The blood enters the atria to fill it, called the Arterial Diastole. The sino-atrial node is present in the right atrium. It generates a nerve impulse. This cause the contraction of the atria called the Atrial Systole. The heart rate increases due to the sympathetic nerve impulses and decreases by the vagus nerve impulses. The blood pressure in the atria is more than in the ventricles. The AV Valve opens and the blood is forced into the ventricles. The impulse then reaches the atrio-ventricular node. A delayed impulse of about 0.2 seconds helps in filling the ventricles, called the Ventricular Diastole. Now the impulse enters the ventricles and moves through the bundle of his present in the septum. Contraction of the ventricles occur which forces the blood out of the aorta and pulmonary artery. This is named as ventricular systole. The AV valves closes to prevent the blood from returning back to the atria. The semi-lunar valves are opened forcefully due to higher blood pressure in the ventricles. When the elastic artery walls expand, it is called a Pulse. The arteries recoil and squeezes the blood away from the heart due to fall in the pressure. The fall in the ventricular blood pressure results in the closing the semilunar valves. So the blood is prevented from flowing back into the ventricles from the arteries.
The heart pumps oxygenated blood through the aorta at about 1.6 km per hour. By the time blood reaches the capillaries, it is moving at around 109 cm per hour
An average human heart beats at 72 beats per minute which adds up to an approximate value of 2.5 billion times during an average lifespan of 66 years.
The EKG is a recording of the electrical impulses produced by the heart.
The body acts as a giant conductor of electrical currents. Any two points on the body may be
connected by electrical leads (electrodes) to register an EKG or to monitor the rhythm of the heart.
The tracing recorded from the electrical activity of the heart forms a series of waves and
complexes that have been arbitrarily labeled (in alphabetical order) the P, Q, R, S, T waves,
and sometimes the U wave. The waves or deflections are separated in most patients by regularly occurring intervals.
Depolarization (electrical firing) of the atria produces the P wave. Depolarization of the ventricles produces the QRS complex .
Repolarization (electrical recharging) of the ventricles causes the T wave. The significance of the U wave is uncertain, but it may be
due to repolarization of the Purkinje system.
The key to rhythm interpretation is the analysis of the form and interrelations of the P wave, the PR interval,
and the QRS complex. The EKG should be analyzed with respect to its rate, its rhythm, the site of the
dominant pacemaker, and the configuration of the P and QRS waves.