For the patient with acute myocardial infarction (AMI) pressing priorities exist. Symptoms must be ameliorated, lethal arrhythmias identified and treated, arteries opened, and complications identified and managed. In many cases, little is needed beyond a targeted history and physical examination, 12-lead electrocardiogram (ECG), and simple, rapid blood work with prompt thrombolysis or emergency coronary arteriography and balloon angioplasty with or without stenting. In such straightforward cases, point-of-care echocardiography will prove interesting and perhaps helpful if potential complications are identified early. Such study, however, should never delay needed efforts at reperfusion. In other cases, the history and physical examination may be confusing, or ECG and enzymatic data may be conflicting, misleading, or delayed. These situations include (1) typical symptoms but normal or equivocal laboratory studies, (2) atypical symptoms with equivocal or abnormal laboratory studies, (3) pacemaker therapy, (4) left bundle branch block (LBBB) on ECG, (5) presence of new systolic murmur, (6) shock including right ventricular myocardial infarction, (7) late clinical presentation including post-myocardial infarction (MI) pericarditis, (8) large, non-Q-wave MI, (9) true posterior MI, and (10) suspected LV thrombus. In these instances, point-of-care ultrasonography is not only beneficial but also it may be critical for improving the understanding of the patient’s condition and selecting appropriate treatment.
Technical and Administrative Issues
For point-of-care echocardiography to prove helpful in the acute MI setting, a simple, rapidly activated and portable machine must be present in the proximate clinical area. This machine must provide good-quality two-dimensional and colored Doppler images on a wide variety of challenging patients (chronic obstructive pulmonary disease, obesity). Handheld machines, which are small enough to fit in a laboratory coat pocket, are now available at reasonable cost. In most situations, a full, formal follow-up echocardiogram should be obtained with results correlated to the point-of-care echocardiography findings. Point-of-care operators require training in theory and hands-on techniques plus proctored imaging and interpretation experience. These providers will need to work closely with institutional credentialing bodies to ensure that standards of initial training, ongoing training, and quality assurance are identified and met.
The three standard windows should be interrogated in each patient with and without color-flow Doppler (Figure 13-1A,B). Apical views should be examined first because the two-chamber, four-chamber, and five-chamber views are often readily obtained and identify all left ventricular myocardial segments in addition to the right ventricle (Figure 13-1A). Aortic, mitral, and tricuspid valves are easily identified. Color-flow interrogation in the apical views readily identifies ventricular septal defects and aortic, mitral, and tricuspid insufficiencies. Left parasternal short-axis views should be obtained next with expected good visualization of the mid-left ventricle and left ventricle at base plus aortic and mitral valves en face (Figure 13-1B). The pulmonic valve is often best seen as the aortic valve is brought into view and the transducer rotated slightly to include the right ventricular outflow tract and main pulmonary artery. The ...