Monday, February 28, 2011

Cardiology: Jugular Venous Pressure (JVP)

If you ask anyone with a clinical background to explain bradycardia, you will get a very simple yet sufficient response: a heart rate below 60 beats per minute (bpm).  However, if you ask that same person to relate it to jugular venous pressure, more often than not you can expect to receive a blank stare.  Why?  Simple: very few actually understand venous pressure waves. 

Jugular venous waveforms quantify the pressure within the venous system—which ultimately feeds into the right side of the heart.  Thus an abnormal waveform suggests the presence of pathology.  To understand an abnormality requires knowledge of the norm.  Without a concrete basis of what jugular venous pressure should be, one will struggle to identify a deviation from the standard.  

First, one must understand basic heart anatomy and function. 

The heart has four chambers.
  •  The Right Atrium, which receives deoxygenated blood from the superior vena cava and inferior vena cava and pumps its blood through the tricuspid valve (one of the atrioventricular valves) into the right ventricle
  •  The Right Ventricle, which receives blood from the right atrium and pumps it through the pulmonic valve and into the pulmonary artery towards the lungs
  • The Left Atrium, which receives blood from the lungs via the pulmonary vein and propels it through the mitral valve (AKA bicuspid valve, one of the atrioventricular valves) into the left ventricle
  • The Left Ventricle, which receives blood from the left atrium and pumps it through the aortic valve into the aorta for systemic circulation
The pumping of blood through the heart occurs in a two step process: diastole and systole, both of which can be thought of through their function in the ventricles.

  • Diastole happens first, in which blood fills the ventricles.  At first the low pressure in the empty ventricles drives the process but ultimately the atria contract to expel their contents into the ventricles
  • Systole happens next, in which the ventricles contract and push their contents into either the pulmonary artery or the aorta

With this very basic foundation of heart structure and function one can now look at the jugular venous pressure waveform, and keeping in mind that the internal jugular vein ultimately feeds into the superior vena cava one can understand how this waveform has clinical significance.

Each letter of the jugular venous pressure wave corresponds with a part of the heart’s normal cycle.
  •  A wave relates to atrial contraction, marking the end of diastole
  • C wave denotes the beginning of systole, at which point the pressure in the ventricles pushes against the atrioventricular valves which causes them to bulge ever so slightly
  •  X depression happens when the lower pressure in the atria allows for blood to fill in
  •  V wave occurs when the pressure in the atrium rises due to an increasing amount of blood along with a closed atrioventricular valve
  •  Y depression occurs when the atrioventricular valve opens and blood begins filling the ventricle right before atrial contraction

Just think of it in terms of blood in the vena cava: an A wave occurs because the pressure of the contracting atria puts resistance against the flow of blood out of the vena cava; and so on.  Thus with an understanding of the norm one can recognize pathology: any deviation from the curve above has significance.  It’s easiest to start at A and move from there:
  •  Large A wave: resulting from an increased pressure against which the atria contract
    • Seen with pulmonic and aortic stenosis and IHSS, seen with normal sinus rhythm in stenosis of the mitral and tricuspid valves, seen in ischemic heart disease, and can also occur due to aging
  • Canon A wave: large intermittent A waves which occur due to a problem with conduction in the heart which results in contraction of the right atrium against a closed tricuspid valve
    • Seen in arrhythmias, including paroxysmal atrial tachycardia and atrial flutter
  • Absent A wave: loss of A wave due to inability of atria to effectively contract
    • Seen with atrial fibrillation
  • Large V wave: due to an increased pressure in the atrium above normal
    • Seen with tricuspid regurgitation
  • Depression wave abnormalities
    • X descent: abnormality suggestive of acute pericardial effusion, such as in tamponade
    •  Y descent: abnormality suggestive of slow pericardial effusion, such as in chronic renal failure and with SLE

Of course all of this information hinges on one very important question: how does one assess the jugular venous pulse?  After all, what good does such data serve if one cannot apply it? 

To find the jugular venous pulse (jvp), the patient should be laying with their head elevated between 30-45 degrees̊.  After finding the pulsation of the internal jugular vein in the neck one should roughly measure from the jvp to the Angle of Louis—right above the sternum, which is typically around 5cm.  A significant deviation would suggest pathology. 

The reliability of the individual practitioner in finding the jugular venous pulse is notoriously unreliable.  Given the safety of ultrasound, its relatively cheap cost and its easy access, recent studies have looked into the possibility of ultrasound guided determination of the jugular venous pulse.  Two separate studies in 2010, one by Northern Ontario Medical School, and the other by the University of Iowa have suggested a much higher reliability in ultrasound-determined jugular venous pulse.  However, as with any new technological method it warrants further research before its application clinically.

Socransky SJ, Wiss R, Robins R, Anawati A, Roy MA, & Yeung IC (2010). Defining normal jugular venous pressure with ultrasonography. CJEM : Canadian journal of emergency medical care = JCMU : journal canadien de soins medicaux d'urgence, 12 (4), 320-4 PMID: 20650024

Deol GR, Collett N, Ashby A, & Schmidt GA (2011). Ultrasound accurately reflects the jugular venous examination but underestimates central venous pressure. Chest, 139 (1), 95-100 PMID: 20798190