NT-proBNP and the Diagnosis of Exercise-Induced Myocardial Ischaemia : Cardiovascular Topic

Background : Amino terminal pro-B-type natriuretic peptide (NT-proBNP) is a sensitive marker of ventricular dysfunction. Exercise causes an increase in the secretion of NT-proBNP; and with myocardial ischaemia the increase is more pronounced. This increase has been found to improve the diagnostic sensitivity of the stress ECG in diagnosing myocardial ischaemia in subjects with normal ventricular function. Objective : To assess whether the change in NT-proBNP can be used to diagnose effort-induced myocardial ischaemia in an unselected population. Methods : We enrolled a total of 51 consecutive patients; referred for exercise stress 99mTc-sestamibi SPECT MPI (single-photon emission computed tomography myocardial perfusion imaging) to diagnose inducible myocardial ischaemia. NT-proBNP was determined at rest and 30 minutes after cessation of exercise. Results : Of the 51 patients; 28 had normal perfusion scans; seven had scans with fixed perfusion defects (previous myocardial infarction with no inducible ischaemia) and 16 had reversible perfusion defects (inducible ischaemia). There was no correlation between ischaemia and resting NT-proBNP; post-stress NT-proBNP or the change in NT-proBNP (delta-NT-proBNP). Conclusion : In an unselected population the change in NT-proBNP cannot be used to diagnose effort-induced myocardial ischaemia

Efficacy of different drug classes used to initiate antihypertensive treatment in black subjects: results of a randomized trial in Johannesburg, South Africa.

BACKGROUND: Thiazides are recommended to initiate antihypertensive drug treatment in black subjects. OBJECTIVE: To test the efficacy of this recommendation in a South African black cohort. METHODS: Men and women (N = 409), aged 18 to 70 years, with a mean ambulatory daytime diastolic blood pressure between 90 and 114 mm Hg, were randomized to 13 months of open-label treatment starting with the nifedipine gastrointestinal therapeutic system (30 mg/d, n = 233), sustained-release verapamil hydrochloride (240 mg/d, n = 58), hydrochlorothiazide (12.5 mg/d, n = 58), or enalapril maleate (10 mg/d, n = 60). If the target of reducing daytime diastolic blood pressure below 90 mm Hg was not attained, the first-line drugs were titrated up and after 2 months other medications were added to the regimen. RESULTS: While receiving monotherapy (2 months, n = 366), the patients' systolic and diastolic decreases in daytime blood pressure averaged 22/14 mm Hg for nifedipine, 17/11 mm Hg for verapamil, 12/8 mm Hg for hydrochlorothiazide, and 5/3 mm Hg for enalapril. At 2 months the blood pressure of more patients treated with nifedipine was controlled: 133 (63.3%, P

Verapamil improves exercise capacity in chronic atrial fibrillation: double-blind crossover study.

Oral verapamil has previously been shown to reduce heart rate at rest and during mild exercise in chronic atrial fibrillation. Its efficacy in improving cardiovascular performance at higher levels of exercise and its safety were investigated in a prospective, randomized, placebo controlled double-blind study preceded by an open label titration phase in 20 digitalized patients with chronic atrial fibrillation. Maximal exercise capacity was improved (from 522 +/- 257 to 806 +/- 348 work units, p less than 0.0005) when tested by a standardized multistage ergometry exercise test. Heart rate was also reduced at rest, at the end of 3 minutes of 300 KPM exercise, and at the point of maximal exercise. Blood pressure and double product were also reduced. Its efficacy and safety may make verapamil the treatment of choice in chronic atrial fibrillation.

The influence of verapamil on serum digoxin concentration.

The effect of verapamil on the pharmacokinetics of digoxin was studied in 49 patients with chronic atrial fibrillation. A dose of 240 mg/day of verapamil was given to the patients who were receiving a stable dose of digoxin. Serum digoxin levels rose from 0.76 +/- 0.54 ng/ml (mean +/- SD) to 1.31 +/- 0.54 ng/ml during verapamil treatment (p less than 0.0005). This effect was dose-dependent, as shown in seven subjects who received 160 mg and then, 240 mg of verapamil: There was a stepwise rise in serum digoxin concentration from a control value of 0.60 +/- 0.11 ng/ml to 0.84 +/- 0.18 ng/ml and 1.24 +/- 0.40 ng/ml, respectively (p less than 0.01 for both steps). The effect of verapamil developed gradually within the first few days in seven subjects in whom serum digoxin concentration reached, within 7 days, 90% of the increase observed 14 days after onset of verapamil. Renal digoxin clearance decreased significantly (26.1 +/- 0.7 vs 55.1 +/- 12.3 ml/min, p less than 0.005) in six patients in whom serum digoxin concentration increased. It did not change in one patient in whom serum digoxin concentration was not influenced by verapamil. Creatine clearance did not change in any of these seven. The same effects on digoxin clearance were observed in three normal subjects. Among the 49 patients, verapamil resulted in the development of signs and symptoms that suggested digitalis toxicity in seven. Verapamil significantly increased serum digoxin concentration. The process is dose-dependent and gradual, and it is at least partially explained by reduced renal excretion without reduction in glomerular filtration. The dose of digoxin may need readjustment in patients who are concomitantly receiving verapamil.

Identification of normal and transposed great arteries by contrast M-echocardiography in the newborn: a combined suprasternal and precordial approach.

Diagnosis of complete transposition of the great arteries (TGA) by M-mode echocardiography depends on the correct identification of the aorta and the pulmonary artery at their roots. We describe a contrast M-mode echocardiographic technique which combines suprasternal and precordial views in which the two great arteries are visualized simultaneously. After venous injection of 1-3 ml 5% dextrose, the sequence and relative intensity of opacification of the great arteries are recorded in both views and then matched to each other. Because in the suprasternal view the aorta is always superior and the pulmonary artery inferior, the characteristics of opacification of these two arteries in the suprasternal view are used as markers for their proper identification in the precordial view. In four normal newborns contrast medium filled only the pulmonary artery. In six newborns with cardiovascular malformations with shunts and normally related great arteries, in which the contrast medium preferentially filled either the aorta (five patients) or the pulmonary artery (one patient), matching the record from the precordial view to that from the suprasteral view proved that the anterior vessel was indeed the pulmonary artery, and the posterior vessel the aorta. In five newborns with d-TGA the contrast medium preferentially filled the aorta, and the combined suprasternal and precordial approach proved that the aorta was anterior and the pulmonary artery posterior. This method is independent of the direction of venous drainage or site of injection.

Mid-systolic click and echocardiographic evidence of mitral valve prolapse during electrical pacing.

A mid-systolic click was present in a patient during three years of follow-up after implantation of a permanent transvenous pacemaker. Echocardiography revealed posterior motion of the anterior leaflet which resembled mitral valve prolapse. Both the click and echocardiographic evidence of prolapse disappeared simultaneously with resumption of sinus rhythm and during supraventricular tachyarrhythmias. Wtih spontaneous change in the position of the electrode three years after initial implantation, both the click and the posterior motion of the mitral valve disappeared. The association of mitral valve prolapse with electrical pacing is most unusual and appears to have a distinct pathophysiological mechanism.

The use of the balloon-tipped floating catheter in temporary transvenous cardiac pacing.

The effectiveness and safety of balloon-tipped, flow guided, electrodes for ventricular pacing as opposed to the fluoroscopy-guided semi-rigid bipolar electrodes have never been compared in a controlled study. A prospective study was therefore undertaken to compare both techniques in semi-elective and emergency procedures. Flow guided electrodes were inserted in 67 patients (group A) and semi-rigid electrodes in 44 patients (group B). The results of group A were judged to be superior to those of group B in four aspects: a) shorter time (6'45" vs. 13'30", p less than 0.0005); b) lower incidence of catheter displacement (13.4 vs. 32.0 percent, p less than 0.05); c) longer interval of time between implantation and catheter displacement (4.4 vs. 1.9 days, p less than 0.0005); d) lower incidence of serious ventricular arrhythmias during insertion (1.5 vs. 20.4 percent, p less than 0.005). Threshold at insertion was not significantly different (0.6 +/- 0.3 vs 0.7 +/- 0.2 milliampere). The superiority of flow-guided electrodes over fluoroscopy-guided electrodes persisted in the comparison of semielective insertions in groups A and B. We conclude that the flow-guided insertion technique is safer, more expeditious and more stable than the fluoroscopy-guided technique in semi-elective as well as in emergency insertions.

Overdrive pacing in quinidine syncope and other long QT-interval syndromes.

Prolongation of QT interval is associated with repetitive paroxysm of a particular ventricular tachycardia. It is a typical complication of quinidine therapy but may occur in various other conditions. We used endocardial pacing in nine patients with prolongation of the QT interval who suffered from bouts of ventricular tachycardia and fibrillation. In six patients, the syndrome was due to quinidine and in three, to prenylamine. Acceleration of heart rate resulted in immediate suppression of all arrhythmias. Pacing was continued until the condition producing the QT prolongation disappeared. In one case, a permanent pacemaker was implanted, as the QT prolongation was congenital and permanent. The absolute QT interval was shortened by overdrive pacing from a mean value of 0.65 s to 0.50 s. The corrected QT interval remained prolonged (about 0.56 s). Thus, the arrhythmia was associated with the duration of the actual QT interval, and overdrive pacing was able to suppress it without shortening the corrected QT interval.