CARDIAC FOCI: ANATOMICAL AND TECHNICAL LOCATION - ANATOMY AND PHYSIOLOGY - 2025

The heart foci are specific areas of the thorax where heart sounds are appreciated, which correspond to the closure of the four heart valves. These foci are in areas where blood passes, once it has passed the valve to be auscultated.

In the process an audible vibration is generated because the sound travels with the bloodstream. Auscultation of the cardiac foci is the method of cardiovascular physical examination that provides the most information in cardiothoracic evaluation.

Heart sounds

Audible physiological heart sounds are the first and second sounds; however, under certain physiological conditions the third and fourth sounds can also be heard.

Between the first and second sounds there is a space called “small silence”, which corresponds to ventricular systole; and between the second and the first noise there is again a space called “great silence”, which corresponds to ventricular diastole.

First noise

The first sound corresponds to the closure of the atrio-ventricular valves, and indicates the onset of ventricular systole (small silence).

Second noise

The second heart sound is made when the aortic and pulmonary (sigmoid) valves close. Under normal conditions, a slight splitting can be heard (hearing the blow in two almost immediate times) due to the slightly early closure of the aortic valve with respect to the pulmonary valve.

Third noise

It is difficult to differentiate the third noise, as an inexperienced ear can mistake it for the doubling of the second noise. It is a low-pitched noise that is produced by the vibration of the ventricular wall at the beginning of diastole.

It is heard in some cases, mainly in children and young adults. When heard in people over 40 years of age, it is usually secondary to mitral regurgitation, which increases the pressure of the blood flow to the ventricle and, therefore, the filling is perceived on auscultation.

Fourth noise

The fourth heart sound is produced by the sudden deceleration of blood flow against a hypertrophied ventricle. It is less frequent than the third noise and its presence usually has pathological significance.

What are the cardiac foci? Anatomical location

With the advancement of medicine, the methods of physical examination of the patient have been refined, and consensus has been reached on the areas that allow the heart sounds important for the cardiovascular physical examination to be clearly detailed. These areas or foci are the following:

Mitral or apex focus

It is the fifth left intercostal space (between the 5th and 6th rib) on the midclavicular line.

It corresponds to the cardiac apex. It is the focus where the closing of the mitral valve can be heard best.

This is because the left ventricle has more contact with the rib wall at this point. Because the flow from the left atrium, after passing the mitral valve, reaches the left ventricle, the sound of the valve closing travels through this chamber.

Tricuspid focus

It is located at the junction of the body of the sternum with the xiphoid appendix or the 4th and 5th left intercostal space next to the sternum.

It corresponds to the noise of the tricuspid valve closure that projects through the right ventricle to the lower portion of the body of the sternum.

Pulmonary focus

It is located in the 2nd left intercostal space with a left parasternal line. It is parallel to the aortic focus.

In this focus, the pulmonary valve closing noises can be perceived more clearly.

Aortic focus

It is parallel to the pulmonary focus on the opposite side and is located in the 2nd right intercostal space with a right parasternal line.

It corresponds to the area where the noises of the aortic valve closure of the supraigmoid portion of the artery are projected.

Accessory or Erb aortic focus

It is located in the left third intercostal space with a left parasternal line. It is also called the Erb focus.

It corresponds to the projection of aortic valve sounds, especially those dependent on valve regurgitation.

Auscultation technique

Initially, the exploration of heart sounds was performed by applying the ear directly to the areas to be explored.

At present, cardiac auscultation consists of listening to the sounds produced in the precordial area and its vicinity through the use of a stethoscope.

The ear pieces of the stethoscope must fit snugly into the ear so that there is an airtight system from the thorax to the eardrum. The length of the tube should not exceed 50 cm.

If possible, the physical examination should be performed in a well-lit, low-noise room. The doctor should be to the right of the patient.

It should be heard directly on the patient's skin, never over clothing. If possible, all foci should be auscultated with the membrane (heart murmurs and lung sounds) and the bell (normal heart sounds) of the stethoscope in order to capture high and low frequency sounds, respectively.

It is usually done in the supine position. If for some reason the heart sounds are not very audible, we proceed to auscultation in the left lateral decubitus position (pachón position).

Some sounds are better heard in different positions, especially pathological sounds.

References

1. Agustín Caraballo. Clinical examination manual. University of the Andes. Publications Council. 2nd Edition. Editorial Venezolana, ca (2008) Mérida, Venezuela. P. 98-102
2. Argente - Alvarez- Medical Semiology. Physiopathology, Semiotechnics and Propedeutics. Teaching based on the patient. Editorial Panamericana. 6th Edition. Physical exam. Physical examination of the cardiovascular system. P. 373-376
3. Charlie Goldberg MD. Examination of the heart. Recovered from: meded.ucsd.edu
4. Salvatore Mangione MD. Cardiac auscultatory skills of internal medicine and family practice trainees. A comparision of diagnostic proficiency. Septembre 3, 1997. Recovered from: jamanetwork.com
5. Andrew N. Pelech, MD. The physiology of cardiac auscultation. Elsevier Saunders. Pediatric Clinics of North America. pediatric.theclinics.com