Carboxyhemoglobin (COHB) and the access to oxygen: An example of human counter-evolution

ABSTRACTS

canine conducting system, Wenckebach structures were observed in response to hypoxia, and perfusion with 4x potassium (K) (10.8 mEq/liter), acetylstrophanthidin or nicotine. Initially the block was low grade, with 10 :9 and 8:7 conduction. Continued exposure to altered perfusate resulted in 3:2 and 2:l exit block. Human papillary muscle exposed to hyperkalemic Tyrode solution initially demonstrated 6:5 and 5:4 Wenckebach block from the stimulus artifact to first action potential. Typical Wenckebach structure was also observed in the interelectrode conduction time. However, action potential amplitude, resting potential and maximal rising velocity of phase 0 were only minimally reduced. Continued perfusion with K+ resulted in higher degrees of block (2 :l and 3 :l), terminating in inexcitability at which time normal Tyrode solution was perfused with restoration of 1 :l conduction. It is suggested from these experiments that one of the underlying mechanisms of exit block in specialized conducting and contractile tissue is conduction depression of the Wenckebach structure similar to that seen clinically in the atrioventricular junction.

Prognbsis of Right Bundle Branch Block and Left Anterior Hemiblock: A New Indication for Permanent Pacing JAMES M. ATKINS, MD; STEPHEN J. LESHIN, BLOMQVIST, MD; CHARLES B. MULLINS, MD,

MD.;

GUNNAR

Dallas, Texas

Right bundle branch block with left axis deviation (RBBB-LAD) has recently been recognized as ominous in acute myocardial infarction (AMI). Of 4’7’7patients admitted to a coronary care unit, 26 had RBBB-LAD. Seven patients presented with syncope and RBBB-LAD and had pacemakers inserted. Six survived (follow-up period from 4 months to 3 years) ; 1 died of unrelated problems. Nineteen patients presented with AM1 and RBBBLAD. Three patients (16%) died of failure in the first week. Twelve patients (63%) had complete heart block (CHB) in the first 48 hours ; 1 of these patients died, and 11 were temporarily paced. The pacemakers were removed in 7 of the 11 patients after reversion to sinus rhythm. Eight patients (42%) with AM1 died suddenly and unexpectedly between 2 weeks and 4 months after AMI; 7 of these had transient CHB early, which reverted to sinus rhythm, and 3 of the patients terminally had documented recurrent CHB. Seven of the patients with AMI and RBBB-LAD survived and have been followed up for 1 to 36 months; 4 of the surviving patients (21%) do not have pacemakers ; 3 have permanent pacemakers. Of the 26 patients, 50% died. The mortality was 10% among the patients with permanent pacemakers and 75% in the group without permanent pacemakers; sudden death accounted for 56% of the mortality in the unpaced group. These data suggest that all patients with RBBB:LAD associated with an AM1 or syncope should be paced initially and considered for permanent pacemakers.

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Carboxyhemoglobin (COHB) and the Access to Oxygen: An Example of Human Counter-Evolution STEPHEN M. AYRES, MD, FACC; STANLEY GIANNELLI, MD, FACC; HILTRUD MUELLER, MD, New York, New York

Jr.,

Cigarette smoking and exposure to community air pollution produce COHB saturations between 3 and 15% and decrease both oxygen capacity and the unloading tension of circulating hemoglobin. An individual with 15% COHB has regressed to a hemoglobin which is functionally intermediate between that of an elephant and a newborn goat. Acute studies performed in 26 subjects demonstrated that elevation of COHB 1eveIs to an average of 7.98% increased cardiac output from 5.01 to 5.56 liters/min, increased minute ventilation from 6.86 to 8.64 liters/ min, and decreased arterial and mixed venous oxygen tension from 81 and 39 to 76 and 31 mm Hg, respectively. Myocardial studies performed by coronary sinus catheterization demonstrated that similar elevations of COHB increased coronary blood flow, decreased coronary artery-coronary sinus oxygen content and decreased coronary sinus oxygen tension. The changes were most marked in patients with coronary artery disease or chronic emphysema, lactate extraction decreasing in 10 of 15 patients. The possibility of adaptation was studied by achieving similar COHB concentrations with both a low and high concentration of carbon monoxide. Hemodynamic changes appeared more marked with administration of the high concentration even though COHB was the same. These studies suggest that COHB concentrations between 5 and 10% may produce abnormal myocardial function in certain individuals. The well-known deleterious effect of cigarette smoking on the heart may be explained by the interaction of COHB and nicotine, the latter increasing cardiac work and the former decreasing oxygen availability. (See Addendum.)

A Quantitative Evaluation of Aortography in Aortic Insufficiency WILLIAM A. BAXLEY, MD; DON HUNT, MD; JOHN W. KENNEDY, MD: TERRANCE P. JUDGE, MD; J. E. WILLIAMS, MD; ALBERT0 BARCIA, MD, FACC; HAROLD T. DODGE, MD, FACC, Birmingham, Alabama and Seattle, Washington

To evaluate the usefulness of aortography in assessing the severity of valvular aortic insufficiency, 69 adults with aortic insufficiency underwent aortography and quantitative biplane angiocardiography. Aortic insufficiency, as graded on a +l to +5 scale from the aortogram, correlated significantly but not closely with the calculated regurgitant flows (r = 0.65 ; P 0.55) tended to have greater regurgitant flows for

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