Wednesday, December 16, 2009

Right Heart Strain

Diagnosis of right heart strain can be of great clinical utility in patients with dyspnea, tachypnea, hypoxemia and/or hemodynamic instability as it significantly reorganizes the differential diagnosis to focus on entities such as massive pulmonary embolism and cor pulmonale of any etiology. Transthoracic echocardiography can be used to identify right heart strain, and the clinician's first goal is to demonstrate an increase in right ventricular diameter. This is one of the core 3 questions clinicians should ask while evaluating the heart during clinical ultrasound examinations (is there a pericardial effusion?, what is the left ventricular function?, and is there evidence of right heart strain?). In patients in cardiac arrest or with severe hemodynamic instability, the finding of right heart strain in the appropriate clinical setting may prompt clinicians to consider the administration of tissue plasminogen activator or other thrombolytic agents.

The normal right ventricular to left ventricular ratio (in size) is 0.6:1.0 (the right ventricle is approximately two thirds the size of the left ventricle). A right ventricle equal or greater in size as compared to the left ventricle strongly suggests right heart strain. Flattening of the interventricular septum resulting in a "D-shaped" left ventricle on the parasternal short axis view occurs with right ventricular pressure overload (where the septum remains flat throughout the cardiac cycle) or right ventricular volume overload (where the septum resumes a normal shape during systole).

Of note, measurement of the velocity of triscuspid regurgitation, often associated with right ventricular pressure and/or volume overload (aka strain), can be used to estimate the degree of pulmonary hypertension present.

Also of note is McConnell's sign, where apical right ventricular systolic function is preserved in the setting of global right ventricular dyskinesis. This was felt to strongly suggest pulmonary embolism as the etiology of right heart strain, but has been called into question recently (see references).

Clinicians should remember, however, that while some features suggest chronic right heart strain (increased trabeculations, hypertrophy of free and septal walls) and some features suggest acute right heart strain (normal wall thickness), it can be difficult to determine if right heart strain is acute or chronic, and by no means does the finding of an enlarged right ventricle confirm the diagnosis of pulmonary embolism.

Thanks to Drs. Chilstrom and Secko for the McConnell's and Triscuspid Regurgitation clips. Be sure to cycle through the clips by clicking on the left or right arrows in the video player.



References:
McConnell MV, Solomon SD, Rayan ME, Come PC, Goldhaber SZ, Lee RT. Regional right ventricular dysfunction detected by echocardiography in acute pulmonary embolism. Am J Cardiol. 1996 Aug 15;78(4):469-73.

Casazza F, Bongarzoni A, Capozi A, Agostoni O. Regional right ventricular dysfunction in acute pulmonary embolism and right ventricular infarction. Eur J Echocardiogr. 2005 Jan;6(1):11-4.

Lodato JA, Ward RP, Lang RM. Echocardiographic predictors of pulmonary embolism in patients referred for helical CT. Echocardiography. 2008 Jul;25(6):584-90.

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Welcome to the Point of Care Ultrasound blog. My hope is to inspire active learning and discussion in a forum for exchange of ideas on the use of ultrasound by clinicians at the patient's point of care (ER, ICU, OR, wards, clinics, pre-hospital, austere, etc.) My hope is to post something whenever time permits, and to include images, videos, lectures and links to references that can help others learn more about the many advantages of incorporating POC ultrasound into clinical practice.