Doppler Waveform Parvus and Tardus A Sign of Proximal Flow Obstruction

Transcription

1 Doppler Waveform Parvus and Tardus A Sign of Proximal Flow Obstruction Pesho S. Kotval, MD, PhD The Doppler linear flow velocity versus time spectrum obtained in an arterial flow system in which there is proximal occlusive disease with or without collateral formation has a tardus-parvus waveform. The condi- W hen high-grade (greater than 80%) stenosis exists proximal to the point of Doppler interrogation, the Doppler waveform exhibits certain characteristics that heretofore have not been described in the literature. This paper describes a characteristic poststenosis Doppler waveform sign, namely the tardus-parvus waveform sign. This Doppler sign is also seen distal to sites of arterial occlusion when collateral flow pathways exist. Pulsus tardus is defined as "a pulse beat slow to rise and fall"; pulsus parvus is defined as "a small pulse.'' 1 These terms, from older clinical practice, are applied to the delayed and small upstroke of the carotid (pressure) pulse in proximal occlusive disease, for example, aortic stenosis. 2 The tardus-parvus Doppler waveform described in this paper is schematically shown in Figure 1. As systole occurs, the normal linear velocity versus time Doppler waveform shows a rapidly rising upstroke to peak systolic velocity (unshaded waveform, Fig. 1). The tardusparvus waveform (shaded) in Fig. 1 reveals a much slower rise to peak systolic velocity (~t in Fig. 1) and a decrease in peak systolic velocity (~v in Fig. 1). n contrast to the sawtooth morphology of the normal Doppler Received August , from the Department of Radiology, New York Medical College, Valhalla, New York, Revised manuscript accepted for publication January 12, Address correspondence and reprint requests to Dr. Kotval: Department of Radiology. New York Medical College, Valhalla, New York tions that cause this Doppler sign are due to a poststen otic pressure drop. KEY woros: Doppler, tardus wave* form, parvus waveform, proximal obstruction, collaterals. (]Ultrasound Med 8:435, 1989) waveform, the tardus-parvus waveform reveals a smoothened, undulating morphology. The time lag to peak systolic velocity and the decrease of peak systolic velocity serve both qualitatively and semiquantitatively as characteristic signs of proximal obstruction to flow. The tardus-parvus waveform sign suggestive of proximal obstruction to flow is demonstrated for different flow situations and, in each case, compared to the Doppler waveform of the contralateral normal vessel. A flow mechanism, based on a Bernoulli pressure drop, to explain this sign is proposed. MATERALS AND METHODS Doppler waveforms obtained from carotid duplex examinations, vertebral duplex examinations, and transcranial Doppler examinations in 21 patients with proximal obstruction to flow at various levels (see Table 1) in the head and neck were analyzed. n each case in which the tardus-parvus waveform sign was noted, proof of prox+ imal stenosis or of proximal occlusion with collateral flow was obtained by duplex sonography andfor by angiography. Examinations were performed with one of three instruments: a 5-MHz linear transducer (Acuson 128; Mountain View, CA) or a 7.5-MHz imaging system with a 3-MHz Doppler dual-head transducer (Diasonics 400; Milpitas, CA) for duplex examinations and a 2-MHz transducer (TECA-64; Pleasantville, NY) for transcranial examination. As summarized in Table 1, the cases are divided into ~ 1989 by the American nstitute of Ultrasound in Medicine /89/$3.50

2 436 DOPPLER WAVEFORM PARVUS AND TAROUS ~ t Figure 1 Schematic d iagram showing the sawtooth mor photogy of a normal Doppler waveform (unshaded waveform). Jn comparison, the tardus ~ parvus waveform (shaded wave ~ fo rm) shows a slower rise to peak systolic velocity (.:1t) and a decrease in peak systolic ve' ocity (.:1v). two groups. The first group consists of 11 patients with a high ~ grade stenosis at the following locations: two in the innominate artery, three cases of proximal internal ca ~ rotid artery (CA) stenosis; two cases of proximal common carotid artery (CCA) stenosis, and four cases of proximal vertebral artery stenosis. All except one of these 11 patients revealed the poststenotic tardus parvus Doppler waveform. The single case in which the tardus-parvus waveform was not observed downstream from a high-grade stenosis was in a patient with proximal right lca plaque with a high carotid bifurcation that did not permit adequate Doppler interrogation of the CA distal to the high-grade stenosis. The second group of ten patients, summarized in Table 1, revealed a tardus-parvus waveform distal to a proximal occlusion with collaterals supplying the distal flow. n three out of four cases of CA occlusion, the tardus parvus waveform was seen in the ipsilateral middle cerebral artery (MCA). Of six cases of total occlusion of the CCA with retrograde flow in the external carotid artery (ECA) supplying the CA, the tardusparvus waveform was seen in the antegrade flow of the collaterally supplied CA in four cases. n those cases in which the tardus parvus sign was not seen, it is suggested that the collateral flows were sufficiently established so that Bernoulli pressure drops did not occur; hence, the conditions for tardus-parvus signs in the Doppler waveforms did not come about. An analysis of the flow dynamics in each of these cases (Table 1) of proximal obstruction to flow is presented together with the results. RESULTS Tardus-parvus Waveforms Downstream from Highgrade Stenoses. Doppler waveforms from the left CCA, at the level of a high-grade stenosis in the left CA and distal to the stenosis are shown in Figure 2 The poststenosis Doppler waveform shows the tardus-parvus sign. The waveform has a markedly undulating morphology. The peak systolic velocity is low (34 cmjs) and the slope of the upstroke is markedly flattened with a rise-time to peak systolic velocity of 260 ms. For comparison, the Doppler waveforms from the left CCA and the left popliteal artery of a normal volunteer (with a synchronously recorded electrocardiogram d isplayed below each Doppler tracing) are shown in Figure 3. n the upper panel of this figure, the end of the electrical QRS complex (ie, the beginning of true systole) is seen to correspond precisely with the beginning of the upstroke of the Doppler systolic velocity. n a vessel relatively close to the heart, for example, the CCA, the true time to Table 1: Doppler Observations Downstream from Proximal Stenoses and Distal to Sites of Occlusion (When Collateral Flow Exists) Location Location of Doppler examination No. of cases Cases witll l1igl1-grade stenosis (greater tllan 80%) Stenosis nnominate artery Right common carot id artery Proximal CA (2 left, 1 right) CA; distal to stenosis Proximal CCA CCA; distal to stenosis Proximal vertebral artery Vertebral artery at C4/CS level Tardus-parvus waveform 4 n n n n 4 n 3 of 4 cases 2 of 2 cases 2 of 3 cases 2 of 2 cases 4 of 4 cases Exemplified in Figure 4 Figure 2 Proximal occlusion (with collaterals supplying distal flow) Occlusion CA CCA (with retrograde flow in ECA supplying CA) psilateral middle cerebral artery Proximal ipsilateral CA CA, internal carotid artery; CCA, common carotid artery; ECA. external carotid artery, 6 n 4 of 6 cases Figure 5 Figure 6

3 L.{;O KOTVAL 437 m~t-t's.. S CCA LT Figure 2 Doppler waveforms from the left common carotid artery (CCA LT), at a high-grade stenosis in the proximal left internal carotid artery (CA LEFT), and distal to the stenosis. The poststenosis waveform shows the tardus-parvus sign. peak systolic velocity is in the range of 120 ms and corresponds to the duration of the upstroke of linear velocity. n a vessel relatively farther from the heart, for example, the popliteal artery (lower panel, Fig. 3), the true time from beginning of systole to the Doppler peak systolic Figure 3 Doppler and simultaneous electrocardio graphic tracings from the left common carotid artery (LCCA) and the left popliteal artery (L Popliteal A.) in a healthy volunteer. The true time from beginning of sys tole to peak systolic velocity is longer in a peripheral vessel than in a vessel closer to the heart. The duration of the Doppler linear velocity upstroke is, however, the same. OVSEC tea tea.,,.._0.120 sees ' 7'5 ----'«-" t 0 leoe,jreulee e:feonelec!tle'''sm''''''''"''tl!!'eeelnncclaoopl OVSEC.,.. L...: :~0.120 velocity is longer (approximately 255 ms). However, the duration of the linear velocity (systolic) upstroke is the same (approximately 120 ms, Fig. 3) in a normal peripheral vessel as in a normal vessel closer to the heart. Thus, the systolic velocity upstroke of the poststenotic tardus- A Popli~eQl Sf!C: v...

4 438 DOPPLER WAVEFORM PARVUS AND TARDUS Figure 4 Doppler spectra from the left (LEFT CCA) and right (R CCA) common carotid ;U'teries superimposed on an arteriogram that demonstrates highagrade innominate artery stenosis. A tardus-parvus Doppler waveform is seen jn the: R CCA. parvus waveform {Fig. 2), when compared to normal upstroke times (Fig. 3), is measurably slowarising (tardus) and reaches only a small (parvus) amplitude of peak systolic velocity. n Figure 4, the left CCA demonstrates a normal Doppler waveform. However, the Doppler spectrum from the right CCA reveals the tardus-parvus waveform sign. Based on the waveforms of the left and right CCA, a proximal high-grade stenotic lesion on the right side was diagnosed. n the case illustrated, the right vertebral artery had reversed flow (Doppler tracing not shown here) that, taken with the tardus ~ parvus waveform of the right CCA, permitted a more precise inference as to the localization of the stenosis to the level of the proximal innominate artery. A subsequently obtained angiogram (Fig. 4) proved the proximal innominate highgrade stenosis. As summarized in Table 1, tardus-parvus waveforms have also been recorded in 2 out of 2 cases of high grade proximal CCA stenosis and 4 out of 4 cases of proximal vertebral artery stenosis. The features shown in Figures 2 and 4 and described above were observed in each of these cases. Tardus-parvus Waveforms Distal to Sites of Arterial Occlusion When Collateral Flow Exists. n four cases (Table 1) of unilateral occlusion of the CA (proven by duplex sonography and angiography), transcranial Doppler examination of the ipsilateral and contralateral MCA was carried out using identical gate depths, gain, and power settings. Figure 5 illustrates tracings ob tained from the right (upper Dopp!er waveform) and left (lower Doppler waveform) MCA in a patient with total right CA occlusion. t is evident that the sharp upstroke of the normal left MCA tracing is not present in the right MCA. nstead, the right MCA reveals a slow rise-time (approximately 220 ms) to peak systolic velocity and an attenuated peak systolic velocity as compared to the normal left MCA, namely the tardus-parvus sign. Angiography demonstrated that flow to the supraclinoid right CA was reconstituted by supply from the basilar artery via the right posterior commun eating artery and,

5 J Ultrasound Med 8: , 1989 KOTVAL 'fc2 :'f => t: 5 " ~.... (... ~ : -!1 ~ : ~.. ~..... t Figure 5 This figure shows 2-MHz transcranial Doppler waveforms obtained at identical power, gain, and gate depths from the middle cerebral arteries (MCAs). Occlusion of the right internal carotid artery was noted in this patient (at refers to the slow rise time to peak systolic velocity in the right MCA). ~~ ~ 2.8 S l" l> : ~. 439 MCA Right '''.. ' 1.,,.... left MCA : " ~.. ' : : - 50 from the left carotid circulation, via the anterior communicating arteries. Three out of four cases revealed the tardus-parvus sign in the MCA distal to ipsilateral CA occlusion. n the one case in which the sign was not seen, well-developed collateral supply was noted. n six cases (Table 1) involving occlusion of the CCA (in which duplex examination revealed antegrade flow in the CA via retrograde supply from the ECA), four showed a tardus-parvus waveform sign. n Figure 6, this type of flow physiology is shown with reversed flow in the ECA (note the high diastolic flow indicating supply to a low-resistance territory) supplying the CA. The tardus parvus waveform of the Doppler tracings from the (resupplied) CA is evident from the smoothed, near ~ sinusoidal morphology of the tracing with a de layed peak and poor amplitude. Figure 6 Schematic diagram of occlusion of the common carotid artery with a patent bifurcation in which retrograde flow in the external carotid artery supplies the internal carotid artery. The Doppler waveforms from the respective vessels are shown in the composite figure. A tardus-parvus Doppler waveform is seen in the internal carotid artery.

6 440 DOPPLER WAVEFORM PARVUS AND TARDUS DSCUSSON A primary assumption in any discussion of normal Doppler waveforms in a high-pressure arterial system is that no significant pressure drop occurs between the left ventricle and the point of Doppler interrogation. n the absence of significant pressure drops, the Doppler spectrum is characterized as a high or low resistance waveform depending on the vascular bed supplied by the artery. Because the Doppler shift frequencies are directly proportional to linear flow velocities, this parameter can be used to evaluate stenosis in a vessel. The concomitant pressure drop is not measured and usually not analyzed. Nevertheless, by Bernoulli's theorem, a pressure drop must exist at every stenosis. This point was demonstrated by West et aj,l who showed a high correlation between change in pressure and the square of the peak systolic velocity at the level of stenosis. The methods used in oculoplethysmography4 are based on late arriving pulses distal to stenoses. n the literature, however, the effect of the poststenotic pressure drops on Doppler spectra distal to stenoses has not been analyzed. The description of the tardus-parvus Doppler sign for proximal occlusive disease presented here is based on a physical diagnosis sign of the late arriving time ~ honored and small carotid pulse in cases of proximal stenotic disease, for example, aortic stenosis. This phenomenon can be appreciated by simultaneous palpation of the left ventricular impulse and the carotid pulse. 2 By use of the Doppler transducer, it has been shown that the tardusparvus sign can be seen in the cervical and intracranial circulation, in which the effects of pressure drops are not easily measured. n the cases of proximal ar terial obstruction (Table 1) described above, the actual pressure gradients have not been measured. However, it is commonly noted on angi ography that delayed filling (of the ipsilateral supraclinoid lca via collaterals) occurs when there is occlusion of the cervical CA. This delayed filling is the direct result of the delayed transmission of an attenuated driving pressure pulse. Analogously, the tardus-parvus Doppler waveforms are a direct consequence of the driving pulse being attenuated and slowed and serve as a valuable sign of collateral resupplied flow. n the one case out of four with CA occlusion in which the ipsilateral MCA did not show the tardus parvus sign, well-developed collateral supply was noted. t is suggested that the driving pressure pulse was sufficiently maintained by the collaterals so that no attenuation occurred. f such is the case, the J Ultrasound Med 8: , 1989 tardus-parvus sign would not be seen. t should be noted that the same conditions that would prevent the tardus-parvus sign would also maintain the most collateral flow and would be expected to leave the patient with the least clinical deficits. n each category of poststenotic flow (upper portion of Table 1) in which the Doppler waveform reveals the tardus-parvus sign, it is readily seen from the discussion above that the sign is a direct result of a pressure pulse that is also tardus-parvus. Analysis of the Doppler waveform, therefore, gives a valuable clue to the pressure drops associated with high-grade stenoses. Similarly, in recent work 5 it was shown that interposing an axillary-axillary graft causes marked delays in the arrival of the pressure pulse and, in the resultant complex flow circuit, causes unique pressure gradients and Doppler waveforms. Recognition of the tardus-parvus Doppler waveform provides a valuable sign for proximal stenotic disease. n addition, when reconstitution of flow by collaterals occurs following an arterial ocdusion, the tardusparvus sign is seen in the distal circulation. The sign provides an indication of the existel'lce of such collaterals proximal to the point at which the Doppler signal is obtained. ACKNOWLEDGMENTS would like to thank Dr. S. Babu for discussions correlating angiographic findings with clinical symptoms. Dr. j. Fakhry brought to my attention two cases of common carotid occlu sion in which the tardus parvus sign wu not seen. REFERENCES 1.. Steadman's Medical Dictionary. Baltimore, Williams & Wilkins, 1979, p Braunwald E: Heart Disease. Philadelphia, W.B. Saunders, 1981, p West FW, Spencer MP, Clark SJ, et al: Noninvasive evaluation of severe carotid occlusive disease with CW Doppler. Bruit 6:46, McRae LR, Kartchner MM: Oculoplethysmography. n: Kempczinskt RF, Yao JS (eds): Practical Non invasive Vascular Diagnosis, Chicago, Year Book, 1982, p Kotval PS, Fitzpatrick J, Fakhry J, et al: Doppler diagnosis of intermittent subclavian steal during systole caused by axiuary-axillary bypass graft. ' Ultrasound Med 7:593, 1988