Monday, 15 August 2016

How to perform an optimal saline bubble contrast echo study

Saline bubble contrast echo studies, sometimes called agitated saline studies, are used in echocardiography to test for the presence of a right-to-left shunt at the intracardiac or intrapulmonary level. But what's the best way to perform such a study? Here are some tips.

Saline bubble contrast echo study showing PFO (right atrium opacified,
and red arrow shows small number of bubbles crossing into left atrium)

In order to perform a saline bubble contrast echo study, we need to create macroscopic bubbles in a syringe of saline. To prepare this, we draw up 8 mL of sterile normal saline in a 10 mL syringe, plus 0.5 mL of room air. We also add 1 mL of the patient's blood to the mixture, which helps create smaller bubbles and thereby provides better opacification of the right atrium.

To create the macroscopic bubbles, the saline/air/blood mixture needs to be agitated, and this is effectively done using a second 10 mL syringe attached to the first syringe via a 3-way tap. Always use Luer-lock syringes to avoid one of the syringes becoming detached and spraying everyone with the mixture!

By agitating the saline/air/blood mixture back and forth between the two syringes, a suspension of macroscopic bubbles is created. This is the saline bubble contrast.

This contrast is then immediately injected as an intravenous bolus via a cannula in an antecubital vein (ideally at least 20-gauge), while the echo images are obtained. A saline bubble contrast procedure can be performed during transthoracic or transesophageal echo. An echo window should be chosen that gives a clear view of both atria and the interatrial septum.

If the patient is suspected to have a persistent left-sided superior vena cava, then both left and right arm injections should be used to help clarify the diagnosis - in PLSVC, a right arm injection will opacify the right atrium normally, but a left arm injection will opacify the coronary sinus before the right atrium.

As soon as the bolus of saline bubble contrast is seen to arrive in the right atrium, the patient should perform a manoeuvre to transiently raise right atrial pressure - if there is a right-to-left shunt, this will increase the likelihood of bubbles crossing into the left atrium, and therefore this increases the sensitivity of the study. Suitable manoeuvres include:
  • coughing
  • release of a Valsalva manoeuvre

The timing with which bubbles appear in the left atrium (if at all) should be noted. With an intracardiac shunt (e.g. a patent foramen ovale), bubbles will normally appear in the left atrium within three cardiac cycles of the right atrium opacifying. However with an intrapulmonary shunt, there will normally be at least five cardiac cycles before bubbles appear in the left atrium.

Useful guidelines on the performance of contrast echo (including both saline bubble contrast and also transpulmonary ultrasound contrast agents) have been published by the ASE and can be found by clicking here.

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Thursday, 11 August 2016

Ten key facts about atrial septal defect

Atrial septal defect (ASD), in which there is a communication in the interatrial septum allowing flow between left and right atria, is one of the commonest congenital heart problems. Here are Ten Key Facts about ASD that you should be aware of in your cardiology clinic:

TEE with colour Doppler, showing a secundum ASD
  1. The commonest form of ASD is the secundum type, which accounts for 80% of cases. A secundum ASD is located in the region of the fossa ovalis.
  2. Primum ASD accounts for 15% of cases, and is located near the crux of the heart, often involving the mitral and/or tricuspid valves.
  3. Primum ASD is the most common congential heart defect seen in patients with Down syndrome.
  4. Other types of ASD include superior sinus venosus defect, inferior sinus venosus defect, and unroofed coronary sinus.
  5. An ASD most commonly causes left-to-right atrial shunting and consequent volume overload of the right heart.
  6. ASD is commonly asymptomatic until adulthood.
  7. Clinical examination findings in ASD include fixed splitting of the second heart sound, and a pulmonary flow murmur in systole.
  8. ASDs can be closed percutaneously or by surgical repair. For secundum ASDs, percutaneous device closure is the preferred method of closure, and is technically feasible in around 80% of cases. 
  9. The development of pulmonary hypertension due to pulmonary overcirculation can, eventually, lead to reversal of the interatrial shunt to right-to-left, and therefore cause cyanosis. This is known as Eisenmenger physiology, and is relatively rare (<5% of cases).
  10. ASD closure should be avoided if a patient has developed Eisenmenger pathology.

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Thursday, 28 July 2016

Spodick's sign: Downsloping TP segment in pericarditis

There are lots of eponymous signs in ECG interpretation (Wellens, Mobitz, Wenckebach and so on), so it's always interesting to discover a new one. That's what happened to me this week when I stumbled across Spodick's sign, which is used in the ECG diagnosis of pericarditis.

Spodick's sign refers to concave JT-segment elevation followed by a slight downsloping of the TP-segment. This slight downsloping in highlighted by the red arrows in the figure below, which shows ECG lead II in a patient with acute pericarditis.

Spodick's sign: Downsloping of the TP segment

Spodick's sign is reported to be present in around 80% of cases of acute pericarditis, although the reliability of the sign as a diagnostic indicator has been questioned by some.

Spodick's sign is named for David H. Spodick, who is Professor of Medicine Emeritus at the University of Massachusetts Medical School. You can read some of his publications on the ECG pericarditis here and here.

Have you spotted Spodick's sign on an ECG in pericarditis? Have you found it diagnostically helpful? Why not post a comment below?

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Monday, 25 July 2016

16 eponymous signs in aortic regurgitation

Aortic regurgitation has more eponymous signs than any other clinical condition. Here are sixteen of them to look out for next time you're in the cardiology clinic.

Colour M-mode study showing aortic regurgitation
Becker's sign
Prominent pulsation of the retinal arteries

Corrigan's sign
Prominent pulsation of the carotid arteries

De Musset's sign
Head nodding in synchrony with the pulse

Duroziez's sign
Systolic and diastolic murmurs heard over the femoral artery while the vessel is being partially compressed by the stethoscope

Gerhardt's sign
Pulsation of the spleen

Hill's sign
A higher systolic blood pressure (>20 mmHg) in the legs than in the arms

Landolfi's sign
Constriction/dilatation of the pupil in synchrony with the pulse

Lighthouse sign
Flushing of the forehead in synchrony with the pulse

Lincoln sign
Prominent (excessive) pulsation of the popliteal artery

Mayne's sign
A drop in diastolic blood pressure of >15 mmHg after raising the arm above the head

Mueller's sign
Pulsation of the uvula

Quincke's sign
Prominent pulsation of the capillaries in the nail beds

Rosenbach's sign
Pulsation of the liver

Sherman sign
Prominent pulsation of the dorsalis pedis artery

Traube's sign
A double sound auscultated over the femoral artery during distal compression

Watson's water hammer pulse
A collapsing pulse palpated at the patient's forearm

If you know of any others, you can add them to the Comment section below this blog.

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Thursday, 21 July 2016

Echo assessment of LV diastolic function

Assessing left ventricular diastolic function can get complicated. However, things were made a bit easier recently with the publication of some new joint ASE/EACVI guidelines on the echo evaluation of LV diastolic function. The guidelines are detailed (they're almost 40 pages long), but the principal take home message can be summarized as follows:

Echo diagnosis of LV diastolic dysfunction

The guidelines recommend measuring four key parameters to assess LV diastolic function:

Annular e' velocity
An abnormal e' velocity is indicated by a septal e' <7 cm/s, or a lateral e' <10 cm/s.

Average E/e' ratio
The authors recommend that an average E/e' ratio is used (rather than separate septal and lateral E/e' ratios), and that the average E/e' ratio is considered to be abnormal if it is >14. If an average can't be calculated, then a lateral E/e' >13, or a septal E/e' >15, is considered to be abnormal.

Left atrial volume index
The left atrial maximum volume index is abnormal if it is >34 mL/m2.

Peak tricuspid regurgitation velocity
This is abnormal if peak TR velocity is >2.8 m/s.

Judging whether LV diastolic function is normal or abnormal depends upon how many of the measured parameters are abnormal:
  • If more than 50% of the measured variables are abnormal, then LV diastolic function is abnormal
  • If less than 50% of the measured variables are abnormal, then LV diastolic function is normal
  • If 50% of the measured variables are abnormal, then LV diastolic function is indeterminate
This method of using the majority of available parameters to make an overall judgement about LV diastolic function is useful, as it allows a conclusion to be made about diastolic function even if all four parameters aren't available.

The guidelines can be found by clicking here, and are well worth reading. As well as giving overall advice about the echo assessment of LV diastolic function, they also contain guidance on assessing diastolic function in specific situations (such as atrial fibrillation and hypertrophic cardiomyopathy).

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Monday, 18 July 2016

Making sense of S2, the second heart sound

In our blog a few days ago, we looked at the first heart sound and how it varies with different clinical conditions. In today's blog, we're going to take a look at S2, the second heart sound.

The second heart sound is made up of two components:
  • A2, caused by aortic valve closure
  • P2, caused by pulmonary valve closure.
In expiration, the A2 and P2 components are virtually indistinguishable (in adults) and are essentially heard as a single sound. However in inspiration, the increase in venous return to the right heart slightly delays right ventricular emptying, which in turn slightly delays P2. Thus in inspiration we hear normal physiological splitting of the second heart sound, with P2 occurring just after A2.

This physiological splitting of the second heart sound gets wider (and therefore easier to auscultate) if P2 occurs late - this happens in right bundle branch block (because of the later contraction of the right ventricle), and also in pulmonary stenosis (due to greater impedance to right ventricular emptying). As you might expect, splitting of the second heart sound also gets wider if A2 occurs early - this is seen with mitral regurgitation, and also in ventricular septal defect, because left ventricular emptying occurs more quickly.

The splitting of the second heart sound becomes reversed (i.e. A2 occurs after P2) if emptying of the left ventricle is delayed - as occurs in left bundle branch block or aortic stenosis. When reversed splitting occurs, it's easiest to hear in expiration.

Transesophageal echo showing a secundum ASD

Fixed splitting of the second heart sound occurs in the presence of an atrial septal defect. In this situation, pressure changes with respiration affect the right and left atria equally, and so we no longer see the delay in P2 that normally occurs during inspiration.

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Thursday, 14 July 2016

Ten key facts about S1, the first heart sound

When we auscultate the heart, we normally hear the first (S1) and second (S2) heart sounds. Here are ten key facts about the first heart sound to be aware of when you're examining patients.

Factors that affect the intensity of the first heart sound (S1)

  1. The first heart sound (S1) results from mitral and tricuspid valve closure.
  2. Although S1 has two separate components (the mitral component and the tricuspid component), they occur so close together that they're normally heard as a single sound.
  3. If the patient's circulation is hyperdynamic, S1 will be louder than usual.
  4. Conversely, S1 will be quiet if the patient has a low cardiac output.
  5. S1 is louder than normal in Wolff-Parkinson-White syndrome. Why? Because the short PR interval in WPW syndrome means that the mitral leaflets are still widely separated at the start of systole.
  6. Conversely, S1 will be quiet in the PR interval is long. This is because the mitral valve leaflets have already started to close by the time that systole begins.
  7. S1 is louder than normal in mitral stenosis, for the same reason as with a short PR interval - in mitral stenosis, the slow exit of blood from the left atrium through the narrowed mitral valve means that the ventricle is still filling with blood, and thus the mitral leaflets are still widely separated, at the start of systole.
  8. In mitral stenosis, S1 can be so loud that it can be palpated at the apex. This is described as a 'tapping' apex beat, the palpable first heart sound in mitral stenosis.
  9. S1 is quieter than normal in mitral regurgitation.
  10. An S1 of variable intensity is heard with atrial fibrillation, ectopic beats and complete heart block.
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Monday, 11 July 2016

Ready for another heart failure subgroup? How about HFrecEF?

In the language of heart failure, we're familiar with the terms HFrEF (heart failure with a reduced ejection fraction), and HFpEF (heart failure with a preserved ejection fraction). More recently, we had a proposed new category of HFmrEF (heart failure with a mid-range ejection fraction, namely an LVEF of 40-49%). In fact we've already talked about HFmrEF in a recent blog post.

We now have another subgroup to consider - HFrecEF. This is heart failure with a recovered ejection fraction, and refers to those patients who have had a reduced ejection fraction in the past, but whose left ventricular ejection fraction (LVEF) has subsequently improved.

HFrecEF, a new subgroup in heart failure

More specifically, HFrecEF is defined when the patient's current LVEF is >40%, but has previously been documented to be ≤40%.

Why is the concept of HFrecEF gaining attention? It's because of a recent paper by Kalogeropoulos and colleagues, published in JAMA Cardiology. This paper looked at patients with HFrecEF in a retrospective cohort study, and found that the clinical course of patients with HFrecEF was different to those with HFrEF and HFpEF, with fewer clinical events such as deaths or hospitalizations during the study period.

Why does this matter? Well, if patients with HFrecEF are a distinct subgroup with different (better) clinical outcomes compared to those with HFrEF and HFpEF, then this may have an impact on the findings of heart failure trials more generally. The authors therefore propose that patients with HFrecEF may need to be considered as a separate group in future heart failure studies.

If you'd like to read the original paper, you can do so here:

Thursday, 7 July 2016

Understanding LVH: Concentric versus eccentric hypertrophy

When we talk about left ventricular hypertrophy (LVH) in cardiac imaging, the terms concentric LVH and eccentric LVH are often used. However the word 'eccentric' sometimes causes confusion - it's important to realise that the word 'eccentric' does not mean 'asymmetric' in the context of LVH. So what is eccentric LVH, and how does it differ from concentric LVH?

Cardiac MRI showing severe concentric LVH

Concentric LVH is seen in situations where there is pressure overload of the left ventricle. Examples include hypertension and aortic stenosis. The heart adapts to pressure overload by adding new sarcomeres in parallel to existing sarcomeres. This leads to an increase in left ventricular wall thickness and left ventricular mass, but the cavity size remains normal.

Eccentric LVH, in contrast, occurs when there is volume overload of the left ventricle. This is seen with valvular regurgitation (aortic or mitral), or can occur as a result of cardiac remodelling in endurance athletes. In this situation, the heart adapts to volume overload by adding new sarcomeres in series with existing sarcomeres. The end result is an increase in left ventricular cavity size and an increase in left ventricular mass, but the wall thickness remains normal.

Concentric versus eccentric LVH

If you'd like to read more on this topic, check out these links:

Monday, 4 July 2016

What's the best probe position to assess aortic stenosis severity?

When you're assessing aortic stenosis using echo, it's essential to make an accurate assessment of stenosis severity. One of the key indicators of severity is the peak flow velocity through the aortic valve (Vmax), as measured using continuous wave (CW) Doppler. Severe aortic stenosis is indicated by a peak velocity >4.0m/s. But where is the best probe position to measure this from?

CW measurement of aortic valve Vmax from the apical echo window

During transthoracic echo, CW Doppler measurements of aortic valve flow are most commonly made from the apical window, as in the image above. But is this always the best place to make this measurement?

In a 2015 paper by Thaden and colleagues, transthoracic echo studies were performed in 100 patients with severe aortic stenosis. The authors used CW Doppler to measure aortic valve Vmax from several different imaging windows during each patient's echo:
  • Apical window
  • Suprasternal notch
  • Right supraclavicular window
  • Right parasternal window
The authors then looked at where the highest value of Vmax was obtained. They found that the right parasternal window was the one where the highest Vmax was most often obtained (50% of cases), followed by the apical window (39% of cases).

The authors also found that if only the apical window was used, then in 23% of cases the Vmax was significantly underestimated (i.e. patients with severe aortic stenosis were misclassified as having moderate or even mild stenosis).

The take-home message from this study is that the sole use of the apical echo window to measure Vmax commonly leads to underestimation of the severity of aortic stenosis, and therefore that the echo assessment of aortic stenosis should include the use of multiple imaging windows (and in particular the routine use of the right parasternal window) to measure Vmax.

If you'd like to read the original paper, it can be accessed here:

Thursday, 30 June 2016

Myocardial crypts in hypertrophic cardiomyopathy

Over recent years there has been interest, and debate, about the significance of myocardial crypts seen on cardiac MRI scanning. Crypts (also known as clefts, crevices or fissures) are defined as an invagination of the myocardium that penetrates >50% of the myocardial thickness in diastole. An example is shown in the figure below: here there are two crypts in the inferior wall.

Two inferior wall myocardial crypts (arrowed)

To see this image as a cine CMR video, click on the video below to play it:

So are myocardial crypts significant? It has been suggested that they may represent a 'prephenotypic marker' of hypertrophic cardiomyopathy, based upon a 2012 paper in which crypts were  found with a high prevalence in genotype-positive (phenotype-negative) hypertrophic cardiomyopathy patients, but in none of a normal control group.

More recently, however, a study has shown that they are not uncommonly seen as an incidental finding in cardiac MRI studies, with an overall prevalence of 6.7%, although the prevalence is higher in patients with hypertrophic cardiomyopathy, myocarditis and hypertension.

So are myocardial crypts significant or not? The jury is still out, but for now the incidental finding of myocardial crypts, especially if multiple, should always prompt a careful review for any other imaging findings, clinical features or family history that might point towards a diagnosis of hypertrophic cardiomyopathy.

Monday, 27 June 2016

Hypokinetic non-dilated cardiomyopathy: a new category of cardiomyopathy

The European Society of Cardiology working group on myocardial and pericardial diseases has recently published a position statement on the diagnosis of dilated cardiomyopathy, and in doing so they have proposed a new diagnostic category: hypokinetic non-dilated cardiomyopathy, or HNDC.

CMR showing an enlarged left ventricle in dilated cardiomyopathy

How is this new category defined? The ESC working group proposes that:

Hypokinetic non-dilated cardiomyopathy is "left ventricular or biventricular global systolic dysfunction without dilatation (defined as LVEF <45%), not explained by abnormal loading conditions or coronary artery disease"

The term 'abnormal leading conditions' refers to cases where there is hypertension or valvular heart disease that has placed abnormal pressure and/or volume loading on the left ventricle, leading to dysfunction.

So why create this new category of HNDC? The reason is that, put simply, dilated cardiomyopathy doesn't always involve left ventricular dilatation. It's been recognised that in some cases there is clear evidence of left ventricular systolic dysfunction, but in the absence of left ventricular dilatation. For example, this has been described in carriers of Lamin A/C gene mutations. To avoid confusion about diagnostic terminology, this new category of HNDC has been proposed.

The new document is well worth a read. As well as the new category of HNDC, it also provides useful guidance on the investigation of dilated cardiomyopathy, and on diagnostic criteria in relatives.

If you'd like to read the guidelines, they can be accessed here:

Thursday, 23 June 2016

The prognostic value of TAPSE in acute PE

Bedside echocardiography has a useful role to play in the identification of right ventricular dysfunction in acute pulmonary embolism. But what's the best way to identify right ventricular dysfunction?

One commonly used criterion is the ratio between right ventricular and left ventricular diameters, measured in a 4-chamber view (which can be done either on echo or on CT). An RV:LV ratio of >0.9 is used to define right ventricular dysfunction in this setting, and has been included in guidance by the American Heart Association.

However, a paper by Pruszczyk and colleagues advocates the use of TAPSE as a better option than RV:LV ratio.

TAPSE is tricuspid annulus plane systolic excursion, and is simply measured using M-mode echo in an apical 4-chamber view. The M-mode cursor is placed at the tricuspid annulus, and the longitudinal displacement of the annulus during systole is measured in millimetres (see illustration).

Measurement of TAPSE using M-mode echo

Pruszczyk and colleagues found that a TAPSE of 15mm or less was associated with a higher risk of 30-day mortality from acute pulmonary embolism, whereas a TAPSE of >20mm was associated with a very low risk of mortality. The authors found that TAPSE performed better than RV:LV ratio in 30-day risk stratification.

If you'd like to read their original paper, it can be accessed by clicking on the reference below:

Monday, 20 June 2016

An incidental finding next to the heart on a CT scan

During cardiac imaging, it's not unusual to make unexpected findings outside the heart. Indeed, during cardiac MRI scanning incidental extracardiac findings are reported in around one-fifth of cases, and during coronary CT scanning the reported prevalence of incidental findings is even higher.

The image below shows a CT scan, and there's an incidental finding of a 'mass' adjacent to the right atrium. So what is the nature of this mass?

CT scan - the 'mass' next to the heart is arrowed

This is a pericardial cyst - an uncommon abnormality. On CT scanning pericardial cysts are well-defined, thin-walled and do not enhance with contrast. On cardiac MRI (see example below) fluid-filled pericardial cysts appear hypointense on T1-weighted images, and hyperintense on T2-weighted images, and do not enhance with gadolinium contrast.

Pericardial cyst on cardiac MRI

Most cases are congenital cysts, but they can also be acquired following cardiac surgery, trauma or pericarditis. Pericardial cysts are found in 1 per 100,000 individuals and can occur anywhere within the pericardium, although they are more commonly found adjacent to the right heart than the left.

Pericardial cysts are usually asymptomatic, but in some cases present with chest pain, palpitations, breathlessness or cough. They are usually benign, but (rarely) life threatening complications such as cardiac tamponade have been reported.

Pericardial cysts are usually managed conservatively, but percutaneous aspiration (sometimes with ethanol sclerosis) or surgical resection can be considered if the patient is symptomatic or in the event of life-threatening complications.

You can read more about pericardial cysts in the following review:

Information about the management of pericardial cysts can be found in the ESC 2015 Guidelines for the Diagnosis and Management of Pericardial Diseases.

Tuesday, 14 June 2016

Ten key facts about coarctation of the aorta

Coarctation of the aorta is a narrowing of the aorta, classically (but not always) just distal to the origin of the left subclavian artery. Here are ten key facts about coarctation of the aorta to be aware of in your cardiology clinic.

MR aortogram showing coarctation of the aorta plus collaterals
  1. Coarctation of the aorta accounts for 5-8% of congenital heart defects, with a prevalence of around 0.03% of live births
  2. The location of coarctation of the aorta is most commonly at the insertion point of the ductus arteriosus (just distal to the origin of the left subclavian artery)
  3. Ectopic coarctation can sometimes occur in the ascending aorta, the descending aorta or even the abdominal aorta
  4. The region of coarctation is most commonly discrete, but it can sometimes extend over a long segment of the aorta. There is often some dilatation of the aorta immediately beyond the coarctation
  5. Bicuspid aortic valve is a frequent association with coarctation of the aorta, reported in up to 85% of cases. Other associations with coarctation of the aorta include Turner syndrome, aortic stenosis (subvalvular, valvular or supravalvular), Shone syndrome and neurofibromatosis
  6. Mild cases of coarctation of the aorta may not present until adulthood. Common presentations include incidental hypertension (affecting the upper body) or a murmur
  7. A blood pressure gradient >20mmHg between upper and lower limbs indicates significant coarctation of the aorta
  8. Chest X-ray findings include rib notching (caused by collaterals) and a double contour of the descending aorta ('figure 3 sign')
  9. Both MRI (see image above) and cardiac CT are useful non-invasive methods for imaging the anatomy of coarctation of the aorta, and the presence of collateral vessels
  10. Treatment options include stenting, resection with end-to-end anastomosis, and resection with interposition of a graft

After primary repair of coarctation of the aorta, long-term survival remains below that of normal controls, and the need for re-operation is relatively common. Patients should therefore remain under lifelong surveillance after surgical repair.

For further reading about the importance of ongoing surveillance after surgical repair, read the following reference:

Wednesday, 8 June 2016

Ten key facts about ARVC

Arrhythmogenic right ventricular cardiomyopathy (ARVC, also known as arrhythmogenic right ventricular dysplasia or ARVD) is one of the genetic cardiomyopathies. Here are ten key facts about ARVC that you should be aware of in your cardiology clinic.

Cardiac MRI showing ARVC (4-chamber view)

  1. ARVC predominantly affects the right ventricle, causing the replacement of myocardium by fibrofatty tissue. However it can also involve the left ventricle as the disease progresses
  2. The population prevalence of ARVC is thought to be somewhere between 1 in 2,500 and 1 in 5,000
  3. ARVC has an autosomal dominant pattern of inheritance (with incomplete penetrance and variable expression), and affects males more often than females (ratio 2.7:1)
  4. The genetic mutations causing ARVC affect the desmosomal proteins, which connect cells and play a role in signal transduction
  5. Common presentations of ARVC include syncope and sudden cardiac death
  6. The diagnosis of ARVC depends upon the presence of major and/or minor criteria (see Task Force reference below)
  7. ECG criteria include the presence of T wave inversion in leads V1-V3 and epsilon waves
  8. Cardiac imaging (e.g. echo, CMR, contrast ventriculography) plays an important role in the diagnosis of ARVC but the diagnosis must not be based solely upon imaging findings, but instead must be based upon Task Force criteria
  9. Cardiac biopsy is of limited value in the diagnosis of ARVC due to the segmental nature of the disease
  10. Treatment options in ARVC include antiarrhythmic drugs, catheter ablation therapy and/or ICD implantation. Treatment with heart failure drugs may also be indicated

You can read more about ARVC in these key references:

Marcus FI, et al. Diagnosis of Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia: Proposed Modification of the Task Force Criteria. Circulation 121: 1533-1541.

Monday, 6 June 2016

How to assess myocardial viability on CMR

In last week's blog, I described how useful cardiac MRI is in the diagnosis of myocardial infarction. The presence of subendocardial late gadolinium enhancement is both a sensitive and specific indicator of the presence of an area of infarction. But what about myocardial viability? We're often asked to assess whether an infarcted region of myocardium has sufficient residual viability to justify coronary revascularization - but how do we do this?

Well, there are two ways: a quick way, and a slightly longer (but more accurate) way.

Viable versus non-viable myocardium on CMR

The quick way simply involves looking at the myocardium, and judging how much of the myocardial thickness is infarcted - i.e., what proportion of the myocardial thickness is occupied by late gadolinium enhancement (LGE). If the LGE occupies less than 50% of the thickness, then we judge the segment overall to still be viable. If the LGE occupies more than 50%, then it's no longer viable. If it's exactly 50%, then we say there's 'partial' viability.

This method is quick and easy, but it's difficult to be precise about the percentages, and it's hard to accept that the difference between 49% and 51% is so clear-cut (especially when it has big implications for revascularization decisions).

A more refined method is to say that if the LGE occupies <25% of the myocardial thickness then it's viable, and >75% means it's non-viable. If it's between 25-75%, then it's indeterminate and we need go on to perform a dobutamine stress CMR study to see whether the myocardial contractility improves with low-dose stress. If it does, then it's viable; if it doesn't, then it isn't.

If you'd like to learn more about the use of CMR in the assessment of myocardial infarction and viability, then check out my Cardiac MRI Essentials course at Medmastery.