Talk:Cardiovascular System - Heart Rate Development

2010

Embryology of the conduction system for the electrophysiologist

Indian Pacing Electrophysiol J. 2010 Aug 15;10(8):329-38.

Mirzoyev S, McLeod CJ, Asirvatham SJ.

Mayo Medical School. Abstract

It is critical for interventional electrophysiologists to thoroughly appreciate the topographic and developmental anatomy of the heart and its conduction system. Not only is understanding cardiac anatomy important to prevent complications from collateral damage and to help guide catheter placement, but developmental anatomy allows a deeper appreciation of the arrhythmogenic substrate. In this article, we briefly review the relevant stages of cardiac development for electrophysiologists. The potential location of normal and abnormal conduction patterns resulting from heterogeneous developmental origin is discussed.

During cardiogenesis, myocytes develop into either contractile or conduction cells. Three models have been proposed by which cardiac cells develop and differentiate [1].

1. The first model has been traditionally adopted by electrophysiologists and is based on a multiple ring theory. It hypothesizes that during heart chamber development and growth, cells in certain regions of the heart tube do not proliferate as rapidly as cells in genetically predetermined atrial and ventricular regions. As the tubular heart grows, the slower-proliferating myocytes form constrictions or rings around which the heart will fold.
2. A second recruitment model is based on the idea that the conduction system framework is present in early development and enables recruitment of adjacent myocytes to form further elements of the conduction system.
3. The third model, the early specification model, postulates that myocytes begin expressing either conduction genes or working (contractile) genes early in the development. Cells expressing conduction system markers slowly proliferate and form components of the conduction system, whereas cells lacking the markers proliferate faster and develop into contractile tissue.

PMID: 20811536 http://www.ncbi.nlm.nih.gov/pubmed/20811536

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2922875/?tool=pubmed

Development of the cardiac conduction system: why are some regions of the heart more arrhythmogenic than others?

Circ Arrhythm Electrophysiol. 2009 Apr;2(2):195-207.

Christoffels VM, Moorman AF.

Heart Failure Research Center, Academic Medical Center, 1105 AZ, Amsterdam, The Netherlands.

PMID: 19808465 http://www.ncbi.nlm.nih.gov/pubmed/19808465

http://circep.ahajournals.org/cgi/content/full/2/2/195

Evaluation of the embryonic and foetal heart rate at 6(+0) to 11(+6) weeks of gestation

Hamela-Olkowska A, Wiech K, Jalinik K, Zaryjewski D, Kornatowski L, Dangel J. Ginekol Pol. 2009 Mar;80(3):188-92. Polish. PMID: 19382610

"RESULTS: FHR varied between 47 and 192 bpm (mean 154 +/- 26 bpm). At 6 weeks, mean EHR was 116 +/- 21 bpm, then slowly increased, reaching mean 172 +/- 9 bpm at 10 weeks. At 11 weeks the mean FHR achieved the level of 165 +/- 7 bpm. The difference was statistically significant. The r-correlation ratio between FHR and the gestational week was 0.58. In case of 7 embryos (2.75%) at 6.1 to 8.1 weeks of gestation slow FHR was noted (< 100 bpm). The scan performed 7-10 days later revealed miscarriages in all cases. CONCLUSIONS: EHR and FHR in the first trimester depends on gestational week. It increases since 6 to 9 weeks and decreases after 10 weeks. The highest values of FHR are observed between 9 and 10 weeks of gestation. The risk of early pregnancy loss increases significantly in case of detecting slow FHR. FHR can be checked by M-mode methods using any kind of ultrasound machine."