Cardiac muscle histology Electrocardiograms Arrhythmias Blood - - PowerPoint PPT Presentation

Cardiac muscle histology Electrocardiograms Arrhythmias Blood pressure measurement Drug treatment of hypertension

Cardiac Muscle

intercalated discs

• mechanical connections between cells
• contain gap junctions

Figure 14.5h, p. 442

Cardiac muscle has intercalated discs

Wheater Figure 8.3 Cardiac muscle—arrows indicate intercalated discs

Be able to identify:

• type of tissue: cardiac muscle
• structure: intercalated disc

Wheater, Fig. 6.26: High magnification electron micrograph

• f an intercalated disc

Cardiac muscle is electrically coupled

• gap junctions are channels that

allow action potentials to be conducted from cell to cell

Figure 3.8b, p. 74

Wheater, Fig. 6.26: High magnification of an intercalated disc FA: fascia adherens: site of mechanical linkage N: nexus junction: region where gap junctions are located

Electrocardiogram

Interpretation of electrocardiograms (ECG)

Figure 14.16f; p.457 From Figure 14.16g; p.457

Patient with arrythmia

A 65-year-old man who had been treated for hypertension for the past 10 years presented with increasing fatigue, dizziness, and palpitations. He did not have chest pain or any other symptoms. An electrocardiogram (ECG) was obtained.

What might cause fatigue and dizziness? Are there P waves? Are there normal QRS waves? What is the heart rate? Is the heart rate regular?

Figure 1 in JAMA (2019) 322(7): 688-689

Atrial fibrillation

• erratic electrical activity in atria

causes fibrillatory waves with no P waves

• excitation of ventricles is via

normal path through AV node so QRS is normal-looking

• excitation randomly enters AV

node to cause irregularly irregular R-R intervals

• can cause tachycardia

Figure 2 in JAMA (2019) 322(7): 688-689 https://jamanetwork.com/journals/jama/fullarticle/2748482

Fibrillation: irregular and uncoordinated contraction of cardiac muscle

atrial fibrillation

• atria don’t pump blood
• treated with anti-

clotting drugs ventricular fibrillation

• ventricles don’t pump blood
• rapidly fatal
• treated with defibrillator

ECG: no P waves ECG: no QRS waves

ECG traces from Figure 14.16g, p. 457

AV node conduction block

Does a QRS wave follow each P wave? Does the QRS wave look normal? What is the heart rate?

AV node conduction block

Does a QRS wave follow each P wave? Does the QRS wave look normal What is the heart rate? What is acting as the pacemaker of the heart?

Premature ventricular contraction

Are there normal QRS waves following P waves? Are there abnormal QRS waves? Are all the QRS waves the same shape? How many ectopic foci are there?

From Becker, D. (2006) Anesth. Prog. 53: 53-64 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1614214/pdf/i0003-3006-53-2-53.pdf

See this page: https://www.physiologyweb.com/calculators/mean_arterial_pressure_calculator.html

• the blood pressure oscillates between a high systolic pressure

and a low diastolic pressure

• the mean arterial pressure (MAP) is the average pressure

throughout the entire cycle

• the pulse pressure is the difference between the systolic

pressure and the diastolic pressure

• systolic and diastolic pressure measured using a

sphygmomanometer

Arterial pressure

MAP

Blood pressure measurement

Figure 14.7, p. 483

Blood pressure measurement

Adapted from Figure 3 https://opentextbc.ca/anatomyandphysiology/chapter/20-2-blood-flow-blood-pressure-and-resistance/ systolic pressure diastolic pressure

What causes the sounds? Turbulent flow through the narrowed artery.

Ensuring accurate measurement of blood pressure

• 1. Cuff should be at the level of the heartàgravity will change the

reading if the arm is above or below the heart. What happens to the blood pressure reading if the cuff is above the heart? What happens to the blood pressure reading if the cuff is below the heart?

• 2. Patient must be positioned properlyàrelaxed, sitting with feet flat
• n the floor an back supported. Patient should be seated for 3-5

minutes without talking or moving before taking the first BP reading.

• 3. Cuff must fit properly and be placed on bare skin.

Source: Hypertension (2019) 73: e35-e36 https://www.ahajournals.org/doi/full/10.1161/HYP.0000000000000087

Automated blood pressure monitor

• scillometric device: measures the waveform of pressure fluctuations in

the artery as pressure in the cuff decreases

• calculates systolic pressure and diastolic pressure based on changes in the

waveform wrist cuff

Calculations

pulse pressure (PP) = systolic pressure (SP) – diastolic pressure (DP) PP = SP - DP mean arterial pressure (MAP) = about a third of the way between DP and SP MAP = DP + 1/3 PP

Blood pressure medications

diuretics ACE inhibitors Angiotensin II receptor antagonists Ca++ channel blockers

Figure 15.8a, p. 485

Mean arterial pressure

Figure 5.1b, p. 123 Figure 16.1, p. 512

Blood plasma is part of the extracellular fluid à blood volume is related to extracellular fluid volume

The kidneys regulate extracellular fluid volume by regulating the amount of Na+ in the extracellular fluid

sensors detecting changes in ECF volume regulated variable

Diuretics decrease ECF volume by inhibiting Na+ reabsorption in the nephron

The kidneys regulate extracellular fluid volume by regulating the amount of Na+ in the extracellular fluid

sensors detecting changes in ECF volume regulated variable increased renin secretion part of kidney response to decreased ECF volume

Renin-angiotensin-aldosterone system

• ACE inhibitors decrease formation of angiotensin II
• angiotensin II receptor antagonists block angiotensin II signaling

aldosterone promotes Na+ reabsorption in the distal nephron angiotensin II causes vasoconstriction

Ca++ channel blockers decrease peripheral resistance by reducing vascular smooth muscle contraction

Wheater Figure 8.12a

arterioles M: smooth muscle