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AbsiW: Energyurclmnge h s e d on N e w m i a n principles is t b m o s r appropriate way to express the fuffctiou ofpngpuwrp - inctudiq the k&. Using infomwmbn obtained ar cardiac cathereriration, we h e measured the total work energv (ET) of rhp It$ ventricle (L V) (mean 1.63 3) iri p"rrclrs with cawre m i r d regurgitarion~ean.rqpusgianrfracrion0.66). E T was approximarefy.CbP4Ai abaw n o d . Of the regorghnr mergy (J#E)-{mm0.95 J), on average, 314 ( 7 3 . g q b f w ~ s 4 i & c{KE)and (23.~)poientipIfPE). Both conrponenrs represent wasred L V r e - ' & &&tic energg assmiPiQd'mith t&dmlemee'~r as heat, rke potenrial energy r&$&ej&a& in LeJz A m a l y L A ) pressure. T k a w w u n t of PE as a percentage of t o t a b q w g & n i h r g y (RE) varied c a s d c m b l y jmm.ahe parient to another (10.5% ro 54.4%) Hence, d m r f k n o mapping which &recisonly KE of rurbulenr jki flow musr una!ercsrimaro I, K w lbrs and, because ojpuiient to piuiemr variation, cannot consisrenrly refIecr severity of rigurghaiion. Measurernewis o{ PE correlaie e e f l with wedge P-uare heifht. Grrespanding non-inoasive esrimures were nude using sphygmodynamonrerer-calibrated indirecr ca&df&e tracings und echouvdiogrqrhir ntasummenrs. 7'hese were nor significantly dfjf&m rke invasivf mcasn&mems. E r w m i e ! y , the calculation of PE is indirect nnd:i&s subrracrion, so rhni measrremenr&@ indivadual parients were not accumie.emugkp6c: clinicui use. *Parr of the nnn-inzrasivc calcubrion involved an estimate oflefr Qmidprt%me basedon chc.b!md pswe'rneasrr&enI a d Doppler velociry of regur;gIratioq, rhis.ph& be.n useful ineasurement m itself. Mmirrement of E l , an index of borh w h m e ard.pressure a w l o t d freflecri~gpe~pheralresisrance changes), should be resred in wid sncdips as Q prediitor oflejr.oeniricuhrfRiZnr in m e r e mirral regargirarion. NOW invasive &urernmrr d d be ustful ro/d!4w p r i & t r with acure severe mrtrai regurgiratio?: Non-invasioe PE meuutremnu p.e,currenr(y mi reliuble enough but an indireci mwqomient 01&b &rial presswc umld. h verv usefil. (AUSINZ J hfed 1992; 22: 532-540.) Key & + @ * ~ ~ q w r u x l a z meid, mural ~ p & v u t ; o n +echo iGrdiqvaphy.

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terns of energy should therefore be our scientific objective. Are there practical advantages at present in doing so? Measurement of energy might give us insi&t k t o the mechanics of ventricular overload and ihto what our diagnostic tools are acfually

Dr .&kw L .Moclsa+, Cardldog). kllow, C a r e Iniestigatlm ~ Unit, Si Vincent's Hospital, hlelbourne, Vic, Australia. currauly fu& by a Narioid Hear1 Foundation Fellowdup. . .. -''Ausk. NZ J Med 1992;: 42 I:hTIR'.R(;Y ANI) AtITRAL REGURGIT.ATION

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Figitre I : An inwsire study, simultaneous clccrrocardiograni (ECC), srandardised l e f t ventricular (1.V) hl-mode and cathetertip iiimometer 1.V pressure (P1.v) recording.

pressure wave, its distortion by catheter transmission does not, in theory, influence calculation of pressure-volume work. After placement of the catheter in the LV, immediately before angiography, and close to the time of measurement of cardiac output, an M-mode echocardiogram and simultaneous left ventricular pressure were recorded (Figure 1). During the M-mode recording, made by an experienced technician, emphasis was placed on the recording of continuous endocardial echoes, and on a standardisation procedure based on the intersection of the ultrasonic beam and the tips of the mitral leaflets.' T h e LV volumes were then estimated from the M-mode dimensions using the Teichholz m e t h ~ d . ~ In six of the patients, and in the four control patients, we also measured the total stroke volume from the LV angiogram, using the single-plane technique of Dodge er al.' This confirmed the good correlations (r = 0.9 1 ) between angiographic and M-mode echocardiography measurements reported previously.'.' We have elected to base our calculations on the echocardiographic method for several reasons. First, steady state conditions are an important requirement for our study. Second, the measurements by echocardiography and angiography showed good agreement, and it would

534

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certainly be unreasonable to attribute all differences to the echocardiographic error. Finally, on practical grounds, angiographic measurements of volume are sometimes not valid, and not even feasible in some patients with severe regurgitation who are in atrial fibrillation. Itivasive Energy Estiinatioii (Table 2) T h e basic assumptions behind these measurements are that energy can be calculated according to basic

TABLE 2 Energy Formulae , lnvasive Energy Formulae

Non-invasive Energy Formulae

EF = (PAs-~ED)OF ELV = IAPLV dOLV EK =APLV.LAQR = ' h e OR V R ~ E p = ELV-EF-EK

EF = ( P A s - ~ L A OF ) ELV = (PAs-~LA)OLV EK = ' h e QR VR' E p = ELV-EF-EK

EF = forward enerqy PAS=mean systolic elecllon a o r k pressure PED = L V end diastolic pressure OF= forward stroke volume E l v = L V energy APLV = systolic ininus diastolic L V prmsure OLV= L V stroke voluine EK = kinetic energy of regurgitalion APLV LA = systolic left ventricular left atrial pressure gradieni OR = regurgitant volume VR =mean regurgitant jet velocity E p = po'enlial energy of regurg taiion e = density of blood

FNERGY AND M I T R A L REGI'R(;ITATION

Figwe 2: Computer display of the digitised left ventricular volume and pressure, the corresponding pressure-volume loops and the pressure-volume work (PV Wk).

Newtonian concepts. Thus, PE can be measured as the product of pressure and volume changes, and KE by multiplying one-half by mass by the square of velocity. T h e modified Bernoulli equation, the mathematical function relating these variables (AP = 4v2), can be used to transform pressure into an equivalent velocity and vice versa.6 Integrated total LV work energy was calculated as the integral product of instantaneous left ventricular volume (M-mode), and pressure. A pressure-volume loop was constructed using software developed specifically for this purpose (Figure 2). Forward stroke energy was measured as the product of mean aortic pressure during systolic ejection, corrected by subtracting the end-diastolic pressure, and the forward stroke volume measured by thermodilution. Energy of regurgitation was

then calculated by subtracting the forward stroke energy from total L v pressure-volume work. KE of regurgitation was estimated as the product of the regurgitant volume and the mean LV. LA pressure gradient during the period of mitral regurgitation (i.e. systole and isovolumic ventricular relaxation). According to the Bernoulli equation, this pressure measurement is simply an alternative formulation to the more Familiar expression of K E in terms of mass and the square of velocity (Table 2). Allowance was made for delay in transmission of the LA pressure to the wedge pressure. We estimated regurgitant volume by subtracting the thermodilution forward stroke volume from the total stroke volume measured from the M-mode echocardiogram." The PE of regurgitation was obtained by subtracting the KE from the RE. A sample calculation has been provided in Table 3. Non-Invasive Studies (Table 2) The non-invasive study was performed immediately before cardiac catheterisation. 12V forward stroke work was derived as the product of an estimate of mean arterial systolic ejection pressure, corrected for atrial pressure, and the forward stroke volume. T h e forward stroke volume was measured as thc product of the area of the LV outflow tract immediately below the aortic valve (estimated from the two-dimensional echocardiogram in the long axis view) and the mean outflow tract velocity from the Doppler recording.' The following method was used to correct the arterial pressure so that it yielded an estimate of the pressure developed by the LV over and above LA pressure. The contour of the indirect carotid pulse tracing has been shown to closely resemble that of the pressure tracing in the aortic root." Hence, by measuring blood pressure with a n auto-

TABLE 3 Sample Calculation Sample lnvasive Calculation Sample Non invasive Calculation Therrnodilution Forward Stroke Volume = 38 rnL 2DiDoppler Forward Stroke Volume =43 rnL = 100 rnrnHg Mean Systol c Ejection Arterial Pressure Mean Systolic Election Aortic Pressure = 103 mmHg LV End-diastolic Pressure = 1 7 mmHg Systolic BP =118 Systolic LA Pressure = 15 mmHg Corrected Mean Election Arterial Pressure = 88 Forward Work=38x(100-17)xO 000133=0 42 joule Forward Work = 43 x 88 x 0 000133 =050J LV Stroke Volume = 100 mL LV Stroke Volume = 112 mL Corrected Mean Ejection Arterial Pressure = 88 mmHg LV Pressure-VolumeWork = 1 37 joule LV Work = 112 x 88 X O 000133 =I31 J Regurgitant Energy = 1 37-0 42 = 0 95 joules Regurgitant Enerqy = I 31 0 4 2 =081 J Regurgitant Volume = 100 38 = 62 TIL Regurgitant Volume =I1743 =69 mL Mean LV LA Gradient = 64 mmHg Mean Regurgitant Jet Velocity 3 64 mkec Kinetic regurgitant energy = 62 x 64 x 0 00013 = 0 54 J Kinetic regurgitant energy = $ 2 x 69 x 3 642= 0 50 joule Poi'ential regurgitant energy

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ENERGY A N D M I T R A L REGURGI I rZ I ION

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535

Figure 3: A non-invasive study, simultaneous electrocardiogram (ECG), left ventricular (LV) M-mode, phonocardiogram (PCG) and indirecr carotid tracc (ICI’).

matically recording instrument (Dinamap 845@ , Critikon, Tampa, Florida), we calibrated the carotid pulse contour. Mean arterial pressure during systolic ejection was estimated by electronic integration. An estimate of the LA pressure during systole was made from the Doppler recording of the regurgitant jet; the Bernoulli equation was used to translate the peak velocity of the jet into an equivalent LV/LA pressure difference.’ This was then subtracted from the systolic blood pressure to yield a systolic LA pressure. This LA pressure was in turn subtracted from the mean arterial systolic ejection pressure to yield an estimate of the pressure generated by the LV.

536

Ausr K Z J .\Id 1992. 22

Total LV work energy was calculated as the product of the corrected arterial pressure and the total LV stroke volume measured from the M-mode echocardiogram (Figure 3). Initial attempts to use a biplane echocardiographic methodlo were thwarted by the unreliability of measurements made from single frames in patients with suboptimal image quality. T h e difference between total and forward stroke volumes was used to calculate the RE. KE of regurgitation was calculated from the mean regurgitant Doppler regurgitant velocity and the regurgitant volume. T h e regurgitant volume was calculated as the difference between the Mmode total stroke volume and the LV outflow tract ENERGY AND MITRAI. REGURGITATIOK

TABLE 4 Energy Estimates Total LV Work (ET) Forward Work (EF) Regurgitant Energy (ER) Regurgitant KE (EK) Regurgitant PE (Ep) Initials Cath Echo Cath Echo Cath Echo Cath Echo Cath Echo

1

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1 AK 2. DC 3. JC 4. EG 5. JW 6. WS 7 MS Mean sd

148 115 145 102 099 135 1.37 1.31 2.51 2.20 2 26 198 145 134 164 148 054 044 p=029

0 96 0 56 101 0 59 0 67 101 0 95 0 81 172 141 1.77 1.65 0.95 1.01 1.15 1.01 0.42 0.41 p=028

052 060 044 043 032 034 0.42 0.50 0.79 0.79 049 032 050 033 050 047 015 017 p=038

077 041 046 043 053 064 054 050 135 100 1 24 1.03 0.85 0.63 0.82 0.66 0.35 0.26 p=o.19

019 014 055 0 16 014 037 041 031 036 041 054 062 0.10 0.37 0.33 0.34 0.19 0.16 p=0.46

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forward stroke volume. The mean regurgitant jet velocity was measured from the Doppler recording. As for invasive measurement, PE was the difference between total L V work energy and KE. In each patient the number of measurements used to obtain an average value for each variable reflected the difficulty of measurement and its handling in calculations. For example, at least ten estimates were made of the diameter of the LV outflow tract, a measurement which is squared in the calculation of flow. Interobserver variability was measured for key variables. Pearson's correlation coefficient was used to test the relationship between variables mean values and the regression line to detect systematic differences, and the paired t-test to assess significance of differences between mean values.

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Patients Figure 4: T h e relationship between the potential (Cath PE) and kinetic (Cath KE) components of regurgitant energy, measured invasively, in individual patients. ENERGY AND MITRAL REGURGITATION

RESULTS Invasive Study (Table 4) For the eight patients with mitral regurgitation, the mean total LV stroke work energy was 1.64 joule, range 0.99 to 2.51 J. This was 84% greater than that measured in the four control patients 0.89 J (0.78 to 0.98 J). For patients with mitral regurgitation, mean R E was 1.1 5 J (0.67-1.77 J), to which K E contributed 0.82 J (0.46-1.35 J) and PE 0.33 J (0.10-0.55 J). Thus, approximately three-quarters (73.6%) of the RE was KE. However, this was not a constant proportion in different patients (Figure 4). T h e PE component of R E ranged from 10.5% to 54.4% in individual patients. Since the quantity of regurgitant potential energy (RPE) and the energy capacitance of the L A and pulmonary veins Aust NZ J Med 1992; 22 537

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TABLE 5

Correlation of lnvasive and Non-invasive Estimates Variables

Pearson's r

P-value

QLV " QF PLA ET* EF' ER

0.93 0.89 0.83 0.87 0.79 0.79 0.88 0.18

(