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I bought a blood pressure monitor (A&D UA-851) which has the option to measure irregular heartbeat. I do understand what 'irregular' means, but why do irregular heartbeats happen and what are it's implications short and long term?

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I wouldn't put too much trust in the option to measure irregular heartbeats. Its specificity shouldn't be too high, especially when you consider that some more advanced digital monitors used in hospitals give a lot of false positives. –  Tivie Jun 25 at 11:06

2 Answers 2

up vote -4 down vote accepted

The normal cardiac cycle consists of 7 distinct phases:

  • Atrial systole
  • Isovolumetric ventricular contraction
  • Rapid ventricular ejection
  • Reduced ventricular ejection
  • Isovolumetric ventricular relaxation
  • Rapid ventricular filling

where atrias and ventricles depolarise sequentally; and ventrcles contract after atrias. It is simplification to say that cardiac cycle consists of systolic and diastolic phases. Actually, the isovolumetric relaxation (between #3-#4) of the ventricles precedes the filling phase (between #4-#1):

enter image description here

The exact timing between these events is accurate normally. Heart rests when there is a pause (0.15s) when the action potential is entering the sinoatrial bundle. Any disturbances to the electrical activity of the heart can cause irregular heartbeats.

Irregular heartbeats i.e. arrhythmias arise form interference in the electrical conductivity of the heart. Pacemaker cells (SA node, AV node and Purkinje fibers) maintain the rhythm of the hearth beat. They accommodate depending on the particular situation at hand. They can make the heart beat tachycardic, for instance during sport - not arrhythmia. Those devices which estimate arrhythmias indirectly through arterial blood pressure are sensitive to tachycardia and other factors.

Arrhythmias are rarely benign. The indirect measurement is too insensitive to make final diagnose about irregular heart beats. Most real arrhythmias then again require chronic aggressive treatment. Drugs such as Na+, K+ and Ca+ channel blockers, beta-blockers and Digoxin are used to heal irregular heartbeats. There are many reasons also for arrhythmias where prompt treatment should be applied. The main sources of extrasystoles are the two pacemaker cells of lower frequencies than SA node

  • Sinoatrial node (70-80 Hz)
  • AV node beating too early (40-55 Hz)
  • Bundle of His (40 Hz)
  • Purkinje fibers (15-40 Hz)

Your machine measures indirectly arterial blood pressure. It is very sensitive to distractions from outside in recognising irregular heartbeats, since it tries to measure them indirectly through pressures differences in the arteries. This means that there are distractions, for instance, caused by respiration (thoracic pump), smooth muscles as a pump and current blood volume. It is not trustworthy to diagnose irregular heartbeats. The machine measures the arterial blood pressure where it uses data like It cannot distinguish well between different waves

  • Pulse waves
  • Respiratory waves
  • Vasomotor waves

enter image description here

where Respiratory wave is marked by R and vasomotor wave is wave deduced by trendline, while pulse wave is the one small wave.

The machine also cannot consider situations where different diseases affect decreasing/increasing the pulse pressure (difference between systolic pressure and diastolic pressure):

enter image description here

where it tries to decide through various methods (time-series analysis) the possibility of arrhythmias. You see the mean arterial pressure as the yellow line, the systolic pressure is at the maximum point (blue line) while diastolic (green line). You can imagine the challenges which you get if you happen to have some other problems. These problems can lead to false positive and false negative results. Those machines are developed for the average person and try to satisfy everyone but do not succeed.

Self diagnosing has problems too. The white-coat fear can cause elevated blood pressure. If you are interested about your heart and its possible irregular heartbeats, standard 12-lead ECG is enough show some arrhythmias because it considers directly the electrical activity of the heart i.e. the primary cause of irregular heartbeats. Doing this measurement after some stressful situations can also reveal something about the functioning of your heart. Tthis measurement (standard ECG) is only in the complete time space. It cannot differentiate between different pacemaker frequencies.

In short, irregular heartbeat is the beat where the interference of the electric activity of the heart occur. It can be caused by many reasons. Benign irregular heartbeat can lead to a pathology in a healthy person if prolonged. Arrytmia can be tachycardic but not always. Those machines which estimate the electrical activity of the heart through arterial blood pressure changes are sensitive to tachycardia and other factors.

Sources

  1. Physiology, 4th edition, Linda Costanzo.
  2. Guyton. About different types of waves in indirect measurement of arterial blood pressure.
  3. My notes about types of waves in Physiology courses (three different universities) during years 2012-2014
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There are a number of inaccuracies within this answer - statins are not prescribed for the control of arrhythmias for example –  Rory M Jun 25 at 10:02
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@Masi Arrhythmias are not physiological responses to stress nor a compensatory mechanism. They arise from interference in the electrical conductivity of the heart. While some are, in fact, benign, most arrhythmias require chronic aggressive treatment. Statins are HMG-CoA reductase inhibitors, which inhibit the synthesis of cholesterol. Statins do not regulate directly the cardiac cycle. Other classes of drugs are used such as Na+, K+ and Ca+ channel blockers, beta-blockers and Digoxin. –  Tivie Jun 25 at 10:36
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I think there is a bit too much convolution of the terms arrhythmia and tachycardia. Arrhythmias may be tachycardic but not all tachycardia is arrhythmic. Take the example, when you do intense exercise you will become tachycardic (>100bpm), but this a regular sinus tachycardia and not an arrhythmia. –  Spinorial Jun 25 at 12:55
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There are still a number of issues remaining. Could you clarify what you mean by "too high T waves"? The only T wave related arrhythmia I'm aware of is T wave alternans, which certainly isn't benign. White coat syndrome might be expected to raise a persons blood pressure (partially through a rate increase) but I don't think it causes paroxysmal arrhythmias. –  Rory M Jun 25 at 19:32

The normal cardiac cycle is comprised of two distinct phases: the systolic phase in which the heart contracts, ejecting the blood, followed by the the diastolic phase when the cardiac muscle relaxes, refilling the heart with blood.

This cycle is assured by specialised cardiomyocytes (Cardiac muscle cells) that conduct electrical impulses through the heart. When there's interference in this electric activity, the cycle becomes irregular or arrhythmic.

Arrhythmias can be divided by their place of origin:

  • Atrial (atria are the upper chambers of the heart)
  • Ventricular (ventricles are lower chambers of the heart)
  • Junctional (the junction between the two)
  • Heart blocks (caused by a blockade in the conductivity of the electrical specialised cardiomyocytes)

Some arrhythmias are physiological, such as the Respiratory sinus arrhythmia, a naturally occurring variation in heart rate that occurs during a breathing cycle. Also, in healthy individuals, some extra sistoles might occur without being the translation of a subjacent heart condition and have benign prognosis in individuals without other conditions.

However, some arrhythmias can have a wide range of health implications, from asymptomatic, to a mild intolerance to exercise, to Cerebrovascular Accident (CVA or stroke) or even sudden death due to cardiac arrest.

Therapeutic varies with the underlying cause but can be medical (with drugs such as Na+, K+ and Ca+ channel blockers, beta-blockers and Digoxin) or surgical (ie: Artificial pacemaker).

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Great answer but it would be fantastic if you added some references. –  Bez Jun 25 at 12:30

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