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Posts Tagged ‘myocardial energetics’

Metabolic cost of ventricular ectopic beats : Does VPDs consume extra energy ? If so how ?

Posted in Uncategorized, tagged , , , , , , , , , on September 9, 2026|

Nothing happens without energy cost both in physics and biology. How much is the metabolic cost of an extra systole ? While an occasional VPD is benign and has a negligible effect, a high burden of VPDs can consume extra energy and drain myocardial metabolic reserves.

Three ways it can happen

  • Inefficiency: VPDs cause premature contractions before AV valves fill and hence there is a mechanically wasted work However the electrical cost is small.
  • Dyssynchrony: dys or desynchrony due to the VPDs also hikes myocardial oxygen consumption (MVO₂) for identical workloads.
  • Post-Extrasystolic Potentiation: We know, the beat following a VPD shows increased force due to calcium accumulation. This can elevates contractility and wall tension, increasing energy demands.

Molecular basis of energy depletion

At the cellular level, the variable timing of VPDs disrupts calcium homeostasis in phase 2 of action potential within the myocytes. The sarcoplasmic reticulum must continuously pump calcium ions against concentration gradients via SERCA2 channels, a process requiring ATP hydrolysis. Additionally, the chronic workload mismatch induces mitochondrial oxidative stress, which damages the electron transport chain, impairs ATP synthesis resulting in energy consumption mis mamtch.

What is the cut off number ?

A high VPD burden* (10% to 20% all heart beats in day ) is considered a chronic strain, leading to cardiomyopathy and heart failure.First step is a Holter monitor assessment. Yet, we are not clear about the exact number For example : Does bigeminy counted then 50 % of all beats )

*VPDS and elEctrical SCD is different topic , and is not discussed here.

Does suppression help ?

We think so. If and only if we can document porgressive LV dysfunction.

Final message

VPDs are usually benign unless linked to LV dysfunction, which complicates prognosis. The electrical energy cost of VPDs is negligible . But its impact on the mechanical behaviour on myocardial contractility is the issue. It’s crucial to determine if they are primarily electrical or secondary to associated LV dysfunction. Treatment is based on individual assessment.

Reference

Link to the article

Postamble

Difference between APD and VPDs in terms of energy consumption ?

Need to be discussed further.(We know frequent focal APDs or ATs, MAT can result in AF or atrial cardiomyopathy)

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What do the myocardium need at times of ischemia ? Blood , oxygen, glucose or ATPs ?

Posted in Cardiology - Clinical, Cardiology -Interventional -PCI, cardiology -Therapeutics, cardiology- coronary care, Infrequently asked questions in cardiology (iFAQs), tagged , , , , , , , , , , , , , , , , on October 9, 2008| Leave a Comment »

During acute  ischemia the most immediate requirement for the heart is

A.Blood

B.Oxygen

C.Glucose

D.High energy ATPs

E.Free fatty acid

Answer : A  will be considered  by most , as  correct answer .  A can provide B to E . But it is also a fact heart can survive without  A.  

Myocardium requires energy first  ! it does not in fact bother about from where it is coming at the time of crises.It may be right if you restore the coronary blood flow all other components (B-E) are made available to the heart .

The heart can survive off  the coronary circulation with only chemical support during cardiac surgery and also a during  heart transplantation  explanted  donor heart survives on a ice box during transit and till it is transplanted into the recipient heart

But ironically we spend much of our energy and efforts in restoring blood flow.One need to spare a thought about the quality of blood also . This is especially important  in the setting of ischmia  where a  metabolic centric approach will add further benefit.

Energy based approach to ischemia : Is it relevent ?

Heart is a fascinating  mechano biological organ  pumping   millions of  gallons of blood  .Fuel for this is self generated  on a continuous basis  from the circulation blood .So  the key to human survival is the coronary blood flow that supplies the fuel and nutrients to the heart. When this key supply line is under threat  during  acute coronary syndrome cardiologist have  the only option of restoring the compromised blood supply by any means . But during chronic ischemia there is  no  urgency. There has always been an option of enriching the  blood with energisers like ATPs,  glucose,  hemoglobin etc .Providing energy support to the failing heart has never captured the imagination of cardiac physicians until recently.Still most are skeptical about  the concept of biochemical ischemia.

Click to download full PPT presentation

Metabolic manipulation of  CAD( Will be available shortly)

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