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PubMed1993

A comparison of fenoldopam and nitroprusside in the control of hypertension following coronary artery surgery.

A prospective trial to compare the effects of the synthetic dopaminergic (DA1) agonist, fenoldopam (FEN), with sodium nitroprusside (SNP) for control of blood pressure following coronary artery bypass graft surgery was carried out in 20 patients. Patients were randomly allocated to receive either FEN or SNP when the systolic arterial blood pressure (SAP) rose above 130 mmHg. The goal of therapy was to achieve a stable control of blood pressure below 130 mmHg at a level at least 25 mmHg below the pretreatment value. Treatment was then continued for 2 hours. Hemodynamic measurements were made before treatment, after stable control of blood pressure had been achieved, and thereafter at 30, 60, and 120 minutes. Urine output, sodium, potassium, and creatinine clearance were also measured during the study. Both SNP and FEN caused a rapid and significant fall in SAP (P < 0.001) and a fall in systemic vascular resistance (P < 0.001). FEN caused an increase in cardiac index (P < 0.001) and in stroke volume (P < 0.001) in contrast to SNP. Urine output and potassium clearance fell with SNP (P < 0.05) in contrast to FEN. Thus, FEN would appear to control SAP as effectively as SNP, but may have more beneficial effects on cardiac output and some aspects of renal function.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed2006

Effects of graded exercise on bronchial blood flow and airway dimensions in sheep.

Exercise stimulus-response relationships for airway blood supply and dimensions have not been described in mammalian species. These relationships are vital for postulates concerning integrated reflex factors normally controlling the airways and which may underlie the asthma syndromes of exercise. This study defines airways stimulus-response relationships in exercising sheep. Ewes between 35 and 40kg were instrumented at left thoracotomy under thiopentone/isoflurane general anaesthesia. Pulsed Doppler ultrasonic transducers were mounted on the bronchial artery, and transit-time plus single-crystal sonomicrometers on the left main bronchus. These recorded simultaneously and continuously bronchial blood flow (Q(br)) and conductance (C(br)), bronchial circumference (Circ(br)) and wall thickness (Th(br)). In Protocol 1 (P1), four sheep ran duplicate 5min protocols on a horizontal treadmill at continuous step-up-and-down speeds of 1min duration, namely, 0.8, 1.6, 2.2, 1.6 and 0.8mph (moderate exercise), followed by 10min recovery. In P2, four sheep ran duplicate 2min protocols at constant 4mph (strenuous exercise), and in P3, one sheep ran duplicate protocols each of 3min at 2.2, 4.4 and 6mph (severe exercise). Regression analysis and repeated measures ANOVA were used to assess differences between times, runs and exercise intensity. In P1, airway effects were directly related to graded exercise effort sustained over 5min. Peak effects occurred at 2.2mph, except for Th(br). Heart rate and P(a) rose (to 156% and 111% of resting, respectively), and Q(br) and C(br) fell (to 83% and 75%; both P<0.001). Circ(br) fell to 96% (P=0.02), and Th(br) rose at low speeds early and late, and thinned at the highest speed. In P2 and P3 for all variables the steady-state effects were systematically greater than for P1 (4.4mph: C(br) to 43%, Circ(br) to 93%; 6.6mph: C(br) to 25%, Circ(br) to 82%). There was no significant recovery hyperaemia, but there was residual post-exercise bronchoconstriction. The exercise stimulus-response relationships from rest to a maximal 6mph for sheep airway circumference and its bronchial circulation are inverse and functionally constrictor.

Animals↗
PubMed1998

Evidence for an influence of mechanical restitution on beat-to-beat variations in haemodynamics during chronic atrial fibrillation in patients.

OBJECTIVE: We tested the hypothesis that beat-to-beat changes in haemodynamics during atrial fibrillation include an effect of each preceding R-R interval through the interval-strength relationship (mechanical restitution). BACKGROUND: The variation in stroke volume and pulse pressure characteristic of atrial fibrillation is usually ascribed to time dependent ventricular filling. METHODS: We measured the maximum rate of rise of left ventricular pressure (LVdP/dtmax), and aortic blood velocity and its integral in patients with atrial fibrillation undergoing cardiac catheterisation. The contractile response of isometric human myocardial trabeculae to sequences of atrial fibrillation was also studied, using the recorded ECGs as stimuli. The trabeculae were obtained from the resected right ventricular outflow tracts of patients with Fallot's tetralogy undergoing operative correction. RESULTS: Beat-to-beat variations in contractile function during atrial fibrillation in the patients were recorded as LVdP/dtmax and left ventricular ejection (ascending aortic) velocity integral (proportional to stroke volume). Both these indices correlated well with the response to the same ECG (R wave) sequences in the isometric model measured as the maximum rate of rise of force, dF/dtmax, r = 0.72 to 0.81, p, 0.0001. When short pre-preceding intervals were excluded (minimizing the effect of post-extrasystolic potentiation), these variables showed a positive curvilinear relationship to preceding interval typical of mechanical restitution. CONCLUSIONS: Mechanical restitution, which causes beat-to-beat changes in inotropic state, accounts in part for the changes in stroke volume in atrial fibrillation.

Aged↗
PubMedDate not supplied

Tricuspid annular motion.

Triscupid annular motion is related to right ventricular systolic function in the same way mitral annulus motion is related to left ventricular function. Tricuspid annular excursion reflects the longitudinal motion of the right ventricle, and the systolic descent of the anulus correlates with systolic venous inflow to the right atrium. However, it has not been shown clearly how to reproducibly quantify this motion. Therefore we describe a method to measure triscuspid annular motion using two-dimensional oriented M-mode echocardiography from the apical view. We studied a group of 10 normal subjects (mean age, 28.7 years; range, 25 to 38 years) and a group of 29 patients (mean age, 57.2 years; range, 20 to 84 years) with disease of the left side of the heart but no evidence of involvement of the right side of the heart. In each subject, tricuspid and mitral annular motion were measured respectively at their lateral, septal or medial, anterior, and posterior margin points. The total tricuspid annular motion for normal subjects was, as follows: lateral, 24.9 +/- 3.5 mm; medial, 20.1 +/- 2.5 mm; anterior, 21.6 +/- 3.8 mm; and posterior, 22.3 +/- 2.3 mm. Interobserver and intraobserver variability was low, with a coefficient of variance for the different annular points ranging from 6.19% to 11.56% between observers and from 4.10% to 7.26% within observer. We conclude that it is possible to measure tricuspid annular motion with this method in a reproducible way and to use it as a diagnostic tool in evaluating function of the right side of the heart.

Adult↗
PubMed1998

Surgical treatment of atrial fibrillation.

Surgical therapy has been applied in the treatment of atrial fibrillation for almost two decades. At present, the most commonly used approach is the maze operation developed by Cox. In this operation, atrial fibrillation is prevented by critically located incisional lines. Currently, these lines also are drawn during operation using cryoablation or radiofrequency current. To document the value of the maze operation, randomized studies, not only on arrhythmia prevention but also on atrial transport function and thromboembolic complications, should be performed.

Atrial Fibrillation↗
PubMed1994

Simultaneous transesophageal echocardiography and atrial pacing: assessment of the functional significance of coronary artery disease before surgical treatment of an abdominal aneurysm.

Conventional active stress tests for the evaluation of coronary artery disease are not feasible for patients in whom a significant blood pressure increase during a stress procedure should be avoided, for example, those with a coexisting aortic aneurysm. Transesophageal echocardiography (TEE) with simultaneous atrial pacing is a new, highly specific, and sensitive stress technique for the detection of coronary artery disease. Furthermore, TEE can be performed safely with only mild blood pressure increases. Therefore in the present case report of a 70-year-old male, application of combined TEE and atrial pacing was used successfully to exclude the hemodynamic significance of a circumflex artery stenosis and avoided a significant blood pressure increase before surgical correction of an abdominal aortic aneurysm.

Aged↗
PubMed1998

Cardiac performance early after cardioversion from atrial fibrillation.

BACKGROUND: The mechanism for early improvement in cardiac function after cardioversion from atrial fibrillation is unknown. METHODS: We measured ventricular volumes and load-independent contractility during atrial fibrillation and within 24 hours after cardioversion to sinus rhythm in 15 adult patients (10 men, 5 women; mean age 63+/-4 years, range 31 to 81 years). Duration of atrial fibrillation ranged from <1 day to 6 months. RESULTS: After cardioversion, left ventricular ejection fraction increased from 51%+/-4% to 61%+/-4% (P=.001, 95% confidence intervals for the difference, 7% to 15%), stroke volume increased from 57+/-4 mL to 76+/-6 mL (P < .001, 95% confidence intervals 8 to 32 mL), and mean cycle length increased from 0.77+/-.04 seconds in atrial fibrillation to 1.02+/-.04 seconds in sinus rhythm (P=.002, 95% confidence intervals, 0.1 to 0.4 seconds). Cardiac contractility, as expressed by the slope and the intercept of the relation between rate-corrected circumferential velocity of fiber shortening and end-systolic wall stress (Vcfc/ESWS) remained unaltered in 13 of 15 patients, suggesting that intrinsic inotropic state was unchanged immediately after return of normal sinus rhythm. Finally, a significant correlation was observed between improvement in stroke volume and peak A-wave velocity (r=0.79, P=.035). CONCLUSION: Both left ventricular stroke volume and ejection fraction increase immediately after cardioversion, whereas intrinsic cardiac contractility is largely unchanged. These data suggest that the mechanism of this increase is enhanced left ventricular diastolic filling due mostly to increased cycle length and return of left atrial mechanical function.

Adult↗
PubMed2001

Naloxone improves functional recovery of myocardial stunning in conscious dogs through its action on the central nervous system.

This study tests the hypothesis that naloxone, but not its quarternary salt, naloxone methiodide (which does not enter the central nervous system), improves recovery from myocardial stunning in conscious dogs. Twenty dogs were chronically instrumented for measurement of heart rate, left atrial, aortic and left ventricular pressure (LVP), LV dP x dtmax(-1) and myocardial wall thickening fraction (WTF). Regional myocardial blood flow was determined with coloured microspheres. Occluder around the left anterior descending artery (LAD) allowed induction of reversible LAD ischaemia. Each of the 20 dogs underwent two LAD ischaemic challenges. Experiments (performed on separate days, in crossover fashion) were: (i) 10 min of LAD occlusion after application of naloxone 63 microg kg(-1) or naloxone methiodide 63 microg kg(-1) and (ii) occlusion without naloxone or naloxone methiodide. WTF was measured at baseline and until complete recovery occurred. LAD ischaemia significantly reduced LAD WTF with (mean (SD) 54 (15)% lower than baseline) and without naloxone (55 (16)% lower than baseline), without significant haemodynamic differences. Between I to 30 min of reperfusion, WTF was significantly higher with naloxone (P < 0.05). There was no difference in WTF with or without naloxone methiodide. We conclude that naloxone improved recovery from myocardial stunning in conscious dogs, and that this was centrally mediated.

Animals↗
PubMed1975

Abnormalities of left ventricular function and geometry in adults with an atrial septal defect. Ventriculographic, hemodynamic and echocardiographic studies.

Left ventricular function and motion in 12 adults with an ostium secundum atrial septal defect were analyzed utilizing biplane cineangiography. Values for left ventricular end-diastolic volume index, stroke volume index, ejection fraction, left ventricular end-diastolic pressure and mean rate of circumferential fiber shortening were compared with values in an age-matched group of 11 normal subjects. Comparisons of ventriculographic and echocardiographic data were also made in 5 patients and 10 control subjects. Cardiac index was smaller in patients than in the normal subjects (3.6 vs. 4.5 liters/min per m2, P less than 0.01). Although left ventricular end-diastolic pressure was similar (8 mm Hg in both groups), the end-diastolic volume index was significantly smaller in patients than in normal subjects (56 vs. 76 ml/m2, P less than 0.05). Stroke volume index was also significantly smaller in patients (40 vs. 52 ml/m2, P less than 0.01). The two groups had similar values for ejection fraction (65 +/- 2 percent [standard error of the mean] in patients vs. 68 +/- 2 percent in normal subjects), circumferential fiber shortening velocity (1.67 +/- 0.13 vs. 1.81 +/- 0.15 circumferences/sec.), heart rate (91 +/- 7 vs. 90 +/- 5 beats/min) and mean systemic arterial pressure (92 +/- 5 vs. 87 +/- 3 mm Hg). Early systolic bulging of the upper ventricular septum toward the right ventricle was seen in 10 of 12 patients with an atrial septal defect but in no normal subject. Echocardiographic data supported these findings. No other abnormalities of motion were consistently noted. It is concluded that the left ventricle of patients with an atrial septal defect is subnormal in volume and abnormal in sequence of contraction of the septum and is characterized by apparent decreased distensibility.

Adolescent↗
PubMed1984

Effects of locally generated angiotensin II on noradrenergic transmission in guinea-pig isolated atria.

The extent to which cardiac neuroeffector function may be modulated by angiotensin II (AII) generated locally from angiotensin I (AI) was investigated in guinea-pig spontaneously beating isolated atria radiolabelled with [3H]noradrenaline. AI and AII were equipotent in increasing the rate and force of atrial contractions with a threshold concentration between 0.1 and 1.0 nM. In contrast, AI was approximately twenty times less potent than AII in enhancing the stimulation-induced (S-I) efflux of radioactivity. The actions of AI and AII on rate and force of atrial contractions, as well as those on S-I efflux of radioactivity, were substantially blocked by the AII receptor antagonist saralasin. On the other hand, the converting enzyme inhibitors captopril and MK-422 selectively blocked the actions of AI without affecting those of AII. These results suggest that significant local conversion of AI to AII occurs in guinea-pig isolated atria. This locally generated AII can act on myocardial AII receptors to increase rate and force of atrial contractions, and on AII receptors located on sympathetic nerve terminals to facilitate sympathetic neurotransmission. The lower potency of AI compared to AII in modulating transmitter release, in contrast to the equal potency of the peptides in mediating chronotropic and inotropic responses, may be due to conversion of AI to AII at sites remote from the neuroeffector junction.

Angiotensin I↗
PubMed1996

Effects of intravenous anesthetics on atrial wavelength and atrioventricular nodal conduction in guinea pig heart. Potential antidysrhythmic properties and clinical implications.

BACKGROUND: Supraventricular tachydysrhythmias such as atrial fibrillation frequently complicate the perioperative period. Two electrophysiologic factors critical to the pathogenesis of supraventricular tachydysrhythmias are: 1) atrial wavelength, the product of atrial conduction velocity (CV) and effective refractory period (ERP), and 2) atrioventricular nodal conduction. Modulation of these factors by drugs has important clinical ramifications. The authors studied the effects of propofol, thiopental, and ketamine on atrial wavelength and atrioventricular nodal function in guinea pig isolated atrial trabeculae and hearts, respectively. METHODS: Electrocardiogram recordings in superfused atrial tissue were obtained using hanging microelectrodes. A stimulating and two recording electrodes were placed on a single atrial trabecula, and the interelectrode distance was measured. Atrial ERP determinations were made using a premature stimulus protocol. The time (t) required for a propagated impulse to traverse the interelectrode distance (d) was measured. Conduction velocity was calculated as d/t. Langendorff-perfused guinea pig hearts were instrumented for low atrial pacing (cycle length = 300 ms) and for measurements of stimulusto-His bundle interval, an index of atrioventricular nodal conduction. To investigate the frequency-dependent behavior of the atrioventricular node, computer-based measurements were made of Wenckebach cycle length (WCL) and atrioventricular nodal ERP. RESULTS: Thiopental significantly prolonged atrial ERP in a concentration-dependent manner, whereas propofol and ketamine had no significant effect on atrial refractoriness. In contrast, ketamine caused a dose-dependent decrease in atrial CV, but propofol and thiopental had no significant effect on CV. Therefore, thiopental, ketamine, and propofol caused an increase, a decrease, and no change, respectively, in atrial wavelength. All anesthetics caused a concentration-dependent prolongation of the stimulus-to-His bundle interval, atrioventricular nodal ERP, and WCL. However, on an equimolar basis, significant differences in potencies were found. The concentrations of drug that caused a 20% increase in ERP (ERP20) and WCL (WCL20) for propofol, thiopental, and ketamine were 14 +/- 2 microM, 26 +/- 3 microM, and 62 +/- 11 microM, and 17 +/- 2 microM, 50 +/- 1 microM, and 123 +/- 19 microM (mean +/- SEM), respectively. Therefore, the rank order of potency for frequency-dependent atrioventricular nodal effects is propofol > thiopental > ketamine. CONCLUSION: The authors' results indicate that propofol would be most effective at filtering atrial impulses during supraventricular tachydysrhythmias, whereas thiopental would be most effective at preventing atrial reentrant dysrhythmias. In contrast, ketamine may be most likely to promote atrial reentry while having minimal effect on atrioventricular nodal conduction.

Anesthetics, Intravenous↗
PubMed1998

Atrial septal pacing to synchronize atrial depolarization in patients with delayed interatrial conduction.

The current method of pacing the right atrium from the appendage or free wall is often the source of delayed intraatrial conduction and discoordinate left and right atrial mechanical function. Simultaneous activation of both atria with pacing techniques involving multisite and multilead systems is associated with suppression of supraventricular tachyarrhythmias and improved hemodynamics. In the present study we tested the hypothesis that pacing from a single site of the atrial septum can synchronize atrial depolarization. Five males and two females (mean age 58 +/- 6 years) with drug refractory paroxysmal atrial fibrillation (AF) were studied who were candidates for AV junctional ablation. All patients had broad P waves (118 +/- 10 ms) on the surface ECG. Multipolar catheters were inserted and the electrograms from the high right atrium (HRA) and proximal, middle, and distal coronary sinus (CS) were recorded. The atrial septum was paced from multiple sites. The site of atrial septum where the timing between HRA and distal CS (d-CS) was < or = 10 ms was considered the most suitable for simultaneous atrial activation. An active fixation atrial lead was positioned at this site and a standard lead was placed in the ventricle. The interatrial conduction time during sinus rhythm and AAT pacing and the conduction time from the pacing site to the HRA and d-Cs during septal pacing were measured. Atrial septal pacing was successful in all patients at sites superior to the CS o.s. near the fossa ovalis. During septal pacing the P waves were inverted in the inferior leads with shortened duration from 118 +/- 10 ms to 93 +/- 7 ms (P < 0.001), and the conduction time from the pacing site to the HRA and d-CS was 54.3 +/- 6.8 ms and 52.8 +/- 2.5 ms, respectively. The interatrial conduction time during AAT pacing was shortened in comparison to sinus rhythm (115 +/- 18.9 ms vs 97.8 +/- 10.3 ms, P < 0.05). In conclusion, simultaneous activation of both atria in patients with prolonged interatrial conduction time can be accomplished by pacing a single site in the atrial septum using a standard active fixation lead placed under electrophysiological study guidance. Such a pacing system allows proper left AV timing and may prove efficacious in preventing various supraventricular tachyarrhythmias.

Atrial Fibrillation↗
PubMed2004

Recent topics on the surgical treatment for atrial fibrillation.

After the introduction of endocardial radiofrequency catheter, only two arrhythmias, atrial fibrillation and ischemic ventricular tachycardia require surgical procedures. In this review, we describe recent advancements and problems of surgical treatment for atrial fibrillation. On the basis of multiple-circuit re-entry theory, Cox developed the maze operation with the aim of interrupting the re-entry circuit. Although this procedure has become the gold standard technique for the surgical treatment of atrial fibrillation with approximately 90% success rate, several modifications have been made over time. To obtain a more physiological atrial transport function, radial approach technique or bilateral appendage-preserved maze procedures were developed and to simplify surgical procedures, maze operation with cryo-ablation or radiofrequency-ablation were created. Other topics are concerned with surgical target or approach to atrial fibrillation. Ectopic focus theories from pulmonary veins have been widely recognized recently and the surgical isolation of pulmonary veins orifices is performed with various energy sources. In addition to standard cut-and-sew surgical technique, cryoablation, unipolar or bipolar radiofrequency ablation, or microwave ablation were induced with endocardial or epicardial approach for the achievement of less invasive cardiac surgery. As atrial fibrillation leads to frequent mortality, cardiac surgeons have to treat atrial fibrillation with other cardiac disease more frequently to obtain better quality of operative results.

Atrial Fibrillation↗
PubMed1994

Long-term stability of P wave sensing in single lead VDDR pacing: clinical versus subclinical atrial undersensing.

Optimal function of a single lead P wave synchronous rate adaptive ventricular pacing system (VDDR) requires reliable P wave sensing over time and during daily activities. The stability of P wave sensing and the incidence of sensitivity reprogramming in a single pass lead with a diagonally arranged bipole was assessed in 30 patients with complete atrioventricular block over a follow-up period of 12 +/- 1 months (range 6 months to 3 years). Atrial sensing was assessed during clinic visits, by physical maneuvers (postural changes, breathing, Valsalva maneuver, walking and isometric exercise), maximum treadmill exercise and Holter recordings. P wave amplitude at implantation was 1.21 +/- 0.09 (0.5-3.6) mV, and the atrial sensing threshold remained stable over the entire period of follow-up. Using an atrial sensitivity based on twice the sensing threshold at 1 month, P wave undersensing was found in 2, 4, 3, and 7 patients during clinic visit, physical maneuvers, exercise, and Holter recordings, respectively. Atrial sensitivity reprogramming was performed in three patients based on the correction of undersensing during physical maneuvers. Although eight patients had atrial undersensing on Holter recordings, the number of undersensed P waves was small (total 101 beats or 0.013% +/- 0.001% of total ventricular beats) and no patient was symptomatic. One patient had intermittent atrial undersensing at the highest sensitivity, but the VDDR mode was still functional most of the time. No patient had myopotential interference at the programmed sensitivity. One patient developed chronic atrial fibrillation and was programmed to the VVIR mode. Thus, single lead VDDR pacing is a stable pacing mode in 97% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

A quantitative analysis of reservoir function of the human pulmonary "venous" system for the left ventricle.

By definition, the pulmonary "venous" system consists of the pulmonary veins and the left atrium. The stiffness of the pulmonary "venous" (P'V') system and the left ventricle (LV) at the end of the slow filling period (at the point of pre-a) were estimated sequentially in a total of 26 patients, divided into a control group and mitral stenosis (MS), angina pectoris (AP), hypertrophic cardiomyopathy (HCM) groups. The stiffness (delta P/delta V) of the P'V' system was estimated from the pulmonary artery wedge (PAW) pressure tracings and the stroke volume. The stiffness (dP/dV) of LV was obtained from the pressure-volume (P-V) relationship of LV with a model of P = beaV. The present study is aimed primarily at obtaining factual information. The stiffness of the P'V' system was 0.063 +/- 0.022 mmHg/ml (mean +/- SD) in the control group and 0.052 +/- 0.006 mmHg/ml in the HCM group (p greater than 0.1). The stiffness of LV in diastole was 0.091 +/- 0.016 mmHg/ml in the control group and 0.199 +/- 0.056 mmHg/ml in the HCM group (p less than 0.01). The ratio of the stiffness of LV in diastole to that of the P'V' system was 1.6 +/- 0.6 in the control group and 3.8 +/- 0.7 in the HCM group. The volume elastic constant (a) of the P'V' system was 0.008 +/- 0.005 ml-1 in the control group and the values of (a) occupied a range of 0.007 to 0.008 ml-1 in the remaining 3 groups of patients. The values of (a) of LV were 0.011 +/- 0.004 ml-1 in the control group and 0.022 +/- 0.007 ml-1 in the HCM group (p less than 0.01). The present study suggests that the P'V' system is usually 2 to 3 times more complaint than LV in diastole. On the other hand, the P'V' system remained compliant in spite of the decreased compliance of LV in diastole in the HCM group, maintaining the reservoir function with which pulmonary edema is prevented.

Adolescent↗
PubMed1999

Mechanically induced potentials in fibroblasts from human right atrium.

It has been shown that cardiac fibroblasts of the human heart are electrically non-excitable and mechanosensitive. The resting membrane potential of these cells is -15.9+/-2.1 mV and the membrane resistance is 4.1+/-0.1 G[Omega]. Rhythmic contractions of the myocardium associated with stretch of the surrounding tissue produce reversible changes in the membrane potential of cardiac fibroblasts. These mechanically induced potentials (MIPs) follow the rhythm of myocardial contractions. Simultaneous recording of the action potential of cardiomyocytes and MIPs of cardiac fibroblasts demonstrates a delay of 40.0+/-0.4 ms after the action potential before the appearance of the MIP. Contraction produces a MIP which is more positive or more negative than the reversal potential - the membrane potential due to current injection at which the MIP reverses its direction. Regardless of the initial orientation of the MIP, intracellular polarization increases the amplitude towards the reversal potential if the background MIP had depolarized the membrane or away from the reversal potential if the initial background MIP had hyperpolarized the membrane. Artificial intracellular polarization changed the amplitude but not the frequency of the MIP. The pool of electrically non-excitable mechanosensitive cells, which change their electrical activity during contraction and relaxation of the heart, may play a role in the mechano-electrical feedback mechanism which has to be taken into account in the normal function of the heart as well as in pathological processes.

Aged↗
PubMed2004

Structure and function of beta3-adrenergic receptors.

Beta-adrenergic receptors have been subdivided into three types: beta1-, beta2- and beta3-adrenergic receptors. beta1-adrenergic receptors are predominant in the heart, beta2-adrenergic receptors--in the respiratory system, and beta3-adrenergic receptors--in the adipose tissues. However, since 1989, when beta3-adrenergic receptor was cloned, numerous biochemical and functional studies have confirmed its presence in various species and tissues, including the heart. Unlike beta1- and beta2-adrenergic receptors, it has been shown that beta3-adrenergic receptors possess the cardiodepressant effects in human ventricles, what did not fit to its stimulatory properties of adenylyl cyclase in other tissues. In this regard, the role of beta3-adrenergic receptors in the regulation of cardiac function may be of great importance in pathological conditions and remains undetermined, so far. In this review brief characterization of beta3-adrenergic receptors, concerning their structure, function and possible pathophysiological role is provided.

Adenylyl Cyclases↗
PubMed1997

Safety and efficacy of oral flecainide acetate in patients with cardiac arrhythmias.

We retrospectively studied the clinical efficacy and safety of oral flecainide in 38 patients with symptomatic arrhythmias. Patients received 100 to 200 mg daily of flecainide for a mean of 25 months (range 8 to 50 months). All patients had normal cardiac function. Paroxysmal atrial fibrillation (PAF) was observed in 29 patients (76%). Other forms of arrhythmia included paroxysmal atrial flutter, seen in 3 patients (8%); premature atrial contraction and ventricular premature contraction, each seen in 2 patients (5%); and supraventricular tachycardia and ventricular tachycardia, each seen in 1 patient (3%). A complete response was obtained in 15 (52%) of 29 patients with PAF and a partial response in 8 patients (27%). The remaining 6 patients (21%) showed no response. A complete response was also obtained in 7 of 9 patients with other forms of arrhythmia. There were no differences in cardiac function and ECG parameters before and after treatment. Flecainide was withdrawn in 4 patients due to the development of electrocardiographic abnormalities. Three of these patients showed an atrial proarrhythmic effect. Abnormal ST elevations in the precordial leads were observed in 1 patient who received 200 mg of flecainide daily. In conclusion, flecainide was effective treatment for supraventricular and ventricular arrhythmias, but attention must be paid to the drug's potential proarrhythmic adverse effects.

Administration, Oral↗