EFFECTS OF PITUITARY TUMORS ON THE VISUAL APPARATUS

EFFECTS OF PITUITARY TUMORS ON THE VISUAL APPARATUS

pediagenosis    May 16, 2025    Comment   

EFFECTS OF PITUITARY TUMORS ON THE VISUAL APPARATUS

The optic chiasm lies above the diaphragma sellae. The most common sign that a pituitary tumor has extended beyond the confines of the sella turcica is a visual defect caused by the growth pressing on the optic chiasm. The most frequent disturbance is a bitemporal hemianopsia, which is produced by the tumor pressing on the crossing central fibers of the chiasm and sparing the uncrossed lateral fibers. The earliest changes are usually enlargement of the blind spot; loss of color vision, especially for red; and a wedge-shaped area of defective vision in the upper-temporal quadrants, which gradually enlarges to occupy the whole quadrant and subsequently extends to include the lower temporal quadrant as well.

Pancreas Anatomy

Pancreas Anatomy

pediagenosis    May 16, 2025    Comment   

Pancreas Anatomy

The pancreas is both an exocrine and an endocrine gland. Most of its substance is involved in producing pancreatic juice, which is conveyed by a duct system into the descending duodenum. In addition, microscopic clumps of endocrine tissue, the pancreatic islets (islets of Langerhans), are dispersed throughout the gland.

CARDIAC PACING

CARDIAC PACING

pediagenosis    May 15, 2025    Comment   

CARDIAC PACING

When patients are symptomatic because of symptomatic bradycardia (e.g., syncope, dizziness, lethargy), a cardiac pacemaker can effectively decrease or eliminate symptoms because it treats the pathophysiologic problem: slow heart rate, which can result from sinus node dysfunction or A-V block. Some devices pace only the atrium, some only the right ventricle, and some pace both the atrium and the ventricle sequentially. Some pacemakers also are combined with an implantable cardioverter-defibrillator (ICD), and others can improve cardiac synchronization (e.g., BiV pacemakers).

 

CURRENT TRANSVENOUS PACEMAKERS

A modern pacemaker generator (usually a lithium battery) is placed subcutaneously under the clavicle. This generator is sealed so as not to imbibe body fluids and can deliver electrical impulses to the electrode leads within the right atrial appendage and right ventricle and to the left ventricle by way of a coronary sinus electrode lead (BiV pacing). The pacemaker generator is immunologically inert.

Permanent Pacing

The pacemaker implant procedure is performed under fluoroscopy, usually by a trained cardiologist or cardiac surgeon. Most often, percutaneous access to the left subclavian lead is used to pass the electrode leads into the heart, but the right subclavian vein can be used when the left is not available. Fluoroscopy confirms the positioning of the pacing leads in the right atrial or right ventricular chambers and of the left ventricular epicardial lead when BiV pacing is employed.

Pacemaker Types

Pacemakers can be of three types and are used to pace a single or multiple chambers of the heart. A single-chamber pacemaker involves the placement of a single lead into an atrium or ventricle, which then can sense and pace either the atrium or the ventricle. The most common reason for pacing only the atrium is dysfunction of the sinus node, such as sick sinus syndrome. The most frequent reason for pacing only the right ventricle is atrial fibrillation.

In contrast, a dual-chamber pacemaker consists of two leads inserted into the heart (see Plate 2-29). One lead can be inserted into the right atrial appendage and fixated in that position, pacing the atrium. Another pacing lead can be inserted into the right ventricle and fixated in that position. When activated and functioning, these two pacing leads pace the atrium and ventricle sequentially, closely simulating the natural conduction system of the heart. This type of pacing is the most common type currently used.

A rate-responsive pacemaker is usually a dual-chamber pacemaker (can be single chamber) that responds to increased demand for an increased heart rate. The patient’s increased physical activity (exercise) increases pectoral muscle activity, which is sensed by the pacemaker generator. Once this physical activity is detected, the pacemaker increases the rate of electrical impulses and increases heart rate to meet the patient’s physiologic demands for increased cardiac output. Rate- responsive pacemakers are often used for patients with symptomatic bradycardia.

Biventricular Pacing

In contrast to standard two-lead A-V sequential pacing, biventricular (BiV) pacing consists of three leads: RA appendage lead, RV lead, and a lead introduced into the coronary sinus and advanced to a lateral vein on the epicardial surface of the LV free wall. The position of the epicardial lead corresponds to the position of an obtuse marginal artery. This lead system, in addition to A-V pacing, enables pacing of the LV free wall (see Plate 2-29).

Cardiac resynchronization therapy (CRT) uses BiV pacing because the lead system paces both the septal LV wall and the lateral LV wall. When viable tissue is present in these areas, the left ventricle resynchronizes the contraction of a heart whose opposing walls do not contract in synchrony. Dyssynchrony frequently occurs in patients with systolic heart failure, many with QRS duration longer than 120 msec, which qualifies a patient for CRT. These patients are at high risk for sudden cardiac death because many have an LV ejection fraction of 35% or less. The BiV lead system can be combined with an ICD to prevent sudden cardiac death from ventricular tachycardia or ventricular fibrillation, a common companion to severe heart failure.

EFFECT OF DIGITALIS AND CALCIUM/POTASSIUM LEVELS ON ELECTROCARDIOGRAM

EFFECT OF DIGITALIS AND CALCIUM/POTASSIUM LEVELS ON ELECTROCARDIOGRAM

pediagenosis    May 15, 2025    Comment   

EFFECT OF DIGITALIS AND CALCIUM/POTASSIUM LEVELS ON ELECTROCARDIOGRAM

DRUG EFFECTS: DIGITALIS

The effect of common drugs such as digitalis and other antiarrhythmic agents on the ECG depends on the dose, the rate of excretion, responsiveness of the patient, and previous ECG abnormalities. Small doses of digitalis produce a mild digitalis effect with sagging depression of the ST segment, negative J shifts, and lowering of the T waves (Plate 2-28, A). The QT interval may be shortened slightly because of increases in the rate of ventricular repolarization. Digitalis usually slows the cardiac rate and A-V conduction because of vagal depression of the SA and AV nodes. With large doses a further depression of J occurs, with sagging of the S-T segments and a distinct decrease in the Q-T intervals, which fall outside of normal limits (Plate 2-28, B). With toxic doses there is a depression of the A-V conduction tissue, with prolonged P-R intervals, and a state of ventricular irritability, with ventricular ectopic beats, which may be single or multiple and multifocal (Plate 2-28, C). Coupling is common, and atrial fibrillation or flutter, with paroxysmal atrial tachycardia, and block or variable degrees of A-V block may occur.

Drugs such as procainamide (Pronestyl) and lidocaine (Xylocaine), tend to depress the electric activity of the atria and ventricles. Characteristically, the P waves increase in duration, with a slight increase in amplitude. Drugs such as ibutilide often cardiovert the AF to sinus rhythm, but the patient should receive intravenous magnesium sulfate before treatment, to prevent torsades de pointes. Intravenous amiodarone also prolongs the Q-T interval and frequently will cardiovert the patient to sinus rhythm.

 

CALCIUM AND POTASSIUM LEVELS

Hypercalcemia may be encountered in patients with hyperparathyroidism. The ECG is characterized by shortening of the Q-T intervals, often with increased amplitudes of the T waves (Plate 2-28, H). The T waves begin immediately after the ending of the QRS complexes, so the QRS complexes and T waves appear compressed.

Hypocalcemia increases the duration of the S-T and Q-T intervals (Plate 2-28, J). The QRS complexes and T waves merely appear to be widely separated from each other by long S-T segments, which often are isoelectric.

Hyperkalemia depresses the atria, the A-V node, and the ventricles but has less effect on the sinus node.

Consequently, increases in potassium concentration produce prolonged P-R intervals (Plate 2-28, L), high T waves, SA block with small or absent mechanical contractions of the atria, tenting of the T waves (tall and narrow at base), intraventricular block with widening of QRS complexes, abnormal shifts of the S-T segment, and ventricular standstill or ventricular fibrillation (Plate 2-28, K).

Hypokalemia frequently results from administration of diuretics or cortisone or from vomiting, diarrhea, surgical suction, or low intake of potassium. Hypokalemia causes an amplitude loss in the T waves (Plate 2-28, N) and a prominence of the U waves, with easily measured Q-U intervals. T and U waves are clearly separated in some leads but may fuse in others, causing a T-U complex. Deviations of the S-T segment (depression or elevation) may occur. It is difficult to recognize hypokalemia associated with other abnormal states, such as myocardial ischemia or infarction, or with cardiac drugs.

TACHYCARDIA, FIBRILLATION, AND ATRIAL FLUTTER

TACHYCARDIA, FIBRILLATION, AND ATRIAL FLUTTER

pediagenosis    May 15, 2025    Comment   

TACHYCARDIA, FIBRILLATION, AND ATRIAL FLUTTER

PAROXYSMAL TACHYCARDIA

Paroxysmal Atrial Tachycardia

Paroxysmal atrial tachycardia (PAT) is caused by a pace maker in the atria that gives rise to rapid regular impulses at a rate above 100 beats/min, often as much as 180 beats/min (see Plate 2-27). P waves can usually be identified, although in some cases the P and T waves fall on each other. The R-R intervals are regular. PAT is characterized by an abrupt beginning and ending. The onset and end often occur within the course of a single beat. Carotid sinus pressure may cause a sudden reversion to sinus rhythm, which is diagnostic of PAT.

LYMPHOGRANULOMA VENEREUM

LYMPHOGRANULOMA VENEREUM

pediagenosis    May 15, 2025    Comment   

LYMPHOGRANULOMA VENEREUM

Lymphogranuloma venereum (LGV) is a sexually transmitted disease (STD) that is produced by infection with Chlamydia trachomatis serotypes L1, L2, and L3. The disease progresses through three distinct phases of transmission. This bacterial disease was once limited to tropical regions, but with the ease of worldwide travel, it can now be seen globally. The skin manifestations are found predominantly in the groin and genital region. This disease is often seen in conjunction with other STDs, and screening for other STDs should be done routinely in patients diagnosed with LGV.

SINUS ARREST, SINUS BLOCK, AND ATRIOVENTRICULAR BLOCK

SINUS ARREST, SINUS BLOCK, AND ATRIOVENTRICULAR BLOCK

pediagenosis    May 14, 2025    Comment   

SINUS ARREST, SINUS BLOCK, AND ATRIOVENTRICULAR BLOCK

SINUS ARREST

Sinus arrest is usually a functional condition in which the sinus node fails to send impulses to the atria, resulting in a period of cardiac asystole. Eventually, recovery occurs. The first beat after the asystole may be a normal sinus beat (known as a sinus escape beat), or the A-V node may take over for the first beat, originating from a pacemaker in the A-V node, called a nodal escape beat (see Plate 2-26). Here, the P wave may be detectable when there is retrograde atrial conduction. In this case, inverted P waves either precede or follow the QRS complexes in leads II, III, and aV_F, or there may be no retrograde conduction and hence no P waves. A ventricular escape beat has all the characteristics of a ventricular ectopic beat. Escape beats of these various types may precede sinus rhythm, sinus bradycardia, sinus tachycardia, nodal rhythm, ventricular tachycardia, or other cardiac rhythms or arrhythmias.

PREMATURE CONTRACTION

PREMATURE CONTRACTION

pediagenosis    May 14, 2025    Comment   

PREMATURE CONTRACTION

Three common terms used to describe certain abnormal cardiac contractions are premature contractions (beats occurring early in time), ectopic beats (beats with sites of origin outside the sinus node), and extrasystoles (added beats). Only extrasystoles are truly added or additional beats, often interpolated or added between two normal beats without interfering with the basic rhythm.

SINUS AND ATRIAL ARRHYTHMIAS

SINUS AND ATRIAL ARRHYTHMIAS

pediagenosis    May 14, 2025    Comment   

SINUS AND ATRIAL ARRHYTHMIAS

Certain arrhythmias are caused by a disturbance at the sinus node, including sinus bradycardia, sinus tachycardia, sinus arrhythmia, and wandering pacemaker. The sinus node is under the control of the parasympathetic and sympathetic nerves, and altered function of these nerves may influence cardiac activity. The SA node is depressed by parasympathetic (vagus) functions or stimulated by sympathetic activity.

WOLFF-PARKINSON-WHITE SYNDROME

WOLFF-PARKINSON-WHITE SYNDROME

pediagenosis    May 13, 2025    Comment   

WOLFF-PARKINSON-WHITE SYNDROME

The Wolff-Parkinson-White (WPW) complex is caused by the presence of an accessory pathway. About 20% of patients with an accessory pathway have organic heart disease, and 80% have the ECG abnormality only. The accessory pathway connects the atria to the ventricles, over which depolarization occurs rapidly from atria to ventricles, resulting in ventricular preexcitation. The syndrome related to preexcitation is most often seen in young subjects who have frequent attacks of supraventricular or even ventricular tachycardia. Between attacks of rapid heartbeat, the QRS complexes consist of a short P-R interval (usually <0.11 second), a QRS complex widened by a Δ wave, and, usually, a QRS complex whose duration is from 0.11 to 0.14 second. Actually, the P-R interval is decreased by the amount the QRS complex is increased, so that the P-J interval remains quite normal (see Plate 2-23). (The P-J interval is from the beginning of the P wave to the end of the QRS. “J” stands for the junction between the QRS and ST segment on the ECG.).