30 research outputs found
Recommended from our members
Mechanisms Determining the Ventricular Rate in Wolff-Parkinson-White Arrhythmias
Recommended from our members
Atrioventricular block after reciprocating atrioventricular junctional tachycardia
Short runs of symptomatic atrioventricular (A-V) block occurred after spontaneous cessation of reciprocating A-V Junctional tachycardia in a patient with right bundle branch block, normal H-V interval and sinus nodal dysfunction. These episodes were characterized by long (more than 1 sec) P-P intervals during which the A deflections were not followed by His bundle electrograms. Three possible explanations are: (1) a posttachycardia-induced period of abnormally prolonged A-V nodal refractoriness; (2) pseudo-A-V block produced by concealed A-V Junctional tachycardia, or (3) bradycardia-dependent (phase 4) A-V block at the “upper” His bundle, above the site from which the H deflection was recorded
Recommended from our members
Electrophysiologic Studies in a Patient with Atrial Flutter and 1:1 Atrioventricular Conduction
Intracardiac electrophysiologic studies were performed in a patient having paroxysms of atrial flutter with 1:1 atrioventricular (A-V) conduction. Although duration of conduction intervals was normal during sinus rhythm, the atrio-His (A-H) interval did not show the expected increase when the atria were stimulated at progressively higher rates. The results of pacing with the extrastimulus technique also indicated that the refractory periods of the A-H tissues were shorter than normal. Yet, intravenously administered ouabain produced a significant increase in these refractory periods. The findings in this case are compatible with a partial A-V nodal bypass with a shorter refractory period than the A-V node or with an A-V node with unusual capacity for rapid conduction. The response to ouabain therapy was that of A-V nodal tissues
Recommended from our members
Sextapolar catheter electrode for temporary sequential atrioventricular pacing
A sextapolar catheter electrode for temporary sequential atrioventricular pacing on demand was used in 17 patients. Stimulation was performed as desired provided that the catheter tip was properly placed in the right ventricular apex. This catheter will permit wider use of this modality of pacing in those patients who might benefit from it
Recommended from our members
The use of left atrial electrograms in the evaluation of anomalous conduction pathways capable of only ventriculoatrial conduction
Recommended from our members
Effects of the pacing site in sinus node reentrant tachycardia
His bundle recordings and premature atrial stimulation from coronary sinus, mid-right atrium and high-right atrium were performed in a patient with repetitive supraventricular tachycardias. Regardless of the paced site, there was a range of coupling intervals during which testing stimuli elicited short runs of premature beats. The corresponding P waves were positive in leads I, II and II and had a high-to-low right atrial activation sequence. Their morphology was similar to that of sinus beats. However, sustained tachycardia occurred only when pacing was performed from the coronary sinus. Therefore, it is postulated that the site of stimulation might be important in the genesis and (perhaps) perpetuation of this arrhythmia by changing the site and (or) mode of entry into the area where this type of tachycardia occurs. Though sinus node reentry was the most likely mechanism, it could not be determined whether the circuit involved the sinus node per se or the so called perinodal fibers
Transverse Spread and Longitudinal Dissociation in the Distal A-V Conducting System
Isolated preparations of portions of the canine intraventricular conducting system were studied by microelectrode techniques in order to determine the nature of transverse spread and longitudinal dissociation of impulses in bundle branches and false tendons. Driving stimuli were delivered to an eccentric location on normal conducting tissue, and the arrival times of the propagating impulses were mapped along the length and width of the bundle branch, or along the false tendon ipsilateral and contralateral to the site of stimulation. The difference between the arrival times on the two sides was found to decrease progressively as a function of distance from the site of stimulation, the data suggesting that transverse spread of impulses involves propagation through transverse crossover points between the longitudinally oriented conducting elements. Impulses originating eccentrically became uniformly conducted across the transverse axis of bundle branches 8-15 mm from the level of the stimulating electrode, and of false tendons 2-4 mm from the stimulus site. True longitudinal dissociation, producing conduction maps different from those representing normal transverse propagation, was seen occasionally in tissue having longitudinally oriented strips of abnormal tissue. However, early premature stimulation commonly resulted in longitudinal temporal dissociation of the premature responses, possibly due to functional block in the transverse crossover fibers
Recommended from our members
Mitral valve prolapse: Recent concepts and observations
The conditions associated with prolapse of the posterior leaflet of the mitral valve are multiple. The mechanisms of mitral valve prolapse as well as the pathogenesis of pain and ectopic impulse formation are reviewed. Propranolol appears to be the drug of choice for the symptomatic treatment of patients with this syndrome since it decreases myocardial oxygen demand and wall tension thus reducing or abolishing the discrepancy between myocardial oxygen demand and supply within the mitral apparatus. It has also been reported to modify the auscultatory findings associated with this condition.
The frequency of this mitral valve abnormality in patients with obstructive coronary artery disease is reviewed. It appears that prolapse of the posterior leaflet scallops in patients with significant obstructive coronary artery disease represents an intermediate stage before mitral insufficiency occurs. This group of patients with papillary muscle dysfunction includes those with prolapsed leaflets without mitral insufficiency, those with systolic murmurs and compensated heart failure and others with progressive cardiac decompensation and severe mitral regurgitation
Recommended from our members
Changes in the Pattern of Old Inferior Wall Myocardial Infarction Produced by Acute Left Bundle Branch Block and Hemiblock
Varying degrees of functional conduction disturbances occurred in two patients with old IWMI during aberration of spontaneous, or induced, premature atrial contractions. Ventricular complexes transitional in form between those having normal (control) intraventricular conduction and those showing the most advanced grades of LBBB, LAH, LPH were interpreted as “incomplete” forms of the latter. Increasing degrees of LBBB first obscured, and finally masqueraded, the residual QRS changes of IWMI. On the other hand, IWMI could be suspected in beats showing LAH and RBBB since the left axis shifts produced by LAH were associated with Q waves in leads 2 and 3. However, the diagnosis of IWMI was impossible when LAH appeared without RBBB. Three possible explanations were offered for this paradoxic phenomenon, namely that: a) it was the RBBB not the LAH which permitted the diagnosis of IWMI when both processes coexisted; b) a minor degree of LBBB was present; and c) the site (s) at which the impulse entered into the ventricles varied with different degrees and combinations of functional blocks. Finally, LPH was characterized by an increase in the height of the R waves in leads 2 and 3 without a concomitant change in the size of the q waves. Hence, LPH made the diagnosis of IWMI more difficul