Hemodynamic stenoses

Can U, Furie KL, Suwanwela N, Southern JF, Macdonald NR, Ogilvy CS, Buonanno FS, Koroshetz WJ, Kistler JP. Transcranial Doppler ultrasound criteria for hemodynamically significant internal carotid artery stenosis based on residual lumen diameter calculated from en bloc endarterectomy specimens. Stroke 1997 28(10) 1966-1971. 

While rMTT can depict changes in cerebral hemodynamics, which are due to vessel occlusion of cerebral arteries and the respective compensation mechanisms, the time to arrival of contrast (TTA) is sensitive to vessel diseases, which are more upstream of the arterial flow, most commonly high grade stenoses or occlusions of the carotid arteries. In such patients, blood flow in the hemisphere ipsilateral to the stenosis is mainly supplied by the contralateral carotid artery via the circle of Willis. Due to this detour, TTA is prolonged in the ipsilateral hemisphere (Reith et al. 1997). At the same time, rMTT may be prolonged in the ipsilateral hemisphere resulting from decreased blood flow (Dorfler et al. 2001). If TTP is calculated instead of MTT, the effect of the bolus delay cannot be separated from that of the perfusion decrease, because TTP is influenced by both rMTT and TTA. 

Soinne L, Helenius J, Tatlisumak T, Saimanen E, Salonen O, Lindsberg PJ, Kaste M (2003b) Cerebral hemodynamics in asymptomatic and symptomatic patients with high-grade carotid stenosis undergoing carotid endarterectomy. Stroke 34 1655-1661... 

Using DWI and PI in acute stroke patients with the detection of the acute lesion and the delineation of the area of hemodynamic compromise, the understanding of pathophysiological mechanisms leading to cerebral ischemia in patients with ICA disease has been improved. DWI offers a better chance of detecting not only gross abnormalities but also very subtle acute ischemic lesions. In a systematic study using DWI in 102 consecutive patients with ICA stenosis > 50% or ICA occlusion and acute stroke, we... 

Fig. 15.2. Diffusion-weighted imaging in a 54-year-old patient with acute onset of severe left-sided hemiplegia shows a territorial infarction in the right middle cerebral artery territory, as well as additional bilateral hemodynamic lesions. Ultrasound examination in this patient showed high-grade internal carotid artery stenosis on both sides...

Szabo et al. (2001) 102 >50 or occlusion Territorial stroke (n=30) Subcortical stroke ( =13) Territorial infarction with fragmentation (n=ll) Disseminated small lesions (n=15) Borderzone lesions (n=33) The degree of ICA stenosis may favor certain stroke patterns. In patients with high-grade stenosis the highest frequency of lesions occurs in the hemodynamic risk zones... 

Fig. 15.5. As in this 68-year-old man with a high-grade stenosis of the left internal carotid artery presenting with a fluctuating mild left-hemispheric syndrome, acute ischemic lesions can affect all areas considered to be hemodynamic risk zones...

Fig. 15.13. A 76-year-old woman with a subtotal stenosis of the left internal carotid artery shows no sufficient collateral flow and only faint flow signal in the left middle cerebral artery (upper row), severe hypoperfusion (time-to-peak maps) of the left middle cerebral artery territory (middle row) and small acute hemodynamic stroke lesions on DWI (bottom row). The patient was later successfully treated with carotid endarterectomy...

Schroeder T (1988). Hemodynamic significance of internal carotid artery disease. Acta Neurologica Scandinavica 77 353-372 Schroeder T, Sillesen H, Sorensen O et al. (1987). Cerebral hyperfusion following carotid endarterectomy. Journal of Neurosurgery 66 824-829 Shaw DA, Venables GS, Cartlidge NEF et al. (1984). Carotid endarterectomy in patients with transient cerebral ischaemia. Journal of Neurological Sciences 64 45-53 Silvestrini M, Vernieri F, Pasqualetti P et al. (2000). Impaired cerebral vasoreactivity and risk of stroke in patients with asymptomatic carotid artery stenosis. 

A report from the Mayo Clinic has described 27 elderly patients (mean age 71 years) with aortic stenosis in whom dobutamine stress hemodynamic testing was used to assess the severity of the stenosis (12). There were no severe adverse effects, but relatively minor problems occurred in 16 patients, including chest pain and ventricular extra beats (n = 9 each) and atrial dysrhythmias (n — 4). The authors concluded that the procedure appears to be safe in these high-risk patients, although its diagnostic value may be limited. 

Lin SS, Roger VL, Pascoe R, Seward JB, Pelhkka PA. Dobutamine stress Doppler hemodynamics in patients with aortic stenosis feasibility, safety, and surgical correlations. Am Heart J 1998 136(6) 1010-16. 

These rhythms are usually not directly life-threatening, nor do they generally cause hemodynamic collapse or syncope, but 1 1 atrial flutter (ventricular response 300 beats per minute) is an exception. Also, patients with underlying forms of heart disease that are heavily reliant on atrial contraction to maintain adequate cardiac output (e.g., mitral stenosis and obstructive cardiomyopathy) will display more severe symptoms of atrial fibrillation/flutter. 

Pellika PA, Sarano ME, Nishimura RA, et al. Outcome of 622 adults with asymptomatic, hemodynamically significant aortic stenosis during prolonged follow-up. Circulation 2005 111(24) 3290—5. 

The treatment of patients with symptomatic intracranial atherosclerotic disease can be summarized into prevention of occurrence of intraluminal thrombosis, plaque stabilization, and control of risk factors for atherosclerosis. Anticoagulation (compared with aspirin) has not shown to be beneficial in patients with intracranial atherosclerotic disease [24]. Current guidelines recommend that aspirin alone, the combination of aspirin and extended release dipyridamole, and clopidogrel monotherapy (rather than oral anticoagulants) are aU acceptable options [24]. hi patients with hemodynamically sigifificant intracranial stenosis who have symptoms despite medical therapies (antithrombotics, statins, and other treatments for risk factors), the usefulness of endovascular therapy (angioplasty and/or stent placement) is uncertain and is considered investigational [22, 25],... 

Table 1 Degrees of aortic valve stenosis. Shown are the hemodynamic parameters used to evaluate AS, the most common pathology observed in each stage and the symptoms that the patient may exhibit. AVA aortic valve area, MAVG mean aortic valve gradient, LVEF left ventricular ejection fraction. Table adapted from [65]...

Approximately 1 in 856 people will undergo kidney dialysis, resulting in over 354,000 patients in the US alone [59], During the process, blood is transferred and processed at a rate of 350 mL min via arteriovenous fistulas, which act as a permanent access point to the vasculature [60], Complications due to the hemodynamic stress (wall shear stress) induced by the dialysis needle have been observed. The presence of the outflow needle has been shown to increase turbulence intensities dramatically [61], which in turn increases wall shear stresses, induces intimal hyperplasia, and causes stenosis [60],... 

Chronotropic Support. Temporary pacing should be considered in patients who demonstrate hemodynamic compromise due to bradycardia. Unstable bradycardia is usually caused by either severe sinus node dysfunction or complete AV conduction block, but even mild sinus bradycardia or second-degree AV block can result in instability if there are underlying conditions such as severe dilated cardiomyopathy or critical aortic stenosis. In some patients, the bradycardia is due to intrinsic conduction system disease and temporary pacing is merely a bridge to permanent pacemaker insertion. In others, a... 

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