Arrythmias Flashcards
What is meant by the refractory period
Period following depolarisation of nerve/tissue where
excitation cannot occur
Define pacemaker cells
Specialised cells presenting with automacity (generate
their own depolarisation)
▪ Sets sinus rhythm of the heart to control inotropy and
chronotropy
which three ion channels conduct electrical impulses in the heart?
Sodium, potassium and calcium
What is the sequence of electrical conduction from the SA node?
SA node
Atria
AV node
Bundle of His
purkinje fibers
ventricles
What is the use of the AV node
It slightly delays signals
Give a term for this definition:
At a critical point (the firing threshold for the muscle cell) a self-generating action potential is triggered, causing the membrane potential to reverse and become briefly positive.
Critical firing threshold
Describe these events:
1. Rapid depolarisation
2. Partial repolarisation
3. Plateau achieved
4. Repolarisation
5. Pacemaker potential
Rapid depolarisation
▪ Ionic mechanisms
▪ Cardiomyocyte membrane potential reaches critical
firing threshold (~-60 mV)
▪ Voltage-gated Na+
-channels open
▪ Fast Na+
influx produces steep depolarisation
Partial repolarisation
▪ Ionic mechanisms
▪ Na+ channels transiently open for a few milliseconds,
after which channels are inactivated until the membrane
repolarises fully
▪ Voltage-gated K+ channels open
▪ K+
ions are effluxed from cardiomyocytes
▪ Repolarisation is initiated
Plateau achieved
▪ Ionic mechanisms
▪ Voltage-gated Ca2+ channels open, allowing from slow
Ca2+ influx into cardiomyocyte
▪ K+
ions continues to be effluxed from cardiomyocyte
▪ Plateau maintained in the membrane voltage
Repolarisation
▪ Ionic mechanisms
▪ Ca2+ channels close, however, K+ efflux continues
▪ Repolarisation continues as membrane voltage becomes
more negative (towards resting voltage)
Pacemaker potential
▪ Ionic mechanisms
▪ Voltage-gated K+ channels close when cardiomyocyte is
at resting membrane potential
▪ Some K+ influx occurs via inwardly rectifying K+
channels
▪ Resting membrane voltage maintained until
depolarisation signal received to proceed to phase 0
Define dysrhythmias
disruption of orderly sinus rhythms
What is the mechanism of action of adenosine?
Activates adenosine A1 receptors
▪ Hyperpolarises pacemaker cells
▪ Slows conduction velocity, thus negative
chronotropic effect
Indications for IV adenosine
▪ Termination of supraventricular arrhythmias
How does amiodarone cause hyper/hypo thyroidism?
Amiodarone is made up of iodine. Iodine is the precursor molecule for thyroxin synthesis and it is used by the thyroid gland to synthesis thyroxin. By increasing iodine concentrations the gland overworks and produces excess thyroxin. As a result, a negative feedback loop, Wolff-Chaikoff, kicks in that suppresses thyroid hormone production.
what is blood pressure and what’s it’s relationship to CO and peripheral vascular resistance
the pressure exerted by circulating blood on the walls of blood vessels. It is directly proportional to CO, the amount of blood pumped out by the heart per minute, and PVR
what is the relationship between CO and stroke volume
stroke volume refers to the amount of blood ejected from the ventricles per contraction. if the heart is beating fast, that means more blood is ejected from the ventricle within a minute.
Peripheral vascular resistance
Peripheral vascular resistance
Resistance that must be overcome to pump blood through
circulatory system
what makes hypertension different from a simple sympathetic nervous system hypertension
it is a persistent high blood pressure which may include a health deterioration
Explain what makes gestational, chronic and preeclampsia hypertension so different.
Gestation
No proteinuria, occurs within 20 weeks of pregnancy with a systolic of 140 and diastolic of 90 mmHg
chronic
Within 20 weeks of pregnancy and doesn’t subside 12 weeks after pregnancy
mild
Systolic up to 179 mmHg
diastolic up to 109 mmHg
Severe
systolic ≥190 mmHg
diastolic ≥110 mmHg)
Preeclampsia
as gestational but presents with proteinuria
