Premature Ventricular Depolarizations
A premature ventricular depolarization may be associated with no pulse, a small-amplitude pulse, or a normal arterial pulse depending on timing and whether or not the LV pressure generated is able to open the aortic valve.193 The arterial pulse following a premature beat usually is greatly enhanced because of decreased aortic impedance, increased LV filling, and augmented LV contractility. At times, premature ventricular beats are so common as to produce an irregularly irregular pulse. Then the presence of cannon a waves in the jugular venous pulse should alert one to the correct diagnosis.
The ECG is usually needed for the definitive diagnosis of any abnormality of heart rate or rhythm. On the other hand, careful observation of the arterial and jugular venous pulses frequently leads to the correct diagnosis. Simultaneous cardiac auscultation is also frequently helpful.
Most tachycardias associated with a regular pulse are of supraventricular origin. In sinus tachycardia, the arterial pulse will slow gradually with carotid sinus pressure and then again increase gradually. Paroxysmal atrial tachycardia has an "all or none" response. In patients with atrial flutter, carotid sinus pressure will increase the block at the AV junction, the pulse rate slowing and subsequently returning to its original rate in a "jerky" fashion.
In patients with ventricular tachycardia and AV dissociation, the variation in the atrial ventricular sequence of contraction and resulting variation in pulse amplitude often may be detected by palpation.194
An irregularly irregular pulse with a varying pulse pressure is usually the result of atrial fibrillation; however, multifocal atrial tachycardia is also a common cause of this finding in patients with severe chronic obstructive lung disease.
An unusually slow heart rate frequently is associated with a decrease in the rate of rise and amplitude of the arterial pressure pulse. Complete heart block often is readily diagnosed by the variability in the arterial pulse amplitude, the changing intensity of the first heart sound, and intermittent cannon a waves in the jugular venous pulse, all due to the time-dependent variable contribution of atrial contraction to ventricular filling.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.