Significance of His and left bundle recordings from the left heart in man

Eight patients were studied by simultaneous intracardiac recordings of the specialized conduction system from left and right heart. Five patients had normal A-V conduction, one had left axis deviation (LAD), and two had bundle-branch block. Bundle of His (BH) and right bundle (RB) recordings from the right heart were obtained and validated as previously described. In addition a bipolar electrode catheter was introduced into the root of the aorta and left ventricle via the right brachial artery. BH and left bundle (LB) electrograms were recorded at the level of the aortic cusps and just below the aortic valve, respectively. BH recordings from both sides could be temporally superimposed and were similar in onset and duration. In patients with normal A-V conduction the duration of these deflections was BH 15 to 20, LB 15, and RB 10 msec. The conduction time from the proximal LB to ventricular (V) activation (LB-V) ranged from 20 to 25 msec. The LB-V and RB-V conduction times from comparable points were similar and support the previous observations that interventricular septal activation occurs almost simultaneously on both sides. In the patient with right bundle-branch block (RBBB) and LAD with a slightly prolonged H-V time (50 msec), the delay was localized distal to the main LB (LB-V = 30 msec). During ectopic "ventricular," probably left bundle rhythm, retrograde activation of the BH was demonstrated. Aberration (RBBB) of the supraventricular impulse resulting from invasion of the RB by the preceding interpolated premature "ventricular" beat is suggested.

Haemodynamic effects of glucagon

The central and peripheral vascular haemodynamic effects of glucagon were studied in 29 patients. With a single dose method of 2 or 5 mg. glucagon intravenously the inotropic action of the drug produced immediate increased myocardial contractility with significant increase in cardiac output and enhanced cardiac performance, and lowering of pulmonary arterial pressure and pulmonary vascular resistance. No primary peripheral vascular effect was evident, and the increased systemic pressure and lowered systemic resistance appear to be secondary to the central action of the drug. With the dosage used there were no undesirable side-effects apart from a feeling of slight nausea. Though the haemodynamic effects are abrupt, reaching their maximum values in the first 10 minutes after injection, they tend to be dissipated within half an hour, presumably due to the very rapid destruction of the drug. Repeated booster doses rather than continuous infusion may be the method of choice to maintain an increased cardiac output. The positive chronotropic action of the drug may cause transient palpitations. Glucagon increased the cardiac output in the acute phase of myocardial infarction by 42 per cent. The haemodynamic effects in chronic rheumatic heart disease are more varied, and it may increase left atrial pressure in mitral stenosis, which is undesirable. Hyperglycaemia results from liver glycogenolysis but blood sugar levels rarely exceeded 200 mg./100 ml. These results warrant further study of the value of glucagon as a positive inotropic agent in low output heart failure, especially in acute myocardial infarction with cardiogenic shock, or after cardiac surgery, or in unrelieved chronic congestive heart failure.