Mark A. Rabinovitch

Topography of preemptying ventricular segments in patients with Wolff-Parkinson-White syndrome using scintigraphic phase mapping and esophageal pacing.

We analyzed the sequence of ventricular emptying using the phase image in 10 patients with accessory pathways and in 15 ‐normal subjects. In normal subjects, the earliest emptying occurred in ventricular septal, apical and left basal segments. Eight patients had manifest preexcitation; the earliest emptying occurred ectopically in the right ventricle in one of these patients and in the left ventricle in five. The remaining two patients had normal phase maps. TWo patients had concealed left-sided pathways. Their phase maps showed earliest emptying in left basal segments. Six of the 10 patients underwent electrophysiolgic mapping. There was complete agreement between phase and electrophysiologic maps. Transesophageal atrial pacing increased preexcitation in one patient, normalized the ECG in another and precipitated narrow QRS tachycardia in four patients. Phase maps then showed enlargement, reduction and loss of the ectopic earliest emptying segments, respectively. We conclude that this technique in conjunction with pacing is successful in lateralizing accessory pathways.

ω-123I-Hexadecanoic acid metabolic probe of cardiomypathy

The utility of ω-123I-hexadecanoic acid myocardial scintigraphy as a metabolic probe of cardiomyopathies was investigated. Sixteen patients with a variety of cardiomyopathies and myopathies that involve cardiac muscle and ten volunteers were imaged in the postabsorptive state in a 40° LAO projection after a standard dose of ω-123I-hexadecanoic acid. An elimination T1/2 was calculated from the left ventricular myocardial time-activity curve. An uptake index, corrected for chest wall attenuation, was also computed in 7 of 10 volunteers and 8 of 16 patients.Of the 16 patients, only 2 had distinctly abnormal ω-123I-hexadecanoic acid myocardial tracer kinetics. The first patient had a metabolic disorder of which cartine deficiency was one component. The second patient had endocardial fibroelastosis, a process which has been linked to disorders which deprive the myocardium of oxygen and energy. Therefore, the cardiomyopathy may have been caused by some abnormality of cardiac metabolism other than carnitine deficiency. Although of limited utility in the overall cardiomyopathic population, ω-123I-hexadecanoic acid myocardial scintigraphy should be further investigated as a screening test for carnitine deficiency and related metabolic abnormalities in patients at risk.

Walk-through angina phenomenon demonstrated by graded exercise radionuclide ventriculography: Possible coronary spasm mechanisms

was administered directly into the graft with complete relief of pain and resolution of ST segment elevation. Angiography of the graft (Fig. 2, C) now revealed the graft to be patent; there was normal distal runoff from the graft with a 75”; obstructive lesion of the native RCA just distal to the site of graft insertion. Subsequently, pain again developed associated with ST segment elevation. Graft spasm and complete occlusion was again demonstrated. NTG was administered without subsequent relief of pain or graft spasm. Nifedipine 10 mg was administered sublingually, also without any improvement. The catheterization was terminated at this point. During repair of the brachial artery, ventricular fibrillation developed which was successfully cardioverted. Subsequent observation demonstrated evolution of an inferior wall acute myocardial infarction (AMI). Patients with CAS have been reported to have less satisfactory results following CABG than patients with fixed obstructive disease a1one.3 Spasm of the bypassed native vessel or of additional non-bypassed native vessels has been postulated to be the mechanism for the less beneficial results with CABG in CAS patients. The current case demonstrated spasm of the bypassed native vessel and two additional mechanisms responsible for recurrent angina1 symptomatology; development of a significant lesion at the site of CABG insertion and spasm of the bypass graft itself. Spasm of the graft was transiently reversed by NTG but subsequently recurred resulting in AMI.

Computer analysis of cardiac radionuclide data

HE impact of computers on Nuclear Cardiology and the progress which has been made through computer applications is perhaps best illustrated by several historical observations. First, it is of note that all clinically important types of nuclear cardiologic procedures were initially performed without the aid of a computer. For example, the first gated equilibrium, blood pool ventriculograms performed by Zaret et al.‘** were accomplished by analog imaging. A physiologic trigger or gate was used to turn the gamma camera image recording system on and off to define “end systole” and “end diastole” which were the only two images obtained. The gating “window” used for end diastole was the 60-msec interval immediately prior to the Rwave. For end systole, data were recorded during the T-wave. Quantitative analysis was then accomplished manually. The analog images were projected to life size and the ventricular borders traced by hand. Ventricular volumes and ejection fractions were calculated using area length formulae adapted from contrast angiography. The data obtained in this fashion correlated well with results from contrast angiography and provided a strong motivation for further technical development. Likewise, in early applications of the first pass technique, computers were not used. Rather, data were recorded on video tape for subsequent replay and analysis.3 These analog imaging techniques were extremely time consuming, particularly for purposes of quantitative analysis, took advantage of only a small fraction of the potentially available data, and provided limited visual appreciation of cardiac dynamics. The first logical adaptation of the computer to radionuclide ventriculography was simply to acquire the gated end diastolic and end systolic frames into computer memory, instead of onto film, one frame at a time. Initially the data analysis was again performed by hand by tracing ventricular contours on the computer screen. As before, this analytic approach was quite tedious and partly for this reason very little clinical use was made of radionuclide ventriculography, initially. However, several breakthroughs in computer techniques occurred in the early 1970s which established radionuclide ventriculography as a feasible clinical procedure. First, Seeker-Walker and Parker4,’ recognized that after equilibration in the blood pool the net ventricular count rate resulting from an intravascular tracer (e.g., Tc-99m albumin or Tc-99m RBC) at any time in the cardiac cycle is proportional to ventricular blood volume. This germinal observation permits calculation of the ventricular ejection fraction and other quantitative parameters through analysis of net counts (i.e., background corrected) in the ventricles (a task for which the computer is uniquely suited) rather than by the more laborious geometric technique. The formula for the count based ejection fraction is:

The effect of dobutamine on exercise performance in patients with symptomatic ischemic heart disease.

The effect of dobutamine on exercise performance was assessed in 20 patients with ischemic heart disease (CAD) and a positive stress test. These patients had a wide range of resting left ventricular ejection fraction (range 22% to 69%, mean 42%). Each patient entered a double-blind crossover study in which two identical exercise radionuclide ventriculograms were performed in patients on dobutamine, 5 micrograms/kg/min intravenously, or placebo. Dobutamine increased resting left ventricular ejection fraction. Although ejection fraction fell with dobutamine during submaximal exercise, it remained higher than with placebo. At peak exercise, ejection fraction fell to the same level on dobutamine as with placebo. Dobutamine diminished exercise time and time to ischemia while peak pressure-rate product was unchanged. Four of 20 patients developed complex ventricular premature beats, all while on dobutamine. Although useful when administered to resting patients with acute left ventricular failure, dobutamines effects may be deleterious in exercising patients with chronic ischemic heart disease.

Radionuclide evaluation of postextrasystolic potentiation of left ventricular function induced by atrial and ventricular stimulation

Postextrasystolic potentiation of left ventricular function induced by ventricular and atrial stimulation was compared in 10 patients using radionuclide ventriculography. After insertion of pacing wires, a preliminary radionuclide ventriculogram was obtained and then ventricular and atrial trigeminy was induced in random order, each with identical R-R coupling intervals, each for 6 to 10 minutes. During the stimulation studies, radionuclide data were acquired in electrocardiographic gated list mode format. Left ventricular ejection fraction and relative end-diastolic and end-systolic volume changes were measured for each reformatted composite sinus, atrial and ventricular premature beat and potentiated beat. The volume changes were normalized to the count-based values obtained for the sinus beat of the appropriate study. Postextrasystolic potentiation induced by either ventricular or atrial stimulation was characterized by similar significant increases in left ventricular ejection fraction (mean +/- standard deviation 7 +/- 3 percent, p less than 0.01 versus 7 +/- 5 percent, p less than 0.01; difference not significant [NS]) and decreases in relative end-systolic volume (-12 +/- 12 percent, p less than 0.01 versus -12 +/- 8 percent, p less than 0.01; NS) but little change in relative end-diastolic volume (+5 +/- 10 percent, NS versus +4 +/- 7 percent, NS; NS). This was despite a longer compensatory pause (1,120 +/- 220 versus 1,050 +/- 190 ms, p less than 0.01) after the ventricular premature beat. It is concluded that there is no difference in the postextrasystolic potentiation induced by atrial or ventricular premature stimulation.

Scintigraphic characterization of amyloid cardiomyopathy

Amyloidosis is an important entity in the differential diagnosis of cardiac failure of undetermined etiology. In this case report, the typical pattern of combined systolic and diastolic impairment in amyloid cardiomyopathy was demonstrated by analysis of the cardiac blood pool study. In addition, the patient described had mild uptake of Ga-67 citrate, as well as the characteristically intense myocardial uptake of Tc-99m pyrophosphate. Scintigraphic assessment may be particularly helpful when the diagnosis of amyloidosis is being considered in a patient with unexplained cardiac failure.

Variations on calculating left‐ventricular volume with the radionuclide count‐based method

Various methods for the calculation of left-ventricular volume by the count-based method utilizing red-blood-cell labeling with 99mTc and a parallel-hole collimator are evaluated. Attenuation correction, linked to an additional left posterior oblique view, is utilized for all 26 patients. We examine (1) two methods of calculating depth, (2) the use of a pair of attenuation coefficients, (3) the optimization of attenuation coefficients, and (4) the employment of an automated program for expansion of the region of interest. The standard error of the estimate (SEE) from the correlation of the radionuclide volumes with the contrast-angiography volumes, and the root-mean-square difference between the two volume sets at the minimum SEE are computed. It is found that optimizing a single linear attenuation coefficient assumed for attenuation correction best reduces the value of the SEE. The average of the optimum value from the end-diastolic data and that from the end-systolic data is 0.11 cm-1. This value agrees with the mean minus one standard deviation value determined independently from computed tomography scans (0.13-0.02 cm-1). It is also found that expansion of the region of interest beyond the second-derivative edge with an automated program, in order to correctly include more counts, does not lower the SEE as hoped. This result is in contrast to the results of others with different data and a manual method. Possible causes for the difference are given.

Measurement of left ventricular ejection fraction in pediatric patients using the nuclear stethoscope.

Left ventricular (LV) ejection fraction (EF) was measured in 25 patients, aged 2 weeks to 20 years (mean 8.6 years), using a portable nonimaging scintillation stethoscope. Technically satisfactory studies were obtained in 23 patients. LVEF was validated by cineangiography in 19 patients and by standard gated blood pool scintigraphy in 4. EF measured by the nuclear stethoscope correlated well with values obtained by cineangiography or scintigraphy (r = 0.869, p less than 0.001) over a wide range of EF values (18 to 79%). In children younger than 5 years (n = 11), the correlation (r = 0.728, p less than 0.02) was less satisfactory than in those older than 5 years (r = 0.926; p less than 0.001). Although modifications in the instrument and further clinical trials with the stethoscope are needed before the device becomes clinically useful to pediatric cardiologists, our data indicate that the nuclear stethoscope can provide reliable assessment of LVEF in pediatric patients.