The venous pulse is difficult and variations with subtle changes are common indicating adjustments in the circulation by the state of the heart. Examination of the neck veins is debatable. There are a lot of implications and why the examination of neck veins has a special place in the clinical evaluation of the heart, which has developed over centuries. There are certain peculiarities of such an examination, e.g.,
1. Venous pulses are seen or inspected rather than felt
2. External force or pressure of small magnitude is needed to obliterate a visible venous pulse.
3. Tangential light and a slight turn of the head make the visibility of such pulses better.
4. Venous pulses are best observed at the root of the neck in between the two heads of the sternocleidomastoid on either side.
5. The right internal jugular vein is preferred as it is in direct line with the right atrium of the heart.
6. Skin retraction indicating rapid venous drainage and opening of atrioventricular valves are better visualized than the venous fullness waves.
Predictably prominent veins nearest the heart are the neck veins. As sophisticated instruments are not required, and in most cases, a careful visualization is all that necessary, neck vein examination is so very endearing to clinicians.
Historically, it was James Mackenzie, in 1893, who simultaneously evaluated carotid and jugular venous pulses. Before him, only sporadically did the venous pressure evaluated, and history suggests the famed Italian Lancisi in the 17th century had shown a passing interest at one time. The still-known Lancisi’s sign or the giant upward venous wave of tricuspid regurgitation is mentioned in books today. James Mackenzie understood that the venous pulse was complex and was able to predict the volume status of the heart and the body. That the ‘C’ wave is a transmitted carotid pulse artefact was suggested first by Mackenzie himself. He used a self-designed ‘Mackenzie Polygraph’, to record the venous pulse in the neck. Paul Wood carried his work further and his observations of the jugular venous pulse still hold.
The observation of the venous pulse in the neck has become an integral part of the clinical examination. It enables the physician to form an opinion about the diagnosis. An angle of 45° of the torso makes the right atrium of the heart, superior vena cava, and the right internal jugular vein axial in a straight line. The next step consists of identifying visually the upper level of the venous column in the neck. Two scales are then taken and one scale is held horizontally one end touching the upper end of the column of blood in the neck, while the other scale is held vertically to meet the first scale from the angle of Luis or the sterno-manubrial junction. The horizontal scale is used to mark the exact point where the neck venous pulsation is seen and is projected onto the vertical scale.
The centre of the right atrium is considered, although arbitrarily, 5 cm vertically below the angle of Luis. Measuring the height on the vertical scale where it meets the horizontal scale and then adding 5 cm to it gives a reasonable value of the central venous pressure (CVP). Several studies have been done to find out the exact central point of the right atrium, but there may be variations due to size, position, condition of the lungs, and inherent cardiac defects. The 5 cm value is taken as an average and most natural cases conform with this.
The jugular venous pressure (JVP), as the right internal jugular vein is in direct line and continuity with the heart, gives a more or less accurate estimation of the right atrial pressure (RAP) and the end-diastolic right ventricular pressure as well. Central venous pressure or CVP, as it is commonly known today, is estimated by preoperative internal jugular cannulation. This is routine in stressful and long operations now as it helps mainly in assessing the volume status and requirement. The normal CVP is 5 to 10 cms of water and any jugular pulsation observed more than 3 cms is considered a raised JVP.
The same structural variations, e.g., sparsity of non-striated muscle cells with a pronounced media and the thin walls with occasional interior non-return tricuspid semilunar valves, characterize the neck veins also. The internal jugular veins in the carotid sheath are the largest. It does not have any valves, though there is the suggestion of a functional valve regulating venous inflow to the heart. Other inconsequential small veins join the internal jugular veins throughout their direct downward course. The region where it becomes continuous with the superior vena cava (SVC), is joined by the subclavian on each side. The external jugular veins, two on each side, run obliquely over and across the sternocleidomastoid muscles on either side, conforming to the external jugular lines, and are joined by the anterior jugular veins of either side near the region where they drain into the corresponding subclavian veins. There is at times a transverse jugular arch that joins the anterior jugular veins near the lower ends. The anterior jugular veins are valveless and there are two incompetent valves in the external jugular veins in its lower part – one where it drains into the subclavian vein and the other 4 cm above. The internal jugular vein joins the subclavian on either side and continues as the superior vena cava on the right and the innominate vein on the left. The innominate vein on the left travels horizontally with a slight downward inclination across the manubrium in its interior aspect, ultimately joining the SVC on the right. This short region of the confluence of the various veins and where the internal jugular and the subclavian meet is often called the jugular sinus, and variations are common. Normally the external jugular veins drain the face and scalp, while the anterior jugular veins are involved in the drainage of the larynx and other internal organs like the thyroid in the neck. The internal jugular vein lies deep to the sternocleidomastoid and lateral to the carotid on either side and is not visible in most parts except a small region in the neck. The external and anterior jugular veins are covered only by skin, fascia, and platysma in their course. These become prominent first and alert the clinician about a rise in pressure of the internal jugular veins and their dilatation.
The venous waves are complex. A very close flicker of two upstrokes can be appreciated before the carotid pulse. Then comes the first retraction. The upstroke again appears to be followed by even another descent. The right-sided events are best depicted by the right internal jugular pressure and the venous waveform. This is one cardiac cycle and in the tracing, after cannulation, it looks like as shown below:
So the upstrokes of a venous wave are the ‘A’, ‘C’, and ‘V’ waves, while ‘X’ and ‘Y’ are the descents. When compared with the carotid pulse (as shown on photoplethysmography, PPG) and the ECG in a cardiac cycle, the venous pulse appears as shown. The explanation of the occurrence of the waveforms is as follows:
1. ‘A’ wave – Right atrial (RA) contraction or atrial systole. Atrial contraction occurs against the blood-filled right atrium and forces the tricuspid valve to open to fill the RV.
2. ‘C’ wave – The ‘C’ wave in the tracing seems to follow the ‘A’ wave closely. There are many theories for explaining the ‘C’ wave. Right ventricular contraction against a closed tricuspid valve with its bulging upwards and transmitting the pressure onto the right atrium, superior vena cava, and then onto the internal jugular vein is the commonest and most popular explanation given. Transmission of carotid pulse, as initially suggested by Mackenzie, seems to be the most plausible explanation as of now.
3. ‘X’ descent – relaxation of the atrium in atrial diastole with a displacement of the tricuspid valve and its rim towards the right ventricle in early diastole. The ‘X’ descent has two parts, one before the ‘C’ wave or ‘X’ and the other after the ‘C’ wave, i.e., the ‘X¹’part when the tricuspid valve closes. Right ventricular (RV) contraction starts (with the already filled RV) now. During the end of the ‘X¹’ part of the descent, RV contraction is completed allowing space for a relaxed right atrium.
4. ‘V’ wave – this represents the filling up of the right atrium and the tricuspid valve opens once the atrial filling is completed.
5. ‘Y’ descent – represents a termination of the ‘V’ upstroke and indicates a passive filling of the right ventricle with the tricuspid valve open in late diastole.
Thus the pattern of venous fullness in the neck is suggestive of the volume status of the person and also the state of the heart in management of the volume flowing into the heart. The junior clinicians who take the initial history often write JVD or no JVD, which means jugular vein distension after a cursory look at the neck veins. The preload pathologies of the right heart are better predicted by the venous pulse and its waveforms. Thus in constrictive pericarditis and restrictive cardiomyopathy, there will be an impediment to the venous in-flow into the heart. As a consequence, the neck veins will always remain full. The Kussmaul sign, a true paradox, is an increase in jugular venous pressure with inspiration and is seen in these conditions. In pericardial effusion also the jugular venous pressure (JVP) will be raised. The classical Beck’s triad consisting of raised JVP, low blood pressure, and distant heart sounds are not often appreciated in cardiac tamponade or pericardial tamponade. Even one does not get a chance to elicit paradoxically a low blood pressure (greater than 10mm of Hg) with inspiration before measures are undertaken. In the tamponade situation, however, the heart is normal and it is not allowed to fill and consequently stretch the myocardial fibers to the fullest, within the limits of Starling’s law. The atrioventricular valves open at appropriate times and exaggerated ‘x’ and ‘V’ descents, called a ‘W’ sign, are there as blood is being sucked in from the cavae. Canon waves in jugular venous tracing are caused by a closed right atrioventricular valve during cardiac contraction. Canon waves are irregularly seen and common in third-degree AV block, non-compliant right ventricle ventricular tachycardia, occasional ventricular ectopics, pulmonary stenosis and hypertension, and other asynchronous arrhythmias of the heart. There are no effective and organized contractions of the atrium in atrial fibrillation and flutter hence 'A' waves are not seen. However, cannon A waves may be seen in a flutter. Tricuspid stenosis is a condition where delivery of venous blood to the right ventricle from the right atrium is impeded. As a consequence, there will be a slow build-up of the ‘A’ wave and a gradual ‘X’ descent. Such dominant ‘A’ waves are characteristic of tricuspid atresia and pulmonary stenosis also. Tricuspid regurgitation is a different issue. Mild tricuspid regurgitation is common and even moderate ones are well tolerated. In severe and organic tricuspid regurgitation there is a probability of changes in cardiac dimensions and architecture. Congestive heart failure is always there and the neck veins are full. JVP, obviously raised, on traced in a monitor shows a double-peaked ‘AV’ or ‘CV’ waveform. This is the much-talked-about Lancisi’s sign. The ‘X’ descent is obliterated to a degree conforming to the degree of TR. The ‘X’ descent represents a downward movement of the tricuspid AV valve towards the right ventricle as it empties and this cannot be seen. The ‘Y' descent, which represents a passive filling of the right ventricle in diastole with open leaflets of the tricuspid valve, is steep and with a non-compliant right ventricle a prominent upstroke this is termed a ventricularisation of the JVP.
There are certain other conditions where neck vein examination becomes an important examination tool and helps the clinician to arrive faster at a diagnosis. Absent jugular waves with an enlarged neck vein may indicate an obstruction of the draining SVC. In atrial fibrillation and other disorders of atrial rhythm, there will be occasional giant 'A' waves and if there is heart failure, the neck veins will be engorged. Otherwise, there will be no internal jugular waveforms. The diastolic collapse of neck veins with an exaggerated 'Y' descent (Friedreich's sign) is characteristic of constrictive pericarditis.
Nowadays sophisticated investigations are available and some tools allow the physician to look inside to see the pathology. Nevertheless, examination of the neck vein and looking for venous distension was an important part of the bedside clinical examination which should be learned by all to become a complete clinicians.
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