0722- PV potatos and heart failure- CG

Question 1

What does the PV loop represent? Label the important cardiac parameters on a PV loop diagram

Answer 1

PV Loop describe pressure-volume relationship in the LEFT VENTRICLE

Inferrable parameters are:

Mitral valve opening, Diastolic filling, mitral valve closing, isovolumetric contraction, diastolic pressure (opening of aortic valve), ejection phase, systolic pressure (closing of aortic valve), isovolumetic relaxation

Stroke volume (ejection fraction), total cardiac work, preload, AFTERLOAD??

Question 2

Compare isovolumetric, isotonic and auxotonic contraction

Answer 2

Isotonic- no external work, smaller maximal force production (shortening work),

Volume changes, pressure stays the same

Isovolumetric- no external work, larger maximal force production

Pressure changes, volume stays the same (stoppered)

Auxotonic- yes external work, maximal force between isovolumetric, and isotonic

Determined by diastolic and systolic pressure. Both pressure and volume change

Question 3

What is heart failure

Answer 3

Pathophysiologic state in which an abnormality of cardiac function is responsible for the failure of the heart to pump blood at a rate commensurate with the requirements of the metabolizing tissues, and/or allows it to do so only from a elevated diastolic volume

Question 4

How does heart failure usually manifest?

Answer 4

Either output failure (forward failure) and/or volume retention (backward failure)

Tends to manifest after most compensatory mechanism have been exhausted (decompensation) and typically after a precipitating cause

Question 5

How is HF classified- name at least 3 different classification methods

Answer 5

By cardiac cycle—systolic (inability to contract) or diastolic (inability to relax)

By cardiac output- high output (high demand: anaemia/pregnancy) or low output (ischemic heart disease)

By Development- acute (infarct, infection) or chronic (slow progress with adaptation)

By Anatomy (left sided or right sided)

By Perfusion- forward (insufficient perfusion) or backward (increased venous pressure)

Question 6

Describe the Pathophysiology of acute failure (ie in infarction)

Answer 6

• Acute heart failure as in heart attack.

Decompensation

Low CO = reduced renal perfusion

• Na+ actively retained (RAA system; volume↑) at price of P_RA↑.
• Eventually, over a few days, failure will result.
• “Backward failure”: P_RA↑, activates CP reflex (pooling), distending central veins.

–> accumulation of fluid in venous bed, expansion of plasma volume (Na+ retention, weight gain)

–> increased P_msf =peripheral oedema

• “Forward failure”: activates AB reflex: SY↑ (BP↓).

–> reduced perfusion, reduced CO, urine, increased HR (vicious cycle)

–> shut down unnecessary functions, ie skin (fever), muscle (cold extremities), brain

• CO regained due to SY↑ at price of PRA↑ and HR↑: internal work↑; energy efficiency↓.

Question 7

Describe PV loop in systolic HF

Answer 7

Diastolic filling is normal, systolic pump’s reduced function result in less degree of isotonic contraction, resulting in a ‘thinner taller potato’ and reduced SV, whole loops right shifted due to increased pressure

Question 8

Therapeutic approaches to HF

Answer 8

• Increase SV
– Increase contractility.
– Decrease Pdiast and increase pressure difference. – Reduce central venous pressure (PRA).
– Reduce venous return (volume due to pooling).

• Decrease afterload
– Reduce peripheral resistance.
– Reduce end-systolic volume (increase EF).

• Ensure appropriate electrical pacing
– Reduce HR (where appropriate).
– Convert to sinus or “like” rhythm (constant output).

• Energy sparing treatments - “paradoxical”

– Angiotensin-converting enzyme inhibitors, aldosterone antagonists, β-receptor blockers.”

Question 9

Describe myocardial energy crisis in HF? (affect mitochondria)

Answer 9

Energy depletion

Decreased substrate utilization (fatty acids, glucose)

Decreased oxidative phosphorylation (performance of electron transport chain, etc)

Decreased ATP transfer and utilization (ie creatine kinase)

Research suggests PPARa gene determine substrate utilization switch- hence ?fibrates?

Question 10

Stricker summary

Answer 10

• P-V diagram makes simple predictions about important parameters determining CO like SV, EF, preload, afterload and filling pressure.
• Shape of the P-V loop gives interesting clues about underlying (patho-)physiology.
• HF therapy is conventionally based on CO↑ by SV↑ (contractility), PRA↓, afterload↓ and HR↓ (energy efficiency↑).
• In HF, metabolism is challenged; in future new drug targets (PPAR) may improve function.