in interrupting induced atrial fibrillation/flutter.

[Intermittent atrio-ventricular block induced by exertion. Description of 3 cases]

Three patients with 1:1 atrio-ventricular conduction at rest developed fixed 2nd or 3rd degree atrio-ventricular block during exercise testing. In all patients electrophysiologic study documented block distal to the atrioventricular node. The exercise induced block probably occurred because of increased atrial rate and abnormal refractoriness of the His-Purkinje conduction system. These findings suggest that high degree atrioventricular block appearing during exercise reflects conduction disease of the His-Purkinje system rather than of the atrio-ventricular node, even in absence of bundle branch block. These patients should be considered for permanent cardiac pacing.

[Association of the carotid sinus syndrome and orthostatic hypotension. Another potential cause of the failure of VVI electrostimulation]

The systolic blood pressure was measured during clinostatism and 15'', 1', 5' after standing in 101 patients with carotid sinus syndrome and in 101 controls matched for age, sex, and prevalence of organic heart disease. In the carotid sinus syndrome group we observed a greater systolic blood pressure reduction from the supine to standing position (20 +/- 19 vs 14 +/- 11 mmHg), a lower orthostatic pressure (111 +/- 23 vs 120 +/- 21 mmHg) and a greater incidence of orthostatic hypotension (defined as a blood pressure reduction greater than or equal to 50 mmHg or greater than or equal to 20 mmHg when orthostatic pressure was lower than 100 mmHg) (35% vs 17%). Twenty-three carotid sinus syndrome patients received a VVI pacemaker for control of their symptoms; after a mean follow-up of 12.2 +/- 7.7 months, unchanged or reduced symptoms persisted in 6 out 9 (67%) patients with previous orthostatic hypotension while only in 1 out of 14 (7%) patients without this feature. In conclusion, orthostatic hypotension is frequently associated with a carotid sinus syndrome and may account for relapses in some patients treated with VVI pacing.

[Cardioinhibitory reflex provoked by stimulation of carotid sinus in normal subjects and those with cardiovascular disease]

The normal range and the reproducibility of the cardioinhibitory carotid sinus reflex were studied in 288 apparently healthy subjects of different ages (aged from 17 to 84 yrs., 156 males, 132 females). In each subject we chose the longest RR interval as an activation index of the reflex obtained by carotid sinus massage; its mean value increased slightly with advancing age. In the were 1, 5, 2, 5, 3, 3 sec. respectively, with a 99% confidence limit. No sex difference was found. We studied also a group of 105 patients (aged from 39 to 82 yrs., 67 males, 38 females) with various types of cardiovascular disorders, without a previous history of spontaneous syncope. Abnormal maximum RR values were found in 18 of them (17%). This percentage was significantly higher than in normals (2%). In 11 patients (10%) the carotid sinus stimulation evoked a syncopal attack. It seems therefore that a statistically abnormal carotid sinus hypersensitivity can occur in a substantial number of cardiovascular patients without necessarily leading to spontaneous syncopal attacks. Finally the reproducibility of the cardioinhibitory reflex was tested in 42 patients with maximum RR interval values ranging from normal to extremely abnormal. In each subject a significant correlation (r = 0.79) was found between the maximum RR interval values tested in two occasions at intervals ranging from 1 hour to 3 months; besides a concordance in normal or abnormal result was present in 93% of the cases.

[Myocardial infarction induced by vincristine in patients with Hodgkin's lymphoma. Description of 2 cases and review of the literature]

Five patients with lymphoma and Vincristine induced myocardial infarction are described in the medical literature. We report two new cases, in whom an anterior myocardial infarction developed few hours after the second administration of the drug. In the reported cases a strict cause-to-effect relationship between the drug and acute myocardial infarction seems indicated by: the striking temporal coincidence between Vincristine administration and onset of chest pain; the additional myocardial infarctions in patients in whom the treatment was continued after the first event; the nearly constant absence of important coronary risk factors and the young age of the patients, making preexisting coronary atherosclerosis unlikely. The mechanism for the described association is still unknown: the possible causes are discussed.

[Limitations of the stress test in the diagnosis of the sick sinus syndrome]

Exercise stress test in patients with sick sinus syndrome helps to evaluate the heart rate response to the increased sympathetic and to the decreased parasympathetic discharge. Aim of our study was the assessment of the diagnostic accuracy of exercise stress test in this condition. To do so, we measured the heart rate at peak stress in 18 patients with sick sinus syndrome (16 men and 2 women aged 51-78 years, mean 68). Two control groups were chosen: one of 14 healthy subjects of the same age and sex and a second one of 19 patients of the same age and sex, with comparable heart disease as the patients under study, but without sinus dysfunction. Heart rate at peak stress was expressed as percent of the expected maximal sex--and age--corrected heart rate (% max HR). The sick sinus syndrome group was characterized by the presence of: syncope and/or near-syncope in 10 patients; slight (2), moderate (9), severe (7) sinus bradycardia; corrected sinus node recovery time longer than 500 msec in 7 out of 15 patients, detected during an electrophysiological study; abnormal intrinsic heart rate in 5 out of 11 patients, obtained by means of drug-induced autonomic blockade (metoprolol 0,2 mg/Kg i.v. and atropine 0,04 mg/Kg i.v.), and evaluated according to Jose's equation; abnormal intrinsic corrected recovery time (greater than 450 msec) in 8 out of 11 patients; increase in heart rate after atropine infusion (0,02 mg/Kg i.v.) of less than 90 beats/min in 15 out of 18 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

[Influence of beta block and autonomic nerve block on the recovery time of the sinus node in sick sinus syndrome and carotid sinus syndrome]

In order to evaluate the relative role of the automatic nervus system and of the intrinsic electrophysiologic properties on the sinus node function, we measured the corrected sinus node recovery time before and after autonomic nervous system blockade in 24 patients. Fourteen had a sick sinus syndrome, five had a carotid sinus syncope, two had syncope of unknown origin associated with bradycardia. Beta blockade was obtained by infusing metoprolol intravenously at a dosage of 0.2 mg/kg; complete automatic blockade was achieved by further i.v. administration of atropine at a dosage of 0.04 mg/kg. After beta blockade, the corrected sinus node recovery time increased in patients with sick sinus syndrome and intrinsic slow heart rate, whereas it decreased in patients with carotid sinus syncope or with syncope and bradycardia. In patients with sick sinus syndrome and normal intrinsic heart rate the response was variable. A positive direct correlation was found between the changes of the corrected sinus node recovery time induced by beta blockade and those induced by autonomic blockade; that is, both either prolonged or shortened the corrected sinus node recovery time. The changes of the corrected sinus node recovery time after beta blockade alone were inversely correlated with the intrinsic heart rate. We conclude that patients with intrinsic depression of the sinus node have an increased sympathetic tone.