Feeds:
Posts
Comments

Archive for the ‘Anatomy of heart’ Category

Does the Aortic root contract or relax during ventricular systole? Some time back, I asked this question in one of my classes for the fellows and found no takers. Not even a guess? I realized later, it was indeed a tough question. The heart is not the only dynamic organ, as we generally believe. The entire aorta which is an extension of the left ventricle has to be dynamic according to the physics of ventricular-arterial coupling and the momentum of blood flow.

What happens to the aortic dimension with systole?

Even prior to systole, there is evidence, the aorta gets ready to receive the blood from the LV. So, the Aortic root must be larger at the onset of systole. (Ref 2 ) It is been generally agreed now, that the systolic dimension is slightly more by a few mm. That is why aortic dimensions are measured in peak systole as per the American society of echocardiography.

There has been an opposite argument as well. The diastolic aortic dimension could be larger, as the aortic valve is in the closed position and the aortic root distended, & becomes a reservoir of blood that’s meant to be distributed during diastole. What determines the aortic dimension on a moment-to-moment basis?  Is it the, LV contractility, pressure, or volume, or the compliance of the aortic wall that determines the aortic dimension and pulsatility? How does a prosthetic valve alter this?

So, what exactly happens to the aortic dimension during the cardiac cycle ? 

A wonderfully done study from University Medical Center Utrecht, The Netherlands throws some important facts with their analysis of ECG-gated CT scans in 108 Aortas.(Ref 1)

It is surprising, to note the aortic root behaves independently. It either contracts or relaxes with a range of 4 mm swing on either side of the systole and diastole. Another stunning fact is, it remains static in a significant number. (One possible explanation is the true aortic annulus is less dynamic because it is bordered by the fibrous skeleton, while the rest of the aortic root only can distend or shrink )

Clinical implication of aortic pulsatility

The implication of knowing (or not knowing )the dynamism of the aorta can be huge.

  • Age-related stiffening and onset of systolic hypertension
  • Aortic diameter, pulsatility, and shear stress are the key parameters in initiating dissection and its propagation
  • Choosing the right sized valve for AVR
  • Current interventional heart-throb TAVI involves just a passive placement of the valve in the aortic root. Imagine what will happen, if the foundations are excessively dynamic and shaky   

It is surprising, even after decades of vascular research, we lack clarity on what exactly happens to aortic root during various phases of the cardiac cycle. (Currently, paravalvular leak, & migration of TAVI remains a major worry, which has a direct relationship with pulsatility of the aortic root ) One thing is obvious,.Young cardiologists have a lot of work to do in this arena.

Final message

 Though the aorta is a direct extension of LVOT, its vaso-motion doesn’t seem to be in complete sync with the cardiac cycle. It tends to have an independent behavior, out of phase with the heart. 

As per available evidence, the aortic root dimension can either increase, decrease, or be static in response to LV contractility.

Reference

1.de Heer LM, Budde RP, Mali WP, de Vos AM, van Herwerden LA, Kluin J. Aortic root dimension changes during systole and diastole: evaluation with ECG-gated multidetector row computed tomography. Int J Cardiovasc Imaging. 2011 Dec;27(8):1195-204.

2. Pang DC, Choo SJ, Luo HH, et al. Significant increase of aortic root volume and commissural occurs prior to aortic valve opening. J Heart Valve Dis. 2000;9:9–15. [PubMed] [Google Scholar]

3. Vesely I. Aortic root dilation prior to valve opening is explained by passive hemodynamics. J Heart Valve Dis. 2000;9:16–20. [PubMed] [Google Scholar]

 

 

 

Read Full Post »

The commonest cause* for repeated entry of right radial catheter to descending aorta is not due to any anomaly. Most times,it is just a skewed angle between right brachio-cephalic artery with Aortic arch, that deflects the catheter to the descending aorta . Just make sure, aortic root is entered with a deeply held inspiration.

*Anomalies of the aortic arch, aberrant right subclavian, Kommerell’s diverticulum, vascular ring must be kept in mind.

 

Postamble: A true abnormal course

Though, It might appear prudent to avoid the radial route when encountering anomalous subclavian arteries, the reality is different and adventurous. We have acquired great expertise and successful PTCAs have been done through these tortuous vascular highways.

This is a case report from Dr H.S. Isser, Gunjan Garg, from Safdarjung hospital New Delhi. 

A successful PTCA through arteria lusoria : The right subclavian connect to the descending aorta, distal to the left subclavian at the level of ductus arteriosus. and pass retrotracheal and retroesophageal before reaching right arm. Image source and courtesy: H.S. Isser, Gunjan Garg, Arteria lusoria: A challenge for transradial coronary interventionist, IHJ Cardiovascular Case Reports (CVCR), Volume 4, Issue 1, 2020,

 

Read Full Post »

Heart is not like a rigid structure built with  bricks . . . . so , its too architectural mindset to describe cardiac chambers to be made up of walls. Rather , Its a four chambered muscle mass moulded together in a complex 3D interface with distinct surfaces rather than walls. It’s also important to realise, since the heart is positioned (rather hanging )delicately in the middle mediastinum resting on the diaphragm , its subjected to one more dynamism due to respiratory motion blurring the definition of surfaces as well. (Vertical vs Horizontal)

4415_21_26-heart-human-posteriorly

Posterior surface is now referred to as infero-posterior

The posterior aspect of heart contains essentially the venous channels and the atrium (LA in particular)pulmonary veins and coronary sinus.  This happens right from 8 week heart open stage when venous end of lower straight heart tube folds up and posteriorly .

cardaic-looping-posterior-wall

It should be recalled only a small portion of lower aspect of posterior wall is alloted to left ventrilce.Instead the Infero diaphragmatic surface is formed by two-thirds  the LV and one-third Right ventricle.

anatomy-of-heart-posterior-wall-mi-lcx-rca-grays-grants-anatomy-netter

Image courtesy : From the great Netter

Nomenclature  issue 

The term posterior wall is now abandoned in most Echocardiography texts its replaced by inferior .The implication is more for Electrophysiologists with reference to accessory pathway localization

What is true posterior wall MI ?

As discussed before ,posterior surface of heart is different from posterior aspect of left and and right ventricle.

What does leads V7 V8 V9 record ?

It actually records electrical signals arising from posterior  aspect  of heart.  Left atrium,  pulmonary vein along with insulatory  effect of lungs dampens the potential . This makes the sensitivity of ST elevation  in posterior MI is low.

Blood supply of posterior surface

It’s highly variable.Both RCA and LCX arteries contribute with its  posterior left ventricular branches (PLV)

It can be inferred , LCX has more territorial rights than RCA in this unique zone of heart as the artery covers more posterior areas.

Read a related article

Back pain from anterior MI : Is it possible ?

 

Read Full Post »

RCA is known for unusual variants.Here is a right main trunk which divides into two major branches, both taking a surprisingly similar course.Shall we refer it to as Dual RCA  or is it an early RV branch ? But how can both run posterior and parallel ?

PS: His LAD and LCX  were  normal.

Read Full Post »

One casual question in my class led to this search for an anatomical mystery. When we were discussing why left atrial oxygen saturation never reaches 100 % ? , it was attributed to desaturated bronchial venous blood draining into pulmonary vein.

How does this bronchial vein enter pulmonary venous circulation ? How many bronchial veins are there ? What anatomical plane it runs ?

Surprisingly, even in this hi-tech era of academic excess, literature is sparse for this basic anatomical question. It is reported (In Greys anatomy ? ) Bronchial veins are two in number and both drain to Azygos and Hemiazygos veins (systemic) rather than pulmonary veins.

So is our assumption wrong ?

May not be.We realise these are only two visible and named bronchial veins .It is learnt they probably carry only about 13 % of bronchial venous blood to systemic venous circuit.

bronchial venous drainage bronchial circulation

Image showing right and left bronchial veins draining to Azygos and hemiazygos veins.

It is assumed , remaining 87 % of bronchial venous blood drains to pulmonary venous circuit in an invisible fashion (By unnamed twigs ?) desaturating the LA blood by about one percent from 100 to 99 %. This is our current understanding. I haven’t come across any specific human research that quantifies the bronchial venous channels and it saturation . It’s gratifying to find one study specifically looked answer this question in sheep study .(Charan H.B et all Reference 1 )

where does bronchial vein drain drainage circulation pulmonary vein saturation

True physiological bronchial venous drainage seems to be different from anatomical bronchial venous circuits .

Clinical implication of bronchial venous circulation.

In physiology it may not be important . However bronchial circulation (both arterial and venous) can take many anatomical tracts when pulmonary micro vascular bed is structurally and functionally altered as in COPD, , pulmonary atresia with aorto-pulmonary collaterals , congenital left to right shunts,post Fontan circulation pulmonary AV malformations,lung tumors etc .

Hemoptysis in acute pulmonary venous hypertension is thought to be due to rupture of these bronchial veins as elevated pulmonary venous pressure reflect into bronchial veins (As in mitral stenois and other conditions. ) This again would vouch for bronchial veins draining to pulmonary veins.

Final message

As on today , it can be concluded bronchial vein drainage goes both systemic and pulmonary venous circuit.Bulk of them appear to end in pulmonary veins though clear anatomical evidence is lacking.

Postamble

Exploring human anatomy appear a grossly unfinished agenda even today, especially the micro and histo-anatomy. Teachers of basic sciences should impress upon youngsters entering the medical school to pursue translational research relevant to specific clinical problems.

Students may contact <drsvenkatesans@yahoo.co.in> for specific areas of clinical cardiac anatomy topics that still requires answers.

Reference

Read Full Post »

Car tyres warrant  replacement  every  20,000 km or so .Its batteries do require periodic attention. Human heart , which runs non stop from womb to tomb . . . deserves how much ? Unfortunately no one (What about your cardiologist?) can  provide  a flawless lifetime maintenance contract to this restless bio-mechanical pump ! Fortunately still, God has  created this wonder organ ,that can with stand the stress of life for nearly 10 decades . . . if we live a proper life !

However ,there are many areas in heart that are prone for mechanical stress even if it’s structurally normal .These are  the zones where the relatively fixed parts  rub against the dynamic zones .The joint between inflows ,outflows to the respective ventricle are at risk . Aortic root, along with the leaflets and annulus  formed by the fibrous skeleton is delicately close to the critical part of the conduction system namely the branching portion of AV node and His Purkinje.The process of degeneration is linked to age, valvular abnormality and genetic and  systemic metabolic profile also seem to matter in few .(Hypercalcemia and cardiac calcification ?)

Importance of the interface between Aortic valve and  AV conduction system in the current Era 

Degenerative aortic valve disease along with  the adjacent conduction system  of elderly is going to be a key cardiovascular disease in the future as the population is aging .We have made a big step forward in tackling this with innovative percutaneous aortic valve implantation  (TAVI) . However ,the artificial valve  is positioned vulnerablely  close to conduction system and incidence of complete heart block either during implantation or follow up is  high and a permanent pacemaker seems to be an integral part of this procedure for many.

aortic valve his bundle complete heart block 003

Heart seen from behind , Mitral annulus to left and tricuspid valve ring to the right .

Read Full Post »

Right ventricle,being a venous chamber has distinct anatomical and physiological features to carry out this function.RV has a complex shape, its triangular in long axis and  crescent like in short axis , thin (<5mm)  more distendable  .Contraction of RV begins slightly early but ends later than LV  (30ms )

RV receives blood from RA and ejects in to PA in a sequential manner .The inflow, body and outflow contract somewhat like  intestinal peristalsis. This is facilitated  by the incremental  delay in the electrical depolarization of right ventricle.In physiological conditions, the later half of QRS  is  responsible for RV activity and RVOT is the last to contract. (This intrinsic electrical and mechanical  delay in RV contraction is a physiological inter ventricular  desynchrony . One  should be aware of this when planning cardiac resynchronisation therapy in cardiac failure.  )

Click over the image for an animation of RV contraction.

wpid-wp-1430586787404.gif

Image courtesey Oxford spcialist hand book in cardiology :Echocardiography Paul Leeson , Second edition ,.Oxford university press 2012 Multi media .

Note:LV is  a fairly   elliptical and strongly  muscular pump and contracts in a  single go with maximum force.(dp/dt).

Final message

Though both right and  left ventricle originate from same  straight heart tube , developmentally the right ventricle evolves for a different form and function . Now,we realise there are lots of sharing of parental muscle fibers that engulfs and bonds both chambers.(Mind you ,This is the fundamental mechanism of ventricular interdependence.Of course ,IVS is a common wall shared lifelong by both chambers  without any (sibling related?)  hemo-dynamic dispute !

3D echocardiography and MR imaging has helped us to understand the RV morphology better and exciting articles written by pioneers are available  free for those who are interested.

Reference

Read Full Post »