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Mitral regurgitation, also known as mitral insufficiency or mitral incompetence, is the backward flow of blood from the left ventricle, through the mitral valve, and into the left atrium, when the left ventricle contracts, resulting in a systolic murmur radiating to the left armpit.
Ventricular pacemaker cells discharge at a slower rate than the SA or AV node. While the SA node typically initiates a rate of 70 beats per minute (BPM), the atrioventricular node (AV node) is usually only capable of generating a rhythm at 40-60 BPM or less. Ventricular contraction rate is thus reduced by 15-40 beats per minute. [3]
Electrical waves track a systole (a contraction) of the heart. The end-point of the P wave depolarization is the start-point of the atrial stage of systole. The ventricular stage of systole begins at the R peak of the QRS wave complex; the T wave indicates the end of ventricular contraction, after which ventricular relaxation (ventricular diastole) begins.
[1] [5] Depending on where the rhythm originates in the AV node, the atria can contract before ventricular contraction due to retrograde conduction, during ventricular contraction, or after ventricular contraction. If there is a blockage between the AV node and the SA node, the atria may not contract at all.
The faster the contractions are, the shorter the filling time and both the EDV and preload are lower. [1] The relationship between ventricular stretch and contraction has been stated in the Frank-Starling mechanism which says that the force of contraction is directly proportional to the initial length of muscle fibre. So that the greater the ...
Ventricular systole is the contractions, following electrical stimulations, of the ventricular syncytium of cardiac muscle cells in the left and right ventricles. Contractions in the right ventricle provide pulmonary circulation by pulsing oxygen-depleted blood through the pulmonary valve then through the pulmonary arteries to the lungs.
The patient is subjected to stress in the form of exercise or chemically (often dobutamine). After the target heart rate is achieved, 'stress' echocardiogram images are obtained. The two echocardiogram images are then compared to assess for any abnormalities in wall motion of the heart. This is used to detect obstructive coronary artery disease ...
An example of premature ventricular contraction is the classic athletic heart syndrome. Sustained training of athletes causes a cardiac adaptation where the resting SAN rate is lower (sometimes around 40 beats per minute). This can lead to atrioventricular block, where the signal from the SAN is impaired in its path to the ventricles. This ...