Raymond J. Pietras

The Effects of Cycle Length on Cardiac Refractory Periods in Man

The effects of pacing-induced changes in cycle length on the refractory periods of the atrium, A-V node and His-Purkinje system were studied in 24 patients using the extra stimulus technique. Refractory period determinations were made at two or more cycle lengths in all patients. Slopes relating cycle length and refractory periods were calculated using the least squares method.Both the effective and functional refractory periods (ERP and FRP) of the atrium shortened with decreasing cycle lengths, with a mean slope of +0.155 and +0.129 respectively. A-V nodal ERP lengthened (mean slope, −0.177) while A-V nodal FRP shortened slightly (mean slope, +0.126). Bundle branch refractory periods as well as relative refractory periods of the His-Purkinje system also decreased, with mean slopes of +0.270 and +0.360, respectively. The ERP of the A-V node at any cycle length was related to the A-H at that cycle length (r = +0.646, P < 0.001).The responses of the human heart to changes in cycle length are generally similar to those previously described in the animal laboratory. Such information contributes to our understanding of electrocardiographic phenomena such as aberrant conduction.

Paroxysmal Ventricular Fibrillation in Two Patients with Hypomagnesemia Treatment by Transvenous Pacing

Paroxysmal ventricular fibrillation unassociated with heart block occurred in two patients with hypomagnesemia. In neither patient were other causes of the arrhythmia apparent. Temporary transvenous pacing successfully suppressed the episodes after drug therapy failed. Prolongation of the Q-T interval was a prominent electrocardiographic feature in both patients and is postulated to have resulted from a loss of intracellular potassium secondary to hypomagnesemia.

Demonstration of sustained sinus and atrial re-entry as a mechanism of paroxysmal supraventricular tachycardia.

Electrophysiological studies in five patients with documented (4) or suspected (1) paroxysmal supraventricular tachycardia (PSVT), suggested sinus or atrial re-entrance (SR or AR). Two of the patients had preexcitation, three had evidence of atrial enlargement, and all had organic heart disease. The following observations supported a diagnosis of SR and AR: 1) induction of sustained PSVT with atrial extrastimulus technique allowing definition of an echo zone; 2) induction of sustained PSVT during constant rapid atrial pacing at a rate less than that producing A-V nodal Wenckebach periods, or producing normalization of QRS complex in patients with pre-excitation; 3) P waves preceding each QRS during PSVT with an A-H interval appropriate for the rate of the PSVT; 4) antegrade P wave morphology during PSVT, and normal high to low sequence of right atrial activation (SR), or P wave morphology and atrial activation sequence different from sinus (AR); 5) lack of correlation of PSVT induction with critical A-H interval. The rates of induced sustained PSVT ranged from 114 to 143 beats/min, and were similar to those observed during spontaneous episodes of PSVT in the four patients. PSVT could be terminated with critically timed extra-stimuli or carotid massage. In conclusion, SR and AR appear to be mechanisms of spontaneous PSVT in man. Rates of SR and AR PSVT tend to be relatively slow.

Correlation of Vectorcardiographic Criteria for Myocardial Infarction with Autopsy Findings

One hundred eight patients who had had vectorcardiograms and electrocardiograms recorded were followed to autopsy, and their hearts were carefully studied postmortem. Vectorcardiographic criteria previously proposed using the Frank corrected lead system were tested against the anatomic findings. These criteria correctly predicted the presence of infarction in 49 (92%) of 53 hearts and correctly localized the infarct in 39 (74%). In four hearts (8%) infarction could not be identified. In 18 (32%) of 55 hearts in which infarcts were not present, these criteria falsely indicated infarction. The reasons for the false positive predictions are discussed. The criteria tested will prove useful in the diagnoses and localizations of myocardial infarcts when the pitfalls of deformities of the vectorcardiogram produced by ventricular hypertrophy and bundle-branch block are avoided.

Hypovolemia in Shock Due to Acute Myocardial Infarction

Twelve patients with the clinical features of shock following acute myocardial infarction were treated with low molecular weight dextran (LMWD) as a plasma volume expander. Two of the patients had elevated central venous pressures (CVP), and neither responded favorably to plasma volume expansion. The remaining 10 patients had CVPs under 7 mm Hg prior to dextran infusion; five survived. Each survivor responded favorably to dextran infusion manifested by an increase in arterial pressure and cardiac index. The average increase in CVP in these patients was 1.0 mm Hg per 100 ml of dextran infused. The other five patients died either without recovering from shock or in chronic cardiac failure. These patients failed to show a significant increase in arterial pressure or cardiac index after dextran infusion; CVP increased by an average of 1.9 mm Hg per 100 ml infused. Hypovolemia must be considered in all patients in whom clinical evidence of shock develops as a complication of acute myocardial infarction, and if the CVP is normal or low, plasma volume expansion should be undertaken with caution. Increase in arterial pressure and evidence of improved cardiac index with little rise in CVP indicate a good response to the infusion and excellent prognosis for survival.

Sites of Conduction Disease in Aortic Stenosis: Significance of Valve Gradient and Calcification

Electrophysiologic studies were done in 32 patients with aortic stenosis. In 24 patients with intact A-V conduction, A-H intervals ranged from 55 to 145 msec and were prolonged in two. Two had split His bundle potentials. The H-V intervals ranged from 25 to 94 msec and were prolonged in 12. The mean H-V interval was 63 +/- 2.6 msec in 12 patients with calcific aortic stenosis compared with 50 +/- 4.9 msec in 12 without calcification (P less than 0.05). The mean H-V in 10 patients with aortic gradients greater than 40 mm Hg was 62 +/- 5.6 msec compared with 47 +/- 3.1 msec in nine with gradients less than 40 (P less than 0.05). In patients with aortic stenosis and A-V block, the site of the block was distal to the His bundle in three and within the His bundle in five. All eight had calcified valves. Aortic stenosis was commonly associated with latent and manifest conduction disease in the His bundle and the trifascicular conduction system. Conduction disease was more extensive with calcified valves and greater valve obstruction.

Assessment of left ventricular function by radionuclide angiography during induced supraventricular tachycardia

Electrocardiographically synchronized radionuclide angiography was performed before, during and after induced paroxysmal supraventricular tachycardia in 13 patients. Data were acquired with a computer-interfaced Anger camera in a left anterior oblique projection. No data were acquired during tachycardia until tachycardia had been sustained for 1 minute. Patients ranged in age from 20 to 64 years (mean +/- standard deviation 42 +/- 14.5). Three patients had organic heart disease and 10 did not. Baseline and tachycardia heart rates (beats/min) were 59 to 99 (73 +/- 11) versus 141 to 228 (157 +/- 22). Baseline and tachycardia left ventricular measurements (mean +/- standard error) were as follows: ejection fraction 64 +/- 2 versus 62 +/- 4 percent (not significant), ejection rate 3.0 +/- 0.1 versus 4.3 +/- 0.4 mean ventricular counts/s (p less than 0.001), normalized end-diastolic counts 72.7 +/- 7.8 versus 48.7 +/- 6.7 X 10(3) counts (p less than 0.001), normalized stroke counts 37.1 +/- 3.4 versus 23.3 +/- 2.7 X 10(3) counts (p less than 0.001) and normalized count cardiac output 2,717.5 +/- 273.0 versus 3,620.2 +/- 403.7 X 10(3) counts/min (p less than 0.005). Although ejection fraction for the whole group did not change significantly, it decreased during tachycardia by 5 percentage points or more in five patients. These were the three patients with heart disease and the two normal patients with the fastest heart rate during tachycardia (228 and 214 beats/min, respectively). In summary, paroxysmal supraventricular tachycardia was characterized by a marked decrease in left ventricular end-diastolic and stroke volumes but increased ejection rate and cardiac output without significant change in ejection fraction. Heart disease or rapid heart rate during tachycardia appeared to have a deleterious effect on ejection fraction.

Hemodynamic measurements in a coronary care unit.

H YPOTENSION, shock, congestive heart failure or any other manifestation of present or impending circulatory collapse in a patient with acute myocardial infarction is indication for hemodynamie monitoring of his cardiovascular system. The measurements to be made include central venous pressure, intra-arterial pressure, cardiac output and central temperature. Such monitoring will soon assume importance equal to electrocardiographic monitoring of patients developing arrhythmias in this disease. Such measurements can be made clinically and should be available in most community hospitals when sufficient personnel are trained. Other measurements of value and available include arterial blood gases, pH, lactic acid and pyruvie acid. The potency of modem therapeutic agents and the impending development of mechanical circulatory assistance make necessary the perfection of routines for application of hemodynamic monitoring methods to patients with acute myocardial infarction. Although on-line computer analysis and correlation of data plus use of transponders to alter therapy may be an ultimate goal of developing more sophisticated methods for measurements of hemodynamic events in a coronary care unit, 1-s present methods provide information which may be crucial for patient care. It is our purpose to discuss the experience of our shock unit with such hemodynamic measurements in patients with acute myocardial infarction and in patients referred because they were thought to have myocardial infarction.

Comparative angiographic right and left ventricular volumes

Comparative angiographic right and left ventricular volumes and right and left ventricular ejection fractions have been reported in the same normal infants and children. This relationship was assessed in adult patients to determine if these pediatric observations persist in later life. Seventeen adults, who had both right and left ventricular angiograms and who had no demonstrable organic heart disease, were studied. Right ventricular end-diastolic volume ranged from 54 to 98 (76 +/- 14, mean +/- SD) cc/m2 and left ventricular end-diastolic volume ranged from 48 to 90 (70 +/- 12) cc/m2; p less than 0.03. Right ventricular end-systolic volume ranged from 22 to 47 (33 +/- 8.0) cc/m2 and left ventricular end-systolic volume ranged from 13 to 34 (22 +/- 5.3) cc/m2; p less than 0.00005. Calculated right ventricular stroke volume ranged from 31 to 60 (43 +/- 8.3) cc/m2 and left ventricular stroke volume ranged from 29 to 70 (48 +/- 11) cc/m2; p = NS. Calculated right ventricular ejection fraction ranged from 0.48 to 0.62 (0.57 +/- 0.04) and the left ventricular ejection fraction ranged from 0.57 to 0.84 (0.68 +/- 0.07; p less than 0.00005. Both right ventricular end-systolic and end-diastolic volumes were greater than left ventricular end-systolic and end-diastolic volumes. This resulted in decreased right ventricular ejection fraction compared to left ventricular ejection fraction. The difference between the two ventricles may be due to compliance, muscle mass, and anatomic configuration with a net result of one chamber more completely emptying than the other. Thus it appears that the relationships between right and left ventricular volumes noted in infancy and childhood persist in adult life.

Equilibrium Radionuclide Gated Angiography in Patients With Tricuspid Regurgitation

Equilibrium gated radionuclide angiography was performed in 2 control groups (15 patients with no organic heart disease and 24 patients with organic heart disease but without right- or left-sided valvular regurgitation) and in 9 patients with clinical tricuspid regurgitation. The regurgitant index, or ratio of left to right ventricular stroke counts, was significantly lower in patients with tricuspid regurgitation than in either control group (range and mean +/- standard error of the mean 0.4 to 1.0, 0.7 +/- 0.1 versus 1.0 to 1.5, 1.3 +/- 0.1 and 1.0 to 2.9, 1.5 +/- 0.1, respectively, p less than 0.001). Time-activity variation over the liver was used to compute a hepatic expansion fraction which was significantly higher in patients with tricuspid regurgitation than in either control group (1.4 to 11.4, 5.8 +/- 1.0% versus 0.6 to 3.4, 1.9 +/- 0.3% and 1.0 to 5.1, 2.3 +/- 0.2%, respectively, p less than 0.001). Fourier analysis of time-activity variation in each pixel was used to generate amplitude and phase images. Only pixels with values for amplitude at least 7% of the maximum in the image were retained in the final display. All patients with tricuspid regurgitation had greater than 100 pixels over the liver automatically retained by the computer. These pixels were of phase comparable to that of the right atrium and approximately 180 degrees out of phase with the right ventricle. In contrast, no patient with no organic heart disease and only 1 of 24 patients with organic heart disease had any pixels retained by the computer. In conclusion, patients with tricuspid regurgitation were characterized on equilibrium gated angiography by an abnormally low regurgitant index (7 of 9 patients) reflecting increased right ventricular stroke volume, increased hepatic expansion fraction (7 of 9 patients), and increased amplitude of count variation over the liver in phase with the right atrium (9 of 9 patients).