Similarly, infiltrative heart diseases, including amyloidosis, sarcoidosis, and hemochromatosis, are unlikely in view of echocardiographic findings that are consistent with systolic dysfunction rather than diastolic dysfunction and the absence of infiltration on imaging.
Hypertrophic cardiomyopathy would not be an appropriate diagnosis because echocardiography failed to show an increase in wall thickness, notable diastolic dysfunction, intracavitary gradient, or a hyperdynamic state with preserved or increased ejection fraction. Ischemic cardiomyopathy is unlikely in this patient given the normal findings on coronary artery catheterization. Placement of an ICD has been shown to improve survival by reducing the incidence of sudden cardiac death in patients with severe left ventricular dysfunction, but evaluation for the presence of major coronary artery disease and the need for revascularization should be considered before ICD placement. An electrophysiologic study is premature at this point because the coronary anatomy is not clearly defined. The current standard for confirming the presence or absence of coronary stenosis is angiography. Although an exercise or stress test such as adenosine technetium Tc 99m sestamibi myocardial perfusion imaging can indirectly suggest the presence of flow-limiting stenosis leading to myocardial ischemia, perfusion defects can also be seen with nonischemic causes of left ventricular dysfunction. The lack of regional wall motion abnormalities on this patient's echocardiogram argues against the presence of an old infarction but cannot rule out coronary artery disease. If coronary artery disease is present, the feasibility of revascularization should be assessed because an area of ischemia could be the site of origin of the VT. Given the prevalence of coronary artery disease, all patients with notable left ventricular dysfunction should undergo coronary angiography to rule out coronary artery disease. Because the patient had documented symptomatic VT, electrophysiologic studies are not indicated at this time because the results would not alter therapy, including the decision to place an implantable cardioverter-defibrillator (ICD). Although cardiac catheterization may be necessary in the future, it is invasive and the condition of the coronary arteries is not the immediate question. Transesophageal echocardiography is superior for assessing posterior structures of the heart, prosthetic valves, cardiac vegetations, and the presence of thrombus, but it is not indicated at this stage in the patient's evaluation. To assess for structural heart disease such as regional wall motion abnormalities, valvular disease, arrhythmogenic right ventricular dysplasia, hypertrophic obstructive cardiomyopathy, and tumor, transthoracic echocardiography is the most appropriate initial study. Evidence of cardiomegaly on chest radiographs, although nonspecific, also suggests the presence of structural heart disease. Monomorphic VT, even when accompanied by metabolic abnormalities such as hypokalemia and hypomagnesemia, is typically associated with some form of structural heart disease. Because treating VT as SVT can result in serious harm and a delay in appropriate treatment whereas treating SVT as VT usually causes no harm, all wide-complex tachycardias should be treated initially as VT until proven otherwise. Differentiating VT from SVT is oftendifficult, especially from a single-lead rhythm strip. The recorded rhythm showed no variation in amplitude or direction and thus is not representative of torsades de pointes. The differentiation between monomorphic and polymorphic VT (which includes torsades de pointes) is important because patients with monomorphic VT typically have some degree of structural heart disease, whereas patients with polymorphic VT characteristically have electrolyte abnormalities, a drug effect, ischemia, or a genetic cardiac channelopathy. More specifically, the rhythm can be further described as sustained VT, which is defined as lasting more than 30 seconds or requiring intervention. The regular, wide-complex tachycardia in this patient is characteristic of monomorphic VT.
Because the strip showed no evidence of P-wave activity, the diagnosis of SVT with bundle branch block is unlikely. The rhythm was regular and therefore not indicative of atrial tachycardia with variable conduction or ventricular fibrillation. The rhythm strip obtained by the EMS team showed wide-complex tachycardia with a heart rate of 250 beats/min and a QRS complex duration of 240 ms.
0 kommentar(er)
