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Archive for July, 2024

Two troubling medical quotes in tandem …

Posted in Uncategorized, tagged , , , , , on July 28, 2024|

One

Two

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This one, is not an easy question about VPDs !

Posted in Uncategorized on July 19, 2024|

A 40 year old women with palpitation found to have complex multiple VPDs and elevated thyroid hormones.

The GP has refered for further management to a cardiologist, frightened by the morphology and frequency of VPDs.

The cardiologist has sent him to a EP guy .I guess he was not briefed well about the patient, and he decided to do , what he is best at .He tried to fix and shoot down the VPDs. The apparemt inappropriate procedure went on, as per the demand of patients and science . Now, let us question the basics .

The question is,

Where will be the focus of VPD in hyperthyroidism?

A. LV apex or septum

B. RVOT

C.Papillary muslce of LV or Intra -cavity

D. It is an invisble microrentry , or automaticity. Focus can be anywhere and can not be loclaised.

E. Technically there can not be a focus, it is simply enhanced adrenergic drive by free T 3 & T 4

Answer

There has to be a focus for every arrhythmia.It is my thinking. Some of my EP colleagues, say once circuit is established the focus looses it value . In systemic causes of cardiac arrhythmia , there need not have a visible focus. Make a Pardon , as of now , I can only frame a question, not the answer.

Final message.

Leave alone the answer to this question, I am sure every physician knows the correct treatment. Treat the cause, forget the manifestation. If some one is adamant he can do a RF ablation …not in the heart , but in thyroid gland.

Postamble

Even though , it is hyperthyroidism, we have a responsibility to rule out any tissue level substrate because, not every hyperthyroid patient throws this much of VPDs. It is highly possible, thyroid hormomes can un-mask a hitherto non -arryhthmogenic myocardial focus.

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I know, we can measure “cardiac-output” accurately in two minutes by Echo, but, I rarely do it !

Posted in Uncategorized on July 18, 2024|

One of the foundational lessons in echocardiography is, How to measure the cardiac output ?

Echo formula for estimating cardiac output is

(HR X LVOT area X LVOT-VTI*)

* VTI (Velocity time Integral -a Link ) is complex sounding, but a simple parameter. It is expressed in CMs .In simple terms, it tells how many cm, the blood will move per second ? with a single ventricular contraction.

Image courtesy : http://www.pocus101.com

Sample calculation

If the normal LVOT diameter is about 2cm. Area will be πr2 . Since the radius is 1cm, area will be same as value of π ie 3.14

Normal LVOT VTI is about 20 cm & HR is 70

Stroke volume = 3.14 X 20 =63 ml . Cardiac out put = 63 X 70 = 4410 ml

It can be converted to cardiac Index with body surface area.

Stroke volume measurement is not a big deal .

All currently available echo machine has automated soft ware .It beams the cardiac index live. How reliable it is ? It is as bad or as good as our trust levels. We can Imagine, how the machine vision traces the borders of LVOT. But, carefully done manually measurement is always reliable . Even then, many of us are reluctant to use echo for stroke volume . Here is an Important paper that compared cardiac output calculated by Echo with that of the the gold standard of thermo-dilution technique. Zhang Y, Wang Y, Shi J, Hua Z, Xu J. Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis. PLoS One. 2019 Oct 3;14(10)

Such a simple calculation, why is it not popular among cardiologists. ? (Many ER physicians still use it effectively )

I guess being a humble and simple, works against it. It is surprising, the awareness about EF% is all to pervasive (which is a crude and load dependent parameter) while the info about stroke volume per beat finds difficult to enter bed side cardiology. Generally, we tend to trust complex things and ready to spend ( waste) lots of time with equations, such as in PISA, EROs , DVIs , PAPIs, , stroke work etc . Mind you the probability of error increase directly with number of factors you take in a calculation

The potential bed side usage of stroke volume data

1.Cardiac Index is one of defining criteria for cardiogenic shock. I rarely see my fellows documenting LV stroke volume in any major STEMI, that can detect an impending cardiogenic shock.

2. It will help assess the efficacy of inotropes .Find, objectively how much the Dobutamine really worked in LVF ? and correlate it with clinical assessment of S3, rales and BP. (Mind you BP is very poor surrogate marker. for stroke volume. )

3. More Importantly, Similar to LV stroke volume, we can measure RV stroke volume by RVOT area x VTI x HR. This can be of critical value in the management of RV infarct, where two ventricular stroke volumes often mis-match often. Once RV stroke volume equals the LV , we can presume recovery.

4.The enigma of high output cardiac failure can be studied with this simple formula.

5.In any mechanical assisted circulation LV, stroke volume is going to give important prognostic info.

6.Finally, assessing stroke volume will aid in fluid therapy in ER with any cause of systemic hypotension.

.Final message

Its time, we concentrate & fine tune the echo derived stroke volume as a definitive circulatory volume data in day to day practice.

A request to all ER physicians and cardiology fellows, try measuring the cardiac output whenever you see patient in shock and hypotension .Make it a habit to measure the stroke volume. You need just two minutes. It is cheap, you can repeat as many times as you want in follow up. It can totally change the way you understand hemodynamics of cardiac failure and shock.

Reference

Zhang Y, Wang Y, Shi J, Hua Z, Xu J. Cardiac output measurements via echocardiography versus thermodilution: A systematic review and meta-analysis. PLoS One. 2019 Oct 3;14(10):e0222105. doi: 10.1371/journal.pone.0222105. PMID: 31581196; PMCID: PMC6776392.

Further reading

There is one more methodology, called EIT electrical Impedance tomography, that can provide live online stroke volume , comes inbuilt in ECMO and other MCS systems

da Silva Ramos FJ, et al Estimation of Stroke Volume and Stroke Volume Changes by Electrical Impedance Tomography. Anesth Analg. 2018 Jan;126(1):102

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Why tackling fake, with facts is a daunting task? but,..there is an illegitimate solution!

Posted in Uncategorized on July 12, 2024|

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Blind faith in EBM, could be an early sign of Impaired clinical wisdom.

Posted in Uncategorized on July 3, 2024|

I don’t want to do this …but EBM compels me to do it

The word “Evidence” is the most powerful in the world of science and enjoys disproportionate bias towards positivity (of course in any walk of life). But, the fact of the matter is, it can result in either monumental breakthroughs or mindless havoc to mankind in equal quantities.

EBM is not a sacred movement. It came into the medical domain in the early 1970s and grew at an unprecedented pace, invading the medical practice and literally robbing the charm & goodness in clinical medicine.In fact, many point out ,EBM is in direct conflict with Individual-based holistic medicine. If you rely only on EBM without Individual patient data, it might take you to the doorsteps of department of clinical negligence.

But, unfortunately, EBM in an unpure form has grown to gargantuan proportions and penetrated deep into medical academics. Armed with a possible legal authenticity, ignoring it, could easily push us into clutches of criminal negligence. (In fact, the opposite may be true)

Final message

Does trusting EBM too much imply a reduced wisdom?

If you offer a free pass to EBM*, to enter into all your decision-making process, then wisdom will quietly leave through the back door. Taking evidence, at its face value is going to be the biggest intellectual insufficiency or inefficiency for the future world, especially in medical science.

Further reading

Wyer PC, Silva SA. Where is the wisdom? I–a conceptual history of evidence-based medicine. J Eval Clin Pract. 2009 Dec;15(6):891-8. doi: 10.1111/j.1365-2753.2009.01323.x. PMID: 20367679.

Postamble

*I know, It is unwise to blame EBM in such a disparaging manner, rather we need to cleanse and eliminate the limitations of the EBM .That would be a more correct approach, but is it possible ? , since both appear to be built into it.

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Learning some crucial cardiovascular hemodynamic lessons* from Giraffe 

Posted in Uncategorized, tagged , , , , , , , , on July 1, 2024| Leave a Comment »

*This post may not be meant for cardiology fellows but for young students of medicine

Have you ever thought about how a Giraffe’s heart can pump blood to the summit of a lengthy neck and perfuse the brain?

Unlike a blue whale which has a huge heart, a Giraffe’s heart is not as big as one would Imagine, A Giraffe’s heart weighs .5 to . 6 % of total body mass. If the average weight of a Giraffe is 650kg, the heart would be around 3 kg.It is almost in similar proportion to the human heart.( In a 70 kg man heart weighs about 350 grams). However, it generates more power and pressure, up to 300mmhg BP. 

Lessons from Giraffe heart

1. Although the heart is not big, the walls are thicker many times times. In simple terms it mimics a heart of Hypertrophic cardiomyopathy, which we know has brisk ejection. The combination of thick wall and a small cavity attenuates the wall stress significantly .This enables the heart to pump a good stroke volume, high into the brain located more than 5 to 8 feet above the heart. What a remarkable phenomenon.(Laplace law executed in the best manner in biology) *Laplace law states , the wall stress is directly proportional to the cavity diameter, indirectly related to the thickness of the wall

2.We can also understand the principles of the management of cardiomyopathy from a Giraffe’s heart. If the ventricles assume a tubular morphology, optimal energy and cardiac power can be accrued. This forms the basis behind the ventricular reduction and reconstruction surgery for Ischemic dilated cardiomyopathy.(Batisda procedure etc)

3.The innovators and engineers of new-age mechanical assist systems could learn a few crucial insights from these unique and humble animal beings. (Shall we think about,axial pumps in ascending Aorta in series with LV. An Aortic Impella device, that is distal to the aortic valve and devoid of LV-related issues. )

With each systole, blood has to travel a maximum of up to 8 feet up, with enough power at the same time not to injure the vessel wall

When bending the opposite happens, and the valves in both arterial and venous systems come to protect by dampening the flow and avoiding congestion.

 An alternate hypothesis: Siphon effect in cranial circulation 

Some believe the heart is assisted by an alternate mechanism in the Giraffes. The carotid artery could act like a siphon from the heart. Siphons can defy gravity. Is it a reality in living beings? How is this possible? I am not clear. If so, that can be tried in human experiments on cerebral insufficiency.

 Final message 

Every living and (even non-living things) surrounding us, keep sending some silent scientific messages. The hemodynamic of the Giraffe’s vascular system is a good physiologic model of circulation, that defy gravity. It reinforces a basic, but important learning point* that a tubular & cylindrical heart can generate more power than a large globular one.

Reference

1.Graham Mitchell Shane K. Maloney, Duncan Mitchell  The origin of mean arterial and jugular venous blood pressures in giraffes The Journal of Experimental Biology 209, 2515-2524

 2.Aalkjær C, Wang T. The cardiovascular challenges in giraffes. J Muscle Res Cell Motil. 2023 Jun;44(2):53-60. doi: 10.1007/s10974-022-09626-0. Epub 2022 Jul 25. PMID: 35879488.

3.Aalkjær C, Wang T. The Remarkable Cardiovascular System of Giraffes. Annu Rev Physiol. 2021 Feb 10;83:1-15. doi: 10.1146/annurev-physiol-031620-094629. Epub 2020 Nov 9. PMID: 33167747.

 

 

 

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