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The first finding is that junctional rhythms are regular rhythms. This means that the time interval between beats stays constant. The next normal finding is a normal QRS. Since the impulse still travels down the bundle of His, the QRS will not be wide. Junctional rhythms can present with either bradycardia, a normal heart rate, or tachycardia. [9]
It is the ability of the heart to maintain a relatively stable relation between its systole and diastole. Not increasing one on the expense of the other. However, external factors may lead to the disruption of the heart's rhythmicity.
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.
The aortic and pulmonary valves known as the semilunar valves open, and a defined fraction of blood within the heart is ejected into the aorta and pulmonary trunk. Ejection of blood from the heart is known as systole. Ejection causes pressure within the ventricles to fall, and, simultaneously, the atria begin to refill (atrial diastole).
The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. [1] It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, called systole. [1]
Two endocardial tubes form here that fuse to form a primitive heart tube known as the tubular heart. [36] Between the third and fourth week, the heart tube lengthens, and begins to fold to form an S-shape within the pericardium. This places the chambers and major vessels into the correct alignment for the developed heart.
The heart wall is a three-layered structure with a thick layer of myocardium sandwiched between the inner endocardium and the outer epicardium (also known as the visceral pericardium). The inner endocardium lines the cardiac chambers, covers the cardiac valves , and joins with the endothelium that lines the blood vessels that connect to the heart.
The normal heart rate of the fetus is between 110 and 160 beats per minute. Any rhythm beyond these limits is abnormal and classed as a fetal arrhythmia. These are mainly the result of premature atrial contractions, usually give no symptoms, and have little consequence.