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Biomedical subjects

S M Yabek

Publications and source records attributed to S M Yabek.

At least 37 records · Page 2Linked to original sources
PubMed1985

Acute effects of amiodarone on the electrophysiologic properties of isolated neonatal and adult cardiac fibers.

The acute cellular electrophysiologic actions of amiodarone on isolated neonatal and adult canine ventricular muscle and Purkinje fibers were evaluated using standard microelectrode techniques. Amiodarone, 10(-6) to 5 X 10(-5) M (0.68 to 34 micrograms/ml), significantly (p less than 0.05) prolonged adult ventricular muscle action potential duration and voltage-dependent refractoriness at all concentrations, thereby demonstrating typical class III antiarrhythmic effects. Similar concentrations had no significant effects on neonatal ventricular muscle. Amiodarone significantly shortened action potential duration and refractoriness of both neonatal and adult Purkinje fibers, with neonatal fibers having a greater sensitivity to the drug. At the standard stimulation rate of 1 Hz, amiodarone had no effects on action potential amplitude or maximal rate of rise of phase 0 of the action potential (Vmax) of any tissues. At faster stimulation frequencies (2 to 4 Hz), amiodarone produced frequency-dependent decreases in action potential amplitude and Vmax of all neonatal and adult preparations. The data indicate that amiodarone exhibits a complex aggregate of electrophysiologic actions that include significant frequency-related class I effects. Compared with adult myocardium, neonatal tissues demonstrated altered responsiveness to amiodarone, a feature common to many antiarrhythmic compounds.

Action Potentials↗
PubMed1985

Effects of hypoxia on the cellular electrical activity of adult and neonatal canine ventricular myocardium.

Standard microelectrode techniques were utilized to evaluate the effects of acute hypoxia on the cellular electrical activity of neonatal and adult ventricular myocardium. Control action potential parameters from adult and neonatal tissues were not significantly different. Thirty minutes of acute hypoxic superfusion significantly (p less than 0.05) reduced all adult action potential indices. In neonatal preparations, only action potential duration at 50% repolarization (-17%) and action potential duration at 90% repolarization (-12%) were reduced significantly. After 60 min of hypoxia, action potential amplitude, maximum diastolic potential, and phase 0 upstroke velocity from neonates were still not reduced significantly. The alteration in neonatal action potential parameters induced by 1 h of hypoxic superfusion (5.5 mM glucose) were all reversed by 16.5 mM glucose despite continued hypoxia. Exclusion of glucose from the hypoxic superfusate did not greatly affect the response of neonatal tissues to hypoxia. In adult action potentials, the degree of decrease for each action potential parameter was markedly greater compared to the hypoxic solution with normal (5.5 mM) glucose. Following hypoxic superfusion of neonatal preparations with 0 mM glucose, reoxygenation with 16.5 mM glucose resulted in action potential parameters with exceeded control values by 4 to 25%. Our data indicate a greater resistance of developing myocardium to the detrimental effects of hypoxia on cellular electrical activity. This seems to be related to a greater glycolytic activity of neonatal myocardium compared to adult hearts.

Action Potentials↗
PubMed1984

Right ventricular contractile function in children with congenital heart disease.

Indexes of right ventricular (RV) systolic function were evaluated in 41 patients undergoing cardiac catheterization. High-fidelity tracings were used to determine RV pressure, maximal RV dP/dt and the velocity of contractile element shortening at a developed pressure of 10 mm Hg (VCE10). In 14 children with an RV systolic pressure less than 35 mm Hg, normal RV volume, pulmonary vascular resistance (PVR) less than 3 units X m2 and no shunts (our normal group), mean (+/- standard deviation) RV dP/dt was 437 +/- 116 mm Hg X s-1 and VCE10 was 1.15 +/- 0.33 muscle length X s-1. In patients with RV systolic hypertension due to valvular pulmonary stenosis or isolated increases in PVR, mean values for RV dP/dt and VCE10 were significantly (p less than 0.05) greater than the normal values. In patients with a ventricular septal defect, RV hypertension and normal PVR, VCE10 was normal but RV dP/dt was significantly elevated. Children with chronic RV volume overload had normal RV contractile indexes. No patient in any group had values for RV dP/dt or VCE10 that were less than normal (mean normal - 2 standard deviations). This study establishes for the first time the indexes of RV isovolumic systole in children. It also shows that RV contractile function is preserved in young patients with chronic RV pressure or volume overload who do not have overt congestive heart failure.

Adolescent↗
PubMed1984

Total tracheal reconstruction in a three-month-old infant.

Total tracheal reconstruction with a reversed segment of left bronchus was attempted in a 3-month-old infant with an extensive tracheal stenosis. The patient survived for 48 hours. The details of the procedure and its potential applications are discussed.

Animals↗
PubMed1983

Effects of digoxin in infants with a congested circulatory state due to a ventricular septal defect.

Digoxin alone was used to treat a congested circulatory state in 21 infants (mean age, 2.7 months; mean weight, 3.8 kg) with a ventricular septal defect. The dose was adjusted on the basis of pharmacokinetics to achieve a mean steady-state concentration of 1.6 +/- 0.3 ng of digoxin per milliliter of serum. The mean red-cell level of sodium-potassium ATPase fell from 23.1 +/- 7.0 to 12.6 +/- 5.2 nmol per milligram per minute with treatment. Only 6 of the 21 patients had an inotropic response, as reflected by echocardiographic measurements, but the drug was of clinical benefit to 12 infants (including these 6). These results show that not all infants with a congested circulatory state due to a ventricular septal defect benefit from digoxin therapy. Furthermore, in some subjects clinical improvement occurs in the absence of a measurable inotropic response.

Digoxin↗
PubMed1982

Asplenia syndrome with atypical cardiac anomalies.

Two infants with asplenia and complex cyanotic congenital heart disease showed unusual findings at cardiac catheterization. Each had a patent pulmonary outflow tract and a severe obstructive lesion of the aortic arch. These cases emphasize the heterogeneity of the asplenia-polysplenia syndromes. Pulmonary atresia or critical pulmonic stenosis is not an invariable accompaniment of the asplenia syndrome. Obstructive lesions of the aortic outflow tract, which occur in about 1/3 of patients with the polysplenia syndrome, also can occur with asplenia.

Blood Gas Analysis↗
PubMed1982

Electrophysiologic effects of propranolol on sinus node function in children.

Little is known regarding the effects of propranolol (P) on sinus node function in children. In this study, corrected sinus node recovery time (CSNRT) and estimated sinoatrial conduction time (SACT) were measured in 10 children (ages 3 to 16 years; mean 8.3 years) without clinical evidence of sinus node dysfunction before and after intravenous P. The spontaneous sinus cycle length (SCL) increased after P(0.1 mg/kg) in all patients. Mean SCL increased 13.4% from 635 +/- 200 msec (+/- SD) to 720 +/- 202 msec (p less than 0.01). Maximum CSNRT increased in nine patients after P and mean CSNRT increased 63% from 203 +/- 61 msec to 330 +/- 190 msec (p less than 0.05). SACT changed in a random fashion after P. Mean SACT did not change significantly. We conclude that P significantly suppresses sinus node automaticity in children with normal sinus node function but has little or no effect on sinoatrial conduction.

Adolescent↗
PubMed1982

Noninvasive pulsed Doppler determination of cardiac output in neonates and children.

Mean blood flow velocity (VAo) in the ascending aorta was measured noninvasively in 33 children, ages 3 days to 17 years, by pulsed Doppler technique at the time of cardiac catheterization. Measurements were made from a suprasternal approach with a portable, range-gated device. The ascending aortic diameter was determined echocardiographically and aortic cross sectional area calculated (A = pi d2/4 cm2). Aortic flow (QAo) was computed from Doppler recordings: QAo (ml/minute) = VAo (cm/second) X A (cm2) X 60 (second/minute). Values were compared with cardiac outputs determined according to the Fick principle, using measured oxygen consumption calculated oxygen capacity, and oxygen saturation. Subjects with aortic valve abnormalities or left ventricular outflow tract obstruction were excluded from study. Agreement between the two methods was excellent (linear regression r = 0.98, slope = 1.07, y-intercept = -4.5 ml, range 403 to 5.540 ml/minute). The Doppler technique is a quick, noninvasive, and accurate method of determining ascending aortic blood flow in neonates and children.

Adolescent↗
PubMed1982

The effects of ouabain in lambs with depressed myocardial function.

The effects of ouabain infusion were tested in six lambs before and after depression of myocardial function by halothane anesthesia. Halothane reduced the left ventricular rate of pressure rise (dp/dt), stroke work, and stroke volume; the ratio of preejection period to left ventricular ejection time rose. Heart rate and systemic vascular resistance did not change. Before halothane, ouabain infusion did not alter the hemodynamic variables measured. After myocardial depression, ouabain infusion returned dp/dt, stroke work, stroke volume and the ratio of preejection period to left ventricular ejection time to control levels. Pacing studies showed a biphasic relationship between left ventricular dp/dt and heart rate. Maximal dp/dt occurred at a heart rate 42 beats/min higher than the resting rate. These studies suggest resting myocardial performance in the healthy, newborn lamb is at near maximal level.

Anesthesia, General↗
PubMed1982

Symptomatic sinus node dysfunction in children without structural heart disease.

Symptomatic sinus node dysfunction rarely occurs in children with structurally normal hearts. Three children with syncope and bradycardia are described. Noninvasive and invasive testing revealed isolated sinus node dysfunction and normal cardiac anatomy. Electrophysiologic evaluation showed abnormalities of sinus node automaticity and sinoatrial conduction. All three patients were treated with permanent ventricular pacemakers and have remained asymptomatic. Sinus node dysfunction should be considered in the differential diagnosis whenever a child is seen with unexplained dizziness or syncope.

Adolescent↗
PubMed1982

Evaluation of infants with bronchopulmonary dysplasia using cardiac catheterization.

Nine infants with bronchopulmonary dysplasia underwent cardiac catheterization to define thier circulatory status. In room air, the mean cardiac index was normal (3.4 liters/min/sq m), but pulmonary arterial pressure (39 mm Hg, mean) and pulmonary vascular resistance (8.6 Wood units . sq m) were elevated. Preejection period/right ventricular ejection time ratios determined echocardiographically correlated well with values obtained at catheterization, but did not correlate well with hemodynamic values. Administration of 40% and 88% oxygen caused variable responses in hemodynamic measurements. Studies of left ventricular function were normal in all patients. These findings raise questions about the long-term prognosis of infants with bronchopulmonary dysplasia.

Bronchopulmonary Dysplasia↗
PubMed1981

Vascular ring due to left aortic arch and right descending aorta.

Two children presented with symptoms suggestive of a vascular ring. Barium esophagrams in each case showed a posterior impression caused by a retroesophageal aortic arch. Angiographic studies defined a rare form of vascular ring resulting from an ascending left-sided aorta, a descending right-sided aorta and a right-sided ligamentum arteriosum. At surgery, the diagnosis was confirmed and the anomaly was corrected in each patient. Left pulmonary anomalies were present in each patient.

Aorta, Thoracic↗
PubMed1981

Aberrant systemic arterial supply to the left lung with congestive heart failure.

A six-month-old girl with an aberrant systemic arterial supply from the descending thoracic aorta to the left lower lobe had congestive heart failure. Although the pulmonary parenchyma was normal, there was an absence of normal pulmonary arterial supply to the left lower lobe. Main pulmonary arterial and aortic cineangiograms led to the correct diagnosis. Left lower lobectomy was performed and resulted in clinical and hemodynamic improvement.

Aorta, Thoracic↗
PubMed1981

Bedside evaluation of postoperative sinus node function in children.

Sinus node dysfunction in children frequently results from the surgical correction of congenital heart defects. We evaluated postoperative sinus node function at the bedside in 25 children by utilizing atrial epicardial electrodes which were placed near the sinus node at the time of operation. Sinoatrial conduction times (SACTs) and corrected sinus node recovery times (CSNRTs) were determined within 3 days of operation in each patient. Group 1 consisted of 20 patients (aged 1 month to 13 years) with normal postoperative sinus node function. Mean (+/- SD) SACTs and CSNRTs were 122 +/- 33 msec (range 61 to 187 msec) and 165 +/- 54 msec (range 52 to 253 msec), respectively. Preoperative evaluation of sinus node function during cardiac catheterization showed that preoperative and postoperative SACTs and CSNRTs were not significantly different (p greater than 0.05) in any of nine patients. Group 2 was composed of five children (aged 1 to 14 years) with postoperative sinus node dysfunction. Three had abnormal SACTs of 230 msec or greater and two children had first-degree sinus node entrance block. Two patients had prolonged CSNRTs. Electrocardiographic (ECG) monitoring revealed evidence of sinus node dysfunction in four of the five patients in Group 2. This report describes a simple and safe means of evaluating postoperative sinus node function at the bedside. The data are comparable to those obtained using more conventional methods during cardiac catheterization.

Adolescent↗
PubMed1980

Use of atrial epicardial electrodes to diagnose and treat postoperative arrhythmias in children.

Temporary Teflon-coated stainless steel wires were placed on the right atrium of 100 consecutive infants and children undergoing open heart surgery. The patients' ages ranged from 1 day to 17 years. The wires were used for diagnosis or treatment 40 times in 30 patients. Atrial electrograms were recorded 14 times to diagnose arrhythmias and conduction disturbances that were unsuspected or misdiagnosed from the standard electrocardiogram. In 10 patients, atrial pacing was used to treat postoperative arrhythmias. Atrial pacing was also used as an adjunct to therapy in 16 children with postoperative low cardiac output and bradycardia with intact atrioventricular conduction. The wires were removed before discharge and no complications resulted from their use. Previous studies have demonstrated the usefulness of temporary atrial wires after cardiac surgery in adults. This experience confirms that the technique is easy and safe and can be of great diagnostic and therapeutic value in children.

Adolescent↗
PubMed1980

Effects of prostacyclin (PGI2) and indomethacin on neonatal lamb mesenteric and renal artery responses to electrical stimulation and norepinephrine.

The effects of prostacyclin (PGI2) and indomethacin on isolated neonatal lamb mesenteric and renal artery responses to electrical stimulation and injected norepinephrine were investigated. PGI2 (1 micro M) decreased baseline tension and significantly reduced vasoconstrictor responses to electrical stimulation and norepinephrine. Indomethacin raised baseline tension and potentiated the constrictor responses. PGI2 reversed completely the potentiating effects of indomethacin. These results suggest that PGI2 may modulate the response to adrenergic stimuli in the mesenteric and renal arteries of neonatal lambs.

Animals↗