The hemodynamic effects of paroxysmal supraventricular tachycardia in patients with the Wolff-Parkinson-White syndrome∗

Cardiovascular responses to hot skin at rest and during exercise

Integrative cardiovascular responses to heat stress during endurance exercise depend on various variables, such as thermal stress and exercise intensity. This review addresses how increases in skin temperature alter and challenge the integrative cardiovascular system during upright submaximal endurance exercise, especially when skin is hot (i.e. >38°C). Current evidence suggests that exercise intensity plays a significant role in cardiovascular responses to hot skin during exercise. At rest and during mild intensity exercise, hot skin increases skin blood flow and abolishes cutaneous venous tone, which causes blood pooling in the skin while having little impact on stroke volume and thus cardiac output is increased with an increase in heart rate. When the heart rate is at relatively low levels, small increases in heart rate, skin blood flow, and cutaneous venous volume do not compromise stroke volume, so cardiac output can increase to fulfill the demands for maintaining blood pressure, heat dissipation, and the exercising muscle. On the contrary, during more intense exercise, hot skin does not abolish exercise-induced cutaneous venoconstriction possibly due to high sympathetic nerve activities; thus, it does not cause blood pooling in the skin. However, hot skin reduces stroke volume, which is associated with a decrease in ventricular filling time caused by an increase in heart rate. When the heart rate is high during moderate or intense exercise, even a slight reduction in ventricular filling time lowers stroke volume. Cardiac output is therefore not elevated when skin is hot during moderate intensity exercise.

Pacing site in pacemaker dependency: is right ventricular septal lead position the answer?

The right ventricular apex has been the traditional site for lead placement in patients with atrioventricular block. Pacing at the right ventricular apex may have long-term deleterious effects on left ventricular (LV) function, promoting heart failure and increasing mortality. Pacing at the right ventricular septum has been proposed to minimize deterioration in LV function. Although experimental data suggest that septal pacing protects LV function, clinical studies have provided conflicting results. A recent large study in patients with heart block did not show a protective effect with septal pacing. Other pacing approaches are becoming increasingly relevant; however, prediction of what method should be employed in which patient is not currently possible. Other factors such as baseline LV function and associated co-morbidities impact LV function, irrespective of pacing site. Continued monitoring of cardiac function post-implant is therefore critical to ongoing care. An algorithm for managing patients with atrioventricular block is proposed.

Both diastolic and systolic function alternate in pulsus alternans: a case report and review

Pulsus alternans is occasionally seen in the setting of heart failure. This case describes a patient with both these findings, and alternating diastolic and systolic left ventricular function on color Doppler and Doppler tissue imaging.

Reversibility of left ventricular dysfunction after successful catheter ablation of supraventricular reentrant tachycardia

Fourteen patients (mean age, 48 +/- 19 years) with left ventricular dysfunction in the absence of underlying organic heart disease underwent catheter ablation (nine with direct-current energy and five with radiofrequency energy) to treat drug-refractory, symptomatic supraventricular reentrant tachycardia (mean duration of tachycardia, 22 +/- 17 years). Clinical tachycardias were accessory pathway-mediated tachyarrhythmia (12 patients) and atrioventricular nodal reentrant tachycardia (two patients). Changes of ventricular function after successful ablation, as assessed by radionuclide ventriculography and echocardiography, showed a decrease in left ventricular end-systolic dimension (39 +/- 6 mm to 34 +/- 6 mm; 32 +/- 6 mm; p < 0.05) and in left ventricular end-diastolic dimension (55 +/- 5 mm to 52 +/- 3 mm; 51 +/- 3 mm; p < 0.05) in the early (2 to 3 months) and late (6 to 8 months) follow-up periods, increase of nuclear ejection fraction (38% +/- 8% to 46% +/- 7%; p < 0.05) and fractional shortening (28% +/- 7% to 36% +/- 8%; p < 0.05) in the late follow-up period. Increase of fractional shortening was mainly due to decrease in the end-systolic dimension. These findings suggest that prolonged attacks of uncontrolled supraventricular tachycardia may result in left ventricular dysfunction, which is reversible after successful catheter ablation of the arrhythmias.

The release mechanism for atrial natriuretic factor during blood volume expansion and tachycardia in dogs

Atrial natriuretic factor (ANF) is released during blood volume expansion and tachycardia, but only blood volume expansion causes atrial distension, which presumably promotes ANF release. Our study was undertaken to search for a common release mechanism. In five anaesthetized, closed-chest dogs, plasma immunoreactive (IR) ANF was measured at three levels of blood volume, which were obtained by infusing a Ringer's solution. At each level of blood volume, plasma IR-ANF was measured at three pacing frequencies. Plasma IR-ANF increased as mean right atrial pressure (mRAP) was raised from 2 to 10 mmHg by volume expansion, whereas pacing tachycardia (at heart rates (HR) 50 +/- 3 and 98 +/- 1 beats min-1 above control) at each level of blood volume expansion increased plasma IR-ANF and systolic RAP (sRAP) at constant mRAP. Plasma IR-ANF was more strongly correlated to sRAP (r = 0.83) than to mRAP (r = 0.69), but the product sRAP x HR had the highest correlation coefficient (r = 0.86). According to the multiple regression equation: plasma IR-ANF = k1 + k2mRAP + k3sRAP + k4sRAP x HR, the product sRAP x HR had the highest coefficient of determination (r2 = 0.75) and was the only significant determinant. We conclude that atrial tension or stress, developing during each atrial systole, is an important determinant of ANF release. Since atrial diastolic and systolic dimensions do not increase during pacing tachycardia, ANF release is not dependent on atrial distension.

Pulsus alternans induced by inferior vena caval occlusion in man

To assess the effect of rapid preload reduction on left ventricular performance in nonischemic cardiomyopathy, 11 patients were studied during inferior vena caval (IVC) balloon occlusion. Five developed sustained pulsus alternans. During pulsus alternans, the strong beats demonstrated systolic performance characteristics similar to baseline values, despite a drop in both left ventricular (LV) end-diastolic diameter (66 +/- 13 to 61 +/- 13 mm; p less than 0.05) and LV end-diastolic pressure (21 +/- 8 to 9 +/- 6 mmHg; p less than 0.05). In contrast, the weak beats demonstrated a reduction in peak systolic pressure (130 +/- 36 to 109 +/- 33 mmHg; p less than 0.02), fractional shortening (20% +/- 4% to 17% +/- 9%; p less than 0.05) and peak positive dP/dt (1,006 +/- 224 to 921 +/- 287 mmHg; p less than 0.05). Measures of diastolic performance (peak negative dP/dt, the time constant of LV relaxation, the length of diastasis, and LV end-diastolic stress) were not different between baseline beats and the strong beats; and only LV end-diastolic stress differed when baseline beats were compared to the weak beats. When the strong beats were compared to the weak beats during induced pulsus alternans, significant differences were observed in peak systolic pressure, peak positive dP/dt, and fractional shortening, but no differences in any measured diastolic parameter was observed. A slight difference was noted in the left ventricular end-diastolic diameters, with the weak beat consistently beginning at a slightly smaller diameter (61 +/- 13; mm vs 59 +/- 13; p less than 0.05). In summary, these data are consistent with an augmentation and deletion of intrinsic contractile forces in association with an alternation in preload on a beat-to-beat basis as best describing left ventricular performance during pulsus alternans.

Failure of episodic high-dose oral verapamil therapy to convert supraventricular tachycardia: a study of plasma verapamil levels and gastric motility

The practicality of administering large oral doses of verapamil tablets to terminate supraventricular tachycardia (SVT) was investigated in 10 patients. A pilot study in four patients showed that unexpectedly low plasma levels (less than 40 ng/ml) were obtained 60 minutes after administering 160 mg or 240 mg of verapamil during SVT. Nuclear studies in the six other patients showed that fractional liquid gastric emptying times (T) were significantly prolonged in SVT compared to sinus rhythm (SR), p less than 0.05 from T 1/3 onward. Further verapamil absorption studies (200 to 360 mg) performed during SVT and SR in five of six patients showed that peak verapamil levels in four patients in SVT were 23% to 71% lower than in sinus rhythm, where they had peaked at greater than 250 ng/ml 60 minutes post verapamil ingestion, and areas under the plasma concentration time curves were 26% to 100% (mean 67%) less in SVT than in SR for all five patients. SVT was terminated by verapamil in one patient after 40 minutes and the rate of SVT was slowed after 90 minutes in two other patients. Thus plasma verapamil levels are considerably reduced during SVT as compared to SR, and changes in gastric emptying are likely a contributing cause. Since SVT was converted to sinus rhythm in only 1 of 10 patients within 1 hour, large oral doses of verapamil tablets appear unsatisfactory for the episodic treatment of SVT.

Tachycardia-induced cardiomyopathy: a reversible form of left ventricular dysfunction

Eight patients, aged 5 to 57 years, with uncontrolled symptomatic tachycardia for 2.5 to 41 years (mean 15) and significant left ventricular (LV) dysfunction in the absence of any other apparent underlying cardiac disease underwent evaluation. Incessant tachycardia was present for 0.5 to 6.0 years (mean 2.1) in 7 patients. One patient had an ectopic atrial tachycardia and 7 patients had an accessory atrioventricular pathway that participated in reciprocating tachycardia. Six patients underwent surgery; the ectopic focus was ablated in 1 patient and an accessory pathway was divided in 5 patients. One patient underwent open ablation of the His bundle and 1 patient underwent closed-chest ablation of the atrioventricular conduction system. Myocardial biopsy specimens were obtained from 5 patients, none of which yielded a specific diagnosis. Pretreatment radionuclide angiography demonstrated a mean ejection fraction (EF) of 19 +/- 9% (range 10 to 35%). Following tachycardia control a marked improvement in LV function was noted in 6 of 8 patients at rest and in 1 additional patient during exercise. The EF increased to 33 +/- 17% (range 16 to 56%) an average of 8 days after treatment and to 45 +/- 15% (range 22 to 67%) at late follow-up 3.5 +/- 40 months (mean 17) later (p less than 0.005). Seven patients remain asymptomatic 11 to 40 months (mean 22) after the corrective procedure and have resumed normal activities. These findings suggest that chronic uncontrolled tachycardia may result in significant LV dysfunction, which is reversible in some cases after control of the arrhythmia.

Studies on left ventricular function during sustained ventricular tachycardia

The acute effects of rapid ventricular pacing and sustained ventricular tachycardia on left ventricular function were examined in patients with recurrent sustained ventricular tachycardia. Programmed electrical stimulation and left ventricular hemodynamic measurements were performed in 20 patients (19 men and 1 woman), with an age range of 49 to 79 years (mean 63 +/- 9). Indexes of left ventricular function that were analyzed included left ventricular peak systolic pressure, end-diastolic pressure, first derivative of peak left ventricular pressure (dP/dt) and negative left ventricular dP/dt. Measurements were obtained during sinus rhythm, after paced premature ventricular depolarizations, during rapid ventricular pacing (cycle lengths 600 to 250 ms) and immediately after induction of sustained ventricular tachycardia. Mean left ventricular peak systolic blood pressure was 123 +/- 19 mm Hg during sinus rhythm, decreased to 77 +/- 23 mm Hg (p less than 0.05) at the induction of ventricular tachycardia and remained decreased during arrhythmia (p less than 0.01). Mean left ventricular end-diastolic pressure was 22 +/- 5 mm Hg during sinus rhythm, did not change after arrhythmia induction (22 +/- 9 mm Hg, p greater than 0.2) and remained unchanged during sustained ventricular tachycardia (p greater than 0.2). Mean peak left ventricular dP/dt was 1,400 +/- 620 mm Hg/s in sinus rhythm, decreased to 810 +/- 580 mm Hg/s (p less than 0.05) at ventricular tachycardia induction and remained decreased during sustained ventricular tachycardia (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Two-dimensional echocardiographic studies during sustained ventricular tachycardia

We evaluated left ventricular function in patients with recurrent sustained ventricular tachycardia (VT) using two-dimensional echocardiography (2DE). Thirteen patients, 11 men and 2 women, age range 42-77 (mean 62 +/- 12) years were studied in sinus rhythm (SR) and immediately after VT induction. 2DE parameters analyzed included wall motion, mitral valve leaflet motion, and ejection fraction (EF). In SR, 21 segments/walls in 12 patients showed wall motion abnormalities (WMA) ranging from hypokinesis to dyskinesis and one patient had generalized LV hypokinesis. In VT, new WMA were noted in 2 patients. Thirteen segments/walls in 8 patients showed further worsening of pre-existing WMA. In 1 patient there was worsening of generalized LV hypokinesis. Three patients showed apparent improvement in pre-existing WMA during VT. In 2 patients large apical aneurysms showed a reduction of dyskinesis in VT. Mitral valve opening was intermittent in patients with shorter VT cycle lengths and was maximal when atrial systole preceded or coincided with ventricular depolarization. Doppler echocardiography in 1 patient confirmed the pattern of intermittent mitral flow, with greatest flow occurring when mitral valve opening occurred well before the QRS peak. In 5 patients, 2DE permitted EF measurements. EF in SR ranged from 24-56% (mean 36 +/- 13), decreased to 6-33% (mean 21 +/- 11) within the first ten beats of VT and 6-25% (mean 19 +/- 8) after twenty beats of VT. EF decreased more in patients with shorter VT cycles as compared to those with longer VT cycle lengths.(ABSTRACT TRUNCATED AT 250 WORDS)

The hemodynamic consequences of cardiac arrhythmias: evaluation of the relative roles of abnormal atrioventricular sequencing, irregularity of ventricular rhythm and atrial fibrillation in a canine model

To evaluate the hemodynamic consequences of various cardiac arrhythmias, hemodynamic and angiographic studies were performed on 20 open-chest, atrioventricular (AV) heart-blocked dogs during various programmed pacing protocols. Protocols included AV pacing at intervals of 100 msec and -100 msec, ventricular (V) pacing during AV dissociation, and V pacing during atrial fibrillation (AF). In addition, the effects of regular versus irregular V pacing were also evaluated. During regular V pacing, cardiac output was optimal at an AV interval of 100 msec, but decreased by 25% at AV -100 msec and by 18% during both AV dissociation and AF. During irregular V cycles, cardiac output decreased further (e.g., by an additional 7% during AF). Pulmonary venous regurgitation was observed only during AV dissociation and during regular pacing at AV -100 msec. Notably, mitral valvular regurgitation was observed only during irregular V cycles, but not during regular V pacing, even in the presence of AV dissociation or AF. Using these methods it was possible to resolve some previously reported controversies regarding the relative importance of AV sequencing, atrial systole versus AF, regular versus irregular rhythms, as well as the possible contribution of mitral and/or pulmonary venous regurgitation to the adverse hemodynamics of various cardiac arrhythmias.

Reevaluation of the role of atrial systole to cardiac hemodynamics: evidence for pulmonary venous regurgitation during abnormal atrioventricular sequencing

Twenty open-chest dogs with experimental AV heart block were evaluated hemodynamically, angiographically, and by M-mode echocardiography to further elucidate mechanisms whereby abnormal AV sequencing results in decreased cardiac hemodynamics. During fixed-rate AV pacing, there was a consistent decrease in cardiac output, left ventricular and aortic pressures, and left ventricular dimensions with an increase in left atrial pressure as the AV interval was decreased from 100 to 0 msec, and there were further changes when the AV interval was set at -50 and -100 msec. The hemodynamic consequences of atrial fibrillation with regular ventricular rhythms were similar to the effects of an AV interval of 0 msec. It is important to note that retrograde blood flow into the pulmonary venous system (pulmonary venous regurgitation) was demonstrated by left atrial angiography at AV intervals of both -50 and -100 msec. However, left ventricular angiography failed to reveal mitral regurgitation during fixed-rate pacing at any AV interval or during atrial fibrillation with regular ventricular rates. Thus, during tachyarrhythmias characterized by abnormal AV sequencing, not only is there the loss of active atrial contribution to ventricular filling but there is also evidence for a retrograde or "negative atrial kick" further compromising cardiac hemodynamics.

Reflex mechanisms responsible for early spontaneous termination of paroxysmal supraventricular tachycardia

The incidence and possible mechanism of early spontaneous termination of paroxysmal supraventricular tachycardia was studied in 20 consecutive patients. Episodes of induced tachycardia that terminated spontaneously within the 1st minute after initiation were included. Tachycardias ending spontaneously were associated with a reproducible course of hypotension at the onset followed by blood pressure recovery above control levels and termination. Spontaneous termination of tachycardias occurred within the A-V node 18 to 45 seconds (mean +/- standard error of the mean 27.9 +/- 5.3) after their onset. In the supine position (0 degrees) 9 (45 percent) of 20 patients showed spontaneous termination in 36 (16 percent) of 219 episodes of tachycardia. In the head-dependent position (-20 degrees) only 1 (8 percent) of 13 patients manifested spontaneous termination in 2 (4 percent) of 54 episodes. In the head up position (+60 degrees) only 1 (6 percent) of 18 patients exhibited termination in 2 (2 percent) of 102 episodes. After partial cholinergic blockade with intravenous hyoscine butylbromide, 20 mg, or atropine, 0.6 mg, none of five patients showed spontaneous termination in 25 episodes. After beta adrenergic blockade with 10 mg of propranolol intravenously, none of 16 patients showed spontaneous termination in 87 episodes of tachycardia. We conclude that the initial hypotension during tachycardia evokes a sympathetic response that increases blood pressure and this increase in turn causes a rise in vagal tone that breaks the tachycardia.

Myocardial dysfunction during paroxysmal supraventricular tachycardia

Paroxysmal supraventricular tachycardia (PSVT) is associated with altered hemodynamics. We describe the echocardiographic features of myocardial dysfunction during a prolonged episode of PSVT in an 11-year-old male. The abnormality of the phases of cardiac activity presented as a markedly prolonged left ventricular systole (320 msec) and isovolumic relaxation phase (220 msec) and a shortened and delayed diastolic filling period (140 msec). These abnormalities reverted to normal immediately after spontaneous conversion to sinus rhythm. Propranolol, which was used to prevent PSVT in this child, may have been involved in the mechanism of the altered mechanical events.

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.

Arrhythmogenic epilepsy: an hypothesis

This report describes a clinical syndrome of arrhythmias that may have neural origin. Two patients presented with episodes of loss of consciousness, disorientation, and paroxysmal supraventricular tachycardia (PSVT). One patient reported experiencing neurologic symptoms without tachycardia. When electrophysiologic testing with intracardiac recordings and programmed stimulation yielded no abnormalities that could account for the arrhythmias, a primary neurologic abnormality was sought. The electroencephalograms of both patients showed epileptiform discharges that supported this hypothesis. Arrhythmias and neurologic symptoms were controlled by treatment with the antiepileptic drug carbamazepine in one patient. Findings in these two patients suggest that in some patients arrhythmias may be a manifestation of seizures.

The hemodynamic effects of induced supraventricular tachycardia in man

The circulatory effects of supraventricular tachycardia (SVT) were studied in eight patients who reported disabling symptoms during paroxysms of the arrhythmia. Supraventricular tachycardia was induced in each patient by rapid atrial pacing or with atrial premature stimuli. Hemodynamic parameters in sinus rhythm and following the initiation of SVT were recorded and compared. The following mean values were observed in sinus rhythm (SR) and SVT. Heart rate (beats/min): SR 79, SVT 183; P-R interval (msec): during SR, 154; during SVT, 256; ratio of mean P-R intervals to mean R-R cycl lengths: SR 20%, SVT 76%; brachial artery pressures (mmHg): SR 141, SVT 99; cardiac index (L/min/m2): SR 3.6, SVT 2.2; pulmonary artery pressures (mmHg): SR 18/7, SVT 26/15; peak right atrial pressures (mm Hg): SR 4, SVT 17. Large waves appeared in the right atrium during SVT due to atrial contraction against closed tricuspid valves. Pulsus alternans were observed in each case during SVT. Despite the presence of chest pain during SVT, the coronary arteries were normally patent in four patients who underwent coronary arteriography.

Pulmonary arterial pulsus alternans secondary to primary pulmonary hypertension

Pulsus alternans of the pulmonary artery without systemic pulsus alternans is uncommon and is associated with multiple diseases. Two cases of pulmonary hypertension with pulmonary arterial pulsus alternans and right-sided heart failure are described. Primary pulmonary hypertension was demonstrated at autopsy in both cases. These two case reports constitute another previously unreported cause for pulsus alternans in the pulmonary circuit.

Systemic embolism in chronic sinoatrial disorder

We attempted to estimate the prevalence of systemic embolism in patients with chronic sino-atrial disorder. In a group of 100 patients, evidence of embolism was found in 16, of whom 15 had the bradycardia-tachycardia syndrome. In 712 controls with chronic complete heart block, who were matched for age and sex, embolism had occurred in only 1.3 per cent (P less than 0.001). A second group of 41 patients with chronic ventricular bradycardia and atrial flutter or fibrillation had an embolic prevalence of 7.3 per cent, which was also greater than that in the controls (P less than 0.05). All patients with sinoatrial disorder in whom systemic embolism developed were over 54 years of age; multiple episodes occurred in six. The risk of embolization remains even if the bradycardia-tachycardia syndrome is replaced by stable atrial fibrillation. Impaired atrial function appears to be a key factor in predisposing to intracardiac thrombosis, and paroxysmal supraventricular tachycardia increases the risk of subsequent embolization.

Hemodynamic consequences of cardiac dysrhythmias

To understand the hemodynamic changes produced by arrhythmias is to understand cardiovascular physiology. The changes in rate are accompanied by changes in contractility, receptor stimulation, peripheral vascular response, and flow to other vital organs. In addition, one must keep in mind the underlying pathology of the cardiovascular system. As a therapeutic program is initiated and adjusted, it must be done in accordance with the changes produced in the hemodynamics as well as the rhythm.

Role of mineralocorticoids in the natriuresis of water immersion in man

The role of aldosterone suppression in mediating the natriuresis of water immersion was assessed in six normal male subjects. All subjects were studied on four occasions while they were in balance on a diet containing 150 mEq of sodium and 100 mEq of potassium daily: during a control period, following deoxycorticosterone acetate (DOCA) treatment for 24 hours (Cont + DOCA), during water immersion to the neck (immersion), and during water immersion following DOCA treatment (Imm + DOCA). Immersion resulted in highly significant increases in the rates of sodium and potassium excretion compared with control beginning in the first hour. Although treatment with DOCA decreased the natriuresis of immersion ( P < 0.01), the rate of sodium excretion was still three- to fourfold greater during Imm + DOCA than it was during the comparable Cont + DOCA periods ( P < 0.01). Cessation of water immersion resulted in a marked decrease in urine flow and free water clearance occurring within the initial 30 minutes of recovery ( P < 0.005). Although the rate of sodium excretion also decreased following cessation of immersion, it continued to exceed both preimmersion values ( P < 0.01) and the comparable control values throughout the recovery hour ( P < 0.01). These observations suggest that the natriuresis of immersion cannot be completely accounted for by immersion-induced suppression of aldosterone. The continuing natriuresis occurring despite the progressive volume contraction induced by immersion suggests that the natriuretic stimulus is sufficiently potent to override the compensatory mechanisms which are known to participate in defense of volume homeostasis. Furthermore, the delay in the disappearance of the natriuresis suggests that a humoral factor rather than more rapidly acting hemodynamic and neural mechanisms may mediate the natriuresis.

Hemodynamic sequelae of cardiac arrhythmias

The hemodynamic consequences of cardiac arrhythmias depend on various factors, including the ventricular rate and the duration of the abnormal rate, the temporal relationship between atrial and ventricular activity, the sequence of ventricular activation, the functional state of the heart, the irregularity of the cycle length, associated drug therapy, the peripheral vascular vasomotor system, disease in organ systems other than the heart, and the degree of anxiety caused by the disease processes. Sinus bradycardia, even with rates as low as 40 beats/min, may not be associated with significant hemodynamic consequences unless the stroke volume is limited by myocardial or valvular disease, as in acute myocardial infarction. Cardiac output usually, but not invariably, falls when atrial fibrillation replaces normal sinus rhythm, even at comparable ventricular rates, both at rest and during exercise. Similar observations have been made during the development of atrial flutter despite the persistence of effective mechanical atrial activity in at least some cases. Marked hemodynamic changes are frequent in the course of ventricular tachycardia with systemic arterial hypotension, a decrease in cardiac output, and evidence of cerebral, coronary, and renal vascular insufficiency. Cyclic variations in systemic and pulmonary arterial pressures are common during atrioventricular dissociation. Cardiac output is generally depressed during the severe bradycardia of acquired complete heart block with evidence of atrioventricular valvular insufficiency. Increase of the heart rate by ventricular pacing reverses all or some of these abnormalities. The changes in congenital complete heart block are considerably less severe because myocardial insufficiency is less frequently seen in congenital complete heart block.

Haemodynamic changes during paroxysmal tachycardia in a patient with Wolff-Parkinson-White syndrome

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The Wolff-Parkinson-White syndrome: problems in evaluation and surgical therapy

Two patients with WPW syndrome underwent surgery to ablate accessory conduction pathways. Endocardial and epicardial mapping in both patients had indicated an area of early right ventricular depolarization. Surgical transection of the areas of early depolarization failed in both cases to normalize the electrocardiogram. In the first patient, additional resection in the area of the A-V node failed to produce heart block and the ECG remained abnormal. However, the paroxysmal tachycardia ceased, and she has remained asymptomatic and active 12 months after surgery. In the second patient, as the A-V node was about to be sectioned, pressure and procaine near the A-V node caused the ECG to normalize transiently and after resection permanently. Microscopic study of this tissue showed "P cells." Postoperatively the patient demonstrated normal A-V nodal function. He was discharged with a normal ECG but expired soon after discharge. Postmortem examination of the heart demonstrated the A-V node and bundle of His plus the location of the resection adjacent to the bundle of His. These two cases illustrate disparities between electrophysiologic mapping and actual site of the accessory conduction pathway. In one of the cases an accessory bundle was demonstrated histologically.

Control of recurrent tachycardia of Wolff-Parkinson-White syndrome by surgical ligature of the A-V bundle

In a patient with WPW, type A, pharmacological therapy and radioactive iodine failed to control the disabling, life-threatening arrhythmia. Surgical ligation of the A-V bundle was undertaken in view of the rapidly deteriorating clinical course. Failure to identify A-V block after several sutures were placed in the A-V junction and subsequent activation of the ventricles in a heart with known A-V block demonstrates that the accessory A-V bundles may completely activate the ventricles. Complete elimination of the recurrent tachycardias after A-V ligation suggests that the normal A-V transmission system may be a crucial link in the circus pathway of WPW tachycardia.

Paradoxical use of a demand pacemaker in treatment of supraventricular tachycardia due to the Wolff-Parkinson-White syndrome. Observation on termination of reciprocal rhythm

This paper describes a new technique for terminating attacks of supraventricular tachycardia in a patient with Wolff-Parkinson-White syndrome by using a demand pacemaker. The circuitry of this demand pacemaker generator is designed so that a magnet held near the generator converts the unit from demand to fixed mode at a pre-set discharge rate of 72/min. During an attack of tachycardia, a magnet held near the generator pocket activates a fixed rate discharge and produces competitive pacing. Retrograde atrial depolarization occurs with resultant reversion to sinus rhythm.

Mechanisms of pulsus alternans

The mechanisms of pulsus alternans were studied in three patients by cineangiographic determinations of left ventricular volume. In two patients with left ventricular disease, pulsus alternans occurred without detectable variation in left ventricular enddiastolic pressure (LVEDP) or end-diastolic volume (EDV), although in the second case these values did alternate in the initial postextrasystolic beats. Another patient with normal left ventricular function had brief postextrasystolic pulsus alternans associated with LVEDV alternations. Twenty-nine patients with valvular aortic stenosis who showed pulsus alternans during left heart catheterization were also studied. Persistent alternation in LVEDP occurred in eight, with transient LVEDP alternation appearing after extrasystoles in 22 cases. Cardiac cycle length and diastolic interval alternation occurred inconsistently.