Myocardial Hypertrophy and Congenital Cardiac Pathology

Question 1

Myocardium.

Answer 1

Striated cardiac muscle.
- Sarcomeres made up of lots of myofibrils – actin and myosin.
– functional units of the myocardiocytes.
–> contraction and relaxation.
Some collagen for support and capillaries.
Permanent cells - cannot undergo hyperplasia, only hypertrophy or atrophy.

Question 2

1. Physiological myocardial hypertrophy.
2. Pathological myocardial hypertrophy.

Answer 2

1. Increased demands e.g. due to exercise.
   This is a normal increase in cardiac mass.
2. Often secondary to some underlying disease that is going on, leading to myocardial hypertrophy.

Question 3

1. Primary pathological myocardial hypertrophy.
2. Secondary pathological myocardial hypertrophy.

Answer 3

1. Problem intrinsic to the myocardium.
   Cardiomyopathy.
   - Genetic.
   - Idiopathic.
2. Myocardial adaptive change (remodelling) secondary to another disease.
   - Congenital or acquired cardiovascular disease, causing volume overload or pressure overload, leading to a secondary myocardial hypertrophy.

Question 4

Volume overload.

Answer 4

Hypertrophy - New sarcomeres (contractile component) added IN SERIES forming longer myofibrils to accommodate the higher volume (so more mass so as chamber dilates, the wall stays roughly the same size or slightly thickened).
Dilation of the ventricle - larger ventricular space to accommodate the blood.
This is eccentric hypertrophy.

Question 5

Causes of volume overload.

Answer 5

• Shunts – abnormal patterns of blood flow between heart chambers or the great vessels. – e.g. septal defect between L+R ventricles.
• Valvular insufficiencies e.g. nodular swellings of the left AV valve leaflets – interfere w/ functional closure of the valve –> regurgitation of blood into the atrium in systole (atrial dilation to accommodate regurgitated blood).
  –> additional blood into the ventricle in systole due to the regurgitation in diastole.

Question 6

Pressure overload.

Answer 6

Hypertrophy - New sarcomeres added IN PARALLEL forming more myofibrils within cardiomyocytes (broader and wider).

Question 7

Causes of pressure overload.

Answer 7

• Increased systemic or pulmonary pressure (hypertension).
• Stenosis of a ventricular outflow tract e.g. pulmonic stenosis.

Question 8

Ventricular pressure overload key features.

Answer 8

• Hypertrophy of the ventricular myocardium (increased mass).
• Ventricular wall thickness increased.
• Ventricular lumen may be normal or reduced in size.
• Concentric hypertrophy.

Question 9

Maladaption and impairment of myocardial function.

Answer 9

• Myocardial blood supply unable to meet metabolic demands of increased myocardial mass.
  – Cardiomyocyte death and fibrosis.
  –> reduced ventricular wall compliance (increased stiffness of the wall) – can impair ventricular relaxation and filling.

Question 10

Main congenital cardiac malformations.

Answer 10

• Malformations causing left to right shunting of blood.
  – within the heart or from systemic to pulmonary circulation.
• Valvular or outflow tract malformations.

Question 10

Stages of maladaption and impairment of myocardial function.

Answer 10

Compensated stage - resting CO maintained.
Exhaustion stage - development of overt heart failure.

Question 11

Malformations causing left to right shunting of the blood.

Answer 11

• Patent ductus arteriosus (PDA).
• Septal defects:
  – atrial septal (ASD).
  – ventricular septal defect (VSD).

Question 12

Foetus heart features and flow.

Answer 12

Placenta provides foetus w/ oxygenated blood.
Foetal lungs are collapsed.
Ductus arteriosus connects pulmonary artery to the aorta, allowing blood flow from pulmonary artery, into the aorta.
Foramen ovale, allowing blood flow through cardiac septum between the left and right atrium.
Oxygenated blood from placenta flows into the right atrium, with some flowing through the foramen ovale to the the left atrium, blood pumped into the ventricles and then pumped from ventricles.
Blood in the aorta carries on to the systemic circulation.
More blood from the pulmonary artery flows into the aorta via the ductus arteriosus and into the systemic circulation, less blood from the pulmonary artery flows to the uninflated lungs due to higher resistance.

Question 13

What happens to the circulation after birth?

Answer 13

Lungs inflate - resistance of blood flow to them drops.
Closure of the ductus arteriosus (turns to fibrous ligamentum arteriosus).
Closure of the foramen ovale.

Question 14

Defects on the heart after birth…
Failure of the ductus arteriosus to close.

Answer 14

Not enough muscle to allow contraction of the ductus arteriosus or asymmetry of muscle mass on the ductus arteriosus, causing improper closure of it.
Now causing blood flow from the higher pressure aorta to the pulmonary artery (left to right shunting).

Question 15

Potential secondary effects of an abnormally patent ductus arteriosus in an uncomplicated state.

Answer 15

-Left to right shunting.
- Turbulent blood flow through patent ductus arteriosus so heart murmur.
- Too much blood flow to the lungs so pulmonary over circulation so potentially oedema in the lungs.
- Too much blood being returned to left side of heart (volume overload - left atrial dilation, left ventricular eccentric hypertrophy).
- Sometimes a raised pressure in the pulmonary system, so RV overcomes pressure to be able to eject blood, so pressure overload of RV so some degree of concentric hypertrophy

Question 16

Potential secondary effects of abnormally patent ductus arteriosus

Answer 16

Issue with the lungs leads to pulmonary hypertension.
Pressure in pulmonary circuit rises to a level that is equal to or exceeding the aortic pressure.
Blood flowing from the right (unoxygenated) to the left (oxygenated) side - cyanosis blood is by-passing the lungs.
Poor and grave prognostic situation.

Question 17

Atrial septal defect.

Answer 17

May be at or near the foramen ovale or in the lower part of the atrial septum.
Could be due to improper closure of the foramen ovale or just a different defect elsewhere in the septum.

Question 18

Potential secondary effects of a VSD.

Answer 18

• Blood flow from the higher pressure left side to the lower pressure right side (shunt).
• May cause turbulent blood flow so may hear heart murmur.
• RV supplemented by blood flowing from LV so pulmonary over-circulation and potential oedema in lungs.
• More blood returns to left side of the heart so volume overload w/ left ventricular eccentric hypertrophy and left atrial dilation.
• Volume, pressure or both overload on RV – dept on size of defect, resistance of the vasculature, location of the septal defect. e.g. subaortic VSD may not cause as much volume overload as can move quickly through the pulmonic valve, but a muscular VSD may go further into the ventricular chamber so cause more volume overload.

Question 19

Ventricular septal defect.

Answer 19

More common than ASDs.
Can have perimembranous/subaortic VSDs.
Can have muscular VSDs, lower down in the muscular part of the septum.

Question 20

Terms referring to malformations involving both atrial and ventricular septum.

Answer 20

• Endocardial cushion defects.
• Atrioventricular septal defects.
• Atrioventricular canal defects.

Question 21

Groups of valvular or outflow tract malformations.

Answer 21

Stenosis - aortic, pulmonic.
Atrioventricular valve dysplasia (disorderly growth).

Question 22

Aortic and pulmonic stenosis.

Answer 22

Affects ability of heart to push blood out of the respective ventricular chamber.
Caused by:
- Malformations that affect valve (valvular).
– Most commonly in pulmonic valve
–> valvular leaflet thickening, fusion and/or hypoplasia of the valve annulus.
- Malformations that affect some other component of the outflow tract (sub-valvular, supravalvular).
– Sub-valvular most commonly in the aorta –> caused by plaques, ridges or rings of excess CT.

Question 23

Potential functional consequences of AV valve dysplasia.

Answer 23

• Valvular insufficiency (leaky valve).
• Stenosis of the AV canal (may impair blood flow into the ventricle).

Question 24

Tetralogy of Fallot.

Answer 24

• VSD.
• Overrides aorta so blood flow from both ventricular chambers into the aorta.
• Pulmonic stenosis.
• Right ventricular hypertrophy (due to the stenosis).