Case of the week #12
Severe right heart strain due to
pulmonary arterial hypertension (PAH)
In this young female patient with no past medical history and no DVT/PE risk factors presenting with shortness of breath and dyspnea on exertion, the physical exam is unrevealing. The POCUS exam revealed a dilated right ventricle. Upon noting this abnormal cardiac finding, we must go through our differential to determine if this is acute or chronic, and what could be causing such strain on her right ventricle.
Parasternal Long Axis View
A dilated right ventricle partially seen on the parasternal long view. Even in this limited RV slice, you can see that it is similar in size to the left ventricle. For a better appreciation of the RV size relative to the LV, the parasternal short and apical 4 chamber view are much more useful.
Parasternal Short Axis View
In short axis, comparing LV and RV is more straightforward. A normal right ventricle is more of a crescent moon shape while a normal left ventricle is circular. In this patient, the RV has expanded into an orange-slice shape, and flattened the septum, turning the left ventricle into a D-shape.
The 'D sign' or flattening of the interventricular septum is not sensitive for PE or other signs of right heart strain but is specific for causes of right heart strain. In this patient with no previous echo to compare, an acute PE must be ruled out with a CT chest angiography study.
Apical 4 chamber view
In the apical view, it is extremely important to orient yourself and your probe before interpreting the image. Normally the LV would be larger and you can identify it that way. In this patient, the RV is larger, so if your probe marker is accidentally on the wrong side, you may interpret this as a normal study.
This RV is larger than the LV which would qualify as severe RV dilation. For more on how to properly acquire these images go here.
Assessing the right ventricle
Since it usually pumps against low pressures, the RV has a thin wall and is smaller than the left ventricle. If it is approaching the same size as the LV it already is moderately dilated, and severely dilated if larger than the LV. Another important aspect to look for is the dominant chamber at the apex. When the RV becomes the dominant ventricle represented at the apex, this is further evidence that RV dilation has occured.
As noted in the parasternal short axis view above, the RV is normally a small, crescent-moon shape while the LV is more circular. When there is RV dilation, the RV chamber switches to a more orange-slice shape and enlarges.
Right heart strain
Acute vs Chronic RV failure
As the condition becomes more chronic, the RV wall thickness will increase to deal with the chronically elevated pulmonary pressures. This can be a clue as to how acute or chronic the RV dilation is. Measured in subcostal 4 chamber view, a normal RV wall thickness should be less than 5mm. If it is greater than 1cm, it is likely a chronic process. Of course finding a thickened RV does not exclude a patient with a chronic RV dilation presenting with an acute PE.
RV systolic function
Like the left ventricle, an 'eyeball' approach or qualitative method is usually sufficient to be able to say it is normal or severely reduced.
For a more quantitative approach, the Tricuspid Annular Plane Systolic Excursion (TAPSE) is employed. This is done by obtaining the apical 4-chamber view and placing the M-mode cursor over the tricuspid annulus, then measuring the side of the peak of one of the m-mode tracings
Decreased is defined as less than 1.6cm
For a quick and excellent tutorial on TAPSE, go here.
If no pulmonary embolus?
If there is no sign of pulmonary embolus, then other causes of elevated pulmonary pressures must be considered. There are 5 classes of pulmonary hypertension as defined by the WHO:
Group 1: pulmonary arterial hypertension
Group 2: elevated right sided pressures related to left heart disease (congestive heart failure, valvular disease)
Group 3: Lung diseases such as COPD, interstitial lung disease, obstructive sleep apnea
Group 4: Chronic Thromboembolic Pulmonary Hypertension (CTEPH) due to chronic small clot formation
Group 5: Pulmonary hypertension causes by other conditions
Pulmonary Arterial Hypertension (PAH) & Sirius Satellite Radio
PAH is a difficult to treat disease characterized by increasing pulmonary vascular resistance that eventually leads to RV failure and premature death. Up until 1994 there were no good treatment options. In 1994, Flolan (continuous infusion of epoprostinol) was approved. It is a prostacyclin that requires continuous infusion due to its short half life of only 6 minutes. The half life was so short that interruptions in infusion were life threatening. It was also not stable at room temperature, required ice packs at all times to keep the molecule stable. To top it off, the pump was 3-5 pounds, overall making for a terrible patient experience.
At around this time a person by the name of Martine Rothblatt would start on a journey that would eventually help save millions of lives.
Martine (at the time was still Martin Rothblatt), initially interested in space and satellite technology, studied law and focused on telecommunications, eventually working as a lobbyist and then at a company that made a precursor to the modern GPS of today. She had a dream to broadcast music she loved to all corners of the globe, not just via AM and FM frequencies.
After jumping through many hoops, changing broadcasting laws, developing grass roots support of such technology, she eventually founded Sirius Satellite Radio in 1990, what we now know as SiriusXM radio.
The 'Jenesis' of a drug
A few years later in 1994 her daughter Jenesis was diagnosed with pulmonary arterial hypertension (PAH) at the age of 10 years old. At the time, the prognosis was very poor with only a few years to live without treatment.
When at the hospital with her daughter, Martine would go to the library and scour the literature on pulmonary hypertension, learning everything she could about the disease, eventually becoming an expert in this condition. She realized there was a possibility that a chemical called treprostinil may have a chance of working to treat PAH. A pharmaceutical company at the time, GlaxoWelcome, had the patent on this chemical, but was not in development for any treatment with no hope that it would work. After getting multiple rejections to buy the patent, eventually Martine teamed up with a retired pharmacologist named James Crow and GlaxoWelcome agreed to sell the patent and a small amount of the treprostinil for $25,000 and 10% of any revenue they may make on it in the future.
Eventually this developed into the drug we know today as Remodulin. Compared to Flolan, it is stable at room temperature, has a better half life of 3-4 hours, but still requires a pump and continuous infusion. It was an incredible achievement for a satellite technology expert, and it helped his daughter stay alive.
Martine formed United Therapeutics and entered the pharmaceutical business. Since then they developed an inhaled version of treprostinil called Tyvaso, and oral version called Orenitram (Martine Ro spelled backwards), and Adcirca, a PDE-5 inhibitor. Thanks in large part to her newly developed drugs, Martine's daughter Jenesis is still alive today, as are thousands of others who suffer from pulmonary hypertension.
Due to the remarkable success of United Therapeutics and Remodulin, every year they pay over $100M a year to GlaxoWelcome for that initial license of their treprostinil patent, quite a return on investment.
Martine (center) with her daugher Jenesis (left) and her wife Bina. via
Treating PAH in 2020
While this story is absolutely miraculous, the efficacy of the drugs have been questioned. Orenitram improved 6-minute walk time by 23 minutes in one study, but failed in another two (here and here). Remodulin on the other hand has been shown to be safe and effective in improving 6 minute walk test, pulmonary pressures and more.
Martine and United Therapeutics are investing heavily in "3D-printed stem cell-grafted organs using fiber from genetically altered tobacco plants, while simultaneously restoring previously unusable human lungs to functioning status through an ex-vivo lung perfusion technology that allows the lungs to be flushed and ventilated in isolation, and later re-evaluated for health and suitability for transplant. Also, in what may seem like the stuff of science fiction, at Revivicor, a subsidiary company in Blacksburg, Virginia, staff are producing genetically engineered pigs with organs that are directly transplantable into humans."
For more on Martine, we strongly recommend this TED talk from 2015.