An Uncommon Cause of Shortness of Breath in the Emergency department: Acute Mitral Regurgitation
CASE
The patient is a 52 year-old female with a past medical history of hypertension, hyperlipidemia, hypothyroidism, and a 2 pack a day smoking history who presented to the emergency department in respiratory distress.
When EMS arrived to the patient’s home, she was hypoxemic with a pulse oximetry reading of 70s on room air and hypotensive with systolic blood pressures in the 80s. She was placed on nasal cannula with improvement in her saturations and she was given aspirin, fentanyl, and nitroglycerin without relief.
Upon arrival her vitals were significant for respiratory rate of 34, pulse oximetry of 98% on 6L NC. She was noted to be in acute distress.
The patient was placed on positive pressure ventilation via BiPAP and broad blood work, chest X-ray and electrocardiogram (ECG) were obtained.
As the patient improved clinically, an abbreviated history could be obtained. The patient awoke this morning, approximately 7 hour prior to arrival with intense progressive chest discomfort which radiated to the back. Other than shortness of breath and dyspnea on exertion she had no associated symptoms and was without fevers or chills, fatigue, leg swelling, palpitations, nausea, vomiting, diarrhea. She reported having a cough and a cold within the last month but none currently.
Physical exam revealed a middle aged woman in extremis and in respiratory distress. She was diaphoretic, with coarse rales throughout all lung fields and a grade 3/6 systolic murmur. There was no jugular venous distension, her abdominal exam was benign and her musculoskeletal exam was normal without edema in her lower extremities.
Point of care ultrasound (POCUS) was performed showing a hyper-dynamic left heart and B-lines throughout the bilateral lungs.
Her EKG showed Q waves in an inferior pattern suggestive of previous MI. Her chest X-ray showed bilateral pulmonary edema and her labs were indicative of a mixed metabolic and respiratory acidosis with a whole blood lactate of 12. She had a slightly elevated troponin which was stable when repeated after 3 hours. Because she had chest pain radiating to the back, a CTA Chest aortic dissection protocol was performed, revealing ground glass opacities consistent with pulmonary edema but no acute aortic pathology. She subsequently underwent cardiac catheterization showing 100% distal circumflex blockage and severe mitral regurgitation.
DIAGNOSIS
Acute Mitral Regurgitation secondary to Papillary Muscle Rupture
DISCUSSION
Figure 1: Lewis (1918) Gray's Anatomy 20th Edition
Acute mitral regurgitation is a rare cause of cardiogenic shock and is most commonly caused by papillary muscle rupture.[1,2,3] This differs from chronic mitral regurgitation in that there are no compensatory physiologic adaptations and the patient will suffer from left heart failure in an accelerated pattern. The rationale for this deserves a review of the anatomy of the heart.
As the blood flows through the heart it passes through four valves; tricuspid, pulmonary, mitral and aortic, in that order. The two intra-cardiac valves (mitral and tricuspid) prevent backflow from the high pressure generated in the ventricles and are anchored by thick fibers, chordae tendineae, to extensions of the heart muscle called papillary muscles. The mitral valve has two leaflets and is named after the Pope’s hat (mitre). It is held in place during systole via an anterior and posterior papillary muscle with numerous chordae tendineae.[3] The mitral valve, as you might expect by its location, is subjected to the highest intra-vascular pressures because it must withstand the full brunt of the ventricular systolic surge of blood.
There are numerous etiologies by which blood flow can be reversed across the mitral valve. Any disease which causes damage or changes the shape of the leaflets, i.e endocarditis, rheumatic heart disease, myxomatomas, cardiac tumors etc. can subvert the valve’s function.[3] Other mechanisms cause a stretch of the chamber of the heart leading to the leaflets no longer closing all the way, similar to a door, which is too small for its frame and therefore not able to latch.
Lastly and most devastating is papillary muscle rupture, due to acute onset and dramatic backflow across the valve. Although it can occur with trauma or spontaneously, papillary muscle rupture most commonly occurs after a myocardial infarction (MI).[1, 4, 8] The posterior papillary muscle is the most commonly injured. This is hypothesized to be because it is on the posterior aspect and fed by only one blood supply (in ~ 80% of all hearts) and therefore is more likely with inferior MI and due to right or circumflex coronary artery blockages.[1, 4]
Acute mitral valve regurgitation leads to acute cardiogenic shock for a number of reasons. Some of the blood is now going the wrong direction in the heart, leading to increased hydrostatic pressure in the lungs and pulmonary edema, which leads to hypoxia and tachypnea. This increased pressure also affects the left atria possibly dilating it and leading to worsening regurgitation across the valve. Because not all of the left ventricle’s force is being transmitted during systole the patient may present with hypotension with a narrow pulse pressure.
All of this together leads to the most impressive physical exam finding of acute mitral regurgitation, the systolic murmur. Usually best heard at the apex and described as low and holosystolic, this murmur actually disappears as the disease gets worse. So if your patient presents very late in their disease, and the atrial and ventricular pressures are nearly equal they may not have a murmur at all.
Diagnostic workup:
The best way to diagnose valve dysfunction is with ultrasound. In fact in a study with greater than 250 patients with acute severe MR, only a third had a systolic murmur, 60% were initially misdiagnosed, and all of them were eventually correctly diagnosed by echocardiogram [12]. In our patient the point of care ultrasound (POCUS) was interpreted as hyper-dynamic left heart. This makes sense if you think about it, our patient presents early in her disease, and her heart was able to work “overtime” to keep the blood flow moving forward. Due to underlying respiratory distress and hyper-expanded lungs from COPD adequate sub-xiphoid views were not obtained limiting the study. In fact, even with trained ultra-sonographers the sensitivity for transthoracic echocardiogram (TTE) is between 65% and 85%. This is in stark comparison to the sensitivity of transesophageal echocardiogram at around 95-100% [9]. The main takeaway from this is not “don’t bother with POCUS,” but rather “don’t trust POCUS if it’s negative.”
Management of acute mitral regurgitation:
In order for this patient to be stabilized, a thorough understanding of cardiac physiology is key. Recalling the Starling Curve, one can intuit that by reducing afterload and increasing preload cardiac function can improve. Enter vasodilator therapy. Many of these patients will improve on a nitroglycerin drip especially if hypertensive. Just as in acute congestive heart failure exacerbations these patients can tolerate high doses of vasodilators.[11]
In addition, positive pressure ventilation with BiPAP or intubation will assist in squeezing the fluid out of water-logged lungs and the increased intra-thoracic pressure is thought to augment systolic function.[10]
Although ultimately surgical repair or replacement of the mitral valve is the only definitive treatment for acute mitral regurgitation, placement of an intra-aortic balloon pump (IABP) can stabilize the patient for transfer to a tertiary care center.[5]
CASE RESOLUTION
The patient had an IABP placed by cardiology and was transferred to a tertiary care center where she underwent emergent mitral valve replacement. Although her case was complicated by alcohol withdrawal she was discharged approximately 1 week after initial presentation.
CLINICAL PEARLS
Suspect acute mitral regurgitation in patients with acute cardiogenic shock.
Acute MR is most often a delayed complication of inferior myocardial infarction.
Murmur will decrease and disappear late in the disease.
Diagnose with ultrasound; transesophageal is best and don’t be fooled by negative point of care ultrasound.
Treat with vasodilators, positive pressure ventilation, intra-aortic balloon pump and surgery.
Author: Russell Prichard MD is a third year emergency medicine resident at Brown University/Rhode Island Hospitals program
Faculty Reviewer: Melanie Lippman MD is an attending physician at Brown University/Rhode Island Hospitals
CITATIONS
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Cheung KH, Graham CA, Alexander CG. Prompt diagnosis of ST-elevation myocardial infarction with papillary muscle rupture by point-of-care ultrasound in the emergency department [published correction appears in Clin Exp Emerg Med. 2017 Nov 28;4(4):258. Alexander CG [corrected to Graham CA]]. Clin Exp Emerg Med. 2017;4(3):178-181. Published 2017 Sep 30. doi:10.15441/ceem.16.172
Crawford MH. Mitral Regurgitation. In: Crawford MH. eds. CURRENT Diagnosis & Treatment: Cardiology, 5e. McGraw-Hill; Accessed August 25, 2020. https://accessmedicine.mhmedical.com/content.aspx?bookid=2040§ionid=152995482
Czarnecki A, Thakrar A, Fang T, et al. Acute severe mitral regurgitation: consideration of papillary muscle architecture. Cardiovasc Ultrasound. 2008;6:5. Published 2008 Jan 18. doi:10.1186/1476-7120-6-5
Dekker AL, Reesink KD, van der Veen FH, et al. Intra-aortic balloon pumping in acute mitral regurgitation reduces aortic impedance and regurgitant fraction. Shock. 2003;19(4):334-338. doi:10.1097/00024382-200304000-00007
Figueras J, Calvo F, Cortadellas J, Soler-Soler J. Comparison of patients with and without papillary muscle rupture during acute myocardial infarction. Am J Cardiol. 1997;80(5):625-627. doi:10.1016/s0002-9149(97)00435-9
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Minami H, Mukohara N, Obo H, et al. Papillary muscle rupture following acute myocardial infarction. Jpn J Thorac Cardiovasc Surg. 2004;52(8):367-371. doi:10.1007/s11748-004-0012-4
Sochowski RA, Chan KL, Ascah KJ, Bedard P. Comparison of accuracy of transesophageal versus transthoracic echocardiography for the detection of mitral valve prolapse with ruptured chordae tendineae (flail mitral leaflet). Am J Cardiol. 1991;67(15):1251-1255. doi:10.1016/0002-9149(91)90936-f
Wright SE, Heffner JE. Positive pressure mechanical ventilation augments left ventricular function in acute mitral regurgitation. Chest. 1992;102(5):1625-1627. doi:10.1378/chest.102.5.1625
Yoran C, Yellin EL, Becker RM, Gabbay S, Frater RW, Sonnenblick EH. Mechanism of reduction of mitral regurgitation with vasodilator therapy. Am J Cardiol. 1979;43(4):773-777. doi:10.1016/0002-9149(79)90077-8
Zhou L, Grushko M, Tauras JM, Taub CC. Initial misdiagnosis of acute flail mitral valve is not infrequent: The role of echocardiography. J Cardiovasc Dis Res. 2013;4(2):123-126. doi:10.1016/j.jcdr.2013.05.004