I must confess that myocarditis was not on my diagnostic radar until Andrew Redfern talked about it at BADEMFest. The context he was talking about is very different from the one I face – there is very little HIV or TB to consider in my part of the world – but the challenge of making the diagnosis is still there.
Before the advent of endomyocardial biopsy, the only time that clinicians could make the definitive diagnosis was at autopsy. Although several criteria make the diagnosis of myocarditis more likely, there is no way to differentiate actual from possible myocarditis when looking at clinical features alone.
Why are we talking about this now?
SARS-CoV-2 makes its way into cells via ACE₂ receptors and may also directly attack cardiac myocytes in a similar fashion to the Coxsackie virus. It is also possible that mRNA vaccines may cause a focal antibody response in a subset of the population in the same way that the virus causes MIS-C/PIMS-TS. Certainly, post-vaccination myocarditis is not an unheard-of entity. Back in 1957, when smallpox was the scourge, myocarditis complicated the provision of preventative vaccination. Is this a case of preventing an illness being worse than the disease it was created to treat?
In mid-June 2021, Israeli health regulators reported 275 cases of myocarditis (from December 2020 to May 2021). This cohort was drawn from over 5 million people that had received mRNA vaccines against COVID-19 (Pfizer–BioNTech and Moderna). This means nothing if you do not know the baseline incidence of the disease – reported as between 1.95 per 100,000 (in Finnish children under 15) and 2.16 per 100,000 in fit, young US military service folk.
It is certainly more prevalent in the male population. The risk of developing some form of cardiac inflammatory process after the second dose is 1 in 100,000 girls and 1 in 16,000 boys (aged 12-17).
PREDICT have developed a flow chart to assist the emergency provider in picking up pericarditis and not missing myocarditis. As a member of the ACEM team that helps come up with some of these guidelines, I wanted to look into the evidence a little more.
So how does a child with pericarditis (or myocarditis) present?
The symptoms may be non-descript. A small case series by Das et al. (2021) described the following, all occurring within five days of the second dose:
- Chest pain (24-42%)
- Fever (31-58%)
- Palpitations (16%)
- Shortness of breath (35-69%)
- Fatigue (25-70%)
- Nausea/vomiting/abdominal pain (28-48%)
- Diarrhoea (8%)
Numbers are based on Law et al.’s Scientific Statement for the American Heart Association in 2021.
So, whilst cardiac-sounding complaints like chest pain and palpitations should set your Spidey-sense tingling, we need to be aware that teens, who have been recently vaccinated, may well present with the very vague complaint of fatigue. If you can find me a teenager who does not complain of fatigue, then we could probably publish a case report. Every piece of information needs to be taken in context.
Physical examination findings
We’ve taken our history and want to move on to the next step – the examination. Are there any examination findings that increase the likelihood of pericarditis being the diagnosis? Once again, the majority of signs are incredibly non-specific.
- Tachypnoea (52-60%)
- Tachycardia (32-57%)
- Murmur (26%)
- Gallop (20%)
- Diminished pulses (16-21%)*
- Hepatomegaly (21-50%)*
- Oedema (7%)*
- Signs of low cardiac output*
*Clearly these are signs of imminent cardiovascular collapse.
Pericardial friction rub
Have you ever heard it? First described by Victor Collin, an assistant of René Laënnec, in 1824, it has made its way into exam questions and textbooks alike. I remember being told to imagine sandpaper on stone. I would close my eyes and listen, oh so intently, until one day, I heard it. And, like a lot of historical signs, there have been little data around either specificity or sensitivity, with a reported prevalence between 35% and 85%.
It is mainly heard over the left sternal border and louder on leaning forward and on inspiration (as the pericardium is brought nearer to the stethoscope’s diaphragm). It’s worth considering that you may not be able to hear a friction rub if a large pericardial effusion is present.
The pericardial friction rub is typically triphasic – heard in atrial systole, ventricular systole and ventricular systole. It shouldn’t be mistaken for the biphasic pleural rub. That sounds more like an old leather-bound family bible being creaking open and disappearing if you ask the patient to hold their breath.
(MP3 taken from University of Washington Department of Medicine)
If you measured my blood pressure as I sit here, calmly writing this post, you might spot that my systolic blood pressure drops a little as I breathe in, then goes back up when I breathe out. This is completely normal.
Swings of more than 10mmHg produce pulsus paradoxus. Increased intrathoracic pressure (in acute severe asthma, for example) reduces left ventricular stroke volume and, thus, systolic BP. Biventricular interdependence also plays a role, so in cardiac tamponade, one can see big swings in systolic blood pressure and pulsus paradoxus. It’s an early sign that develops before the ensuing hypotension of tamponade. So, not specific to pericarditis, pericardial effusion, or tamponade, but another clue.
Although, officially, you should be using a sphygmomanometer to measure the systolic BP, most of us tend to rely on a surrogate marker, the pulse oximetry trace.
Distant heart sounds
Distant or muffled heart sounds suggest that there is some acoustic barrier between your stethoscope and the heart. In this case, we are worried about a pericardial effusion.
We know that paediatricians could better interpret ECGs, though I would challenge most adult cardiologists to interpret paediatric ECGs successfully (there’s a study in that). What should you be looking for?
The most common findings are sinus tachycardia, or non-specific ST changes, followed by more specific changes related to the underlying pathology.
Pericardial inflammation causes ECG changes through four classical stages. These are present in about 50-60% of cases.
- Widespread ST elevation and PR depression with reciprocal changes in aVR (first couple of weeks)
- Pseudonormalization – ST changes resolve, and T waves flatten (1 to 3 weeks)
- Flattened T waves invert (3 to several weeks)
- ECG normalizes (several weeks onwards)
The global ST changes make pathophysiological sense as the underlying disease process is not associated with any particular arterial territory.
As a pericardial effusion develops, the QRS voltages shrink, pulsus paradoxus develops, and the patient may develop AV conduction delays. There are no ECG changes that can differentiate myocarditis from pericarditis. The sensitivity of ECG in diagnosing myocarditis has been estimated to be around 47%.
As the pericardial effusion grows, the heart swings from beat to beat, subtly altering the axis. This is known as electrical alternans.
It’s clear that if the history and exam do not suggest myo/pericarditis and the ECG is normal; then we can stop. Do not pass go. Do not collect $200. And reassure the patient and parents and send them on their merry way with good safety netting advice and reassurance that they made the right decision to get vaccinated. But what value do blood tests hold?
It would be nice if viral serology helped, but it has a low negative predictive value compared to the gold-standard biopsy. Many reported cases of mRNA vaccine-associated pericarditis had had a normal WBC, a normal CRP and a normal ESR.
I am not a fan of the Completely Random Protein as a test in the emergency department though I do understand how some of my impatient colleagues love to draw pretty graphs charting its rise and fall. Fortunately (or unfortunately, depending on your point of view), a normal CRP does not rule out acute inflammation of the myocardium.
It may be more useful to monitor disease progression or the impact of treatment.
A rise in troponin suggests concomitant myocardial injury.
Although not a commonly requested test in paediatric medicine BNP (Brain Natriuretic Peptide) and NT-proBNP (N-terminal pro-BNP) are often raised in fulminant myocarditis with deteriorating myocardial function. Hopefully, you should be able to detect heart failure signs long before you consider ordering this blood test.
Let me know if any Paediatric Emergency Medicine provider has access to same-day cardiac MRI. The rest of us mere mortals might want to do something else – a chest x-ray or bedside echocardiogram, perhaps?
The latest NSW safety notice recommends a chest x-ray as one of the initial investigations for a young person presenting with symptoms of pericarditis or myocarditis. However, chest X-rays are usually normal. A moderate to large-sized pericardial effusion can manifest as an increased cardiothoracic ratio.
It is probably more useful to help rule out alternative causes of chest pain.
If chest radiographs are not overly sensitive for potential peri/myocarditis, it may be time to wield the trusty ultrasound probe. The following changes have been reported, but it is important to note that normal ventricular function does not rule out myocarditis:
- Altered global ventricular function
- Isolated left or right ventricular dysfunction (including regional wall motion abnormalities)
- LV enlargement
- Thickened myocardium from wall oedema
- Pericardial effusion
- Intracardiac thrombus
- Functional valvular regurgitation
It takes little training to visualize an effusion, so watch this great video from Jacob Avila for five minutes.
I doubt any of us have easy access to cardiac MRI, but it can help clinch the diagnosis if it is in doubt. 69% of cases of myocarditis in the Das et al. series had late-phase gadolinium enhancement.
The Bottom Line
Young people with a normal ECG and a normal troponin do not need any further workup.
Those with an abnormal ECG AND/OR troponin AND who are haemodynamically stable should be followed up and ideally get an echocardiogram within 48 hours.
Those who are not haemodynamically stable require more emergent imaging, not so much to define cause but define myocardial function.
In the setting of COVID-19 infection, the incidence of myocarditis is estimated to be around 11 cases per 100,000 people. The incidence of myocarditis after vaccination is estimated to be around 2.7 cases per 100,000 people vaccinated.
mRNA vaccines have made a difference and have reduced both the number and severity of cases of COVID worldwide. But it can also reduce the complications of long COVID too – something that many forget to consider. There are also indirect benefits to the individual. Higher community vaccination levels will mean less disruption to education as transmission in schools becomes less of an issue.
Most reported cases of myocarditis are mild and resolve with rest and symptomatic treatment and with no serious sequelae.
Current advice is that if someone has developed probable or confirmed myocarditis due to an mRNA vaccine, they should not receive a second dose or a booster. The advice is less clear if the patient has developed mild pericarditis, so liaison between the local cardiology team and the primary is vital.
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