Transient reversal of blood flow in an internal thoracic artery to coronary artery graft during syncope.

Transcutaneous duplex ultrasound can be used to image and quantify blood flow in the proximal part of the internal thoracic artery to coronary artery bypass grafts. In addition to providing information about graft patency and blood flow for follow-up purposes, the technique also provides an opportunity to study the physiology and pharmacology of the coronary circulation. In this paper we describe and attempt to interpret an unusual pattern of internal thoracic artery graft blood flow observed during inadvertent nitrate-induced syncope.

Effects of exercise and nitrates on blood flow in internal mammary artery to coronary artery grafts: a non-invasive study.

1. The aim of the present study was to investigate the effects of exercise and of sublingual glyceryl trinitrate on the pattern of blood flow, as studied by Doppler ultrasound, in internal mammary artery grafts performed to relieve severe stenosis of the left anterior descending coronary artery. The accessibility of the graft to transcutaneous ultrasound examination allows the effects of exercise and nitrate administration on coronary blood flow to be studied non-invasively. 2. Angina-free patients with left internal mammary to left anterior descending coronary artery grafts were studied using transcutaneous duplex ultrasound at rest, after leg exercise and after sublingual administration of 0.5 mg or 1 mg of glyceryl trinitrate. 3. Resting graft blood flow showed a biphasic pattern, with forward flow in both systole and diastole. Exercise caused an increase in time-averaged velocity of graft blood flow from 17.3 (3.3) to 24.0 (7.2) cm/s (P = 0.001), and of calculated volume flow from 44.7 (3.08) to 59.8 (5.89) ml/min (P = 0.002). Diastolic peak velocity increased from 36.1 (9.9) cm/s to 46.8 (16.2) cm/s (P = 0.04), while peak systolic velocity was unchanged. Nitrate administration caused a fall in systolic and diastolic blood pressure and an increase in heart rate; graft flow was maintained [time-averaged velocity 18.3 (6.2) cm/s before and 16.7 (5.7) cm/s after 500 micrograms of glyceryl trinitrate], but systole was shortened and the proportion of blood flow in diastole increased [systolic/diastolic flow ratio 0.558 (0.139) before and 0.374 (0.156) after 500 micrograms of glyceryl trinitrate, P = 0.01].(ABSTRACT TRUNCATED AT 250 WORDS)

Ventricular aneurysmectomy: indications, operative findings and outcome at a single centre.

We assessed all patients (n = 120) who underwent left ventricular aneurysmectomy as part of a cardiac surgical procedure at the Groby Road Hospital subregional cardiothoracic centre (1980-1990). Of these, 71% had had only one prior myocardial infarction and 84% had symptoms generally associated with aneurysms (congestive cardiac failure, ventricular arrythmias or systemic embolism). The indication for surgery was a combination of angina and aneurysm-related symptoms in 43%, one or more aneurysm-related symptoms in 35%, and angina alone in 22%. The majority of patients (57%) underwent aneurysmectomy and coronary artery bypass grafting, although 35% underwent aneurysmectomy alone. Most (61%) aneurysms were > 6 cm in size, and 75% were located at the apex of the left ventricle. Forty per cent had a mural thrombus, and there was no relationship between prior warfarin use and occurrence of mural thrombus. Overall perioperative mortality was 17% (20 patients), although mortality halved between the first and second halves of the study period. The main reason for perioperative was pump failure. Seventeen patients died late during follow-up (mean 52.5 months), the main cause being further myocardial infarction. Nevertheless, 65% were still alive at 5 years, and 81% and 66% of survivors were still better than pre-operatively at 5 and 8 years, respectively. Post-operative improvement was equally as good in patients who underwent aneurysmectomy alone, or those operated on for aneurysm-related symptoms, as in the whole group. In logistic regression analysis, the only predictor of adverse long-term outcome was the number of previous myocardial infarctions.(ABSTRACT TRUNCATED AT 250 WORDS)

When should we diagnose incomplete right bundle branch block?

An rSr' pattern with QRS duration of less than 0.12 s in the right precordial leads can be due to incomplete right bundle branch block (which may progress to complete right bundle branch block) or can be a normal electrophysiological variant. To identify other ECG features that may help to distinguish between these two possibilities, ECGs of 15 patients who progressed from normal to complete right bundle branch block through an intermediate rSr' pattern of incomplete right bundle branch block were analysed. The following features in the right precordial leads (V1, V2) that preceded or accompanied the appearance of the rSr' were identified: diminution of the S wave depth (100%), inversion of ratio of the S wave depth to SV1 > SV2 (93%), slurring of the downstroke or upstroke of the S wave (27%) and prolongation of the QRS duration to > or = 0.10 s (73%). When a further 79 subjects with rSr' pattern in the right precordial leads and QRS duration of < 0.12 s were divided into those with SV1/SV2 ratio > 1.0 and those with SV1/SV2 < 1.0, compared with the latter the subjects with SV1/SV2 ratio > 1.0 were found to be significantly older (59.8 +/- 18.4 years vs 32.8 +/- 18.1 years, P < 0.001), to exclusively show S wave slurring (37% vs 0%), and to more likely have a QRS duration > or = 0.10 s (74% vs 7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of the glomerular filtration rate by identification of sinistrin kinetics.

A computer-based method of system identification and estimation of parameter variance for two-compartment models matched to dynamic sinistrin concentration profiles for the determination of glomerular filtration rate is described. Thereby a procedure for the judgment of the optimal sampling time horizon is presented. Since single-injection techniques are suspected of yielding systematic overestimation of the glomerular filtration rate, a method is demonstrated confirming that such a technique employing sinistrin kinetics can be used to correctly determine the glomerular filtration rate. The validation of the system parameters gained by the single-injection method is made through prediction of the concentration contour under a constant infusion regimen in the same subject on a different occasion. This was performed in healthy controls and in patients with various degrees of renal insufficiency. Upon consideration of the dependence of the clearance estimates and their variances on the protocol duration in test subjects examined from four to ten hours, an adaptive design of the protocol length is developed.

Transcutaneous ultrasound assessment of internal thoracic artery to coronary artery grafts in patients with and without ischaemic symptoms.

OBJECTIVE: To evaluate transcutaneous duplex ultrasound in the assessment of internal thoracic artery to coronary artery grafts. SETTING: Regional cardiothoracic centre. METHODS: Prospective duplex ultrasound evaluation of 83 consecutive patients undergoing left internal thoracic artery to coronary artery grafts, together with combined angiographic and duplex ultrasound evaluation of 17 patients with suspected recurrent myocardial ischaemia after internal thoracic artery grafting. RESULTS: The grafted internal thoracic artery was imaged in 65 (78%) of 83 consecutive postoperative patients, and in 13 (75%) of 17 patients with suspected graft dysfunction. Grafts were recognised by their characteristic position and biphasic blood flow pattern. Resting graft flow was estimated from the time averaged velocity and graft cross sectional area. Median resting flow in patients without ischaemic symptoms was 36 ml/min (interquartile range 24 to 49 ml/min). Of 13 patients with recurrent ischaemia in whom the graft could be imaged, nine patients with estimated flow in the lowest quartile or abnormal flow profiles, or both, had graft disease or anastomotic problems on angiography, while four with satisfactory graft flow on ultrasound examination had normal graft flow on angiography, but had evidence of native disease progression in other vessels. Two of four patients in whom it was not possible to image the graft on ultrasound had satisfactory graft function on angiography. CONCLUSIONS: For those patients whose internal thoracic artery graft can be imaged, transcutaneous duplex ultrasound is a helpful non-invasive guide to graft function. The main limitations to the technique are an inability to image the graft in about 20% of patients, and possible inaccuracy in estimating graft diameter.

System identification of the low-dose kinetics of p-aminohippuric acid.

The renal clearance of p-aminohippuric acid, due to tubular secretion in addition to glomerular filtration, can only be determined by kinetic experiments. Maximal information can be gained from observed temporal marker concentration profiles by fitting dynamic mathematical models of the processes involved, such as absorption, distribution, and elimination, to the kinetic data. Thereby the values of the system constants, such as fractional elimination or fractional distribution rates, and their accuracy measures are determined by methods which are based firstly on measured time-dependent data elicited in an individual test object by perturbing inputs and secondly, on mathematical formulations of prior knowledge of the underlying physiological system. Such methods of model adaptation are called system identification. In this context a computer-based method of system identification and error estimation for the system constants of two-compartment models matched a dynamic concentration profiles of p-aminohippuric acid is presented. The method is used of single-injection experiments to demonstrate that such a technique is able to correctly estimate the clearance of p-aminohippuric acid if sufficiently long experimental protocols are chosen, and to ascertain the sufficient length of a protocol for an individual subject. The renal clearance of p-aminohippuric acid is known to exhibit concentration-dependence generally, but to achieve its maximal value when low doses are applied. The present study deals with the low-dose kinetics of p-aminohippuric acid.