Failure of the Conduction System of the Heart-Commotio Cordis

Failure of the Conduction System of the Heart

The sinuatrial node is the spontaneous source of the cardiac impulse. The atrioventricular node is responsible for picking up the cardiac impulse from the atria. The atrioventricular bundle is the only route by which the cardiac impulse can spread from the atria to the ventricles. Failure of the bundle to conduct the normal impulses results in alteration in the rhythmic contraction of the ventricles (arrhythmias) or, if complete bundle block occurs, complete dissociation between the atria and ventricular rates of contraction. The common cause of defective conduction through the bundle or its branches is atherosclerosis of the coronary arteries, which results in a diminished blood supply to the conducting system

Commotio Cordis

This condition results in ventricular fibrillation and sudden death and is caused by a blunt nonpenetrating blow to the anterior chest wall over the heart. It occurs most commonly in the young and adolescents and is often sports-related. The sudden blow is frequently produced by a baseball, baseball bat, lacrosse ball, or fist or elbow. The common incidence in the young is most likely due to the compliant chest wall due to the flexible ribs and costal cartilages and the thin undeveloped chest muscles. Apparently, timing of the blow relative to the cardiac cycle is critical; ventricular fibrillation is most likely to occur if the blow occurs during the upstroke of the T wave of the electrical activity of the cardiac muscle.

  

Valvular Disease of the Heart-Valvular Heart Murmurs-The Anatomy of Cardiopulmonary Resuscitation

Valvular Disease of the Heart

Inflammation of a valve can cause the edges of the valve cusps to stick together. Later, fibrous thickening occurs, followed by loss of flexibility and shrinkage. Narrowing (stenosis) and valvular incompetence (regurgitation) result, and the heart ceases to function as an efficient pump. In rheumatic disease of the mitral valve, for example, not only do the cusps undergo fibrosis and shrink, but also the chordae tendineae shorten, preventing closure of the cusps during ventricular systole.

Valvular Heart Murmurs

Apart from the sounds of the valves closing, lu¯ b-du˘ p, the blood passes through the normal heart silently. Should the valve orifices become narrowed or the valve cusps distorted and shrunken by disease, however, a rippling effect would be set up, leading to turbulence and vibrations that are heard as heart murmurs.

 

The Anatomy of Cardiopulmonary Resuscitation

Cardiopulmonary resuscitation (CPR), achieved by compression of the chest, was originally believed to succeed because of the compression of the heart between the sternum and the vertebral column. Now it is recognized that the blood flows in CPR because the whole thoracic cage is the pump; the heart functions merely as a conduit for blood. An extrathoracic pressure gradient is created by external chest compressions. The pressure in all chambers and locations within the chest cavity is the same. With compression, blood is forced out of the thoracic cage. The blood preferentially flows out the arterial side of the circulation and back down the venous side because the venous valves in the internal jugular system prevent a useless oscillatory movement. With the release of compression, blood enters the thoracic cage, preferentially down the venous side of the systemic circulation.

Rib and Costal Cartilage Identification- Pleural Reflections- Position and Enlargement of the Heart

Rib and Costal Cartilage Identification

When one is examining the chest from in front, the sternal angle is an important landmark. Its position can easily be felt and often be seen by the presence of a transverse ridge. The finger moved to the right or to the left passes directly onto the second costal cartilage and then the 2nd rib. All other ribs can be counted from this point. The 12th rib can usually be felt from behind, but in some obese persons this may prove difficult

Pleural Reflections

It is hardly necessary to emphasize the importance of knowing the surface markings of thepleural reflections and the lobes of the lungs. When listening to the breath sounds of the respiratory tract, it should be possible to have a mental image of the structures that lie beneath the stethoscope. The cervical dome of the pleura and the apex of the lungs extend up into the neck so that at their highest point they lie about 1 in. (2.5 cm) above the clavicle. Consequently, they are vulnerable to stab wounds in the root of the neck or to damage by an anesthetist’s needle when a nerve block of the lower trunk of the brachial plexus is being performed.

Remember also that the lower limit of the pleural reflection, as seen from the back, may be damaged during a nephrectomy. The pleura crosses the 12th rib and may be damaged during removal of the kidney through an incision in the loin

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Position and Enlargement of the Heart

The surface markings of the heart and the position of the apex beat may enable a physician to determine whether the heart has shifted its position in relation to the chest wall or whether the heart is enlarged by disease. The apex beat can often be seen and almost always can be felt. The position of the margins of the heart can be determined by percussion.