Cardiac Conduction

At the latter end of the p-q interval, atrial contraction occurs forcing additional blood into the ventricles. At the beginning of the QRS interval on an ECG reading, the mitral valve closes and the ventricles are at EDV (135ml). During the QRS interval, ventricular contraction occurs increasing the pressure in the ventricle and the aorta. When the pressure continues in the ventricle exceeds the pressure in the arteries, the aortic valve opens and blood is ejected. The increased pressure continues through the t peak. The ventricles are now in ESV (65ml) and the aortic valve is closed. Now the ventricles are relaxed causing pressure to fall and the cardiac cycle starts over again. This ECG reading was from a normal tracing. Keep in mind that an ECV is easy to obtain, but there are some subtleties that are very complex.

4. Atrial hypertrophy would probably have what effect on an electrocardiogram? *spike the p wave

An electrical stimulus was applied to the heart; the following graph shows the refractory period of the frog’s heart when an extra-systole was induced. It can be seen that right after the recording was marked “Refractory 3,” an extra-systole was detected.

R E V I E W S H E E T 30 Anatomy of the Heart

5. Conduction, pp.1099-1103. Conduction system of the heart. Specialized cardiac muscle cells in the wall of the heart rapidly conduct an electrical impulse throughout the myocardium. The signal is initiated by the SA node (pacemaker) and spreads to the rest of the atrial myocardium and to the AV node. The AV node then initiates a signal that is conducted throught the ventricular myocardium by way of the AV bundle (of His) and Purkinje fibers.

Transmission occurs when the action potential reaches the presynaptic terminal in the dorsal horn of the spinal cord. A-delta and C fibres release

In the normal conduction of the heart the electrical impulse starts in the SA node, also called the pacemaker of the heart. The electrical impulse travels through the right atrium and through the Bachmann’s bundle into the left atrium. This stimulates the atria to contract. Next the signal travel to the AV node. The AV node slightly delays the signal. This delay is needed for the heart to beat properly. Without this delay the atria and ventricles would beat at the same time. The electrical signal then travels to the Bundle of His where it is split into the signals going to the right and left ventricle. The signal

Meaning The Sa node and Av node work together, forcing blood into the ventricles, which contract, forcing the blood to leave from the left side of the heart. The blood that enters the right side of the heart enters through veins as it is under less pressure. Blood with co2 in it will exit the right side of the heart through the pulmonary artery to the lungs where gaseous exchange occurs.

The labels of the waves indicate a particular action on the heart. P waves represent atrial depolarization or atrial contraction. The QRS complex indicates ventricular depolarization. While QRS is normally seen not ever complex has Q (negative deflection), R (positive

of atria and ventricle. Impulses not being transmitted from atria to the ventricle; no whole number relationship between atrial and ventricular contractions was demonstrated.

FIGURE 4: Effect of atrial extrastimulation on preexcitation. A: Manifest preexcitation during normal sinus rhythm (NSR) with HV interval value of -11 msec. Atrial extrastimulation (AES) increased the degree of preexcitation (HV interval value of -64 msec). B: An earlier coupled AES produced more pronounced preexcitation with HV interval value of -93 msec. C: A more premature AES produced full preexcitation with the His bundle activated retrogradely , with VA conduction over the AVN & an echo beat (atrioventricular reentry) (Issa et al, 2012).

This node produces electrical impulses that spread across the surface of each chamber, causing them to contract. The signals begin by spreading through the atria. As the atria contract, the blood within is forced through the corresponding valves into the ventricles.

Heart contraction is produced by stretching of sarcomere units, which produces strokes between myosin head and actin monomers located in the thin filament of sarcomere (Robinson, Dong et al. 2004). Changes in the resting tension of heart muscle affect the range of heart contraction. The heart has the capacity to adjust its contraction force as result of variations in ventricular filling (end-diastole), this effect is known as the Frank–Starling Law (Sequeira and van der Velden 2015). An increased systolic contraction is the results of the ventricle stretching due to greater end-diastolic volume happens (Schneider, Shimayoshi et al. 2006). However,

Choice "D" is not the best answer. The vignette states that the QRS length is less than 120 milliseconds. Ventricular tachycardia consists of wide QRS waves that are greater than 200

The atrial contraction is represented by the P wave. This is an upward, or positive wave of the line on the graph. The ventricular contraction is displayed by the QRS complex. The QRS