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PubMed1980

[Existence and properties of a chloride-sensitive conductivity in atrial myocardium].

Investigated are the intracellularly recorded action potentials (A. P.) of the rabbit atrial trabeculae (length 2-4 mm, diameter 150-800 micrometers). After a pacing pause the first A. P. shows a rapid initial repolarization (I. R.) up to -40 mV within 4-6 ms. By increasing the duration of the pacing pause the I. R. is accentuated. It is diminished by repetitive stimulation after the pause and disappears within 2-4 s. At variation of the extracellular Ca++ concentration and under verapamil, tetraethyl ammonium chloride load (TEA load) the I. R. is unchanged. On the other hand, the I. R. is very sensitive to the variation of the external Cl- concentration. When decreasing the external Cl- concentration, the I. R. is diminished. At 10 mmol x 1(-1) the I. R. disappears. Assuming a Cl- current ICl the experimental findings are modelled. During the A. P. a Cl- conductivity gCl is activated instantaneously and inactivated slowly (rate constant 5.09 s-1). Because of the repriming of gCl the I. R. disappears after the post rest pacing. During the pacing pause a recovery of gCl takes place (rate constant 0.06 s-1). The gCl recovery induces the post rest I. R. Estimation of the maximum gCl yields 0.24 mmho . cm-2.

Action Potentials↗
PubMed1984

[Intrinsic function of the sinus node in patients with syncope and positive vagal maneuvers].

This study was undertaken to establish the nature (intrinsic or extrinsic) of sinus node dysfunction in patients presenting with syncope and abnormal response (sinus pause greater than 3'') to vagal manoeuvres (carotid sinus massage and/or eye-ball compression). To this purpose 29 patients (20 males, 9 females, aged 18-79 yrs, mean = 60) underwent an electrophysiologic study. In all we measured before and after autonomic blockade with Propranolol (0.2 mg/kg) and Atropine sulfate (0.04 mg/kg) the following parameters: sinus rate, corrected sinus node recovery time and sino-atrial conduction time. According to the presence or absence of electrocardiographic signs of sinus node dysfunction the patients were divided into three groups: Group A: 11 patients without electrocardiographic signs of sinus node dysfunction; Group B: 13 patients with borderline electrocardiographic signs of sinus node dysfunction (sinus bradycardia between 40 and 60 beats/min); Group C: 5 patients with definite electrocardiographic signs of sinus node dysfunction (sinus bradycardia less than or equal to 39 beats/min and/or sinoatrial block and/or sinus arrest). Fifteen patients (52%) had signs of organic heart disease. The main results obtained were: At least one electrophysiological test (sinus rate, corrected sinus node recovery time or sino-atrial conduction time) was abnormal in 10 patients (34,5%) before autonomic blockade and in 8 patients (27%) after autonomic blockade. Two of these 8 patients belonged to Group A (18%), 1 to Group B (8%) and 5 to Group C (100%). Six of these 8 patients were suffering from an organic heart disease and 2 were not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

[Left ventricular systolic time intervals during paroxysmal supraventricular tachycardia: the difference between A-V nodal re-entry and A-V re-entry].

In this study, the differences in hemodynamic changes during paroxysmal supraventricular tachycardia (PSVT) between A-V nodal re-entry and A-V re-entry were evaluated. In 8 patients with A-V nodal re-entrant tachycardia and 10 with A-V re-entrant tachycardia, electrophysiological studies were performed to measure systolic time intervals (pre-ejection period: PEP, ejection time: ET, PEP/ET ratio: PEP/ET). These measurements were obtained in the control state (atrial pacing at 90/min) and during PSVT with simultaneous recordings of electrocardiogram and femoral arterial pulse tracing. During PSVT, there was no difference in the heart rate between the 2 groups, but ventriculo-atrial conduction time was shorter in A-V nodal re-entry than in A-V re-entry. There was a marked fall in the ET and an increase in PEP/ET in all the patients when PSVT was induced. PEP increased significantly in A-V nodal re-entry, but did not change in A-V re-entry. This resulted in a greater increase in the PEP/ET suggesting a greater deterioration of the hemodynamic consequences in A-V nodal re-entry than in A-V re-ent y. Thus, the hemodynamic changes of PSVT differ between these 2 types of re-entrant circuits, which are mainly influenced by the ventriculo-atrial conduction time.

Adult↗
PubMed1999

Effects of ischemia on P wave dispersion and maximum P wave duration during spontaneous anginal episodes.

P wave dispersion (P dispersion), defined as the difference between the maximum and the minimum P wave duration, and maximum P wave duration (P maximum) are electrocardiographic (ECG) markers that have been used to evaluate the discontinuous propagation of sinus impulses and the prolongation of atrial conduction time, respectively. To study the effects of myocardial ischemia on P dispersion and P maximum, 95 patients with coronary artery disease (CAD) and typical angina pectoris and 15 controls with angina like symptoms underwent 12-lead surface ECG during and after the relief of pain. During pain and during the asymptomatic period, P maximum and P dispersion were calculated from the averaged complexes of all 12 leads. P dispersion increased significantly during spontaneous angina (45+/-17 ms) compared to the asymptomatic period (40+/-15 ms), P < 0.001 only in the patient group. Both P maximum and P dispersion showed higher values during angina in those patients who developed diffuse ischemia, as estimated with ST segment changes in multiple ECG leads. P dispersion showed higher values during the anginal episode in patients with left ventricular dysfunction, independently of the presence of a previous myocardial infarction. Atrial conduction abnormalities, as estimated with P maximum and particularly P dispersion, are significantly influenced by myocardial ischemia in patients with CAD and spontaneous angina.

Adult↗
PubMed1988

[Comparison of permanent cardiac pacing and cardiac pacing on demand in mixed carotid sinus syndrome. Acute- and medium-term follow-up study].

The aim of the study was to evaluate the importance of atrial synchronism for pacing therapy of patients with mixed carotid sinus syndrome. On 23 patients (21 m, 2 f; mean age 69 +/- 8 years) affected by symptomatic mixed carotid sinus syndrome we performed: 1) the study of ventriculo-atrial conduction, 2) the evaluation of pacemaker effect and 3) the carotid sinus massage in standing position during VVI and DVI temporary pacing. All patients received a permanent DVI pacemaker and then underwent a two-month period single-blind, randomized, cross-over study on DVI vs VVI mode. During DVI period, no syncope occurred in any patients, minor symptoms persisted in 11 (48%) of them; during VVI period syncopes recurred in 3 patients, symptoms requiring the withdrawal of VVI pacing and premature DVI reprogramming in 8, minor symptoms were observed in 17 (74%). A comparison between 14 patients who preferred DVI period (Group A) and the remaining 9 patients who had no preference for DVI and VVI period (Group B) revealed that Group A patients had a greater pacemaker effect (-34 +/- 16 mmHg vs -16 +/- 14 mmHg; p less than 0.02) and a higher prevalence of ventriculo-atrial conduction (78% vs 44%; p = 0.1), while the entity of the systolic pressure fall caused by carotid sinus massage was similar in the two groups both during VVI mode (Group A -51 +/- 16 mmHg vs Group B -56 +/- 27 mmHg) and DVI mode (Group A -38 +/- 17 mmHg vs Group B -45 +/- 17 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1988

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 the 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, all 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 B -45 +/- 17 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1999

Congestive heart failure induced by recipient atrial tachycardia conducted to the donor atrium after orthotopic heart transplantation: complete regression after successful radiofrequency ablation.

We describe the case of a 30-year-old female patient who developed an interatrial tachycardia from the recipient to the donor atrium associated with signs of congestive heart failure 5 years after orthotopic heart transplantation. The patient underwent catheter mapping followed by successful radiofrequency (RF) ablation at the site of the presumed electrical connection between the recipient and the donor atria, through the interatrial surgical suture line, with stable recovery of sinus rhythm and disappearance of signs of left ventricular dysfunction. RF catheter ablation is confirmed to be feasible and safe in the treatment of heart transplant patients even in the presence of rare forms of arrhythmias, thus offering a cure for tachycardia to these patients.

Adult↗
PubMed1987

[Possibilities for frequency adjusted heart stimulation].

In the sick sinus syndrome, in sinu-atrial conduction defects or in atrial flutter or fibrillation a stress-adapted, frequency-adapted stimulation cannot be obtained by the processing of the atrial potential. Here one depends on partly extracardiac parameters which contain informations about the metabolic and stress situation, respectively. A survey of the parameters for a frequency-adapted stimulation discussed at present is given and a critical valuation of them is carried out. It is shown that all parameters up to now experimentally and clinically, respectively, tested are more or less problematic and that the way out of the difficulty most consist in deriving the controlled variable for a stress adapted stimulation rate from several parameters.

Bradycardia↗
PubMed2002

[Mechanisms of initiation in atrial fibrillation].

Atrial fibrillation is the most relevant arrhythmia in daily clinical practice. The pathophysiology is determined by multiple independent reentrant wavelets in both atria. Repetitive triggers and an underlying substrate may favor the initiation and maintenance of atrial fibrillation. Mapping studies in patients with drug-refractory paroxysmal atrial fibrillation identified potentials from the ostia of pulmonary veins as a main source of triggers that initiate atrial fibrillation. In ongoing clinical trials, catheter ablation of pulmonary vein foci is used to eliminate atrial premature beats and thereby prevent the initiation of atrial fibrillation. The autonomic modulation of the heart rate and the occurrence of other supraventricular tachycardias that degenerate into atrial fibrillation are also considered as triggering mechanisms of atrial fibrillation. Since symptomatic bradycardia is associated with an increased incidence of atrial fibrillation, atrial pacing therapies for prevention of atrial fibrillation are another concept. Ongoing clinical trials evaluating the efficacy of pacing in patients with and without a primary pacemaker indication are currently under investigation. To date, data to which extent anatomical and electrophysiological characteristics of the atria influence the initiation and maintenance of atrial fibrillation are still missing. The myocardial adaptation to atrial fibrillation, the so-called "atrial remodeling", includes shortening of the atrial refractory period, slowing of atrial conduction, shortening of the atrial action potential, a progressive reduction of L-type calcium channel expression and microfibrosis of the myocardial tissue. New drug developments target atrial remodeling by modulating ion channel function and receptors of the angiotensin metabolism.

Action Potentials↗
PubMed1987

First degree atrioventricular block.

Prolongation of the PR interval is a nonspecific condition. Etiologies include normal physiologic variance, idiopathic bundle branch fibrosis, calcific valvular heart disease, ischemic heart disease, cardiomyopathies, infections resulting in myocarditis, drugs (especially type I antidysrhythmic medications), collagen vascular diseases, tumors, trauma, electrolyte imbalances, and many other miscellaneous causes. Isolated first degrees atrioventricular block is generally not associated with an increased risk of sudden death, syncope, or progression to higher degrees of atrioventricular block. Exceptions include patients with intra-atrial conduction delays prone to atrial fibrillation, acute myocardial infarction, or bundle branch disease where higher degrees of atrioventricular block may develop. Treatment consists of correction of the underlying disorder or discontinuation of the offending medication.

Diagnosis, Differential↗
PubMed2003

Selection of pacing mode after interruption of atrioventricular conduction for atrial fibrillation: observations from the PA3 clinical trial.

The optimal pacing mode for patients with paroxysmal atrial fibrillation (AF) following AV junction ablation remains the subject of some debate. Recent clinical trials have not demonstrated a superior advantage of maintenance of sinus rhythm over the rate control approach. However, clinical trials in pacemaker populations have demonstrated that physiologic pacing reduces the probability of paroxysmal and persistent AF compared to ventricular pacing. In the second phase of the PA(3) study, patients were randomized to DDDR versus VDD pacing in a cross over study design. Of the 67 patients randomized, 42% developed permanent AF within one year following ablation. AF frequency and burden increases early following AV junction ablation suggesting that ventricular pacing even in an atrial synchronous mode promotes AF. Given the high probability of permanent AF developing early following ablation, VVIR pacing appears to be the appropriate pacing mode for symptomatic patients undergoing total AV junction ablation.

Atrial Fibrillation↗
PubMed1998

Recipient to donor conduction of atrial tachycardia following orthotopic heart transplantation.

We report a case of atrial tachycardia in a 60-year-old male 8 years postorthotopic heart transplantation. At electrophysiology study, the clinical rhythm was found to arise from the remnant of the recipient atrium and was successfully terminated by delivery of radiofrequency energy. Surgical scars formed at the anastomosis of the recipient and donor atrium during the time of orthotopic heart transplantation are thought to electrically isolate the two areas. Although rarely recognized, dysrhythmias originating from the recipient atrial remnant may occur more often than previously thought.

Catheter Ablation↗