Chest X-Ray - dextrocardia

Normally, the heart is a midline structure found just posterior to the sternum where 35-40% of the heart mass in the right side of the thorax (chest), and the rest (60-65%) is in the left side of the thorax. In this normal condition the apex of the heart faces slightly inferior and to the left. In fact, there are many books and websites that state (wrongly) that the heart is normally in the “left side of the chest”.

If the above mentioned situation is reversed, we are in the presence of dextrocardia, that is, the heart is still in the midline, but most of the mass of the heart is in the right side of the thorax, and the apex points inferiorly and to the right.

The word dextrocardia is a derivate of the Latin [dexter], meaning “right”, and the Greek term [kardia], meaning “heart”. The word dextrocardia literally means “right-sided heart”.

Dextrocardia is a congenital condition, can be completely asymptomatic and present as an isolated condition. It can also be part of a complex genetic condition called “situs inversus” where the whole body is a mirror image of itself and all organs, including the heart are mirrored. A complete situs inversus is rare, but when present it usually does not cause problems.

The problems start when only part of the body and organs are reversed and others are not, causing an incredible number of potential anatomical variations and associated problems.

The prevalence of dextrocardia is about 1 in 12,00 pregnancies. The reported incidence is about 0.22%. Depending on the situation, dextrocardia can present with additional cardiac congenital disorders.

Sources

1. “Dextrocardia: an incidental finding” Yusuf SW, Durand JB, Lenihan DJ, Swafford J. Tex Heart Inst J 2009;36(4):358-9.
2. Garg N, Agarwal BL, Modi N, Radhakrishnan S, Sinha N. Dextrocardia: an analysis of cardiac structures in 125 patients. Int J Cardiol 2003;88(2–3):143–56
3. Bernasconi A, Azancot A, Simpson JM, Jones A, Sharland GK. Fetal dextrocardia: diagnosis and outcome in two tertiary centres. Heart 2005;91(12):1590–4.

Sinus rhythm electrocardiogram

A contraction, from the Greek [συστολή] (systolí) meaning “contraction”, also [συστελλει] (systellei) meaning “to shrink, to shorten, or to draw together”.

It refers to the contraction of the heart. If you analyze a normal heartbeat (sinus rhythm), there are two systoles: an atrial systole, followed by a short interval, followed by the ventricular systole. The term systole is usually used in reference to the ventricular systole.

Systole was first recognized and named by Herophilus of Alexandria (325-255BC), most probably trough animal vivisection. Herophilus was accused of animal vivisection and the dissection of human cadavers. Because of this, some call Herophilus "The Father of Anatomy".

Galen of Pergamon (129AD - 200AD) used the term [συστελλεσθαι] meaning “contracted”.

The word in English was first used in the 16th century and was originally written as “sistole”, with an "i" instead of the accepted use today with a "y". The modern pronunciation in English follows the Greek pronunciation by ending the word in a long “e” as in “to be”.

Sources
1. "The Origin of Medical Terms" Skinner, HA 1970 Hafner Publishing Co.
2. "Medical Meanings - A Glossary of Word Origins" Haubrich, WD. ACP Philadelphia
3. "Dorlands's Illustrated Medical Dictionary" 26th Ed. W.B. Saunders 1994
4. "Greek anatomist Herophilus: the father of anatomy" Si-Yang, N. Anat Cell Biol. 2010; 43(4): 280–283

Note: Google Translate includes the symbol (?). Clicking on it will allow you to hear the pronunciation of the word.

Sinus rhythm electrocardiogram

Sinus Rhythm (SR), also known as Normal Sinus Rhythm (NSR) is the term used to denote normal cardiac activity. A normal beating heart is in sinus rhythm.

In the normal beating of the heart the left and right atria contract followed by the contraction of the left and right ventricles. These atrial and ventricular contractions are separated by a lag time of 1/10th of a second which allows the atria to relax (atrial diastole) while the ventricles contract (ventricular systole). The addition of the normal action of the four heart valves (tricuspid, mitral, aortic, and pulmonary) allows the heart to work as a blood pump and circulate blood within the heart and through the body and lungs.

SR is coordinated by a complex binary conduction system. The first part of the conduction system is composed of heart muscle cells (cardiomyocytes) which are characterized by automaticity. It is important to state here something that is known, but many times ignored: This portion of the conduction system is not composed of nerves... it is formed by specialized cardiac muscle cells! The description of this cardiomyocyte-based system can be read in a separate article here.

The second component of the conduction system is the cardiac autonomic nervous system (CANS), which acts as a moderator (accelerating or slowing) the cardiomyocyte-based conduction system. A separate article will be written soon and linked here. Suffice it to say (for now) that the CANS has two components, an extrinsic component formed by nerves and ganglia outside the heart, and an intrinsic component of nerves and ganglia that forms a complex network within the superficial aspect of the heart muscle and fat surrounding the heart. These are the ganglionated plexuses, and their dysfunction can cause abnormal heart rhythm.

When these two components and their thousands of cardiac muscle cells, ganglia, and nerves are working property, the heart is in sinus rhythm, and beats between 60 to a 100 times per minute.

Personal note: The term Normal Sinus Rhythm (NSR) is redundant. By definition, if the heart is in SR, it is normal. On the other hand, the term Abnormal Sinus Rhythm is also not correct… if the heartbeat is abnormal, the heart is not in SR! (Dr. Miranda)

Histology image of cardiac muscle*

[UPDATED] Cardiac muscle is one of the three types of muscle found in the human body. It is found exclusively in the heart, where it forms the main component of its middle layer, the myocardium.  

[Myo]=combining form for "muscle"; [-card-]=heart; and [-ium]=layer or membrane. The myocardium is the muscle layer of the heart.

Cardiac muscle has distinct striations and intercalated discs (see accompanying image). The cardiac muscle acts as a functional syncytium. 

The key characteristic of cardiac muscle is automatism or automaticity, its capacity to contract rhythmically in the absence of an external electrical stimulus. The other two types of muscle (smooth and skeletal) lack this characteristic.

The term [cardiomyocyte] can be used to describe each of these cells as the word is composed of [Card(i)o=combining form for "heart"; [myo]=combining form for "muscle"; and the suffix [-cyte]= cell. A cardiomyocyte is a cardiac muscle cell.

One of the components of the conduction system of the heart is made exclusively of cardiomyocytes.

 Image modified from the original on YouTube from the British Heart Foundation.

* Original histology image by S, Girod and A. Becker, courtesy of Wikipedia. 

Anterior view of the heart*

[UPDATED] These two root terms mean "heart".

The first one, [-card(i)-] arises from the Greek [καρδιά] pronounced kardiá, and can be seen in medical words such as: cardiac, echocardiogram, cineangiocardiogram, cardioplegia, myocardial infarction, etc.

The second one [-cord(i)-] arises from the Latin [cor] or [cordis] and can be seen in words such as: precordial pain, cordial, commotio cordis, etc. 

As a point of interest, the original Greek spelling of [kardium]  was used by Nobel prize winner Dr. Willem Einthoven (1860 - 1927) when he invented the electrocardiograph and the electrocardiogram. The German term is [elektrokardiogramm] and the German abbreviation for the procedure is EKG. Since we use the term in English, [electrocardiogram] we use the abbreviation ECG. Both are correct, although if you are speaking English, ECG should be used.

* Image property of:CAA.Inc.. Artist:Victoria G. Ratcliffe

Vine tendril. Image courtesy of Jon Sullivan

The term [pampiniform] comes from the Latin term [pampinus] meaning "a vine tendril". It refers to a twisted, curved structure as seen in the accompanying image.  The second portion of the word also comes from Latin, [forma] means "shape" or "in the shape of".

Pampiniform then means "in or with the shape of a vine tendril"

Although mostly associated with the pampiniform plexuses found in both the testicular veins in the spermatic cord and the ovarian veins found within the infundibulopelvic ligament, the term is also used to denote the coiled aspect of the organ of Rosenmuller, also known as the pampiniform body or paraovarium.

The pampiniform body is a non-functional embryological remnant of the development of the female reproductive system. It is composed of a blind longitudinal duct and 10-15 transverse smaller ducts. It is located in the mesosalpinx, an extension of the broad ligament related to the uterine tube (Fallopian tube).

Thanks to David Van Tol for suggesting this article!

Image courtesy of Jon Sullivan, Public domain, via Wikimedia Commons https://jonsullivan.com/